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Science Forum Index » Electronics - Misc Forum » Help needed with a Pye P35 valve radio
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| eu.thundernews.com |
 Posted: Thu May 01, 2008 3:45 pm |
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Hi, I am planning to restore the above as I can get hold of the components.
The radio receives lw/mw and 6 sw bands.
It was working ok and then the volume suddenly dropped to about half that it
should be, the potts have been cleaned and are not noisy.
The radio picks up all the channels it did previously but it is quiet and
turning the volume pott up or down does pretty much nothing.
Could anyone point me in the general direction of which component/s to look
for as the culprit/s?
Any help would be massively appreciated.
I will post the schematic on alt.binaries.schematics.electronic entitled
'Pye P35 Schematic'
Thanks for any help guys. |
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| Don Bruder |
| Posted: Thu May 01, 2008 4:44 pm |
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In article <c_pSj.1458$Cr1.1372@newsfe18.ams2>,
"eu.thundernews.com" <blib@blop.flob> wrote:
Quote: It was working ok and then the volume suddenly dropped to about half that it
should be, the potts have been cleaned and are not noisy.
The radio picks up all the channels it did previously but it is quiet and
turning the volume pott up or down does pretty much nothing.
Could anyone point me in the general direction of which component/s to look
for as the culprit/s?
Based on what you're describing, the first place I'd look would be the
heater of the output amp tube. Betcha a nickel the filament died...
--
Don Bruder - dakidd@sonic.net - If your "From:" address isn't on my whitelist,
or the subject of the message doesn't contain the exact text "PopperAndShadow"
somewhere, any message sent to this address will go in the garbage without my
ever knowing it arrived. Sorry... <http://www.sonic.net/~dakidd> for more info |
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| Stephen J. Rush |
| Posted: Thu May 01, 2008 8:37 pm |
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On Thu, 01 May 2008 14:44:40 -0700, Don Bruder wrote:
Quote: In article <c_pSj.1458$Cr1.1372@newsfe18.ams2>,
"eu.thundernews.com" <blib@blop.flob> wrote:
It was working ok and then the volume suddenly dropped to about half
that it should be, the potts have been cleaned and are not noisy.
The radio picks up all the channels it did previously but it is quiet
and turning the volume pott up or down does pretty much nothing.
Could anyone point me in the general direction of which component/s to
look for as the culprit/s?
Based on what you're describing, the first place I'd look would be the
heater of the output amp tube. Betcha a nickel the filament died...
If the audio output tube died, you'd get no sound at all, not about half-
volume. It's not uncommon for old carbon resistors to increase in
value. Coupling capacitors develop leaks, but that usually causes
obvious distortion. The nice thing about troublshooting tube gear is
that you can measure resistors in-circuit (With the power off!). If you
have the schematic, it probably gives DC voltages; knowing which voltage
is out of spec you can usually deduce which component might be bad. |
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| Sky |
| Posted: Sat May 03, 2008 6:19 am |
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"Stephen J. Rush" <sjrush@comcast.net> wrote in message
news:k4CdncifEdzf7YfVnZ2dnUVZ_jGdnZ2d@comcast.com...
Quote: On Thu, 01 May 2008 14:44:40 -0700, Don Bruder wrote:
In article <c_pSj.1458$Cr1.1372@newsfe18.ams2>,
"eu.thundernews.com" <blib@blop.flob> wrote:
It was working ok and then the volume suddenly dropped to about half
that it should be, the potts have been cleaned and are not noisy.
The radio picks up all the channels it did previously but it is quiet
and turning the volume pott up or down does pretty much nothing.
Could anyone point me in the general direction of which component/s to
look for as the culprit/s?
Based on what you're describing, the first place I'd look would be the
heater of the output amp tube. Betcha a nickel the filament died...
If the audio output tube died, you'd get no sound at all, not about half-
volume. It's not uncommon for old carbon resistors to increase in
value. Coupling capacitors develop leaks, but that usually causes
obvious distortion. The nice thing about troublshooting tube gear is
that you can measure resistors in-circuit (With the power off!). If you
have the schematic, it probably gives DC voltages; knowing which voltage
is out of spec you can usually deduce which component might be bad.
Thanks to you both for your replies (I'm on another pc that's why my name's
changed)
I didn't know that you could test resistors in-circuit with tube gear-nice
tip! My friend has the same model of radio and has offered me the chance to
use his tubes to test in mine.I am concerned that if something has damaged
one of my tubes it might blow one of his-do you think this is a possibility? |
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| Stephen J. Rush |
| Posted: Sat May 03, 2008 12:39 pm |
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On Sat, 03 May 2008 12:19:33 +0100, Sky wrote:
Quote: I didn't know that you could test resistors in-circuit with tube
gear-nice tip! My friend has the same model of radio and has offered me
the chance to use his tubes to test in mine.I am concerned that if
something has damaged one of my tubes it might blow one of his-do you
think this is a possibility?
Tubes are mechanically fragile, but electrically rugged. After my post,
I noticed that you'd posted the schematic. With a transformer power
supply, you don't have to worry about a short in the filament string
blowing one of the filaments, as sometimes happened in transformerless
sets that had the filaments in series. About the only thing that could
damage a tube is a shorted coupling capacitor that dumps one tube's plate
voltage onto the following grid. Even that won't kill a tube instantly.
If you're still worried, swap your tubes, one at a time, into your
friend's radio.
Having a working set of the same model lets you probe DC voltages to
compare with yours. Coupling capacitors between audio stages usually
leak or short, but I've seen them fail open, which will leave the DC
voltages unchanged but block the signal. An old trick is to turn the
volume control up and touch its center terminal with a finger. A loud
buzz of AC coupled through your body capacitance means the the whole
audio half of the set is working. Just be sure you don't touch anything
else; plate and screen voltages are high enough to bite you. |
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| Geo |
| Posted: Sat May 03, 2008 2:50 pm |
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On Sat, 3 May 2008 12:19:33 +0100, "Sky" <nono@nono.com> wrote:
Quote: My friend has the same model of radio and has offered me the chance to
use his tubes to test in mine.I am concerned that if something has damaged
one of my tubes it might blow one of his-do you think this is a possibility?
Me again - I would not risk it. If C40 is leaky and putting a positive voltage
on the EL33 grid it will not be happy. Check the voltages first - guessing about
5v on the EL33 cathode and 260v on the anode.
If your weak volume is especially lacking bass then c40 may just have reduced in
value - try a parallel cap (correct voltage rating).
Geo |
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| Sky... |
| Posted: Wed May 14, 2008 11:36 am |
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Guest
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"Geo" <9w0b-safk at (no spam) disposable.spamcon.org> wrote in message
news:p7gp141ik2g78p3c4qgm52qagdashlmgj7 at (no spam) 4ax.com...
Quote: On Sat, 3 May 2008 12:19:33 +0100, "Sky" <nono at (no spam) nono.com> wrote:
My friend has the same model of radio and has offered me the chance to
use his tubes to test in mine.I am concerned that if something has
damaged
one of my tubes it might blow one of his-do you think this is a
possibility?
Me again - I would not risk it. If C40 is leaky and putting a positive
voltage
on the EL33 grid it will not be happy. Check the voltages first - guessing
about
5v on the EL33 cathode and 260v on the anode.
If your weak volume is especially lacking bass then c40 may just have
reduced in
value - try a parallel cap (correct voltage rating).
Geo
Thanks for the help guys, I found that r12 had gone open. I changed it and
the radio sounds great now. Still going to change all the paper caps etc
though.
By the way sorry for multi posting -I posted in sci.electronics.repair- I've
since learned the rules. |
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