SVT 3 Pro woes

[klaw]

my SVT 3 Pro has recently started to sort of fade out intermittently.
it comes right back after a couple of seconds.
i've swapped cables several times so it is not that.
the jack is not loose.
anyone else enjoy this special feature and know what to do aboutit?
tia,
mcnewsxp

[Dave Curtis]

On 5 May 2007 05:23:12 -0700, klaw <mcourter@mindspring.com> wrote:

>my SVT 3 Pro has recently started to sort of fade out intermittently.
>it comes right back after a couple of seconds.
>i've swapped cables several times so it is not that.
>the jack is not loose.
>anyone else enjoy this special feature and know what to do aboutit?
>tia,
>mcnewsxp

Hiya!

Run a short patch cord from the preamp out to the power amp in. Your
jacks may be a bit dirty. Get some Caig d5 from RadShack, give each
jack a short burst, then stick a plug in and out several times. This
is the first thing to do on an amp with pre/power and/or send/return
jacks.

If this doesn't fix it, try reseating the tubes or treat the tube pins
with Caig XgL.

If none of the fix it, you likely have a "connection issue" in there
somewhere, and there are *hundreds* of connections in there. The main
problem with any SLM amp is what I call "solder anemia". Just adding
solder to the joints that are subjected to mechanical stress goes a
long way towards SLM longevity.

-DC

[5 String]

klaw wrote:
> my SVT 3 Pro has recently started to sort of fade out intermittently.
> it comes right back after a couple of seconds.
> i've swapped cables several times so it is not that.
> the jack is not loose.
> anyone else enjoy this special feature and know what to do aboutit?
> tia,
> mcnewsxp
>
my vote goes to anyone of the five 12AX7's tubes in the preamp bring
loose or cooked. There is only one Groove tube in the chain, although
they would like you believe it's loaded with em. The rest in mine were
generic. Mine is just two years old and I just re-tubed it. Had similar
issues. Cost about 50 bux.

--
> www.google.com <enter> <
> search<insert query here> <enter> <
> <
> avoiding newsgroup wiseasses.... PRICELESS. <
> <
> For some things there is usenet <
> For everything else there is google............. <

[klaw]

On May 5, 11:41 am, 5 String <catdri...@gmail.com> wrote:
> klaw wrote:
> > my SVT 3 Pro has recently started to sort of fade out intermittently.
> > it comes right back after a couple of seconds.
> > i've swapped cables several times so it is not that.
> > the jack is not loose.
> > anyone else enjoy this special feature and know what to do aboutit?
> > tia,
> > mcnewsxp
>
> my vote goes to anyone of the five 12AX7's tubes in the preamp bring
> loose or cooked. There is only one Groove tube in the chain, although
> they would like you believe it's loaded with em. The rest in mine were
> generic. Mine is just two years old and I just re-tubed it. Had similar
> issues. Cost about 50 bux.
>

cool
DIY?

[5 String]

klaw wrote:
> On May 5, 11:41 am, 5 String <catdri...@gmail.com> wrote:
>> klaw wrote:
>>> my SVT 3 Pro has recently started to sort of fade out intermittently.
>>> it comes right back after a couple of seconds.
>>> i've swapped cables several times so it is not that.
>>> the jack is not loose.
>>> anyone else enjoy this special feature and know what to do aboutit?
>>> tia,
>>> mcnewsxp
>> my vote goes to anyone of the five 12AX7's tubes in the preamp bring
>> loose or cooked. There is only one Groove tube in the chain, although
>> they would like you believe it's loaded with em. The rest in mine were
>> generic. Mine is just two years old and I just re-tubed it. Had similar
>> issues. Cost about 50 bux.
>>
>
> cool
> DIY?
>
yes. pop the top cover (with the unit unplugged of course...) the tubes
are three up front and two in the back. Without looking inside mine, I
remember there are four 12ax7a's and one 12ax7u. Pay attention to which
one go where and they are a simple job to replace. Beware of the power
caps, since these can pack a lot of voltage even powered down. You can
get an idea of what's cooked and what's not by looking at the tubes when
the unit is powered up. If it's not glowing a healthy orange it's
likely as not going bad. They say to replace power tubes in sets (there
aren't any power tubes in the IIIpro) but I took that approach and
replaced everything in mine.
The hardest choice to make is what brand to put back in, since not
all tubes are created equal, and supposedly they all impart a different
sound to your rig.... I was only able to get Mesa tubes locally and
needed the rig back in service quickly so that's what it's packing now.
It may be a bit louder and maybe more in your face than with the
generics. If you have time a quick google search will give you more
choices for suppliers than you'll know what to do with. I was
considering using these guys: http://www.boiaudioworks.com/index.php
because they were geographically nearby and priced reasonably. If you
can order online you should be able to do the job for less than 2/3's
what it cost me.
--
> www.google.com <enter> <
> search<insert query here> <enter> <
> <
> avoiding newsgroup wiseasses.... PRICELESS. <
> <
> For some things there is usenet <
> For everything else there is google............. <

[5 String]

this site may also be helpful:
http://www.thetubestore.com/gainfactor.html
BTW looking at pricing it appears that you're gonna spend about what I
did or a bit more, it looks as though things are a bit more expensive
then the were 6 months ago.
--
> www.google.com <enter> <
> search<insert query here> <enter> <
> <
> avoiding newsgroup wiseasses.... PRICELESS. <
> <
> For some things there is usenet <
> For everything else there is google............. <

[Middle C]

> my vote goes to anyone of the five 12AX7's tubes in the preamp bring
> loose or cooked. There is only one Groove tube in the chain, although
> they would like you believe it's loaded with em.

Not to burst your bubble, but 'Groove Tubes' does not make tubes - they only
're-market' generics with their own stamp on them. No telling who makes
actually makes their tubes but if they make you feel good about what your
plopping in - go for it.


--
keith c..
www.la11.net

[5 String]

Middle C wrote:
>> my vote goes to anyone of the five 12AX7's tubes in the preamp bring
>> loose or cooked. There is only one Groove tube in the chain, although
>> they would like you believe it's loaded with em.
>
> Not to burst your bubble, but 'Groove Tubes' does not make tubes - they only
> 're-market' generics with their own stamp on them. No telling who makes
> actually makes their tubes but if they make you feel good about what your
> plopping in - go for it.
>
>
No bubble to burst here, I was fully aware of the tube situation. Mine
got a load of Mesa's (which could be anything since they just rebadge
someone else's stuff too.) and one Electro Harmonics because that's what
I could get locally on 2hours notice.. Most tubes are Russian or
Chinese. I also believe that many are brought in by one "broker" but
aare made in a couple of different plants. Theree is a good run down of
what's what on teh second site I posted.
--
> www.google.com <enter> <
> search<insert query here> <enter> <
> <
> avoiding newsgroup wiseasses.... PRICELESS. <
> <
> For some things there is usenet <
> For everything else there is google............. <

[Mike Rieves]

"5 String" <catdriver@gmail.com> wrote in message
news:f1n8u2$81k$1@news.xmission.com...
> Middle C wrote:
>>> my vote goes to anyone of the five 12AX7's tubes in the preamp bring
>>> loose or cooked. There is only one Groove tube in the chain, although
>>> they would like you believe it's loaded with em.
>>
>> Not to burst your bubble, but 'Groove Tubes' does not make tubes - they
>> only 're-market' generics with their own stamp on them. No telling who
>> makes actually makes their tubes but if they make you feel good about
>> what your plopping in - go for it.
>>
>>
> No bubble to burst here, I was fully aware of the tube situation. Mine
> got a load of Mesa's (which could be anything since they just rebadge
> someone else's stuff too.) and one Electro Harmonics because that's what I
> could get locally on 2hours notice.. Most tubes are Russian or Chinese. I
> also believe that many are brought in by one "broker" but aare made in a
> couple of different plants. Theree is a good run down of what's what on
> teh second site I posted.
>
Not sure about today, but a few years ago, there were only two or three
tube manufacturers left in the world, one in Russia and one or maybe two in
China. The companies who sold higher-end tubes just bought carloads of the
tubes cheap, then tested and matched the best ones, re-marked them with
their brand and sold them for many times what they paid for them. The not-so
good tubes were sold under lesser brand names, for only four or five times
what they paid for them. To give an example, they bought 6L6 tubes for
around a dollar apiece and sold the good ones in matched pairs for around a
hundred bucks.
The not-so-good ones sold under a lesser brand name for ten or fifteen
dollars apiece. You actually did get better tubes from the high-end
companies but they still all came from the same plants, you just got tubes
that had tested out the highest.

[5 String]

Mike Rieves wrote:
> "5 String" <catdriver@gmail.com> wrote in message
> news:f1n8u2$81k$1@news.xmission.com...
>> Middle C wrote:
>>>> my vote goes to anyone of the five 12AX7's tubes in the preamp bring
>>>> loose or cooked. There is only one Groove tube in the chain, although
>>>> they would like you believe it's loaded with em.
>>> Not to burst your bubble, but 'Groove Tubes' does not make tubes - they
>>> only 're-market' generics with their own stamp on them. No telling who
>>> makes actually makes their tubes but if they make you feel good about
>>> what your plopping in - go for it.
>>>
>>>
>> No bubble to burst here, I was fully aware of the tube situation. Mine
>> got a load of Mesa's (which could be anything since they just rebadge
>> someone else's stuff too.) and one Electro Harmonics because that's what I
>> could get locally on 2hours notice.. Most tubes are Russian or Chinese. I
>> also believe that many are brought in by one "broker" but aare made in a
>> couple of different plants. Theree is a good run down of what's what on
>> teh second site I posted.
>>
> Not sure about today, but a few years ago, there were only two or three
> tube manufacturers left in the world, one in Russia and one or maybe two in
> China. The companies who sold higher-end tubes just bought carloads of the
> tubes cheap, then tested and matched the best ones, re-marked them with
> their brand and sold them for many times what they paid for them. The not-so
> good tubes were sold under lesser brand names, for only four or five times
> what they paid for them. To give an example, they bought 6L6 tubes for
> around a dollar apiece and sold the good ones in matched pairs for around a
> hundred bucks.
> The not-so-good ones sold under a lesser brand name for ten or fifteen
> dollars apiece. You actually did get better tubes from the high-end
> companies but they still all came from the same plants, you just got tubes
> that had tested out the highest.
>
>
that's about how it is now, there are two big plants in Russia,
different branding, run by the same holding company. A couple in China
and one in Hungary or the Czech Republics that is supposedly going to
vanish... There is another in the UK that is highly erratic in it's
output.. at least that's what I gleaned from on of the online sellers.
At least now it's easier to buy a tube that is actually labeled with the
makers brand.

