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  #81   Report Post  
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fryzz fryzz is offline
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Default what is causing this problem?



In the guitar amp built for nephew I also used a 'single' connection
on the bias pot wiper but the configuration is different. The pot ends
go to -Bias and the grid resistor with the wiper going to ground
through another resistor. -Bias through the pot and ground resistor
then forms a variable divider but if the wiper breaks contact bias
goes full negative so it's 'fail safe'.


Excellent!

  #82   Report Post  
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cipher cipher is offline
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Posts: 42
Default what is causing this problem?

bigwig wrote in
:

On 6 Dec, 23:24, Peter Wieck wrote:
On Dec 6, 4:35*pm, mick wrote:





On Sat, 06 Dec 2008 15:18:51 -0600, cipher wrote:


snip


Sir, I will take good detailed pictures and post them up.


who around these parts would be able to work on my amp?


Around Mordor? Saruman Electronics, I suppose... Give him a *Ring*!


im sure most of you could, but who would??


Difficult to guess when no-one knows where you are, isn't it?


I suck at soldering, so id rather send it so someone that wont
look l

ike
a monkey ****ing a football.


Have you got, perhaps, a local guitar amp repair place or, maybe, a
rad

io
amateur or someone like that who might do it?


There's a valid email address on my web site (Feedback and Links
page)

if
you want to take this off-group.


--
Mick * * * * * * * * * * *(Working in a M$-free z

one!)
Web:http://www.nascom.info
Filtering everything posted from googlegroups to kill spam. * *


He is in Florida - and he would have to ship the amp anyway. So, as
far as practicalities are concerned, the Continental US is all the
same to him.

I would be glad to do it, if he didn't mind waiting 30 - 90 days, as
that is about how long it takes me to get to any fresh project these
days.

Peter Wieck
Melrose Park, PA- Hide quoted text -

- Show quoted text -


Cipher,
If you mean Twickenham UK. Then try John at
http://www.chambonino.com/
He is the guy.
Your amp really does look rough. What is the switch on the back panel
in the middle of the warning label?. The fault is clearly a bias
problem but looking at the state of the thing it has more wrong than
that, its a mess. Dont be disheartened by this the transformers and
all major components should be fine. You could just go mad and strip
it right down. You then have no option but to learn. A great way to
get into valve gear!. This is what I would do.
Matt.


Hey Sir,

I am in Wilmington, North Carolina.

My buddy Mick is in the UK, and I Spent some time there with NATO, but
now I just get my mic preamps there. Sorry for any confusion!



  #83   Report Post  
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cipher cipher is offline
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Posts: 42
Default what is causing this problem?

Paul G. wrote in
:

On Sat, 6 Dec 2008 05:18:46 -0800 (PST), fryzz
wrote:

....snip!.....
I'm guessing you have an intermittent bias problem. Your amp has a
separate bias supply, so the 68 ohm resistors are mostly just a
convenient way of adjusting the idle current. If those bypass
capacitors on the 68 ohm jobs are leaky, it would actually have the
effect of increasing the negative voltage on the grid, which reduces
the idle current, so that's not why the tubes would draw too much
current.

The first thing I would look at is the bias potentiometers, pots do
tend to be trouble prone due to the moving parts. You could try
cleaning them with something like Caig Deoxit. You might also try
feeling those two filter caps in the bias supply after the amp has
been on for a while. They'll pick up some heat just from being in a
tubeamp, but if one is warmer than the other it's a sign that cap is
leaking. Another thing you might try is touching up all of the solder
joints in the bias supply. You might also just leave your multimeter
hooked up, to see if the output of the bias supply is dropping when
the amp gets that "close encounters" look. When you measure the
output of the bias supply, it should be stable and noise free.

The fact that just ONE tube goes red, and not the pair, suggests
that the bias supply & adjustment is not a problem, since both tubes
on each channel run off the same connection. If it is just the one
tube that goes, and it's always the same socket (even if you switch
tubes around), then I'd zero in on the socket, or the traces on the
circuit board. That will require very careful inspection, resoldering,
or possibly checking the springiness of the socket contacts. Since the
socket gets alternately hot and cold with the accompanying
expansion/contraction, it is very common for the socket contacts to
break away from the circuit board. This is one of those applications
where point-to-point wiring can be more reliable than circuit boards.
I worked at RCA when they made tube sets..... there was no end of
troubles with printed circuits and tube sockets that were soldered
into them. I would also solder over the solder traces in case there
was a crack in the board. That might not be practical, since most
mfr.'s put stuff over the traces so when the boards are soldered, it
won't adhere and waste solder.
Very carefully inspect all the connections and traces between grid
(pin 5) of the EL34's and the bias control. Make sure nothing is
loose.
If the caps in parallel with the 68 ohms were to get real leaky and
short, the tube might get red, but the resistors would not cook (the
caps would shunt all the current). My guess is your problem is in the
grid circuit of the tube that cooks.
If the 0.68 uF caps were to fail and break down, you would see
symptoms similiar to what you're experiencing. Also if "R1K" and
"R220K" in the grid circuits were to open up, you would get similiar
behaviour. That's not very common for resistors, unless they have been
mechanically abused. "Opening up" by a poor solder connection, thermal
expansion, or bad trace would do the same (and more common).
I also assume that this unit unit used common solder with tin/lead,
and not the lead free (ROHS) kind. The lead free solder is not as
reliable (critical equipment can duck out of the lead-free
requirements!). How old is this unit? Did the manuals make any remark
about being lead-free?
A possible problem (but not likely, since the mfr. should have run
into this) is that the system could be oscillating at some very high
frequency. There are already grid stoppers, I'd be paranoid and put
stoppers (100 ohms) in the screen circuit. If it did oscillate,
probably both tubes would run red, and from your symptoms, that hasn't
ocurred.
I don't think you need this, but I would solder a resistor (100K)
from the wiper of the bias pot to the (-) end where the cap is. If the
wiper failed to make contact (as they do when dirty), you will still
maintain a bias that won't destroy anything.

Once you got mad in a previous post, and put down all the symptoms,
it became a lot easier to troubleshoot. Just to make sure, is it just
ONE tube that goes at a time? Does the same resistor cook each time?
If so, it's probably a circuit issue. If the problem moves around, it
MIGHT be a tube problem.
Usually when I have a customer bringing in a naughty piece of
equipment, it takes a few minutes of careful questioning to pin down
the problem. Just a list of symptoms from the customer aren't
enough..... I usually run them through what is for me a
"troubleshooting tree". Knowing the history of the unit, what it does
when naughty, what it does when you wack it (that's inevitable) helps
enormously. The fact that it misbehaves intermittently makes it very
difficult to service, and even more dependent on knowing the unit.
Chances are, that on a bench, this thing could run properly for years!

-Paul G.



thanks for that info sir..

weird behaviour.... i hooked it up yesterday for a bit, with the tubes
that I had used the day It went assed on me.... and now everything is
running ok, or seems to be.... the same tube that was glowing bright red
before is fine now, and the sound from both channels seems to be fine..
I am going to be sending this thing far away for someone to do it
proper, hopefully one o you gents can take it on for me. I do not feel
comfortable working on this thing.. it is the same resistors, and the
same tube that goes up every time.

is someone willing to take this on??
  #84   Report Post  
Posted to rec.audio.tubes
Arny Krueger Arny Krueger is offline
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Posts: 17,262
Default what is causing this problem?

"Ian Bell" wrote in message

Arny Krueger wrote:
"Ian Bell" wrote in message

Arny Krueger wrote:
"Ian Bell" wrote in message

Phil Allison wrote:
"Ian Bell"

So why have a completely transparent amp when the
speakers and room are so relatively poor.
** Very accurate, low distortion speakers are readily
available - but not necessarily cheap.
The prices are coming down, and they are not
prohibitive.
Indeed, and there's the rub for most people.
Treating a listening room so it does very little harm
to the sound
MORON. The whole point is that an untreated room does
a lot of harm to the room.

So resolved, if you have rotten speakers and a very
poor, untreated room, then tubed audio is for you!


No, all I said was a transparent amp in an already
seriously flawed system is pointless.


Right, but since when is our pursuit of the audio hobby
about intentionally using a seriously flawed system?



Who said intentionally? The average hi-fi person does not
have a clue about acoustics.


Since when do any of us aspire to the like the average hi fi person?


  #85   Report Post  
Posted to rec.audio.tubes
Peter Wieck Peter Wieck is offline
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Posts: 2,418
Default what is causing this problem?

On Dec 7, 3:47*pm, cipher wrote:
Paul G. wrote :





On Sat, 6 Dec 2008 05:18:46 -0800 (PST), fryzz
wrote:


....snip!.....
I'm guessing you have an intermittent bias problem. *Your amp has a
separate bias supply, so the 68 ohm resistors are mostly just a
convenient way of adjusting the idle current. *If those bypass
capacitors on the 68 ohm jobs are leaky, it would actually have the
effect of increasing the negative voltage on the grid, which reduces
the idle current, so that's not why the tubes would draw too much
current.


