[Kevin D.]

I apologize in advance for the long post. Many thanks to anyone who can help
me resolve this!

I'm not a tube amp expert but have a bass tube amp (Ampeg SVT-2 Pro) that's
only 1 1/2 years old. I purchased it brand new with factory tubes installed.
I recently (about 2 months ago) replaced ALL of the tubes in the head with
the following (from www.thetubestore.com):

Winged "C" (SED) 6550C (3 pairs, all matched)
Electro-Harmonix 12AU7A (3)
Electro-Harmonix 12AX7-EH (5)
Sovtek 12AX7-WB (2)

For the 12AX7's and 12AU7's, I don't know exactly which combination went
into the amp as I took it to my local guitar shop to have done. The amp
itself calls for only 5 12AX7's and 3 12AU7's. I can pull my extra preamp
tubes out of storage and figure out what's in the amp based on what isn't in
the amp, if that's necessary, just let me know.

My problem is that when I first power up the amp and plug in, everything
sounds great. No line noise above what is to be expected and the tone is
"solid" (clear, with some nice throaty growling, etc.). In general, the amp
behaves exactly as expected.

After about 15-25 minutes of playing (pretty loud, I might add), I start
getting a harsh distortion noise. It sounds kind of like a tearing or ugly
type of static. This is what was happening BEFORE I replaced the tubes. I
thought that getting new (better-than-factory) tubes would clear up the
problem. Well it hasn't.

I've also taken the amp in to an "authorized service center" since it's
under Ampeg warranty still. All they said was to replace the tubes.

Any suggestions? I know my bass has a touchy input jack. If I bump the cable
the wrong way I get some crackling. However, in general the bass sends a
clean signal to every other amp I've tried.

Thank you very much!

- Kevin

[Armand]

In article U0QCg.5798$Gv.1562@fed1read09,
says...

I apologize in advance for the long post. Many thanks to anyone who can
help
me resolve this!

I'm not a tube amp expert but have a bass tube amp (Ampeg SVT-2 Pro)
that's
only 1 1/2 years old. I purchased it brand new with factory tubes installed.
I recently (about 2 months ago) replaced ALL of the tubes in the head with
the following (from www.thetubestore.com):

Winged "C" (SED) 6550C (3 pairs, all matched)
Electro-Harmonix 12AU7A (3)
Electro-Harmonix 12AX7-EH (5)
Sovtek 12AX7-WB (2)

For the 12AX7's and 12AU7's, I don't know exactly which combination went
into the amp as I took it to my local guitar shop to have done. The amp
itself calls for only 5 12AX7's and 3 12AU7's. I can pull my extra preamp
tubes out of storage and figure out what's in the amp based on what isn't in
the amp, if that's necessary, just let me know.

My problem is that when I first power up the amp and plug in, everything
sounds great. No line noise above what is to be expected and the tone is
"solid" (clear, with some nice throaty growling, etc.). In general, the amp
behaves exactly as expected.

After about 15-25 minutes of playing (pretty loud, I might add), I start
getting a harsh distortion noise. It sounds kind of like a tearing or ugly
type of static. This is what was happening BEFORE I replaced the tubes. I
thought that getting new (better-than-factory) tubes would clear up the
problem. Well it hasn't.

I've also taken the amp in to an "authorized service center" since it's
under Ampeg warranty still. All they said was to replace the tubes.

Any suggestions? I know my bass has a touchy input jack. If I bump the
cable
the wrong way I get some crackling. However, in general the bass sends a
clean signal to every other amp I've tried.

Thank you very much!

- Kevin

Kevin: post your question here. They are knowledgable, helpful and
will make you feel at home there. Post it to the Tech Bench forum:

http://p210.ezboard.com/bampworkshop

Good Luck.

[Kevin D.]

"Armand" wrote in message
...
In article U0QCg.5798$Gv.1562@fed1read09,
says...

I apologize in advance for the long post. Many thanks to anyone who can
help
me resolve this!

I'm not a tube amp expert but have a bass tube amp (Ampeg SVT-2 Pro)
that's
only 1 1/2 years old. I purchased it brand new with factory tubes
installed.
I recently (about 2 months ago) replaced ALL of the tubes in the head with
the following (from www.thetubestore.com):

Winged "C" (SED) 6550C (3 pairs, all matched)
Electro-Harmonix 12AU7A (3)
Electro-Harmonix 12AX7-EH (5)
Sovtek 12AX7-WB (2)

For the 12AX7's and 12AU7's, I don't know exactly which combination went
into the amp as I took it to my local guitar shop to have done. The amp
itself calls for only 5 12AX7's and 3 12AU7's. I can pull my extra preamp
tubes out of storage and figure out what's in the amp based on what isn't
in
the amp, if that's necessary, just let me know.

My problem is that when I first power up the amp and plug in, everything
sounds great. No line noise above what is to be expected and the tone is
"solid" (clear, with some nice throaty growling, etc.). In general, the
amp
behaves exactly as expected.

After about 15-25 minutes of playing (pretty loud, I might add), I start
getting a harsh distortion noise. It sounds kind of like a tearing or ugly
type of static. This is what was happening BEFORE I replaced the tubes. I
thought that getting new (better-than-factory) tubes would clear up the
problem. Well it hasn't.

