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Philco model 77
09-14-2016, 10:24 PM
This is a model 77 chassis that is in a model 96 or similar cabinet. I have fixed some of the questionable caps but and done some testing but all I get is just a light hum no radio at all. I probably need to find out if this is the correct speaker for this chassis. I'll include photos. Tube numbers for this model is #80, 3 24A's, 27, and 2 45's.
09-14-2016, 10:25 PM
09-16-2016, 03:17 AM
The speaker is correct, my model 96 has one as well, the standard console speaker in use in the 1929-31 models was the Model H speaker. As for why it does not play these sets pretty well need all the capacitors replaced, many of the resistors too. One think to check for is if the audio output transformer is open, each leg of the primary should be connected to the plate pins of the #45 tubes. It could also be an open audio interstage transformer, though that often results in low volume and not a dead radio. Have you tried connecting the antenna lead to the grid caps of each of the #24 tubes? Sometimes one or more of the RF coils can go open, so if one coil is bad between the antenna and the following stage the radio might not pick up anything. Fortunately the RF coils are single layered so they should be easy to repair if they are open.
Regards Arran
09-16-2016, 09:52 PM
Now with connecting the antenna to the grid cap, do I go directly from the antenna connection to a grid cap, or all of them? I haven't checked the transformers yet as it is doing the same thing is was the last time it was turned on and that was around 1970. If I get a chance I'll check the transformers. Unfortunately this thing has been worked on before.
09-17-2016, 03:50 AM
(09-16-2016, 09:52 PM)flatheadjr Wrote: Now with connecting the antenna to the grid cap, do I go directly from the antenna connection to a grid cap, or all of them? I haven't checked the transformers yet as it is doing the same thing is was the last time it was turned on and that was around 1970. If I get a chance I'll check the transformers. Unfortunately this thing has been worked on before. Connect an antenna wire directly to each grid cap from the last #24 tube ahead of the #27 detector tube to the first one after the antenna coil. You don't have to remove the grid cap leads from the grid caps either, the grid is the signal input to each RF amplifier tube so it's a quick way of telling you where the defective RF amplifier stage is, that is if the audio amplifier itself is working Regards Arran
09-17-2016, 08:25 PM
Okay so I have the chassis on the table now and checked a couple things, doesn't appear that the audio output transformer is open, but I did get a reading of 3.1k on the primary winding. I hooked leads to each of the grid caps of the 24A's and same thing still. Still just a really faint hum from the speaker, and almost a fast pulse sound as well.
09-17-2016, 09:21 PM
Ok Lets try measuring the voltages at pin 2 of each 45 tubes to the chassis. Should see about 250v or so. Next pin 3 on each 45 tube to the chassis. Should see about -45vdc. Then pin 2 of the 27 tube to chassis. Should see about 150vdc. So what you got?????? 3k seems a bit high across the opt would think it would be about 1k or a bit less. The plate voltage will tell the tale.
When my pals were reading comic books I was down in the basement in my dad's workshop. Perusing his Sam's Photofoacts Vol 1-50 admiring the old set and trying to figure out what all those squiggly meant. Circa 1966 Now I think I've got! Terry
09-17-2016, 09:38 PM
Okay so on the 45's one on pin 2 is at 187 vdc and the other is at 226 vdc. Pin 3 on both 45's read -13 vdc. The number 2 pin on the 27 is at 203 vdc.
09-18-2016, 12:08 AM
Well hmmmmm. Have you replaced any of the caps in the power supply? HV seems good but the bias voltage is pretty low. Try measuring the voltage from pin 1 or 4 to pin 3 w/ the neg lead at 1 or 4 and the plus at pin 3. See if you get a higher reading there for the bias voltage. Seems like your driver and output transformers are good. Both 45's should have the same voltage on the plate, I would suspect that one of your 45's is weak ( the one w/the higher plate voltage). You can try switching the two tubes around and see if same tube have higher voltage on it in the other socket. We need to sort the bias voltage issue out as it's causing the 45's to draw current than they need to.
GL When my pals were reading comic books I was down in the basement in my dad's workshop. Perusing his Sam's Photofoacts Vol 1-50 admiring the old set and trying to figure out what all those squiggly meant. Circa 1966 Now I think I've got! Terry
09-18-2016, 12:47 AM
So I moved the tubes around and those voltages don't change they stay at that socket, they don't move with the tubes. Now when I check the voltages from pins 1 or 4 to pin 3 I get -33vdc. (Same -33 on both tubes) As far as the power supply I've only changed one electrolytic there. That area has been worked on before and I don't know what they did or why they did it. Maybe they made a mess of it.
09-18-2016, 02:52 PM
After doing a little looking around methinks your opt is bad. Should be about 550 ohms end to end not 3.1K. That's why there is such an imbalance between the plate voltage on the 45 tubes. I can't seem to locate a pin out for the spkr plug but the combination of any two pin should yield a resistance of 3.4K (field coil), or 275 ohms (ct to plate), or 550 ohms (end to end of the opt), or 3.9K (fc+1/2 of opt primary). Unplug spkr when measuring.
When my pals were reading comic books I was down in the basement in my dad's workshop. Perusing his Sam's Photofoacts Vol 1-50 admiring the old set and trying to figure out what all those squiggly meant. Circa 1966 Now I think I've got! Terry
09-18-2016, 04:12 PM
Okay so I unplugged the speaker and measured the 2 pins that would go to the 45's and with different leads I measure 2.7k now. If I move to any of the other pins I either read the same or at 2.9k, not sure I should be getting a reading from the other 2 pins should I? I did some looking around on some other forums, couldn't find much on the model H speaker but people have been getting those high readings with working speakers. But there is little information on the model H speaker.
09-18-2016, 04:46 PM
(09-18-2016, 04:12 PM)flatheadjr Wrote: Okay so I unplugged the speaker and measured the 2 pins that would go to the 45's and with different leads I measure 2.7k now. If I move to any of the other pins I either read the same or at 2.9k, not sure I should be getting a reading from the other 2 pins should I? I did some looking around on some other forums, couldn't find much on the model H speaker but people have been getting those high readings with working speakers. But there is little information on the model H speaker. H 10-1/2" used on models 77, 96 Push-Pull 45's 2766 opt pn 6,700 Ω plate impedance 0.7 Ω VC 36-3170 550 Ω opt primary 2850 fc pn 40 mA fc current 3200 Ω fc resistance H-17 We at the Philco Phorum specialize on Philcos When my pals were reading comic books I was down in the basement in my dad's workshop. Perusing his Sam's Photofoacts Vol 1-50 admiring the old set and trying to figure out what all those squiggly meant. Circa 1966 Now I think I've got! Terry
09-18-2016, 06:11 PM
So I guess if that's the case I'm on the lookout for another model H speaker and or output transformer.
09-18-2016, 07:37 PM
The 2766 opt was used in a lot of set:
40,41,20,21,90(early w/pp45's),65,76,77,87,95, and 96. E,F,G,H, and F10 spkrs When my pals were reading comic books I was down in the basement in my dad's workshop. Perusing his Sam's Photofoacts Vol 1-50 admiring the old set and trying to figure out what all those squiggly meant. Circa 1966 Now I think I've got! Terry
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