| Author |
Message |
Ryan Stalter
Guest
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 Posted:
Fri Oct 28, 2005 11:47 pm Post subject:
Tube Amp Troubles |
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Hello. This is my first time posting to this group and I hope some of you
might be able to provide me with some direction. I'm a college kid who's
trying to learn as much as I can about tube amps and after so much reading
I wanted to get my hands dirty. I've fixed a few amps for my friends and
one of them had a broken Ampeg V4 that was giving him extremely low volume.
Needless to say, I took it off his hands to see if I could get it up and
running. First I just played it to see what was happening. On 10 it wasn't
at all uncomfortable to listen to. Maybe slightly louder than a television.
Both channels were doing this so I figured it was after the channels
converged. Then I took this Sunn Coliseum I have and ran the preamp out
into the power amp in on the Ampeg. No appreciable difference in volume. I
opened it up and took voltages and everything was within a few volts of the
schematic I have so I swapped the tubes out. No change still. I found some
resistors that drifted so I swapped them out and still nothing. I don't
have a scope yet but I tested the AC across the primary of the output
transformer and got a reading of about 20 volts which according to one
books power table is about right for a 100 watt amp into a 4 ohm load. So
just the other day I had some free time on my hands so I went through and
heated up some joints in the power amp and it seemed to get a little bit
louder so I played for a minute and just looked at the tubes and while
idling, the power tubes have a normal blue glow about them but when I hit a
note and hold it the plates start to turn red and when I let go they go
back to that blue glow. I'd really just like to get this thing up and
working and back to my friend. Any suggestions? I'd really appreciate it.
Thanks!
-Ryan
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west
Guest
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| Posted:
Sat Oct 29, 2005 4:42 am Post subject:
Re: Tube Amp Troubles |
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"Ryan Stalter" <ryangobie@hotmail.com> wrote in message
news:Xns96FD923419FA3ryangobiehotmailcom@130.81.64.196...
| Quote: |
Hello. This is my first time posting to this group and I hope some of you
might be able to provide me with some direction. I'm a college kid who's
trying to learn as much as I can about tube amps and after so much reading
I wanted to get my hands dirty. I've fixed a few amps for my friends and
one of them had a broken Ampeg V4 that was giving him extremely low
volume.
Needless to say, I took it off his hands to see if I could get it up and
running. First I just played it to see what was happening. On 10 it wasn't
at all uncomfortable to listen to. Maybe slightly louder than a
television.
Both channels were doing this so I figured it was after the channels
converged. Then I took this Sunn Coliseum I have and ran the preamp out
into the power amp in on the Ampeg. No appreciable difference in volume. I
opened it up and took voltages and everything was within a few volts of
the
schematic I have so I swapped the tubes out. No change still. I found some
resistors that drifted so I swapped them out and still nothing. I don't
have a scope yet but I tested the AC across the primary of the output
transformer and got a reading of about 20 volts which according to one
books power table is about right for a 100 watt amp into a 4 ohm load. So
just the other day I had some free time on my hands so I went through and
heated up some joints in the power amp and it seemed to get a little bit
louder so I played for a minute and just looked at the tubes and while
idling, the power tubes have a normal blue glow about them but when I hit
a
note and hold it the plates start to turn red and when I let go they go
back to that blue glow. I'd really just like to get this thing up and
working and back to my friend. Any suggestions? I'd really appreciate it.
Thanks!
-Ryan
|
Hi Ryan,
According to your long description, I do not think anyone will be able to
really help you. I might suggest to describe your problem as a completely
non-technical person would. For example, " Here is my ----, model # ----
amplifier and the sound out of both speakers is about 25% of the normal
volume. I know the problem is not my preamp because when I play my CD and
preamp with another amplifier, all is OK." Forget for now all the technical
talk about voltage, load, etc. Remember ... layman. Then someone might
suggest to try something more specific. I'm not trying to be rude, but a
little knowledge can be dangerous, especially with the LETHAL voltages in a
tube amp. Good luck.
Cordially,
west |
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Pooh Bear
Guest
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| Posted:
Sat Oct 29, 2005 12:30 pm Post subject:
Re: Tube Amp Troubles |
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Ryan Stalter wrote:
| Quote: | Hello. This is my first time posting to this group
|
A suggestion.
Learn about paragraphs. A large solid block of text is very uninviting - and
actually unnecessarily difficult - to read.
Keep your life history to minimum.
Concentrate on the relevant facts and ask a specific well-considered ( not
vague ) question ( s ).
Graham |
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Robert McLean
Guest
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| Posted:
Sat Oct 29, 2005 6:15 pm Post subject:
Re: Tube Amp Troubles |
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"Ryan Stalter" <ryangobie@hotmail.com> wrote in message
news:Xns96FD923419FA3ryangobiehotmailcom@130.81.64.196...
| Quote: |
Hello. This is my first time posting to this group and I hope some of you
might be able to provide me with some direction. I'm a college kid who's
trying to learn as much as I can about tube amps and after so much reading
I wanted to get my hands dirty. I've fixed a few amps for my friends and
one of them had a broken Ampeg V4 that was giving him extremely low
volume.
Needless to say, I took it off his hands to see if I could get it up and
running. First I just played it to see what was happening. On 10 it wasn't
at all uncomfortable to listen to. Maybe slightly louder than a
television.
Both channels were doing this so I figured it was after the channels
converged. Then I took this Sunn Coliseum I have and ran the preamp out
into the power amp in on the Ampeg. No appreciable difference in volume. I
opened it up and took voltages and everything was within a few volts of
the
schematic I have so I swapped the tubes out. No change still. I found some
resistors that drifted so I swapped them out and still nothing. I don't
have a scope yet but I tested the AC across the primary of the output
transformer and got a reading of about 20 volts which according to one
books power table is about right for a 100 watt amp into a 4 ohm load. So
just the other day I had some free time on my hands so I went through and
heated up some joints in the power amp and it seemed to get a little bit
louder so I played for a minute and just looked at the tubes and while
idling, the power tubes have a normal blue glow about them but when I hit
a
note and hold it the plates start to turn red and when I let go they go
back to that blue glow. I'd really just like to get this thing up and
working and back to my friend. Any suggestions? I'd really appreciate it.
Thanks!
-Ryan
|
Do you really mean primary ??
20 volts on the Primary is very low.
20 volts on the Secondary is correct for 100 Watts into 4 ohms. If it does
not sound loud then there is something wrong with your speaker. ( or your
hearing ) |
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Lord Valve
Guest
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| Posted:
Sat Oct 29, 2005 9:18 pm Post subject:
Re: Tube Amp Troubles |
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Pooh Bear wrote:
| Quote: | Ryan Stalter wrote:
Hello. This is my first time posting to this group
A suggestion.
Learn about paragraphs. A large solid block of text is very uninviting - and
actually unnecessarily difficult - to read.
Keep your life history to minimum.
Concentrate on the relevant facts and ask a specific well-considered ( not
vague ) question ( s ).
Graham
|
Yeah - who do you think you are, George Gleason or something?
LV |
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Ryan Stalter
Guest
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| Posted:
Sun Oct 30, 2005 4:42 am Post subject:
Re: Tube Amp Troubles |
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Thank you for your reply West. I cut it down as short as possible. I have
an Ampeg V4 that has low volume and the left two output tubes glow red
after a few seconds if a signal is applied.
I admit my first post was a bit long winded but in many ventures, it seems
like the more information provided the easier it is to get a good answer.
And paragraphs? I passed all my college writing courses and I'm not writing
a formal letter. Sorry. Just trying to learn.
Thanks
Ryan |
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Sander deWaal
Guest
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| Posted:
Sun Oct 30, 2005 7:49 pm Post subject:
Re: Tube Amp Troubles |
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Ryan Stalter <ryangobie@hotmail.com> said:
| Quote: | Thank you for your reply West. I cut it down as short as possible. I have
an Ampeg V4 that has low volume and the left two output tubes glow red
after a few seconds if a signal is applied.
|
That could be a number of things, varying from a leaky coupling
capacitor to the grids of both output tubes (assuming they have one in
common), to an intermittent or permanent broken wiring in/to the
output transformer, causing the other 2 tubes to supply a (distorted)
signal on their own to the transformer.