I've also taken the amp in to an "authorized service center" since it's
under Ampeg warranty still. All they said was to replace the tubes.

Any suggestions? I know my bass has a touchy input jack. If I bump the
cable
the wrong way I get some crackling. However, in general the bass sends a
clean signal to every other amp I've tried.

Thank you very much!

- Kevin

Kevin: post your question here. They are knowledgable, helpful and
will make you feel at home there. Post it to the Tech Bench forum:

http://p210.ezboard.com/bampworkshop

Good Luck.

awesome, thank you very much, Armand!

[Armand]

In article 9MQCg.5800$Gv.816@fed1read09,
says...


"Armand" wrote in message
...
In article U0QCg.5798$Gv.1562@fed1read09,
says...

I apologize in advance for the long post. Many thanks to anyone who can
help
me resolve this!

I'm not a tube amp expert but have a bass tube amp (Ampeg SVT-2 Pro)
that's
only 1 1/2 years old. I purchased it brand new with factory tubes
installed.
I recently (about 2 months ago) replaced ALL of the tubes in the head with
the following (from www.thetubestore.com):

Winged "C" (SED) 6550C (3 pairs, all matched)
Electro-Harmonix 12AU7A (3)
Electro-Harmonix 12AX7-EH (5)
Sovtek 12AX7-WB (2)

For the 12AX7's and 12AU7's, I don't know exactly which combination
went
into the amp as I took it to my local guitar shop to have done. The amp
itself calls for only 5 12AX7's and 3 12AU7's. I can pull my extra preamp
tubes out of storage and figure out what's in the amp based on what isn't
in
the amp, if that's necessary, just let me know.

My problem is that when I first power up the amp and plug in, everything
sounds great. No line noise above what is to be expected and the tone is
"solid" (clear, with some nice throaty growling, etc.). In general, the
amp
behaves exactly as expected.

After about 15-25 minutes of playing (pretty loud, I might add), I start
getting a harsh distortion noise. It sounds kind of like a tearing or ugly
type of static. This is what was happening BEFORE I replaced the tubes. I
thought that getting new (better-than-factory) tubes would clear up the
problem. Well it hasn't.

I've also taken the amp in to an "authorized service center" since it's
under Ampeg warranty still. All they said was to replace the tubes.

Any suggestions? I know my bass has a touchy input jack. If I bump the
cable
the wrong way I get some crackling. However, in general the bass sends
a
clean signal to every other amp I've tried.

Thank you very much!

- Kevin

Kevin: post your question here. They are knowledgable, helpful and
will make you feel at home there. Post it to the Tech Bench forum:

http://p210.ezboard.com/bampworkshop

Good Luck.

awesome, thank you very much, Armand!

Posting is slow there, but what you get from them is a high quality concern for
your problem, so be patient for responses. They've helped me with my
Fender DR on more than one occasion and were spot on on with t-shooting
compared to other forums.

[Kevin D.]

"Armand" wrote in message
. ..
In article 9MQCg.5800$Gv.816@fed1read09,
says...


"Armand" wrote in message
...
In article U0QCg.5798$Gv.1562@fed1read09,
says...

I apologize in advance for the long post. Many thanks to anyone who can
help
me resolve this!

I'm not a tube amp expert but have a bass tube amp (Ampeg SVT-2 Pro)
that's
only 1 1/2 years old. I purchased it brand new with factory tubes
installed.
I recently (about 2 months ago) replaced ALL of the tubes in the head
with
the following (from www.thetubestore.com):

Winged "C" (SED) 6550C (3 pairs, all matched)
Electro-Harmonix 12AU7A (3)
Electro-Harmonix 12AX7-EH (5)
Sovtek 12AX7-WB (2)

For the 12AX7's and 12AU7's, I don't know exactly which combination
went
into the amp as I took it to my local guitar shop to have done. The amp
itself calls for only 5 12AX7's and 3 12AU7's. I can pull my extra
preamp
tubes out of storage and figure out what's in the amp based on what
isn't
in
the amp, if that's necessary, just let me know.

My problem is that when I first power up the amp and plug in, everything
sounds great. No line noise above what is to be expected and the tone is
"solid" (clear, with some nice throaty growling, etc.). In general, the
amp
behaves exactly as expected.

After about 15-25 minutes of playing (pretty loud, I might add), I start
getting a harsh distortion noise. It sounds kind of like a tearing or
ugly
type of static. This is what was happening BEFORE I replaced the tubes.
I
thought that getting new (better-than-factory) tubes would clear up the
problem. Well it hasn't.

I've also taken the amp in to an "authorized service center" since it's
under Ampeg warranty still. All they said was to replace the tubes.

Any suggestions? I know my bass has a touchy input jack. If I bump the
cable
the wrong way I get some crackling. However, in general the bass sends
a
clean signal to every other amp I've tried.

Thank you very much!

- Kevin

Kevin: post your question here. They are knowledgable, helpful and
will make you feel at home there. Post it to the Tech Bench forum:

http://p210.ezboard.com/bampworkshop

Good Luck.

awesome, thank you very much, Armand!

Posting is slow there, but what you get from them is a high quality
concern for
your problem, so be patient for responses. They've helped me with my
Fender DR on more than one occasion and were spot on on with t-shooting
compared to other forums.

I noticed that it's not a high activity forum, but I'm more concerned about
resolving my issue so I don't mind being patient. Thanks again for the
reference and follow-up.

- Kevin

[Armand]

In article 9MQCg.5800$Gv.816@fed1read09,
says...


"Armand" wrote in message
...
In article U0QCg.5798$Gv.1562@fed1read09,
says...

I apologize in advance for the long post. Many thanks to anyone who can
help
me resolve this!

I'm not a tube amp expert but have a bass tube amp (Ampeg SVT-2 Pro)
that's
only 1 1/2 years old. I purchased it brand new with factory tubes
installed.
I recently (about 2 months ago) replaced ALL of the tubes in the head with
the following (from www.thetubestore.com):

Winged "C" (SED) 6550C (3 pairs, all matched)
Electro-Harmonix 12AU7A (3)
Electro-Harmonix 12AX7-EH (5)
Sovtek 12AX7-WB (2)

For the 12AX7's and 12AU7's, I don't know exactly which combination
went
into the amp as I took it to my local guitar shop to have done. The amp
itself calls for only 5 12AX7's and 3 12AU7's. I can pull my extra preamp
tubes out of storage and figure out what's in the amp based on what isn't
in
the amp, if that's necessary, just let me know.

My problem is that when I first power up the amp and plug in, everything
sounds great. No line noise above what is to be expected and the tone is
"solid" (clear, with some nice throaty growling, etc.). In general, the
amp
behaves exactly as expected.

After about 15-25 minutes of playing (pretty loud, I might add), I start
getting a harsh distortion noise. It sounds kind of like a tearing or ugly
type of static. This is what was happening BEFORE I replaced the tubes. I
thought that getting new (better-than-factory) tubes would clear up the
problem. Well it hasn't.

I've also taken the amp in to an "authorized service center" since it's
under Ampeg warranty still. All they said was to replace the tubes.

Any suggestions? I know my bass has a touchy input jack. If I bump the
cable
the wrong way I get some crackling. However, in general the bass sends
a
clean signal to every other amp I've tried.

Thank you very much!

- Kevin

Kevin: post your question here. They are knowledgable, helpful and
will make you feel at home there. Post it to the Tech Bench forum:

http://p210.ezboard.com/bampworkshop

Good Luck.

awesome, thank you very much, Armand!

Kevin: Have you informed Ampeg that you changed the tubes and still have
the same problem? At this point, they would *have to* fix it under warranty.
After taking a look at the amp and seeing that it's pretty expensive, I would
push the issue with them in a serious way.

[Kevin D.]

"Armand" wrote in message
...
In article 9MQCg.5800$Gv.816@fed1read09,
says...


"Armand" wrote in message
...
In article U0QCg.5798$Gv.1562@fed1read09,
says...

I apologize in advance for the long post. Many thanks to anyone who can
help
me resolve this!

I'm not a tube amp expert but have a bass tube amp (Ampeg SVT-2 Pro)
that's
only 1 1/2 years old. I purchased it brand new with factory tubes
installed.
I recently (about 2 months ago) replaced ALL of the tubes in the head
with
the following (from www.thetubestore.com):

Winged "C" (SED) 6550C (3 pairs, all matched)
Electro-Harmonix 12AU7A (3)
Electro-Harmonix 12AX7-EH (5)
Sovtek 12AX7-WB (2)

For the 12AX7's and 12AU7's, I don't know exactly which combination
went
into the amp as I took it to my local guitar shop to have done. The amp
itself calls for only 5 12AX7's and 3 12AU7's. I can pull my extra
preamp
tubes out of storage and figure out what's in the amp based on what
isn't
in
the amp, if that's necessary, just let me know.

My problem is that when I first power up the amp and plug in, everything
sounds great. No line noise above what is to be expected and the tone is
"solid" (clear, with some nice throaty growling, etc.). In general, the
amp
behaves exactly as expected.

After about 15-25 minutes of playing (pretty loud, I might add), I start
getting a harsh distortion noise. It sounds kind of like a tearing or
ugly
type of static. This is what was happening BEFORE I replaced the tubes.
I
thought that getting new (better-than-factory) tubes would clear up the
problem. Well it hasn't.

I've also taken the amp in to an "authorized service center" since it's
under Ampeg warranty still. All they said was to replace the tubes.

Any suggestions? I know my bass has a touchy input jack. If I bump the
cable
the wrong way I get some crackling. However, in general the bass sends
a
clean signal to every other amp I've tried.

Thank you very much!

- Kevin

Kevin: post your question here. They are knowledgable, helpful and
will make you feel at home there. Post it to the Tech Bench forum:

http://p210.ezboard.com/bampworkshop

Good Luck.

awesome, thank you very much, Armand!

Kevin: Have you informed Ampeg that you changed the tubes and still have
the same problem? At this point, they would *have to* fix it under
warranty.
After taking a look at the amp and seeing that it's pretty expensive, I
would
push the issue with them in a serious way.


I told them about the problem BEFORE I changed the tubes, and they told me
to take it to my local "authorized service center" which is a general
electronics repair shop run by people who can't even speak English hardly at
all (seriously). There were literally PILES of electronic gear just sitting
all over the floor and spilling off of the shelving (VCR's, TV's,
projectors, receivers, etc). Against my better judgement I left my amp with
them to service.

