DIYbanter - View Single Post - Tried to recap a tube receiver, and failed.

Derwin

In article , says...

Derwin wrote:
I tried to re-cap a tube receiver (amplifier + tuner), and now when I turn
it
on it starts playing music for a few seconds after it warms up, then the
music
fades out and and hum takes over. I don't really know what I'm doing, and
the
wiring inside looks like a mess of spaghetti. I'm pretty sure I replaced
the
caps properly, but I used .068uf WIMA caps to replace .050uf wax/paper caps,
and I'm wondering if the value difference, added up over 8 caps would make a
difference? Other than that, does anyone have any advice based on my
description of the unit's behavior? Any comments whatsoever might be
helpful..

Obviously what you did caused the problem. Check for cold solder
joints and inadvertent connections via solder flash. If you have
enough information (e.g. a detailed log of what you did, or
before/after photos), go back and recheck your work.

Did it look like spaghetti before you started?

YES. Why are you even replying if you obviously have never looked inside an
old tube amp?

From your description, it sounds like maybe it's drawing more current
now than before, so that the power supply capacitors are no longer
adequate. Does it have a rectifier tube in the power supply?

probably

Is it
glowing red?

they're all glowing and I tested every tube a few months ago and they were all
fine. I no longer have a tube-tester to check again, however.

Perhaps you've dramatically changed the bias point in
the output stage by some misconnection.

All the caps I replaced are connected exactly where they were before I replaced
them. What I'm thinking is that the guy who sold it to me, after having
'restored' it from non-working condition wired it up in some jeri-rigged
fashion to get it to look like it was working enough to be able to sell it to
me. Probably one of the caps was bad and compensating for a bad resistor as
someone else mentioned. However, the wiring he added did not contribute to the
'spaghetti' much. Anyone who has ever looked inside any old electronics from
before the days of circuit-boards will know what 'spaghetti' wiring looks like.
Those who havent, try this: Look at a circuitboard populated with a bunch of
components. Look at the traces the circuit makes on the back of the board. Now
imagine each one of those traces being replaced with a wire. Now perhaps you
will be able to envision the 'spaghetti' wiring that a circuit not build on a
PCB will look like.. Anyway now I'm pretty much screwed. I don't own an
oscilliscope so I will probably just sell off the tubes and toss the chassis.
I prefer the sound of solid-state these days anyway, my interest in tube gear
was a folly that only lasted a couple years.