Check the voltages at the tube's electrodes, especially at the grid
and plate connections of the failing tubes.
Come to think of it, failing grid-grounding resistors may cause such
problems as well (value going up, therefore causing tubes to draw too
much current).
I can't be any more specific because I don't have a schematic at hand,
but the above things I'd check at first.
I haven't seen your initial post, so I don't know if there was any
useful information to add to the above.
You can try to ask Lord Valve, he might have a better idea about this
amp. He posts regularly on this newsgroup, but he can be found for
sure over on alt.guitar.amps.
--
"Audio as a serious hobby is going down the tubes."
- Howard Ferstler, 25/4/2005 |
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Pooh Bear
Guest
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| Posted:
Sun Oct 30, 2005 9:16 pm Post subject:
Re: Tube Amp Troubles |
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Lord Valve wrote:
| Quote: | Pooh Bear wrote:
Ryan Stalter wrote:
Hello. This is my first time posting to this group
A suggestion.
Learn about paragraphs. A large solid block of text is very uninviting - and
actually unnecessarily difficult - to read.
Keep your life history to minimum.
Concentrate on the relevant facts and ask a specific well-considered ( not
vague ) question ( s ).
Graham
Yeah - who do you think you are, George Gleason or something?
LV
|
Uh ? Where are the spelling and grammar errors ? ;-)
The above was my response to being totally put off from reading or responding by
the style of the post.
At times like this you realise what those English teachers were getting at.
Inability to express yourself concisely and accurately has its drawbacks.
Graham |
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Pooh Bear
Guest
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| Posted:
Sun Oct 30, 2005 9:19 pm Post subject:
Re: Tube Amp Troubles |
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Ryan Stalter wrote:
| Quote: | Thank you for your reply West. I cut it down as short as possible. I have
an Ampeg V4 that has low volume and the left two output tubes glow red
after a few seconds if a signal is applied.
|
Glowing red means they're getting hot.
That normally only happens when there lots of volume.
The suppresor grids glow blue when quiescent though ?
You may have a shorted turn in the output transformer. That'll also restrict
the maximum output ( a *lot* ).
Graham |
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Ryan Stalter
Guest
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| Posted:
Sun Oct 30, 2005 10:39 pm Post subject:
Re: Tube Amp Troubles |
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That's exactly it. It's only after you play for a minute or so that they
heat up to the point that they glow. I was in it before sending a signal
through till they just started to glow and the grids on the two glowing
were around -70 whereas the other two were around -90...at idle they're all
around -60
I checked the DC resistance across the primary and it was 99ohms but
between one side and the center tap I got two different readings. One
higher than the other by about 10 ohms. Is that suspicious? Thanks.
Ryan
Pooh Bear <rabbitsfriendsandrelations@hotmail.com> wrote in
news:4364E475.C9293DC6@hotmail.com:
| Quote: |
Ryan Stalter wrote:
Thank you for your reply West. I cut it down as short as possible. I
have an Ampeg V4 that has low volume and the left two output tubes
glow red after a few seconds if a signal is applied.
Glowing red means they're getting hot.
That normally only happens when there lots of volume.
The suppresor grids glow blue when quiescent though ?
You may have a shorted turn in the output transformer. That'll also
restrict the maximum output ( a *lot* ).
Graham
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Jon Yaeger
Guest
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| Posted:
Sun Oct 30, 2005 10:43 pm Post subject:
Re: Tube Amp Troubles |
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in article Xns96FF7250EFF4Bryangobiehotmailcom@130.81.64.196, Ryan Stalter
at ryangobie@hotmail.com wrote on 10/30/05 11:39 AM:
| Quote: | That's exactly it. It's only after you play for a minute or so that they
heat up to the point that they glow. I was in it before sending a signal
through till they just started to glow and the grids on the two glowing
were around -70 whereas the other two were around -90...at idle they're all
around -60
I checked the DC resistance across the primary and it was 99ohms but
between one side and the center tap I got two different readings. One
higher than the other by about 10 ohms. Is that suspicious? Thanks.