It took them about 10 business days before I finally got an answer and if I
hadn't hounded them almost daily I know they would never have gotten back to
me for a LOT longer than that. I would call and they would tell me, "Call
back later. The service guy isn't here now." At one point, they couldn't
find my paperwork based off my name or phone number. It was like I never
even existed to them. Ugh.

Anyway, I finally picked my amp back up and all he said was, "Have you
changed the tubes? Just change them." Now here I am

But that's a good idea. I need to lay into Ampeg for setting me up with such
a sh!tty repair shop in the first place. They should pay to ship my head
back to their headquarters in Missouri and pay to ship it back to me once
it's fixed. Yea, I'll keep dreaming...

- Kevin

[[email protected]]

Kevin D. wrote:

Anyway, I finally picked my amp back up and all he said was, "Have you
changed the tubes? Just change them." Now here I am

But that's a good idea. I need to lay into Ampeg for setting me up with such
a sh!tty repair shop in the first place. They should pay to ship my head
back to their headquarters in Missouri and pay to ship it back to me once
it's fixed. Yea, I'll keep dreaming...

- Kevin

Hi RATs!

Yo! Kevin! Welcome to the future! OK, first, replacing all the tubes is
what the military does. It doesn't work very often, but, it does use up
excess inventory ...

Not just the U.S. military, all the friggin' militaries ...

OK, your amp sounds decent at first then goes to ****. Sounds like a
lame cap. There ARE a few lame caps in this world ...

WHICH ONE? Good question.

If you don't want to teach yourself how to troubleshoot amp circuits
.... why not? I can think of no greater calling ... ship your unit to
Missouri and pray for a competent maintenance technician.

The shop they sent you to was probably decent, once upon a time.
Everything gets worse, daily. Sigh.

And consider a standup string bass. Maybe not as loud, but GOOD!

So, no cheap fix from email. Grow up ... Earth is a turd among
asteroids.

Happy Ears!
Al

[Kevin D.]

wrote in message
oups.com...
Kevin D. wrote:

Anyway, I finally picked my amp back up and all he said was, "Have you
changed the tubes? Just change them." Now here I am

But that's a good idea. I need to lay into Ampeg for setting me up with
such
a sh!tty repair shop in the first place. They should pay to ship my head
back to their headquarters in Missouri and pay to ship it back to me once
it's fixed. Yea, I'll keep dreaming...

- Kevin

Hi RATs!

Yo! Kevin! Welcome to the future! OK, first, replacing all the tubes is
what the military does. It doesn't work very often, but, it does use up
excess inventory ...

Not just the U.S. military, all the friggin' militaries ...

OK, your amp sounds decent at first then goes to ****. Sounds like a
lame cap. There ARE a few lame caps in this world ...

WHICH ONE? Good question.

If you don't want to teach yourself how to troubleshoot amp circuits
... why not? I can think of no greater calling ... ship your unit to
Missouri and pray for a competent maintenance technician.

The shop they sent you to was probably decent, once upon a time.
Everything gets worse, daily. Sigh.

And consider a standup string bass. Maybe not as loud, but GOOD!

So, no cheap fix from email. Grow up ... Earth is a turd among
asteroids.

Happy Ears!
Al

Haha! Thanks for the reply and for the suggestion of what might be wrong. I
would love to learn how to troubleshoot and maintain tube amps. However, I
know literally ZERO about electronics and amplifiers so there's just too
much to learn RIGHT NOW. If I had someone willing to take me under their
wing, that's a different story

Additionally, I'd rather not die opening up my amp and getting pwnd by the
high voltages stored inside. If I have to ship to Missouri, I'll probably
just sell the amp here locally instead... at 70lbs plus the weight of
packing materials, it's going to cost me over $100 to ship it both ways.

Thanks again... here's to the beauty of tubes

[Alan Rutlidge]

"Kevin D." wrote in message
news:LNTCg.5804$Gv.4090@fed1read09...

wrote in message
oups.com...
Kevin D. wrote:

Anyway, I finally picked my amp back up and all he said was, "Have you
changed the tubes? Just change them." Now here I am

But that's a good idea. I need to lay into Ampeg for setting me up with
such
a sh!tty repair shop in the first place. They should pay to ship my head
back to their headquarters in Missouri and pay to ship it back to me
once
it's fixed. Yea, I'll keep dreaming...

- Kevin

Hi RATs!

Yo! Kevin! Welcome to the future! OK, first, replacing all the tubes is
what the military does. It doesn't work very often, but, it does use up
excess inventory ...

Not just the U.S. military, all the friggin' militaries ...

OK, your amp sounds decent at first then goes to ****. Sounds like a
lame cap. There ARE a few lame caps in this world ...

WHICH ONE? Good question.

If you don't want to teach yourself how to troubleshoot amp circuits
... why not? I can think of no greater calling ... ship your unit to
Missouri and pray for a competent maintenance technician.

The shop they sent you to was probably decent, once upon a time.
Everything gets worse, daily. Sigh.

And consider a standup string bass. Maybe not as loud, but GOOD!

So, no cheap fix from email. Grow up ... Earth is a turd among
asteroids.