--
> www.google.com <enter> <
> search<insert query here> <enter> <
> <
> avoiding newsgroup wiseasses.... PRICELESS. <
> <
> For some things there is usenet <
> For everything else there is google............. <

[klaw]

On May 5, 4:21 pm, 5 String <catdri...@gmail.com> wrote:
> klaw wrote:
> > On May 5, 11:41 am, 5 String <catdri...@gmail.com> wrote:
> >> klaw wrote:
> >>> my SVT 3 Pro has recently started to sort of fade out intermittently.
> >>> it comes right back after a couple of seconds.
> >>> i've swapped cables several times so it is not that.
> >>> the jack is not loose.
> >>> anyone else enjoy this special feature and know what to do aboutit?
> >>> tia,
> >>> mcnewsxp
> >> my vote goes to anyone of the five 12AX7's tubes in the preamp bring
> >> loose or cooked. There is only one Groove tube in the chain, although
> >> they would like you believe it's loaded with em. The rest in mine were
> >> generic. Mine is just two years old and I just re-tubed it. Had similar
> >> issues. Cost about 50 bux.
>
> > cool
> > DIY?
>
> yes. pop the top cover (with the unit unplugged of course...) the tubes
> are three up front and two in the back. Without looking inside mine, I
> remember there are four 12ax7a's and one 12ax7u. Pay attention to which
> one go where and they are a simple job to replace. Beware of the power
> caps, since these can pack a lot of voltage even powered down. You can
> get an idea of what's cooked and what's not by looking at the tubes when
> the unit is powered up. If it's not glowing a healthy orange it's
> likely as not going bad. They say to replace power tubes in sets (there
> aren't any power tubes in the IIIpro) but I took that approach and
> replaced everything in mine.
> The hardest choice to make is what brand to put back in, since not
> all tubes are created equal, and supposedly they all impart a different
> sound to your rig.... I was only able to get Mesa tubes locally and
> needed the rig back in service quickly so that's what it's packing now.
> It may be a bit louder and maybe more in your face than with the
> generics. If you have time a quick google search will give you more
> choices for suppliers than you'll know what to do with. I was
> considering using these guys:http://www.boiaudioworks.com/index.php
> because they were geographically nearby and priced reasonably. If you
> can order online you should be able to do the job for less than 2/3's
> what it cost me.

i found 12ax7a but not 12ax7u.
can you tell me where to find both?
what's the difference?

[5 String]

klaw wrote:
> On May 5, 4:21 pm, 5 String <catdri...@gmail.com> wrote:
>> klaw wrote:
>>> On May 5, 11:41 am, 5 String <catdri...@gmail.com> wrote:
>>>> klaw wrote:
>>>>> my SVT 3 Pro has recently started to sort of fade out intermittently.
>>>>> it comes right back after a couple of seconds.
>>>>> i've swapped cables several times so it is not that.
>>>>> the jack is not loose.
>>>>> anyone else enjoy this special feature and know what to do aboutit?
>>>>> tia,
>>>>> mcnewsxp
>>>> my vote goes to anyone of the five 12AX7's tubes in the preamp bring
>>>> loose or cooked. There is only one Groove tube in the chain, although
>>>> they would like you believe it's loaded with em. The rest in mine were
>>>> generic. Mine is just two years old and I just re-tubed it. Had similar
>>>> issues. Cost about 50 bux.
>>> cool
>>> DIY?
>> yes. pop the top cover (with the unit unplugged of course...) the tubes
>> are three up front and two in the back. Without looking inside mine, I
>> remember there are four 12ax7a's and one 12ax7u. Pay attention to which
>> one go where and they are a simple job to replace. Beware of the power
>> caps, since these can pack a lot of voltage even powered down. You can
>> get an idea of what's cooked and what's not by looking at the tubes when
>> the unit is powered up. If it's not glowing a healthy orange it's
>> likely as not going bad. They say to replace power tubes in sets (there
>> aren't any power tubes in the IIIpro) but I took that approach and
>> replaced everything in mine.
>> The hardest choice to make is what brand to put back in, since not
>> all tubes are created equal, and supposedly they all impart a different
>> sound to your rig.... I was only able to get Mesa tubes locally and
>> needed the rig back in service quickly so that's what it's packing now.
>> It may be a bit louder and maybe more in your face than with the
>> generics. If you have time a quick google search will give you more
>> choices for suppliers than you'll know what to do with. I was
>> considering using these guys:http://www.boiaudioworks.com/index.php
>> because they were geographically nearby and priced reasonably. If you
>> can order online you should be able to do the job for less than 2/3's
>> what it cost me.
>
> i found 12ax7a but not 12ax7u.
> can you tell me where to find both?
> what's the difference?
>
I miss typed, I had four 12ax7's and one 12au7... I think the 12au7 was
in one of the two sockets at the back or it might have been in the
socket closest the front.... I'd rather not pull mine out of the rack
and pop the top to verify but.... At any rate if you have five tubes
you've got it.
According to what I read, the 12ax7's the tubes with the highest gain
rating ( from: http://thetubestore.com/gainfactor.html ) and the 12au7
comes in behind. I wondered therefore if the 12au7 was in the circuit
controlled by the tube gain pot, since I suspect it will break up more
easily as is driven harder. Alternatively it was on the bench when my
amp was built and therefore went into one of the sockets.
--
> www.google.com <enter> <
> search<insert query here> <enter> <
> <
> avoiding newsgroup wiseasses.... PRICELESS. <
> <
> For some things there is usenet <
> For everything else there is google............. <

[Mike Rieves]