The first thing I would look at is the bias potentiometers, pots do
tend to be trouble prone due to the moving parts. *You could try
cleaning them with something like Caig Deoxit. *You might also try
feeling those two filter caps in the bias supply after the amp has
been on for a while. *They'll pick up some heat just from being in a
tubeamp, but if one is warmer than the other it's a sign that cap is
leaking. *Another thing you might try is touching up all of the solder
joints in the bias supply. *You might also just leave your multimeter
hooked up, to see if the output of the bias supply is dropping when
the amp gets that "close encounters" look. *When you measure the
output of the bias supply, it should be stable and noise free.


* *The fact that just ONE tube goes red, and not the pair, suggests
that the bias supply & adjustment is not a problem, since both tubes
on each channel run off the same connection. If it is just the one
tube that goes, and it's always the same socket (even if you switch
tubes around), then I'd zero in on the socket, or the traces on the
circuit board. That will require very careful inspection, resoldering,
or possibly checking the springiness of the socket contacts. Since the
socket gets alternately hot and cold with the accompanying
expansion/contraction, it is very common for the socket contacts to
break away from the circuit board. This is one of those applications
where point-to-point wiring can be more reliable than circuit boards.
I worked at RCA when they made tube sets..... there was no end of
troubles with printed circuits and tube sockets that were soldered
into them. I would also solder over the solder traces in case there
was a crack in the board. That might not be practical, since most
mfr.'s put stuff over the traces so when the boards are soldered, it
won't adhere and waste solder.
* *Very carefully inspect all the connections and traces between grid
(pin 5) of the EL34's and the bias control. Make sure nothing is
loose.
* *If the caps in parallel with the 68 ohms were to get real leaky and
short, the tube might get red, but the resistors would not cook (the
caps would shunt all the current). My guess is your problem is in the
grid circuit of the tube that cooks.
* *If the 0.68 uF caps were to fail and break down, you would see
symptoms similiar to what you're experiencing. Also if "R1K" and
"R220K" in the grid circuits were to open up, you would get similiar
behaviour. That's not very common for resistors, unless they have been
mechanically abused. "Opening up" by a poor solder connection, thermal
expansion, or bad trace would do the same (and more common).
* *I also assume that this unit unit used common solder with tin/lead,
and not the lead free (ROHS) kind. The lead free solder is not as
reliable (critical equipment can duck out of the lead-free
requirements!). How old is this unit? Did the manuals make any remark
about being lead-free?
* *A possible problem (but not likely, since the mfr. should have run
into this) is that the system could be oscillating at some very high
frequency. There are already grid stoppers, I'd be paranoid and put
stoppers (100 ohms) in the screen circuit. If it did oscillate,
probably both tubes would run red, and from your symptoms, that hasn't
ocurred.
* *I don't think you need this, but I would solder a resistor (100K)
from the wiper of the bias pot to the (-) end where the cap is. If the
wiper failed to make contact (as they do when dirty), you will still
maintain a bias that won't destroy anything.


* Once you got mad in a previous post, and put down all the symptoms,
it became a lot easier to troubleshoot. Just to make sure, is it just
ONE tube that goes at a time? Does the same resistor cook each time?
If so, it's probably a circuit issue. If the problem moves around, it
MIGHT be a tube problem.
* *Usually when I have a customer bringing in a naughty piece of
equipment, it takes a few minutes of careful questioning to pin down
the problem. Just a list of symptoms from the customer aren't
enough..... I usually run them through what is for me a
"troubleshooting tree". Knowing the history of the unit, what it does
when naughty, what it does when you wack it (that's inevitable) helps
enormously. The fact that it misbehaves intermittently makes it very
difficult to service, and even more dependent on knowing the unit.
Chances are, that on a bench, this thing could run properly for years!


-Paul G.


thanks for that info sir..

weird behaviour.... i hooked it up yesterday for a bit, with the tubes
that I had used the day It went assed on me.... and now everything is
running ok, or seems to be.... the same tube that was glowing bright red
before is fine now, and the sound from both channels seems to be fine..
I am going to be sending this thing far away for someone to do it
proper, hopefully one o you gents can take it on for me. I do not feel
comfortable working on this thing.. it is the same resistors, and the
same tube that goes up every time.

is someone willing to take this on??- Hide quoted text -

- Show quoted text -


If you don't mind waiting. You are third behind two other amps - and I
just finished a receiver and a tuner that were with me for ~90 days.
This is a hobby, so I get to it when I get to it.