Happy Ears!
Al

Haha! Thanks for the reply and for the suggestion of what might be wrong.
I would love to learn how to troubleshoot and maintain tube amps. However,
I know literally ZERO about electronics and amplifiers so there's just too
much to learn RIGHT NOW. If I had someone willing to take me under their
wing, that's a different story

Additionally, I'd rather not die opening up my amp and getting pwnd by the
high voltages stored inside. If I have to ship to Missouri, I'll probably
just sell the amp here locally instead... at 70lbs plus the weight of
packing materials, it's going to cost me over $100 to ship it both ways.

Thanks again... here's to the beauty of tubes


Getting a tube amp diagnosed correctly and repaired isn't exactly rocket
science, however I have to concur with comments already expressed that
getting this type of gear fixed is becoming more difficult. At the expense
of being flamed, I suggest you hunt down an old timer locally who has
previously worked on tube equipment. These guys generally have a good idea
what might be wrong and are capable of fixing it properly. Regrettably, a
lot of the newer and younger "techs" have NFI how to correctly diagnose and
repair faults in any equipment, let alone tube gear.

Cheers,
Alan

[[email protected]]

Kevin D. wrote:
Stuff.

Kevin:

CAUTION: Lethal voltages are present in tube amps. DO NOT attempt to
trouble-shoot unless you understand this and take appropriate
precautions.

That being written:

1. Does this amp have adjustable bias? It really does sound like
something is off given that the problem occurs after warm-up. IF the
bias is adjustable, then it MUST be attended to each time you change
(output) tubes.

2. Not all 12AX7 tubes are created equal. You might try swapping them
around and seeing if any difference(s) follow(s) the tube or remains
the same.

3. Do you have the capacity to test your output tubes? (I mean really
test them, not just emissions). It is my *opinion* that tubes are
changed far too often and as a panecea for actual troubleshooting.

5. Check the amp for any loose connections, overheated components,
dirty controls, intermittent jacks... the usual very basic
troubleshooting stuff.

6. If the amp is more than 20 years old (some would say 10), then I
suggest that you shotgun replace all the small-value caps. Use
high-quality (NOT necessarily expensive) caps of the same value, and at
the same-or-greater voltage.

But-and-usually and simplistically, (with audio stuff anyway)
late-onset distortion will most-often happen with either the bias being
off or a component failing when heated. Often the latter will cause the
former. Those components that are most prone to this failure are first
caps, then resistors. Then, look for a resistor that may be opening
under heat. Or a trace (if there are Printed Circuits) that opens. Are
there any visible signs of this distortion? Such as red plates on the
6550s? This is rude-and-crude, but there is not a whole lot going on
and such problems are seldom terribly subtle.

REMINDER: Lethal Voltages and all that.

Peter Wieck
Wyncote, PA

[Kevin D.]

"Alan Rutlidge" wrote in message
...
Getting a tube amp diagnosed correctly and repaired isn't exactly rocket
science, however I have to concur with comments already expressed that
getting this type of gear fixed is becoming more difficult. At the
expense of being flamed, I suggest you hunt down an old timer locally who
has previously worked on tube equipment. These guys generally have a good
idea what might be wrong and are capable of fixing it properly.
Regrettably, a lot of the newer and younger "techs" have NFI how to
correctly diagnose and repair faults in any equipment, let alone tube
gear.

Cheers,
Alan

Know anyone you can recommend in the Southern California area? I'm mid-point
between LA and San Diego and would prefer Orange County but would be willing
to drive a bit if the guy really knows his stuff. Many thanks for your quick
reply.

- Kevin

[Kevin D.]

wrote in message
ps.com...

Kevin D. wrote:
Stuff.

Kevin:

CAUTION: Lethal voltages are present in tube amps. DO NOT attempt to
trouble-shoot unless you understand this and take appropriate
precautions.


This is why I won't attempt to troubleshoot myself

That being written:

1. Does this amp have adjustable bias? It really does sound like
something is off given that the problem occurs after warm-up. IF the
bias is adjustable, then it MUST be attended to each time you change
(output) tubes.


Yes, and to my knowledge, the bias was properly adjusted by the tech who
installed the new tubes. I have also considered this to be a potential cause
of the problem.

2. Not all 12AX7 tubes are created equal. You might try swapping them
around and seeing if any difference(s) follow(s) the tube or remains
the same.


I believe this is something I can do easily on my own, correct?

3. Do you have the capacity to test your output tubes? (I mean really
test them, not just emissions). It is my *opinion* that tubes are
changed far too often and as a panecea for actual troubleshooting.


No but I would love to eventually learn.

5. Check the amp for any loose connections, overheated components,
dirty controls, intermittent jacks... the usual very basic
troubleshooting stuff.


All controls, switches and jacks on the outside of the amp work great. I
can't say for the inside, though.

6. If the amp is more than 20 years old (some would say 10), then I
suggest that you shotgun replace all the small-value caps. Use
high-quality (NOT necessarily expensive) caps of the same value, and at
the same-or-greater voltage.


It's only 1 1/2 years old, and still under Ampeg warranty. See my reply to
Armand about what happened when I contacted Ampeg about my problem.

But-and-usually and simplistically, (with audio stuff anyway)
late-onset distortion will most-often happen with either the bias being
off or a component failing when heated. Often the latter will cause the
former. Those components that are most prone to this failure are first
caps, then resistors. Then, look for a resistor that may be opening
under heat. Or a trace (if there are Printed Circuits) that opens. Are
there any visible signs of this distortion? Such as red plates on the
6550s? This is rude-and-crude, but there is not a whole lot going on
and such problems are seldom terribly subtle.


