Jim Poore wrote:
Derwin wrote:
In article 5HzYh.5314$Dq6.1620@edtnps82, says...
"Derwin" wrote in message
news:6mzYh.5305$Dq6.3498@edtnps82...
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?
No.
That's not what I've read. Are you sure you're not thinking of
electrolytics?
Other than that, does anyone have any advice based on my
description of the unit's behavior? Any comments whatsoever might
be helpful..
At this point you need to fault find. Does it work OK with tape or
other music input?
Perhaps I should have specified that the unit worked fine before I
recapped it. It had a bit of a squishy sound so I figured it could
use a re-capping but I must've screwed up somehow. But re-capping is
pretty straight-forward, and I think I did it right. So now, what
could have gone wrong? Switching inputs is not going to help me track
down the problem at all. C'mon, I may be a 'self-taught' novice
electronics tinkerer, but that is downright stupid - I already said
the music plays fine for a few seconds after it warms up then it fades
out, so obviously its not a problem of a flakey input.. sheesh.
My guess is that it is a heater-cathode short in one of the audio tubes.
My reasoning is that when a tube is cold the elements are not shorting
but after some thermal expansion they may short out. Why it is doing it
now but not before could be from turning the chassis upside/down and
having a piece of crap in side the tube in question move to a sensitive
area.
Electrolytics if leaky will hum first and then play which is the
opposite of what is happening.
Personally, I would change ALL the caps at least in the ausio section
including the power supply electrolytics.
Hope this may shed some light for you.
Jim
I forgot to mention one thing. What is the voltage rating of the caps
you changed? Is it the same of higher than the ones you replaced? If
the voltage rating is too low that caps might breakdown under voltage.
In tube equipment a good rule of thumb is just go with a 600V rating on
the capacitors. Some amplifiers and I am goin on memory here with
6CA7's may have even higher voltages to deal with.
Jim