[NostalgiaRadioTime]

Hello, Mama, It's Georgie. Your son, from the money every week. I can hardly hear you! Is Terry available?

   

Working on a Belmont 'bullet' model 6D111 series A

   

Here's a link to the Nostalgia Air version of the schematic, so it can be opened as a PDF and enlarged:

http://www.nostalgiaair.org/pagesbymodel...002220.pdf

Despite a complete recap...micas included, all new resistors, new 1 meg volume control / switch, and trying two sets of all new tubes, the set only plays at barely above a whisper with the volume all the way up. Tracing through the schematic didn't offer any glaring errors. Everything checked out to be where it should be.

Tonight I got out the signal generator and injected an audio output signal to see where I'm losing volume. Here's what I found:

1) Audio signal at CT of volume control loud and controllable (but NOT if you just touch it with a screwdriver) without the use of the SG)

2) Audio signal to Pin 2 (Grid) of the 12SQ7 is loud

3) Audio signal to Pin 6 (Plate) of the 12SQ7 is LOW

4) Audio signal to Pin 5 (Grid) of the 35L6 is LOW

5) Audio signal to Pin 3 (Plate) of the 35L6 is DEAD (no noise)

Checking voltages (All to B -, as per schematic):

Pin 3 (Plate) of the 35L6 is 107 VDC (should be 90)

Pin 4 (Grid) of the 35L6 is 91 VDC (should be 70)

Pin 8 (Cathode) of the 35L6 is 4.7 VDC (should be 4.3)

Pin 8 (Cathode) of the 35Z5 is 126 VDC (should be 112)

Pin 5 (Plate) of the 35Z5 is 116 VAC (should be 110)

Pin 6 of the 12SQ7 (Plate) is 58 VDC (should be 40)

Pin 2 (Grid) of 12SQ7 is - .6 VDC (should be 0)

It seems the problem is in the audio output section somewhere, but I have not found a smoking gun. Do you have any thoughts on where to look, Terry?

It doesn't appear the output transformer is open (I get around .4 ohms on the secondary and around 200 ohms on the primary). The set receives stations across the dial but most are barely audible save for the strong local station which can be heard at with the volume pot turned 3/4 open.

[Patrick]

Color me curious, but according to the schematic, pin 2 of the 6SK7 is the heater, and the plate of the R.F. amp is pin 8. Obviously, if you get a strong signal to pin 4 of the RF, then it seems the problem would be in the antenna section.

I've had several radios that had almost no volume until an external antenna was hooked up. Am I missing something?

Pat

[Radioroslyn]

OH NO!!!!!!!!!!!!!!!!!!!!!!!!!!
You found me!!
Ok so disconnect the lead coming from C-15 to the wiper of the volume control . Turn set on and touch the disconnected wire (connected to c-15). Should buzz and the level of buzz is going to be the loudest the set will play. Does it buzz loudly?? I'm not all together sure if an audio amp problem but it's a good place to start troubleshooting. All of the noted voltages look good.

[NostalgiaRadioTime]

Thanks for the tips, guys.

Terry: I disconnected the lead coming from C-15 to the wiper of the volume control as you said and when I touch the lead, there is no change in volume from what it was when it was connected to the volume control. Same faint buzz on the opposite end of the capacitor, where it is connected to the 12SQ7.

I took a few more voltage readings too:

on the 2nd (IF AMP) 12SK7:

Pin 8 (plate) reads 94 VDC (should be 74)
Pin 4 (grid) reads -2.0 VDC
Pin 6 reads 94 VDC (should be 74)

On the 12SA7:

Pin 3 (plate) reads 91.3 VDC (should be 74)
Pin 8 (grid) reads -1.8 VDC

on the 1st (RF AMP) 12SK7:

Pin 8 (Plate) reads 70.8 VDC (should be 40)
Pin 6 (Grid 2) reads 94 VDC (should be 70)
Pin 4 (Grid 1) reads -1.4 VDC

I have a long wire antenna connected directly to the lug on the top of the tuning capacitor. This set was missing the back cover, and also the loop antenna connected to it. I added a similar loop from another AA5 I parted out, connecting one end to the tuning cap and the other to ground as shown on the schematic. The sound is even quieter with just the loop antenna, so the only way to get any volume is to use the long wire at this point.

[Radioroslyn]

Did you replace r-16 or 18 with the wrong value (too low)?????

[NostalgiaRadioTime]

No those are the correct values, Terry. Just double checked. Do you think that the missing load coil that was attached to the missing original loop antenna could be critical? I'm wondering if not having the original antenna can be causing this low volume? Or would a problem in the output if coil cause this? Or even the output transformer (even though it ohms out) ?

[Radioroslyn]

Methinks your issue is in the audio amp rather than the rf/if stages so far. With C-15 disconnected from the vc and you touching it w/ your magnetic personality it should buzz loudly. Is the voice coil stuck to the pole (spkr cone not moving freely) ? If you measure the resistance from the 35L6 p5 to B-  and p2 of the 12SQ7 to B- both should show a high resistance (abt .5M and 5M respectively). Typically the output transformer would cause low audio w/o have other signs ( low plate voltage on the op tube). Does your signal generator have a 400cy audio output?? If so try feeding the 400cy tone into pin 5 of the 35L6 to hear how much volume you can get.

[NostalgiaRadioTime]

Once again, Terry, you zero-ed in on the problem area. It was indeed the speaker. This radio must've been in water at some point. The speaker frame was a total rust bucket (as was a good portion of the chassis itself). I cleaned, de-rusted, and painted the speaker, and did some cone repair but never thought to see how WELL the cone moved. It would not move freely. So I found a similar sized permanent magnet speaker I had on hand with an output transformer attached. I used the attached one rather than try to drill out the rivets and attach one separate from the speaker under the chassis. It has volume now like it should. It's possible the original output transformer was partially to blame, but I think the real culprit was the rust bucket speaker itself. So as of tonight, it's playing as it should. When I get back to it tomorrow night, who knows what it will do, though!

Many thanks, my friend

[Radioroslyn]

Anytime [Image: http://philcoradio.com/phorum/images/smi...n_evil.gif][Image: http://philcoradio.com/phorum/images/smi...on_lol.gif]

[NostalgiaRadioTime]

All back together and singing again. What a relief!