"5 String" <catdriver@gmail.com> wrote in message
news:f21qmc$net$1@news.xmission.com...
> klaw wrote:
>> On May 5, 4:21 pm, 5 String <catdri...@gmail.com> wrote:
>>> klaw wrote:
>>>> On May 5, 11:41 am, 5 String <catdri...@gmail.com> wrote:
>>>>> klaw wrote:
>>>>>> my SVT 3 Pro has recently started to sort of fade out intermittently.
>>>>>> it comes right back after a couple of seconds.
>>>>>> i've swapped cables several times so it is not that.
>>>>>> the jack is not loose.
>>>>>> anyone else enjoy this special feature and know what to do aboutit?
>>>>>> tia,
>>>>>> mcnewsxp
>>>>> my vote goes to anyone of the five 12AX7's tubes in the preamp bring
>>>>> loose or cooked. There is only one Groove tube in the chain, although
>>>>> they would like you believe it's loaded with em. The rest in mine were
>>>>> generic. Mine is just two years old and I just re-tubed it. Had
>>>>> similar
>>>>> issues. Cost about 50 bux.
>>>> cool
>>>> DIY?
>>> yes. pop the top cover (with the unit unplugged of course...) the tubes
>>> are three up front and two in the back. Without looking inside mine, I
>>> remember there are four 12ax7a's and one 12ax7u. Pay attention to which
>>> one go where and they are a simple job to replace. Beware of the power
>>> caps, since these can pack a lot of voltage even powered down. You can
>>> get an idea of what's cooked and what's not by looking at the tubes when
>>> the unit is powered up. If it's not glowing a healthy orange it's
>>> likely as not going bad. They say to replace power tubes in sets (there
>>> aren't any power tubes in the IIIpro) but I took that approach and
>>> replaced everything in mine.
>>> The hardest choice to make is what brand to put back in, since not
>>> all tubes are created equal, and supposedly they all impart a different
>>> sound to your rig.... I was only able to get Mesa tubes locally and
>>> needed the rig back in service quickly so that's what it's packing now.
>>> It may be a bit louder and maybe more in your face than with the
>>> generics. If you have time a quick google search will give you more
>>> choices for suppliers than you'll know what to do with. I was
>>> considering using these guys:http://www.boiaudioworks.com/index.php
>>> because they were geographically nearby and priced reasonably. If you
>>> can order online you should be able to do the job for less than 2/3's
>>> what it cost me.
>>
>> i found 12ax7a but not 12ax7u.
>> can you tell me where to find both?
>> what's the difference?
>>
> I miss typed, I had four 12ax7's and one 12au7... I think the 12au7 was in
> one of the two sockets at the back or it might have been in the socket
> closest the front.... I'd rather not pull mine out of the rack and pop the
> top to verify but.... At any rate if you have five tubes you've got it.
> According to what I read, the 12ax7's the tubes with the highest gain
> rating ( from: http://thetubestore.com/gainfactor.html ) and the 12au7
> comes in behind. I wondered therefore if the 12au7 was in the circuit
> controlled by the tube gain pot, since I suspect it will break up more
> easily as is driven harder. Alternatively it was on the bench when my amp
> was built and therefore went into one of the sockets.
> --

It's been a while, but as best I remember, the 12ax7 and 12au7 are not
interchangable. The pinouts are the same, but the characteristics are
different enough that bias problems will occur if you try to use one in a
circuit designed for the other.

[ptooner]

"Mike Rieves" <mriev@hotspam.com> wrote in message
news:Uwc1i.139$XD3.34@bignews1.bellsouth.net...
>
> "5 String" <catdriver@gmail.com> wrote in message
> news:f21qmc$net$1@news.xmission.com...
>> klaw wrote:
>>> On May 5, 4:21 pm, 5 String <catdri...@gmail.com> wrote:
>>>> klaw wrote:
>>>>> On May 5, 11:41 am, 5 String <catdri...@gmail.com> wrote:
>>>>>> klaw wrote:
>>>>>>> my SVT 3 Pro has recently started to sort of fade out
>>>>>>> intermittently.
>>>>>>> it comes right back after a couple of seconds.
>>>>>>> i've swapped cables several times so it is not that.
>>>>>>> the jack is not loose.
>>>>>>> anyone else enjoy this special feature and know what to do aboutit?
>>>>>>> tia,
>>>>>>> mcnewsxp
>>>>>> my vote goes to anyone of the five 12AX7's tubes in the preamp bring
>>>>>> loose or cooked. There is only one Groove tube in the chain,
>>>>>> although
>>>>>> they would like you believe it's loaded with em. The rest in mine
>>>>>> were
>>>>>> generic. Mine is just two years old and I just re-tubed it. Had
>>>>>> similar
>>>>>> issues. Cost about 50 bux.
>>>>> cool
>>>>> DIY?
>>>> yes. pop the top cover (with the unit unplugged of course...) the
>>>> tubes
>>>> are three up front and two in the back. Without looking inside mine, I
>>>> remember there are four 12ax7a's and one 12ax7u. Pay attention to
>>>> which
>>>> one go where and they are a simple job to replace. Beware of the power
>>>> caps, since these can pack a lot of voltage even powered down. You can
>>>> get an idea of what's cooked and what's not by looking at the tubes
>>>> when
>>>> the unit is powered up. If it's not glowing a healthy orange it's
>>>> likely as not going bad. They say to replace power tubes in sets
>>>> (there
>>>> aren't any power tubes in the IIIpro) but I took that approach and
>>>> replaced everything in mine.
>>>> The hardest choice to make is what brand to put back in, since not
>>>> all tubes are created equal, and supposedly they all impart a different
>>>> sound to your rig.... I was only able to get Mesa tubes locally and
>>>> needed the rig back in service quickly so that's what it's packing now.
>>>> It may be a bit louder and maybe more in your face than with the
>>>> generics. If you have time a quick google search will give you more
>>>> choices for suppliers than you'll know what to do with. I was
>>>> considering using these guys:http://www.boiaudioworks.com/index.php
>>>> because they were geographically nearby and priced reasonably. If you
>>>> can order online you should be able to do the job for less than 2/3's
>>>> what it cost me.
>>>
>>> i found 12ax7a but not 12ax7u.
>>> can you tell me where to find both?
>>> what's the difference?
>>>
>> I miss typed, I had four 12ax7's and one 12au7... I think the 12au7 was
>> in one of the two sockets at the back or it might have been in the socket
>> closest the front.... I'd rather not pull mine out of the rack and pop
>> the top to verify but.... At any rate if you have five tubes you've got
>> it.
>> According to what I read, the 12ax7's the tubes with the highest gain
>> rating ( from: http://thetubestore.com/gainfactor.html ) and the 12au7
>> comes in behind. I wondered therefore if the 12au7 was in the circuit
>> controlled by the tube gain pot, since I suspect it will break up more
>> easily as is driven harder. Alternatively it was on the bench when my
>> amp was built and therefore went into one of the sockets.
>> --
>
> It's been a while, but as best I remember, the 12ax7 and 12au7 are not
> interchangable. The pinouts are the same, but the characteristics are
> different enough that bias problems will occur if you try to use one in a
> circuit designed for the other.