Thank you, Peter. You've been extremely helpful. My next goal is to find a
TRUE repair tech who can perform your suggestions on my behalf, and maybe
even send the bill to Ampeg

REMINDER: Lethal Voltages and all that.

Peter Wieck
Wyncote, PA

[[email protected]]

Kevin:

Note the interpolations.


CAUTION: Lethal voltages are present in tube amps. DO NOT attempt to
trouble-shoot unless you understand this and take appropriate
precautions.


This is why I won't attempt to troubleshoot myself

OK. Eventually, however, self-defense will require you to learn a but
of stuff. Not heavy-duty, but a bit.


That being written:

1. Does this amp have adjustable bias? It really does sound like
something is off given that the problem occurs after warm-up. IF the
bias is adjustable, then it MUST be attended to each time you change
(output) tubes.


Yes, and to my knowledge, the bias was properly adjusted by the tech who
installed the new tubes. I have also considered this to be a potential cause
of the problem.

Betcha not (properly adjusted now). Adjusting bias to new tubes takes
(at least) 40 hours of actual use. You adjust them when the tubes are
installed, then check each five-or-so hours moving forward as the tubes
burn in. Until you go ~10 hours of use with no change, keep checking.

2. Not all 12AX7 tubes are created equal. You might try swapping them
around and seeing if any difference(s) follow(s) the tube or remains
the same.


I believe this is something I can do easily on my own, correct?

Yep. Sure can. But be sure you track the changes accurately so you can
be sure of the results. Did, by any chance, the 12AX7s get changed as
well? If so, did you retain the old ones?

3. Do you have the capacity to test your output tubes? (I mean really
test them, not just emissions). It is my *opinion* that tubes are
changed far too often and as a panecea for actual troubleshooting.

For the record, do not invest in a tube tester for just one amp...
unless or until you trip over a properly calibrated Hickok-or-Equal for
$100 or less. The only point for testing is to have a clue where to
start troubleshooting... eliminating the tubes is a good thing.

No but I would love to eventually learn.

5. Check the amp for any loose connections, overheated components,
dirty controls, intermittent jacks... the usual very basic
troubleshooting stuff.

All controls, switches and jacks on the outside of the amp work great. I
can't say for the inside, though.

6. If the amp is more than 20 years old (some would say 10), then I
suggest that you shotgun replace all the small-value caps. Use
high-quality (NOT necessarily expensive) caps of the same value, and at
the same-or-greater voltage.


It's only 1 1/2 years old, and still under Ampeg warranty. See my reply to
Armand about what happened when I contacted Ampeg about my problem.

Really sounds (reads) like bias issues, then. Not to exclude bad caps,
but usually they last more than a couple of years. But if the bias
turns out to be fine, start in on the caps AFTER making sure everything
is otherwise 'tight'.

But-and-usually and simplistically, (with audio stuff anyway)
late-onset distortion will most-often happen with either the bias being
off or a component failing when heated. Often the latter will cause the
former. Those components that are most prone to this failure are first
caps, then resistors. Then, look for a resistor that may be opening
under heat. Or a trace (if there are Printed Circuits) that opens. Are
there any visible signs of this distortion? Such as red plates on the
6550s? This is rude-and-crude, but there is not a whole lot going on
and such problems are seldom terribly subtle.

The more I think about it, it could be some sort of heat-related
cold-solder joint or broken trace (if PCBs are present) if the tube
sockets were mangled/mashed/stressed when the tubes were changed.

Thank you, Peter. You've been extremely helpful. My next goal is to find a
TRUE repair tech who can perform your suggestions on my behalf, and maybe
even send the bill to Ampeg

Ya'd think that in SoCal there would be all sorts of amp service techs.
But, look for someone with a bit of grey at the temples if you have no
other screening criterion.


REMINDER: Lethal Voltages and all that.


Peter Wieck
Wyncote, PA

[[email protected]]

Kevin D. wrote:

After about 15-25 minutes of playing (pretty loud, I might add), I start
getting a harsh distortion noise. It sounds kind of like a tearing or ugly
type of static. This is what was happening BEFORE I replaced the tubes. I
thought that getting new (better-than-factory) tubes would clear up the
problem. Well it hasn't.

I've also taken the amp in to an "authorized service center" since it's
under Ampeg warranty still. All they said was to replace the tubes.

Any suggestions? I know my bass has a touchy input jack. If I bump the cable
the wrong way I get some crackling. However, in general the bass sends a
clean signal to every other amp I've tried.


Sounds like a grounding problem between the secondary of output
transformer(speaker) and the ground return of the chassis. Check for
corrosion or looseness on the speaker phone jack and while you are
there check the input phone jack. There should be a soldered to
chassis lug, check that too.




Thank you very much!

- Kevin

[Kevin D.]

More inter-posting...

wrote in message
ups.com...
Kevin:

Note the interpolations.


CAUTION: Lethal voltages are present in tube amps. DO NOT attempt to
trouble-shoot unless you understand this and take appropriate
precautions.


This is why I won't attempt to troubleshoot myself

OK. Eventually, however, self-defense will require you to learn a but
of stuff. Not heavy-duty, but a bit.


