The PHILCO Phorum

Firstly, I'm relatively new to this so please excuse my ignorance.

I have been fighting what I feel is low volume on this set. I get sound, can bring in stations from what was once a dead set so I think I'm a good part of the way there. I've replaced all the caps, tested and replaced resistors where needed including the 3 section candohm and tried replacement tubes in all positions.  I've also measured the volume control and its good.  Bypassed the volume control, same.  I do find that where I am expecting 250V I'm getting roughly 300V and where I expect 70V, I get 80V.  I also see 280V on the 6Q7 where the schematic says there should be 150V (to me this is an obvious problem). So one question is, how close should these voltages be to spec? Could this be my issue?

Another place where I checked voltage was on the 3 connections from the radio to the speaker. I have attached a picture.  Readings I get are Top Right 290V, Bottom Right 328V and Top Left 253V.  So another question I have is how do I find what is expected at these connections? Could this be my issue?

Thanks.

Seems like your 6Q7 isn't drawing any current. Weak tube, grid bias too high or cathode too far away from ground. Just for grins check the resistance of the shadow meter coil (abt 1K). If it's it could stop the hv from getting to the mixer and IF amp.

Thanks for the reply Terry.

Uhh, sorry the 6Q7 is at 180V, my mistake can read my own notes.

As for the spkr connector I'd measure voltage @ the 6F6 it's abt the same thing. Pins 4 screen grid and pin 3 plate will tell the health of the p/s and if the opt is good. Pin 5 tells if you've got the filter caps grounded to the chassis and much bias voltage you have on the output stage.

Terry:

I see #3 P at 247V, #4  S at 291 and #5 G at -16V on the 6F6 and 6.5VAC on the H. Not sure what the reading should be at #5?

Thanks.

The grid bias voltage is spot on but the screen is a bit high and the plate a bit low. I'd have a look @ the screen buss and see if there anything gone amiss. Check the sm and maybe swap the 6F6 if you have spare.
Is your line voltage kinda high?

Thanks Terry, my line voltage is 121.4V. The set came with a 6V6 that I replaced with a 6F6 but both both act the same. I'll scape over the screen bus in the hope I see something. What should the target range be for screen and plate, plus/minus?

The plate voltage is going to be the same as the screen except for the drop across the resistance of the primary the the opt. Roughly abt 10-20vdc difference.

In the past, I've seen a case where a schematic showed the negative of a cap going to ground when in fact it should have been the positive going to to ground.  So, here is my question?  If the #60 8Mfd cap was reversed, would it simply blow up or could it cause other issues and more importantly, can anyone confirm that the negative of the #60 indeed go to ground?

Yes...

Thanks Terry.

#62 on this radio is a 12Mfd Electrolytic in the schematic.  I replaced it with a 16Mfd thinking that won't be an issue.  Am I wrong or will this affect voltage?

Wouldn't loose any sleep over it.

Sounds good, I think I need to take a rest from this project for a few days. Thanks.

Volume problem found.  When replacing the #48 .015 cap the space was tight and I had a bad solder joint.  Repaired, now working well.