I have a Univox Amp I purchased off the back of a guy's truck. It powers on,
but all I get is a hum output. I attach a microphone or guitar cable to any
of the inputs and *nothing* changes the output sound. The volume control
doesn't change the level of the hum output either. I should say, I've been
around guitars and amps for about 20 years and the output of this sounds
normal, not necessarily a "hum". It soulds like a normal amp with the input
(guitar or mic) turned off. I've tested all transistors with a VOM and they
seem OK. I've cleaned all pots/boards contacts with contact cleaner. I do
not have a o-scope or a signal generator, so I realize troubleshooting will
be difficult. I do have a schematic. My question is this: Do any of you
have advice for troubleshooting this with just a voltmeter?

I've tested all transistors with a VOM and they
seem OK.

God Almight.... VOM's should be banned from public use.....

"Just Another Theremin Fan" wrote in message
oups.com...
I've tested all transistors with a VOM and they
seem OK.

God Almight.... VOM's should be banned from public use.....

The first thing to check with this kind of fault, is that the + and -
supplies to the front end are present. They are often derived from the main
high + and - rails that feed the output stages, by a simple power resistor
and power zener circuit. It is quite common in this type of arrangement for
the power resistors to go bad jointed, due to the temperature that they
typically run at, or the zeners to go short circuit, or the decoupling caps
across them to go short circuit. You will normally expect something of the
order of + / - 15v for the front end opamps.

Arfa

"Daremo" bravely wrote to "All" (05 Feb 06 21:13:38)
--- on the heady topic of "Help with Univox Guitar Amp"

Da From: "Daremo"
Da Subject: Help with Univox Guitar Amp
Da Organization: Road Runner High Speed Online http://www.rr.com
Da Xref: core-easynews sci.electronics.repair:357600



Da I have a Univox Amp I purchased off the back of a guy's truck. It
Da powers on, but all I get is a hum output. I attach a microphone or
Da guitar cable to any of the inputs and *nothing* changes the output
Da sound. The volume control doesn't change the level of the hum output
Da either. I should say, I've been around guitars and amps for about 20
Da years and the output of this sounds normal, not necessarily a "hum".
Da It soulds like a normal amp with the input (guitar or mic) turned off.
Da I've tested all transistors with a VOM and they seem OK. I've
Da cleaned all pots/boards contacts with contact cleaner. I do not have
Da a o-scope or a signal generator, so I realize troubleshooting will be
Da difficult. I do have a schematic. My question is this: Do any of you
Da have advice for troubleshooting this with just a voltmeter?


Troubleshooting need not be difficult. Nor do you need a signal
generator or a scope. Simply inject some audio program into an input
and use a small amplifier to trace the audio path in the circuit.
Where the signal stops will be the bad part. Easy as pie!

A*s*i*m*o*v

.... A stereo system is the altar to the god of music.

Thanks to you all. I just got lucky. I was using the 10% rule, where
common components tested within 10% of each other I called them good. I
found 2 PNP Germanium Triodes that were identical but tested way different
than each other. I removed them from the circuit to test properly, and they
tested the same (both returned the same values, I mean). Upon re-installing
them, the amp worked fine. Maybe a cold/bad solder joint? (No way, not
after 30+years!) I think these were the preamp transistors? Anyway, like I
said, I got lucky.





"Daremo" wrote in message
...
I have a Univox Amp I purchased off the back of a guy's truck. It powers
on, but all I get is a hum output. I attach a microphone or guitar cable
to any of the inputs and *nothing* changes the output sound. The volume
control doesn't change the level of the hum output either. I should say,
I've been around guitars and amps for about 20 years and the output of this
sounds normal, not necessarily a "hum". It soulds like a normal amp with
the input (guitar or mic) turned off. I've tested all transistors with a
VOM and they seem OK. I've cleaned all pots/boards contacts with contact
cleaner. I do not have a o-scope or a signal generator, so I realize
troubleshooting will be difficult. I do have a schematic. My question is
this: Do any of you have advice for troubleshooting this with just a
voltmeter?

"Daremo" wrote in message
...
Thanks to you all. I just got lucky. I was using the 10% rule, where
common components tested within 10% of each other I called them good. I
found 2 PNP Germanium Triodes that were identical but tested way different
than each other. I removed them from the circuit to test properly, and
they tested the same (both returned the same values, I mean). Upon
re-installing them, the amp worked fine. Maybe a cold/bad solder joint?
(No way, not after 30+years!) I think these were the preamp transistors?
Anyway, like I said, I got lucky.


What is a " PNP Germanium Triode " for goodness sake ?

Arfa

Arfa Daily spake thus:

"Daremo" wrote in message
...

Thanks to you all. I just got lucky. I was using the 10% rule,
where common components tested within 10% of each other I called
them good. I found 2 PNP Germanium Triodes that were identical but
tested way different than each other. I removed them from the
circuit to test properly, and they tested the same (both returned
the same values, I mean). Upon re-installing them, the amp worked
fine. Maybe a cold/bad solder joint? (No way, not after 30+years!)
I think these were the preamp transistors? Anyway, like I said, I
got lucky.

What is a " PNP Germanium Triode " for goodness sake ?

A transistor.


--
If the United States government, with all its capacity to collect
and interpret information, did not see Hamas doing very well in the
Palestinian election in the wake of these other Islamist victories,
then it is either willfully blind or totally incompetent—-
and neither possibility is a very comforting thought.

- Rami G. Khouri, editor at large of the Beirut-based _Daily Star_

"David Nebenzahl" wrote in message
s.com...

Thanks to you all. I just got lucky. I was using the 10% rule,
where common components tested within 10% of each other I called
them good. I found 2 PNP Germanium Triodes that were identical but
tested way different than each other. I removed them from the
circuit to test properly, and they tested the same (both returned
the same values, I mean). Upon re-installing them, the amp worked
fine. Maybe a cold/bad solder joint? (No way, not after 30+years!)
I think these were the preamp transistors? Anyway, like I said, I
got lucky.

way to go! we all need a bit of luck now and then.

in the early day of transistors technicians were cautioned to heatsink the
leads of transistors when soldering so as not to damage them. tiny little
aluminum spring loaded clamps were sold to aid in this process. (haven't
seen any of those for years now). it's vaguely possible that you fixed the
bad transistor by applying heat, however a bad solder connection is the more
likely culprit.

in the early day of transistors technicians were cautioned to heatsink the
leads of transistors when soldering so as not to damage them. tiny little
aluminum spring loaded clamps were sold to aid in this process.

Ack! Those were "the early days of transistors"??? I feel old...I'd
better sit down.

It's been about 100 years since I've had electronics training, that's just
what the schematic said.

NTE 158



"David Nebenzahl" wrote in message
s.com...
Arfa Daily spake thus:

"Daremo" wrote in message
...

Thanks to you all. I just got lucky. I was using the 10% rule, where
common components tested within 10% of each other I called them good. I
found 2 PNP Germanium Triodes that were identical but tested way
different than each other. I removed them from the
circuit to test properly, and they tested the same (both returned
the same values, I mean). Upon re-installing them, the amp worked
fine. Maybe a cold/bad solder joint? (No way, not after 30+years!)
I think these were the preamp transistors? Anyway, like I said, I
got lucky.

What is a " PNP Germanium Triode " for goodness sake ?

A transistor.


--
If the United States government, with all its capacity to collect
and interpret information, did not see Hamas doing very well in the
Palestinian election in the wake of these other Islamist victories,
then it is either willfully blind or totally incompetent—-
and neither possibility is a very comforting thought.

- Rami G. Khouri, editor at large of the Beirut-based _Daily Star_

"Daremo" wrote in message
...
It's been about 100 years since I've had electronics training, that's just
what the schematic said.

NTE 158


and the 'vox is only about 35 grin

and i suspect the transistor(s) are much younger

"Arfa Daily" bravely wrote to "All" (07 Feb 06 01:37:49)
--- on the heady topic of " Help with Univox Guitar Amp"

AD From: "Arfa Daily"
AD Xref: core-easynews sci.electronics.repair:357674

AD What is a " PNP Germanium Triode " for goodness sake ?


And here I thought you knew it all, eh?!

A*s*i*m*o*v

.... From small chips to big breasts, silicone is great!

Asimov spake thus:

... From small chips to big breasts, silicone is great!

Silicon != silicone.


--
If the United States government, with all its capacity to collect
and interpret information, did not see Hamas doing very well in the
Palestinian election in the wake of these other Islamist victories,
then it is either willfully blind or totally incompetent—-
and neither possibility is a very comforting thought.

- Rami G. Khouri, editor at large of the Beirut-based _Daily Star_

"David Nebenzahl" bravely wrote to "All" (06 Feb 06 21:49:50)
--- on the heady topic of " Help with Univox Guitar Amp"

DN From: David Nebenzahl
DN Xref: core-easynews sci.electronics.repair:357687

DN Asimov spake thus:

... From small chips to big breasts, silicone is great!

DN Silicon != silicone.


The Earth's crust is about 25% silicon and 50% oxygen. They should
have called it Silicon Oxide instead of Dirt. Go figure...

A*s*i*m*o*v

.... Letterman of Borg - "Ok, Top 10 reasons why resistance is futile:"

"Asimov" wrote in message
...
"Arfa Daily" bravely wrote to "All" (07 Feb 06 01:37:49)
--- on the heady topic of " Help with Univox Guitar Amp"

AD From: "Arfa Daily"
AD Xref: core-easynews sci.electronics.repair:357674

AD What is a " PNP Germanium Triode " for goodness sake ?


And here I thought you knew it all, eh?!

A*s*i*m*o*v

.... From small chips to big breasts, silicone is great!

I know what PNP is and I know what germanium is and I know what a PNP
germanium transistor is ( sheesh ! ) but I have never in 40 years seen a
semiconductor device referred to as a " Triode " ( and yes, I can see " Tri
" for 3 and " ode " for electrode, and yes, I am fully aware that a
conventional transistor has three electrodes ). This side of the Atlantic,
triodes have always been vacuum tubes, or in English English, valves.

The name " transistor " is a condensation of the words " transfer " and "
resistor " and to the best of my knowledge, that's the name it was
christened with by Bell Labs in the US, and the name that it has commonly
been known by throughout the world ever since.

Arfa

IF YOU PURCHASED IT OFF THE BACK OF A GUY'S TRUCK CHANCES ARE IT'S
PROBABLY STOLEN.

ENJOY YOUR "HUM"

DOES YOUR BOYFRIEND ALSO "HUM"