I completely agree with you. However, a cursory search for valve amplifier
repair and maintenance yields too many results for me to know where to
begin. And since we're dealing with the possibility of frying myself, I've
got to make sure I get all my facts straight before I do anything. Any
recommended reading?


That being written:

1. Does this amp have adjustable bias? It really does sound like
something is off given that the problem occurs after warm-up. IF the
bias is adjustable, then it MUST be attended to each time you change
(output) tubes.


Yes, and to my knowledge, the bias was properly adjusted by the tech who
installed the new tubes. I have also considered this to be a potential
cause
of the problem.

Betcha not (properly adjusted now). Adjusting bias to new tubes takes
(at least) 40 hours of actual use. You adjust them when the tubes are
installed, then check each five-or-so hours moving forward as the tubes
burn in. Until you go ~10 hours of use with no change, keep checking.


This is the first I've heard of this. However, it sounds very reasonable and
makes complete sense. I highly doubt any significant burn-in period was
exhausted.

2. Not all 12AX7 tubes are created equal. You might try swapping them
around and seeing if any difference(s) follow(s) the tube or remains
the same.


I believe this is something I can do easily on my own, correct?

Yep. Sure can. But be sure you track the changes accurately so you can
be sure of the results. Did, by any chance, the 12AX7s get changed as
well? If so, did you retain the old ones?


Yup, ALL the tubes were changed. The 6 power tubes, and all the preamp tubes
(5 12AX7's and 3 12AU7's). I feel that I should focus on the power tubes
first, though.


3. Do you have the capacity to test your output tubes? (I mean really
test them, not just emissions). It is my *opinion* that tubes are
changed far too often and as a panecea for actual troubleshooting.

For the record, do not invest in a tube tester for just one amp...
unless or until you trip over a properly calibrated Hickok-or-Equal for
$100 or less. The only point for testing is to have a clue where to
start troubleshooting... eliminating the tubes is a good thing.

No but I would love to eventually learn.

5. Check the amp for any loose connections, overheated components,
dirty controls, intermittent jacks... the usual very basic
troubleshooting stuff.

All controls, switches and jacks on the outside of the amp work great. I
can't say for the inside, though.

6. If the amp is more than 20 years old (some would say 10), then I
suggest that you shotgun replace all the small-value caps. Use
high-quality (NOT necessarily expensive) caps of the same value, and at
the same-or-greater voltage.


It's only 1 1/2 years old, and still under Ampeg warranty. See my reply
to
Armand about what happened when I contacted Ampeg about my problem.

Really sounds (reads) like bias issues, then. Not to exclude bad caps,
but usually they last more than a couple of years. But if the bias
turns out to be fine, start in on the caps AFTER making sure everything
is otherwise 'tight'.

But-and-usually and simplistically, (with audio stuff anyway)
late-onset distortion will most-often happen with either the bias being
off or a component failing when heated. Often the latter will cause the
former. Those components that are most prone to this failure are first
caps, then resistors. Then, look for a resistor that may be opening
under heat. Or a trace (if there are Printed Circuits) that opens. Are
there any visible signs of this distortion? Such as red plates on the
6550s? This is rude-and-crude, but there is not a whole lot going on
and such problems are seldom terribly subtle.

The more I think about it, it could be some sort of heat-related
cold-solder joint or broken trace (if PCBs are present) if the tube
sockets were mangled/mashed/stressed when the tubes were changed.

Thank you, Peter. You've been extremely helpful. My next goal is to find
a
TRUE repair tech who can perform your suggestions on my behalf, and maybe
even send the bill to Ampeg

Ya'd think that in SoCal there would be all sorts of amp service techs.
But, look for someone with a bit of grey at the temples if you have no
other screening criterion.


Oh there are more than plenty. That's the problem! I pretty much randomly
picked the last place to put the new tubes in, and look where I am now :-/

Anyway, I need to make some phone calls and talk directly to the tech to
find out his/her personal experience level. I need to perform a quick "phone
interview" before I leave my precious with anyone again.


REMINDER: Lethal Voltages and all that.


Peter Wieck
Wyncote, PA

[Kevin D.]

" wrote in message
ups.com...

Sounds like a grounding problem between the secondary of output
transformer(speaker) and the ground return of the chassis. Check for
corrosion or looseness on the speaker phone jack and while you are
there check the input phone jack. There should be a soldered to
chassis lug, check that too.


Hmm, unfortunately I don't quite follow you. This is where my very limited
knowledge of electronics and, specifically, amplifiers kicks in. I'm
confused by calling the speaker the secondary output? I'm sure I'm
misinterpreting.

I can tell you that I'm connecting the amp to the speaker cabinet (a single,
8x10 cab wired as two 4x10 cabs @ 8ohms each totalling a 4ohm load) by using
a speakon cable. None of the jacks are loose, nor is there any corrosion
anywhere. The entire setup is only 1 1/2 years old and was purchased brand
new (including the amp, speaker cab and speakon cable).

I appreciate your help, thank you!

- Kevin

[Kevin D.]

"Alan Rutlidge" wrote in message
...
Sorry Kevin, but I'm not in the USA, but here is a starter link -
http://www.webervst.com/techreg/californ.htm
Maybe one of these outfits might be able to assist.

Cheers,
Alan


That's a great resource, thanks for the link, Alan!