I too amd dragging this up from old dusty memory, but if I recall correctly
they are all dual triodes and the at, av and au are interchangeable with
only slight variations but the at was a lower power higher gain dual triode.
I wouldn't want to bet big money on this, however.
Damn, I just went to the net to look it up, and I was actually right!
;-) The ax was designed for about 1.2 ma plate current and the av was
designed for 10ma. Even a blind hog -
Gerry


>

[5 String]

ptooner wrote:
> "Mike Rieves" <mriev@hotspam.com> wrote in message
> news:Uwc1i.139$XD3.34@bignews1.bellsouth.net...
>> "5 String" <catdriver@gmail.com> wrote in message
>> news:f21qmc$net$1@news.xmission.com...
>>> klaw wrote:
>>>> On May 5, 4:21 pm, 5 String <catdri...@gmail.com> wrote:
>>>>> klaw wrote:
>>>>>> On May 5, 11:41 am, 5 String <catdri...@gmail.com> wrote:
>>>>>>> klaw wrote:
>>>>>>>> my SVT 3 Pro has recently started to sort of fade out
>>>>>>>> intermittently.
>>>>>>>> it comes right back after a couple of seconds.
>>>>>>>> i've swapped cables several times so it is not that.
>>>>>>>> the jack is not loose.
>>>>>>>> anyone else enjoy this special feature and know what to do aboutit?
>>>>>>>> tia,
>>>>>>>> mcnewsxp
>>>>>>> my vote goes to anyone of the five 12AX7's tubes in the preamp bring
>>>>>>> loose or cooked. There is only one Groove tube in the chain,
>>>>>>> although
>>>>>>> they would like you believe it's loaded with em. The rest in mine
>>>>>>> were
>>>>>>> generic. Mine is just two years old and I just re-tubed it. Had
>>>>>>> similar
>>>>>>> issues. Cost about 50 bux.
>>>>>> cool
>>>>>> DIY?
>>>>> yes. pop the top cover (with the unit unplugged of course...) the
>>>>> tubes
>>>>> are three up front and two in the back. Without looking inside mine, I
>>>>> remember there are four 12ax7a's and one 12ax7u. Pay attention to
>>>>> which
>>>>> one go where and they are a simple job to replace. Beware of the power
>>>>> caps, since these can pack a lot of voltage even powered down. You can
>>>>> get an idea of what's cooked and what's not by looking at the tubes
>>>>> when
>>>>> the unit is powered up. If it's not glowing a healthy orange it's
>>>>> likely as not going bad. They say to replace power tubes in sets
>>>>> (there
>>>>> aren't any power tubes in the IIIpro) but I took that approach and
>>>>> replaced everything in mine.
>>>>> The hardest choice to make is what brand to put back in, since not
>>>>> all tubes are created equal, and supposedly they all impart a different
>>>>> sound to your rig.... I was only able to get Mesa tubes locally and
>>>>> needed the rig back in service quickly so that's what it's packing now.
>>>>> It may be a bit louder and maybe more in your face than with the
>>>>> generics. If you have time a quick google search will give you more
>>>>> choices for suppliers than you'll know what to do with. I was
>>>>> considering using these guys:http://www.boiaudioworks.com/index.php
>>>>> because they were geographically nearby and priced reasonably. If you
>>>>> can order online you should be able to do the job for less than 2/3's
>>>>> what it cost me.
>>>> i found 12ax7a but not 12ax7u.
>>>> can you tell me where to find both?
>>>> what's the difference?
>>>>
>>> I miss typed, I had four 12ax7's and one 12au7... I think the 12au7 was
>>> in one of the two sockets at the back or it might have been in the socket
>>> closest the front.... I'd rather not pull mine out of the rack and pop
>>> the top to verify but.... At any rate if you have five tubes you've got
>>> it.
>>> According to what I read, the 12ax7's the tubes with the highest gain
>>> rating ( from: http://thetubestore.com/gainfactor.html ) and the 12au7
>>> comes in behind. I wondered therefore if the 12au7 was in the circuit
>>> controlled by the tube gain pot, since I suspect it will break up more
>>> easily as is driven harder. Alternatively it was on the bench when my
>>> amp was built and therefore went into one of the sockets.
>>> --
>> It's been a while, but as best I remember, the 12ax7 and 12au7 are not
>> interchangable. The pinouts are the same, but the characteristics are
>> different enough that bias problems will occur if you try to use one in a
>> circuit designed for the other.
>
> I too amd dragging this up from old dusty memory, but if I recall correctly
> they are all dual triodes and the at, av and au are interchangeable with
> only slight variations but the at was a lower power higher gain dual triode.
> I wouldn't want to bet big money on this, however.
> Damn, I just went to the net to look it up, and I was actually right!
> ;-) The ax was designed for about 1.2 ma plate current and the av was
> designed for 10ma. Even a blind hog -
> Gerry
>
>
>
>
the gist of what I pulled from the tubestore page, the 12a__7's are
interchangeable, but have differing gain values with the 12ax7 having
the highest. you can check the link above and see if I interpreted what
I read correctly..... it's in blue and a sickly yellow that didn't
render well on my screen.

