"CJT" wrote in message
...
Derwin wrote:
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?
You know not of what you speak. I was probably repairing tube
equipment before you were born. And much tube equipment is very
un-spaghetti-like.
Or maybe we have different ideas of what spaghetti looks like.
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.
I meant are the PLATES glowing red. Of course the heaters would be
glowing.
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
... or even know how to spell it.
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.
--
The e-mail address in our reply-to line is reversed in an attempt to
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Even the best of us who've got years of experience can make errors. Unless
you were in a shop working side by side with or had access to other techs -
"tough dogs" could really cause some wasted time. This forum and many others
like it - provides an invaluable asset to all of us for working on things.
None of us could know ALL the answers. Some things don't make sense
sometimes and aren't always so clear to the eye.
I've seen things appear to buck all theory - but - I still found the cause
and corrected the issue. You have to keep an open mind when doing this
stuff. Unless you can definately say an area/circuit has been isolated as
not being at fault - don't rule it out.
It is those issues where you must stop - analyze what has been done, all
previous and current signs and so on. Any "help" issued - is a plus. Of
course - it helps to give a complete and thorough analysis of the problems
before you started, all steps taken and so on - as none of us can see your
project, have a clue what you've done OR know your experience to know
where/how to proceed to help. Are we to give you "basic" electronics
knowledge to help OR are you advanced with lots of equipment we can tell you
to use, etc.?
You said you left out telling us some of the things you've done - which you
apparently thought mundane items. Who knows - one of those steps - might
have clued one of us in - to your problem!
Maybe not ALL of our ideas will help - but only because we do NOT know your
exact situation. So - rather than shoot down any helpful ideas - take them
in stride - try them out - or mark them all down - take a day and do them -
then get back to us with the results.
OH and as for your new parts - IT IS POSSIBLE to buy defective parts. I've
had it happen. I'm sure others have too. Radio Shack was good for that. As
an example, I ordered a transistor once for a CB set - the issue narrowed
down. I was sent a "replacement". I didn't bother to check it before
installation. Turn on the switch - and smoke appeared. I checked it - and
called the parts supplier. Here - THEY had a transistor "marked in their
records" as a Sub - when in fact it was not. They apologized to me for the
error - sent me a new "correct" part and offered to pay me for my time and
any other damaged parts. And with the RS parts - I've had occasion to plug
in a diode, transistor, etc. and find it to be bad. Took back out of circuit
and tests revealed open parts in most cases. It might be extra work, but I
double check my parts (if I can) - before installing. I'd rather know
they're good BEFORE I put them in than to find out after - they weren't. In
most cases, that few seconds can save a lot more time. And I HAVE caught a
few more "defective" new parts since I've learned to do this from
experience.
As to your caps - I've seen many a chat in these groups discussing some
brands to be very poor in quality - so who knows - maybe you latched on to
some of those? At this point - anything is possible. Some of the other folks
gave some damned good advice - best to just take time to prove out one way
or another - what is happening. For now - we're all guessing - since we're
going by what you say and we're not there to see it.
As for "Spaghetti" - that term could be overkill. Wiring used before PC
boards was often labeled as such. Even afterwards. Be it a lot of wiring or
a little - the term could be being used. It is no big deal. The only way it
could make a difference is if a wire "is" going to a wrong place, a piece of
braid or a stray conductor from one of them is shorting OR something along
the lines of inductance is happening as a result.
Don't give up on the project - "LEARN" from it. The knowledge acquired from
repairing it could outweigh any cost you've got into it thus far. I can't
recall if you've got the schematic for it or not - if not - you may want to
get it and study and compare. That could be immeasureable.
As to the sound being "Squishy" - here's where a scope "may" have come in
handy "BEFORE" tearing into it.
So.......... there are lots of things to look at and consider. NO - you
don't want to "waste" time - no one does. But in this case - working in the
dark - there may be little choice til something starts to present itself.
Just my 2 cents.