But, I do good work, or so I am told.

How did those tubes work out, by the way?

Peter Wieck
Melrose Park, PA


  #86   Report Post  
Posted to rec.audio.tubes
Peter Wieck Peter Wieck is offline
external usenet poster
 
Posts: 2,418
Default what is causing this problem?

On Dec 7, 7:58*pm, "Arny Krueger" wrote:

Since when do any of us aspire to the like the average hi fi
person?


Huh?

Peter Wieck
Melrose Park, PA
  #87   Report Post  
Posted to rec.audio.tubes
fryzz fryzz is offline
external usenet poster
 
Posts: 29
Default what is causing this problem?

On Dec 7, 11:14 pm, flipper wrote:
On Sun, 7 Dec 2008 07:16:58 -0800 (PST), fryzz

wrote:


snip



Excellent!


Thank you.


You're welcome.

So 'half way better', regulating only one, is worse than nothing at all.


I did not know that, thanks. Makes sense.

  #88   Report Post  
Posted to rec.audio.tubes
Ian Bell[_2_] Ian Bell[_2_] is offline
external usenet poster
 
Posts: 861
Default what is causing this problem?

Arny Krueger wrote:
"Ian Bell" wrote in message

Arny Krueger wrote:
"Ian Bell" wrote in message

Arny Krueger wrote:
"Ian Bell" wrote in message

Phil Allison wrote:
"Ian Bell"

So why have a completely transparent amp when the
speakers and room are so relatively poor.
** Very accurate, low distortion speakers are readily
available - but not necessarily cheap.
The prices are coming down, and they are not
prohibitive.
Indeed, and there's the rub for most people.
Treating a listening room so it does very little harm
to the sound
MORON. The whole point is that an untreated room does
a lot of harm to the room.
So resolved, if you have rotten speakers and a very
poor, untreated room, then tubed audio is for you!
No, all I said was a transparent amp in an already
seriously flawed system is pointless.
Right, but since when is our pursuit of the audio hobby
about intentionally using a seriously flawed system?


Who said intentionally? The average hi-fi person does not
have a clue about acoustics.


Since when do any of us aspire to the like the average hi fi person?



Oh, so you think you are something better than that?

Cheers

Ian
  #89   Report Post  
Posted to rec.audio.tubes
Arny Krueger Arny Krueger is offline
external usenet poster
 
Posts: 17,262
Default what is causing this problem?

"Ian Bell" wrote in message

Arny Krueger wrote:
"Ian Bell" wrote in message

Arny Krueger wrote:
"Ian Bell" wrote in message

Arny Krueger wrote:


No, all I said was a transparent amp in an already
seriously flawed system is pointless.


Right, but since when is our pursuit of the audio hobby
about intentionally using a seriously flawed system?


Who said intentionally? The average hi-fi person does
not have a clue about acoustics.


Since when do any of us aspire to the like the average
hi fi person?


Oh, so you think you are something better than that?


It's not a matter of being better (and your choice of works is both typical
of you and revelatory), its a matter of being different. And yes, I am
different than the average hi fi person. For openers, the average hi fi
person misses my years of experience by a few decades, simply because on the
average, they are far younger.


  #90   Report Post  
Posted to rec.audio.tubes
Cipher Cipher is offline
external usenet poster
 
Posts: 20
Default what is causing this problem?

Peter Wieck wrote in
:

On Dec 7, 3:47*pm, cipher wrote:
Paul G. wrote
innews:ncemj4h4mdppegc81l7n7nion5rine

:





On Sat, 6 Dec 2008 05:18:46 -0800 (PST), fryzz
wrote:


....snip!.....
I'm guessing you have an intermittent bias problem. *Your amp has a
separate bias supply, so the 68 ohm resistors are mostly just a
convenient way of adjusting the idle current. *If those bypass
capacitors on the 68 ohm jobs are leaky, it would actually have the
effect of increasing the negative voltage on the grid, which
reduces the idle current, so that's not why the tubes would draw
too much current.


The first thing I would look at is the bias potentiometers, pots do
tend to be trouble prone due to the moving parts. *You could try
cleaning them with something like Caig Deoxit. *You might also try
feeling those two filter caps in the bias supply after the amp has
been on for a while. *They'll pick up some heat just from being in
a tubeamp, but if one is warmer than the other it's a sign that cap
is leaking. *Another thing you might try is touching up all of the
solde

r
joints in the bias supply. *You might also just leave your
multimeter hooked up, to see if the output of the bias supply is
dropping when the amp gets that "close encounters" look. *When you
measure the output of the bias supply, it should be stable and
noise free.