--
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> search<insert query here> <enter> <
> <
> avoiding newsgroup wiseasses.... PRICELESS. <
> <
> For some things there is usenet <
> For everything else there is google............. <

[ptooner]

>> I too amd dragging this up from old dusty memory, but if I recall
>> correctly they are all dual triodes and the at, av and au are
>> interchangeable with only slight variations but the at was a lower power
>> higher gain dual triode. I wouldn't want to bet big money on this,
>> however.
>> Damn, I just went to the net to look it up, and I was actually right!
>> ;-) The ax was designed for about 1.2 ma plate current and the av was
>> designed for 10ma. Even a blind hog -
>> Gerry
>>
>>
>>
>>
> the gist of what I pulled from the tubestore page, the 12a__7's are
> interchangeable, but have differing gain values with the 12ax7 having the
> highest. you can check the link above and see if I interpreted what I
> read correctly..... it's in blue and a sickly yellow that didn't render
> well on my screen.

Well, it sort of depends on how you interpret interchangeable. They have
the same pinout and nothing will explode if you mix them. In fact the t,
u,and v are effectively interchangeable regardless. The different in the x
is that it was designed for low signal high gain applications. It has a
voltage gain of approximately 100 as compared to around 60 for the other
models. OTOH, the other models handle about 7 or 8 times more power than
the x model. So, in short they would sort of interchange in a pinch but
they aren't truly interchangeable because of the different ouput voltages
for the same input levels. An input signal of 1 volt on an ax would produce
an output signal of 100 volts. On an AT it would be more like 60 volts.
Yes, I am really old enough to have worked extensively on these things. ;-)

Gerry

[Mike Fleming]

In article <f24gso$ank$1@news.xmission.com>, 5 String
<catdriver@gmail.com> writes:

> the gist of what I pulled from the tubestore page, the 12a__7's are
> interchangeable, but have differing gain values with the 12ax7 having
> the highest. you can check the link above and see if I interpreted what
> I read correctly..... it's in blue and a sickly yellow that didn't
> render well on my screen.

That's what it says on Wikipedia too (12AX7 has a gain of 100, 12AU7
has a gain of 17-20). 12AX7 = ECC83, 12AU7 = ECC82. Don't know where
my copy of Ball has disappeared to so I can't check any other
characteristics out.

--
Mike Fleming

[Mike Rieves]

"ptooner" <someguy@onthe.net> wrote in message
news:vTk1i.740$nh.360@bignews3.bellsouth.net...
>
>
>>> I too amd dragging this up from old dusty memory, but if I recall
>>> correctly they are all dual triodes and the at, av and au are
>>> interchangeable with only slight variations but the at was a lower power
>>> higher gain dual triode. I wouldn't want to bet big money on this,
>>> however.
>>> Damn, I just went to the net to look it up, and I was actually
>>> right! ;-) The ax was designed for about 1.2 ma plate current and the
>>> av was designed for 10ma. Even a blind hog -
>>> Gerry
>>>
>>>
>>>
>>>
>> the gist of what I pulled from the tubestore page, the 12a__7's are
>> interchangeable, but have differing gain values with the 12ax7 having the
>> highest. you can check the link above and see if I interpreted what I
>> read correctly..... it's in blue and a sickly yellow that didn't render
>> well on my screen.
>
> Well, it sort of depends on how you interpret interchangeable. They have
> the same pinout and nothing will explode if you mix them. In fact the t,
> u,and v are effectively interchangeable regardless. The different in the
> x is that it was designed for low signal high gain applications. It has a
> voltage gain of approximately 100 as compared to around 60 for the other
> models. OTOH, the other models handle about 7 or 8 times more power than
> the x model. So, in short they would sort of interchange in a pinch but
> they aren't truly interchangeable because of the different ouput voltages
> for the same input levels. An input signal of 1 volt on an ax would
> produce an output signal of 100 volts. On an AT it would be more like 60
> volts. Yes, I am really old enough to have worked extensively on these
> things. ;-)
>
> Gerry

If I remember right, when interchanging the 12AX7 with the 12AU7, bias
issues crop up with low signal levels too. This affects how the tube passes,
or doesn't pass, the lowest level signals. The 12AT7, 12AU7 and 12AV7 will
interchange with no problem, but none of them will sub for a 12AX7 without
audible problems. When I got my original electronics training, most things
were still all tube, and some hybrid and all-transister circuits were
showing up here and there. The transisters back then were mostly germanium,
which were leaky and noisy.