- Kevin

[[email protected]]

Kevin D. wrote:

I can tell you that I'm connecting the amp to the speaker cabinet (a single,
8x10 cab wired as two 4x10 cabs @ 8ohms each totalling a 4ohm load) by using
a speakon cable. None of the jacks are loose, nor is there any corrosion
anywhere. The entire setup is only 1 1/2 years old and was purchased brand
new (including the amp, speaker cab and speakon cable).

I appreciate your help, thank you!

- Kevin


A ground star is a point in an amp where all the ground or
returns connect. This should be at zero volts, if there is a loose
connection or a cold solder joint there then you will have problems.
The ground star should be near the center of the chassis, the wires
should be black and all the solder joints should be solid and shinny.
You are going to have to open up the amp and have a good look. It
sounds to me like the speaker is not grounded.
Surf my site http://www.retrotech.ca, look under Radio
Television News for an article called guitar amps. I hope this helps.

[Kevin D.]

" wrote in message
ups.com...

Kevin D. wrote:

I can tell you that I'm connecting the amp to the speaker cabinet (a
single,
8x10 cab wired as two 4x10 cabs @ 8ohms each totalling a 4ohm load) by
using
a speakon cable. None of the jacks are loose, nor is there any corrosion
anywhere. The entire setup is only 1 1/2 years old and was purchased
brand
new (including the amp, speaker cab and speakon cable).

I appreciate your help, thank you!

- Kevin


A ground star is a point in an amp where all the ground or
returns connect. This should be at zero volts, if there is a loose
connection or a cold solder joint there then you will have problems.
The ground star should be near the center of the chassis, the wires
should be black and all the solder joints should be solid and shinny.
You are going to have to open up the amp and have a good look. It
sounds to me like the speaker is not grounded.
Surf my site http://www.retrotech.ca, look under Radio
Television News for an article called guitar amps. I hope this helps.

Thanks for the follow-up and link. I'll spend some time reading through your
resources before venturing out on my own.

[Kevin D.]

"Kevin D." wrote in message
news:U0QCg.5798$Gv.1562@fed1read09...
I apologize in advance for the long post. Many thanks to anyone who can
help me resolve this!

I'm not a tube amp expert but have a bass tube amp (Ampeg SVT-2 Pro)
that's only 1 1/2 years old. I purchased it brand new with factory tubes
installed. I recently (about 2 months ago) replaced ALL of the tubes in
the head with the following (from www.thetubestore.com):

Winged "C" (SED) 6550C (3 pairs, all matched)
Electro-Harmonix 12AU7A (3)
Electro-Harmonix 12AX7-EH (5)
Sovtek 12AX7-WB (2)

For the 12AX7's and 12AU7's, I don't know exactly which combination went
into the amp as I took it to my local guitar shop to have done. The amp
itself calls for only 5 12AX7's and 3 12AU7's. I can pull my extra preamp
tubes out of storage and figure out what's in the amp based on what isn't
in the amp, if that's necessary, just let me know.

My problem is that when I first power up the amp and plug in, everything
sounds great. No line noise above what is to be expected and the tone is
"solid" (clear, with some nice throaty growling, etc.). In general, the
amp behaves exactly as expected.

After about 15-25 minutes of playing (pretty loud, I might add), I start
getting a harsh distortion noise. It sounds kind of like a tearing or ugly
type of static. This is what was happening BEFORE I replaced the tubes. I
thought that getting new (better-than-factory) tubes would clear up the
problem. Well it hasn't.

I've also taken the amp in to an "authorized service center" since it's
under Ampeg warranty still. All they said was to replace the tubes.

Any suggestions? I know my bass has a touchy input jack. If I bump the
cable the wrong way I get some crackling. However, in general the bass
sends a clean signal to every other amp I've tried.

Thank you very much!

- Kevin

Just a follow-up to anyone still following this thread. The 'authorized
repair tech' I just took the amp to re-soldered all the pots. I played last
night for 3 hours straight and had none of the problems I was experiencing
before. I'm keeping my fingers crossed. Thanks for all the assistance!

- Kevin

[Sander deWaal]

"Kevin D." said:


Just a follow-up to anyone still following this thread. The 'authorized
repair tech' I just took the amp to re-soldered all the pots. I played last
night for 3 hours straight and had none of the problems I was experiencing
before. I'm keeping my fingers crossed. Thanks for all the assistance!


It's a good thing that most people are deadly afraid of a hot
soldering iron, or else a lot of us guys would be out of a job ;-)


Just kidding, Kevin!

Congrats on the successfull repair!

--
"Due knot trussed yore spell chequer two fined awl miss steaks."

[Kevin D.]

"Sander deWaal" wrote in message
...
"Kevin D." said:


Just a follow-up to anyone still following this thread. The 'authorized
repair tech' I just took the amp to re-soldered all the pots. I played
last
night for 3 hours straight and had none of the problems I was experiencing
before. I'm keeping my fingers crossed. Thanks for all the assistance!


It's a good thing that most people are deadly afraid of a hot
soldering iron, or else a lot of us guys would be out of a job ;-)


Just kidding, Kevin!

Congrats on the successfull repair!

Eventually, I'd like to be able to maintain and repair the amp myself (Ampeg
SVT-2 Pro, btw) but that's a long while down the road since I have basically
*0* knowledge at the moment. However, the repair was covered under warranty
so it was worth having someone else do it anyway. Thanks for the response!