Ryan
Pooh Bear <rabbitsfriendsandrelations@hotmail.com> wrote in
news:4364E475.C9293DC6@hotmail.com:
Ryan Stalter wrote:
Thank you for your reply West. I cut it down as short as possible. I
have an Ampeg V4 that has low volume and the left two output tubes
glow red after a few seconds if a signal is applied.
Glowing red means they're getting hot.
That normally only happens when there lots of volume.
The suppresor grids glow blue when quiescent though ?
You may have a shorted turn in the output transformer. That'll also
restrict the maximum output ( a *lot* ).
Graham
|
Sure sounds like bad (leaky) output tube coupling caps to me . . . .
Jon |
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Sander deWaal
Guest
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| Posted:
Sun Oct 30, 2005 10:50 pm Post subject:
Re: Tube Amp Troubles |
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Ryan Stalter <ryangobie@hotmail.com> said:
| Quote: | That's exactly it. It's only after you play for a minute or so that they
heat up to the point that they glow. I was in it before sending a signal
through till they just started to glow and the grids on the two glowing
were around -70 whereas the other two were around -90...at idle they're all
around -60
|
There you have it.
Meanwhile, I found 2 schematics of this amp, one Ampeg and the other
one a Magnavox.
The 2 sxhematics resemble each other very much:
http://www.drtube.com/schematics/ampeg/vt22-v4-70.gif
http://www.drtube.com/schematics/ampeg/vt22-v4-74.gif
Check C11 and C13, and R35 and R36.
Also the resistors in the anode circuits R39, R40, R46 and R49.
In the latter circuit, bias hovers around -62V.
| Quote: | I checked the DC resistance across the primary and it was 99ohms but
between one side and the center tap I got two different readings. One
higher than the other by about 10 ohms. Is that suspicious? Thanks.
|
Usually, there is a difference between windings DC resistance, but 10%
ranks a little high IMO.
--
"Audio as a serious hobby is going down the tubes."
- Howard Ferstler, 25/4/2005 |
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Pooh Bear
Guest
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| Posted:
Sun Oct 30, 2005 11:16 pm Post subject:
Re: Tube Amp Troubles |
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Jon Yaeger wrote:
| Quote: | Sure sounds like bad (leaky) output tube coupling caps to me . . . .
|
I beg your pardon ?
Graham |
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Pooh Bear
Guest
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| Posted:
Sun Oct 30, 2005 11:20 pm Post subject:
Re: Tube Amp Troubles |
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Ryan Stalter wrote:
| Quote: | That's exactly it. It's only after you play for a minute or so that they
heat up to the point that they glow. I was in it before sending a signal
through till they just started to glow and the grids on the two glowing
were around -70 whereas the other two were around -90...at idle they're all
around -60
|
The point is...... Do they glow at relatively low volume ? That's a fairly
likely sign of a shorted turn.
| Quote: | I checked the DC resistance across the primary and it was 99ohms but
between one side and the center tap I got two different readings. One
higher than the other by about 10 ohms. Is that suspicious? Thanks.
|
Not horribly so.
It's actually quite difficult to exactly match the DC resistance of both halves
of the primary.
Graham |
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Jon Yaeger
Guest
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| Posted:
Sun Oct 30, 2005 11:28 pm Post subject:
Re: Tube Amp Troubles |
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in article 4364FFD7.E6466815@hotmail.com, Pooh Bear at
rabbitsfriendsandrelations@hotmail.com wrote on 10/30/05 12:16 PM:
| Quote: |
Jon Yaeger wrote:
Sure sounds like bad (leaky) output tube coupling caps to me . . . .
I beg your pardon ?
Graham
|
Oops! I guess I overlooked the qualifier, "at idle they ALL are around -60."
Ignore my advice, which might be right if one or two of the grid voltages
were lower at idle.
J |
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