* *The fact that just ONE tube goes red, and not the pair, suggests
that the bias supply & adjustment is not a problem, since both
tubes on each channel run off the same connection. If it is just
the one tube that goes, and it's always the same socket (even if
you switch tubes around), then I'd zero in on the socket, or the
traces on the circuit board. That will require very careful
inspection, resoldering, or possibly checking the springiness of
the socket contacts. Since the socket gets alternately hot and cold
with the accompanying expansion/contraction, it is very common for
the socket contacts to break away from the circuit board. This is
one of those applications where point-to-point wiring can be more
reliable than circuit boards. I worked at RCA when they made tube
sets..... there was no end of troubles with printed circuits and
tube sockets that were soldered into them. I would also solder over
the solder traces in case there was a crack in the board. That
might not be practical, since most mfr.'s put stuff over the traces
so when the boards are soldered, it won't adhere and waste solder.
* *Very carefully inspect all the connections and traces between gr

id
(pin 5) of the EL34's and the bias control. Make sure nothing is
loose.
* *If the caps in parallel with the 68 ohms were to get real leaky

and
short, the tube might get red, but the resistors would not cook
(the caps would shunt all the current). My guess is your problem is
in the grid circuit of the tube that cooks.
* *If the 0.68 uF caps were to fail and break down, you would see
symptoms similiar to what you're experiencing. Also if "R1K" and
"R220K" in the grid circuits were to open up, you would get
similiar behaviour. That's not very common for resistors, unless
they have been mechanically abused. "Opening up" by a poor solder
connection, thermal expansion, or bad trace would do the same (and
more common). * *I also assume that this unit unit used common
solder with tin/le

ad,
and not the lead free (ROHS) kind. The lead free solder is not as
reliable (critical equipment can duck out of the lead-free
requirements!). How old is this unit? Did the manuals make any
remark about being lead-free?
* *A possible problem (but not likely, since the mfr. should have r

un
into this) is that the system could be oscillating at some very
high frequency. There are already grid stoppers, I'd be paranoid
and put stoppers (100 ohms) in the screen circuit. If it did
oscillate, probably both tubes would run red, and from your
symptoms, that hasn't ocurred.
* *I don't think you need this, but I would solder a resistor (100K

)
from the wiper of the bias pot to the (-) end where the cap is. If
the wiper failed to make contact (as they do when dirty), you will
still maintain a bias that won't destroy anything.


* Once you got mad in a previous post, and put down all the
symptoms, it became a lot easier to troubleshoot. Just to make
sure, is it just ONE tube that goes at a time? Does the same
resistor cook each time? If so, it's probably a circuit issue. If
the problem moves around, it MIGHT be a tube problem.
* *Usually when I have a customer bringing in a naughty piece of
equipment, it takes a few minutes of careful questioning to pin
down the problem. Just a list of symptoms from the customer aren't
enough..... I usually run them through what is for me a
"troubleshooting tree". Knowing the history of the unit, what it
does when naughty, what it does when you wack it (that's
inevitable) helps enormously. The fact that it misbehaves
intermittently makes it very difficult to service, and even more
dependent on knowing the unit. Chances are, that on a bench, this
thing could run properly for years!


-Paul G.


thanks for that info sir..

weird behaviour.... i hooked it up yesterday for a bit, with the
tubes that I had used the day It went assed on me.... and now
everything is running ok, or seems to be.... the same tube that was
glowing bright red before is fine now, and the sound from both
channels seems to be fine.. I am going to be sending this thing far
away for someone to do it proper, hopefully one o you gents can take
it on for me. I do not feel comfortable working on this thing.. it is
the same resistors, and the same tube that goes up every time.

is someone willing to take this on??- Hide quoted text -

- Show quoted text -


If you don't mind waiting. You are third behind two other amps - and I
just finished a receiver and a tuner that were with me for ~90 days.
This is a hobby, so I get to it when I get to it.

But, I do good work, or so I am told.

How did those tubes work out, by the way?

Peter Wieck
Melrose Park, PA


Good deal, Sir.

just shoot your mailing address to

luxaeternaaudio AT gmail DOT com

--
Ray
luxaeternaaudio AT gmail DOT com
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