[Mike Rieves]

"Mike Fleming" <{mike}@tauzero.co.uk> wrote in message
news:rcpb43ddjbomjml0iblm6sb06inf07tmn0@4ax.com...
> In article <f24gso$ank$1@news.xmission.com>, 5 String
> <catdriver@gmail.com> writes:
>
>> the gist of what I pulled from the tubestore page, the 12a__7's are
>> interchangeable, but have differing gain values with the 12ax7 having
>> the highest. you can check the link above and see if I interpreted what
>> I read correctly..... it's in blue and a sickly yellow that didn't
>> render well on my screen.
>
> That's what it says on Wikipedia too (12AX7 has a gain of 100, 12AU7
> has a gain of 17-20). 12AX7 = ECC83, 12AU7 = ECC82. Don't know where
> my copy of Ball has disappeared to so I can't check any other
> characteristics out.
>

http://www.mclink.it/com/audiomatica/tubes/ lists the specs on common
tubes

[ptooner]

>
> If I remember right, when interchanging the 12AX7 with the 12AU7, bias
> issues crop up with low signal levels too. This affects how the tube
> passes, or doesn't pass, the lowest level signals. The 12AT7, 12AU7 and
> 12AV7 will interchange with no problem, but none of them will sub for a
> 12AX7 without audible problems. When I got my original electronics
> training, most things were still all tube, and some hybrid and
> all-transister circuits were showing up here and there. The transisters
> back then were mostly germanium, which were leaky and noisy.
>
Ah, memory lane. Yep, I remember when the transistor stuff came in and they
tried to tell us that you could control output with current input instead of
voltage. Created a whole new generation of techs who thought that way.
Then along came JFETS which worked just like tubes and those guys were lost
and the old tube guys were back in business. ;-)

Gerry

[Mike Rieves]

"ptooner" <someguy@onthe.net> wrote in message
news:hVp1i.789$O9.50@bignews7.bellsouth.net...
>
>>
>> If I remember right, when interchanging the 12AX7 with the 12AU7, bias
>> issues crop up with low signal levels too. This affects how the tube
>> passes, or doesn't pass, the lowest level signals. The 12AT7, 12AU7 and
>> 12AV7 will interchange with no problem, but none of them will sub for a
>> 12AX7 without audible problems. When I got my original electronics
>> training, most things were still all tube, and some hybrid and
>> all-transister circuits were showing up here and there. The transisters
>> back then were mostly germanium, which were leaky and noisy.
>>
> Ah, memory lane. Yep, I remember when the transistor stuff came in and
> they tried to tell us that you could control output with current input
> instead of voltage. Created a whole new generation of techs who thought
> that way. Then along came JFETS which worked just like tubes and those
> guys were lost and the old tube guys were back in business. ;-)
>
> Gerry
Ah yes, what's old is new again. There was a TV repair guy in my town who
had started in the early fifties, he refused to believe that transistors
would last more than a few years before tubes would take over again. He
retired from the TV repair business in the early '70s, but made a decent
living fixing and modding tube amps for musicians, He knew just about
everything there was to know about tubes and tube circuits. Up until the day
he died (2003), he said, and truly believed, that tubes would make a
comeback in virtually all electronics equipment.

[Benj]

Mike Rieves wrote:

> Ah yes, what's old is new again. There was a TV repair guy in my town who
> had started in the early fifties, he refused to believe that transistors
> would last more than a few years before tubes would take over again. He
> retired from the TV repair business in the early '70s, but made a decent
> living fixing and modding tube amps for musicians, He knew just about
> everything there was to know about tubes and tube circuits. Up until the day
> he died (2003), he said, and truly believed, that tubes would make a
> comeback in virtually all electronics equipment.

yeah, that was me too! I remember calling transistors "a passing
fad"! But my opinion was based on knowing too much not too little!
Most people don't know it, but there were some amazing developments in
tube technology that never got the chance to make it into production.
Back at the age I'm talking about there was the development of
HEATERLESS cathodes that were actually developed to the point where
they could operate vidicon tubes!

The transistors of the age were nasty, noisy, low gain things that
because of using a current input made amplifiers a total mess to
design and having performance nowhere near those of even production
tubes of the day. Of course FETs changed all that. But the old
advanced tube technology just disappeared without a whimper and seems
lost today like the art of making a decent mummy. Just think of how
cool it would be today to have an amp with heaterless tubes that
lasted forever, sounded great, and didn't crank out all that heat!
<sigh>

Benj
(who also notes that the thing that really put the nails in the coffin
of tube technology was the Fairchild "planar" integrated circuit.
This allowed easy construction of complex circuits that the 3-
dimensional nature of tubes made difficult even when the tubes were
miniaturized)

[Misifus]

Benj wrote:
> Just think of how
> cool it would be today to have an amp with heaterless tubes that
> lasted forever, sounded great, and didn't crank out all that heat!
>

When I joined Firestone's research lab in 1969, they had just recently
replaced the tube computer they had been using (Univac model 2). They
employed three full time plumbers to the keep the cooling water running
on that thing, and it occupied two floors of Plant One. I was big and
hot and small and slow. The 360, model 50 was an improvement.

-Raf


--
Misifus-
Rafael Seibert
mailto:rafseibert@suddenlink.net
blog: http://rafsrincon.blogspot.com/
Photos: http://www.flickr.com/photos/rafiii
home: http://www.rafandsioux.com

[Mike Rieves]

"Benj" <bjacoby@iwaynet.net> wrote in message
news:1179064613.196207.162790@e65g2000hsc.googlegr oups.com...
>
> Mike Rieves wrote:
>
>> Ah yes, what's old is new again. There was a TV repair guy in my town
>> who
>> had started in the early fifties, he refused to believe that transistors
>> would last more than a few years before tubes would take over again. He
>> retired from the TV repair business in the early '70s, but made a decent
>> living fixing and modding tube amps for musicians, He knew just about
>> everything there was to know about tubes and tube circuits. Up until the
>> day
>> he died (2003), he said, and truly believed, that tubes would make a
>> comeback in virtually all electronics equipment.
>
> yeah, that was me too! I remember calling transistors "a passing
> fad"! But my opinion was based on knowing too much not too little!
> Most people don't know it, but there were some amazing developments in
> tube technology that never got the chance to make it into production.
> Back at the age I'm talking about there was the development of
> HEATERLESS cathodes that were actually developed to the point where
> they could operate vidicon tubes!
>
> The transistors of the age were nasty, noisy, low gain things that
> because of using a current input made amplifiers a total mess to
> design and having performance nowhere near those of even production
> tubes of the day. Of course FETs changed all that. But the old
> advanced tube technology just disappeared without a whimper and seems
> lost today like the art of making a decent mummy. Just think of how
> cool it would be today to have an amp with heaterless tubes that
> lasted forever, sounded great, and didn't crank out all that heat!
> <sigh>
>
> Benj
> (who also notes that the thing that really put the nails in the coffin
> of tube technology was the Fairchild "planar" integrated circuit.
> This allowed easy construction of complex circuits that the 3-
> dimensional nature of tubes made difficult even when the tubes were
> miniaturized)
>

Unfortunately, tubes couldn't be miniturized to the point that they could
compete sizewise with even transistor circuitry, much less integrated
circuits. All the big companies dropped tubes and stopped doing further
research on them even though they had desirable traits that would have
continued their usefulness in circuits where high component density wasn't
necessary. Unfortunately, the cold-cathode tube came along just a bit too
late to save tube technology. Today's tube amps are little changed in design
from their sixties and seventies counterparts, mostly because there has been
no advance in tube technology since then. Today's amps are still using the
same tubes that were popular back then.
I've heard rumors that there is a Russian (or Chinese, or Swiss, in
various versions) company working with high power cold-cathode tube audio
amplifier design, but I've seen nothing that would indicate that there is
any truth to it.

[Misifus]

Mike Rieves wrote:
> "Benj" <bjacoby@iwaynet.net> wrote in message
> news:1179064613.196207.162790@e65g2000hsc.googlegr oups.com...
>> Mike Rieves wrote:
>>
>>> Ah yes, what's old is new again. There was a TV repair guy in my town
>>> who
>>> had started in the early fifties, he refused to believe that transistors
>>> would last more than a few years before tubes would take over again. He
>>> retired from the TV repair business in the early '70s, but made a decent
>>> living fixing and modding tube amps for musicians, He knew just about
>>> everything there was to know about tubes and tube circuits. Up until the
>>> day
>>> he died (2003), he said, and truly believed, that tubes would make a
>>> comeback in virtually all electronics equipment.
>> yeah, that was me too! I remember calling transistors "a passing
>> fad"! But my opinion was based on knowing too much not too little!
>> Most people don't know it, but there were some amazing developments in
>> tube technology that never got the chance to make it into production.
>> Back at the age I'm talking about there was the development of
>> HEATERLESS cathodes that were actually developed to the point where
>> they could operate vidicon tubes!
>>
>> The transistors of the age were nasty, noisy, low gain things that
>> because of using a current input made amplifiers a total mess to
>> design and having performance nowhere near those of even production
>> tubes of the day. Of course FETs changed all that. But the old
>> advanced tube technology just disappeared without a whimper and seems
>> lost today like the art of making a decent mummy. Just think of how
>> cool it would be today to have an amp with heaterless tubes that
>> lasted forever, sounded great, and didn't crank out all that heat!
>> <sigh>
>>
>> Benj
>> (who also notes that the thing that really put the nails in the coffin
>> of tube technology was the Fairchild "planar" integrated circuit.
>> This allowed easy construction of complex circuits that the 3-
>> dimensional nature of tubes made difficult even when the tubes were
>> miniaturized)
>>
>
> Unfortunately, tubes couldn't be miniturized to the point that they could
> compete sizewise with even transistor circuitry, much less integrated
> circuits. All the big companies dropped tubes and stopped doing further
> research on them even though they had desirable traits that would have
> continued their usefulness in circuits where high component density wasn't
> necessary. Unfortunately, the cold-cathode tube came along just a bit too
> late to save tube technology. Today's tube amps are little changed in design
> from their sixties and seventies counterparts, mostly because there has been
> no advance in tube technology since then. Today's amps are still using the
> same tubes that were popular back then.
> I've heard rumors that there is a Russian (or Chinese, or Swiss, in
> various versions) company working with high power cold-cathode tube audio
> amplifier design, but I've seen nothing that would indicate that there is
> any truth to it.
>
>


If true, I'll bet there would be a number of useful applications for it.
As we've seen, there are some pretty good uses for tube technology,
it's just not a replacement for solid state everywhere.

-Raf

--
Misifus-
Rafael Seibert
mailto:rafseibert@suddenlink.net
blog: http://rafsrincon.blogspot.com/
Photos: http://www.flickr.com/photos/rafiii
home: http://www.rafandsioux.com

[klaw]

Update -

got the EH tubes and popped them in.
the amp started making a crackling sound and shut itself down.
i freaked - mildy, of course.
i put the groove tube back in and made sure all tubes were seated
frimly.
tried again.....
this is the best i can remember this amp sounding!
punch, clarity, volume - and no drop-out.

the GT is a 12ax7R.
maybe that's the difference.