I changed out the 35w4,50c5,12ba6,12be6 but don't have a better 12at6 at the moment.
All connections have been reverified, new caps and ecaps and resistors checked. Any other ideas appreciated.
Thanks,
:I changed out the 35w4,50c5,12ba6,12be6 but don't have a better 12at6 at the moment.
:All connections have been reverified, new caps and ecaps and resistors checked. Any other ideas appreciated.
That tube has 2 diodes as you've seen...and usually only one is used.
Check the print... sometimes they tie both together.
If you really suspect this as the problem.. you can simply use the other diode.
But the problem may be elsewhere.
:Thanks,
:
If not do that.
Especially the coupling cap feeding the grid of the output tube.
. |
:Have you already replaced all the old paper caps?
:If not do that.
:Especially the coupling cap feeding the grid of the output tube.
:
:
Detector diodes can test very weak and still operate perfectly well.
Norm
:Have you already replaced all the old paper caps?
:If not do that.
:Especially the coupling cap feeding the grid of the output tube.
:
:
Edd -- this is an Arvin 956t / chassis 392.
On the fading issue: Set is playing normally for 30 seconds then slowly becomes distorted sounding but you can still make out what is being said and also the volume drops. Sometimes the sound comes back to near normal and then drops back off.
I switched the radio antenna to a long wire and still had the same result, but need to further look at antenna coil.
Norm- I will check voltage on grid to cathod of 50c5.
Thanks gentlemen.
1. New coupling cap on 50c5 checked out ok.
2. Grid voltage in relation to cathode was very close to 5v at 4.9v.
3. B+ seems good throughout the set. To pin 7 of 12AT6 that Warren mentioned was 48v….calls for 54.
Also the 330k resistor coming off pn 7 is within tolerance.
So I tried aligning the set, although at times a bit noisy from static. There was some fading in and out of signal but was able to achieve a little bit better alignment than original settings. When adjusting the primary IF there was increase in static/cut out of signal. Clue?
On a strong signal the radio performs fairly good , although I have not had it on for more than 15min.
On weaker signals the noise level increases plus more prone to total fade out.
My current thinking is that there is mica disease in IF 1. (thanks Warren for mentioning this.) Any thoughts?
Other question: This receiver had a 4 part electrolytic. I wired the negative connection , tacking the smaller valued ec’s neg to the 70mfd neg and then routed this to the original neg connection. Any problems caused by this method?
Thanks.
Could you have outside interference? Computers, lights, motors, other electronic equipment all cause noise that will be noticed more on weaker signals. Weaker stations may also fade in and out.
Silver mica disease usually causes static crashes, similar to lightening. With a meter you may be able to measure a slight positive voltage on secondary of IF Transformers.
Norm
:Well, here is where I am at on this Arvin.
:1. New coupling cap on 50c5 checked out ok.
:2. Grid voltage in relation to cathode was very close to 5v at 4.9v.
:3. B+ seems good throughout the set. To pin 7 of 12AT6 that Warren mentioned was 48v….calls for 54.
: Also the 330k resistor coming off pn 7 is within tolerance.
:
:So I tried aligning the set, although at times a bit noisy from static. There was some fading in and out of signal but was able to achieve a little bit better alignment than original settings. When adjusting the primary IF there was increase in static/cut out of signal. Clue?
: On a strong signal the radio performs fairly good , although I have not had it on for more than 15min.
:On weaker signals the noise level increases plus more prone to total fade out.
:My current thinking is that there is mica disease in IF 1. (thanks Warren for mentioning this.) Any thoughts?
:
:Other question: This receiver had a 4 part electrolytic. I wired the negative connection , tacking the smaller valued ec’s neg to the 70mfd neg and then routed this to the original neg connection. Any problems caused by this method?
:Thanks.
:
The ground tie points of your filter capacitors and bypass cap seems okay they way you describe.
Warren ... rebuilt IF's but slug is frozen in 2nd IF so got to work this out. Have a slight signal generated signal at 500hz but very slight. This is with 100pf caps installed. Definitely had silver mica disease going on.Pulled the mica, clipped the crossing terminals and reassembled.
Side question: In IF transformers is the primary always the lower coil on the form?
Thanks again.
I have replacements but they are not exact.
1 IF is 16.4 primary / 22.8 secondary
2 IF is 16.8 primary / 21.6 secondary
Will these be ok to substitute?
Excuse me for bad english ...
I would bet on the power amplifier section. See the grid resistor of an amplifier 50C5 and replace the capacitors in this section ... which comes from the 12AV6 plate to the grid of a ceramic that 50C5 and eliminates the RF valve 12AV6.
The cap of the midpoint of the potentiometer, and the grid resistor of 1 12AV6 should be replaced ...
All this after adjusting for the friend have replaced capaditor of the 50C5 plate .... should also be suspicious of the audio transformer .... those are responsible for the defect ....
Best Regard´s
:I have a problem with 5 tube radio and wondering if it isn't the 12AT6 tube. The 1st diode tests just ok and the 2nd diode tests much better. The radio plays ok for a short while but then fades and sounds like announcer is under water. Is it important for diodes to be close in measurment?
:I changed out the 35w4,50c5,12ba6,12be6 but don't have a better 12at6 at the moment.
:All connections have been reverified, new caps and ecaps and resistors checked. Any other ideas appreciated.
:Thanks,
: