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Philco 45 ECaps - Printable Version

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Philco 45 ECaps - dconant - 11-10-2025

Hello, 

Are e-caps #62 and #63 supposed to be in parallel? I'm thinking thre must be a dot missing where #59 and #63 cross otherwise how else would the 75 tube get its plate voltage?

Dan

RE: Philco 45 ECaps - morzh - 11-10-2025

No. I think, the #63 is missin the tie-dot to the other side of the field coil (marked "white").

Missing tiedots of the second cap are a popular Philco docs error.

RE: Philco 45 ECaps - dconant - 11-12-2025

Thanks Mike. I have added the missing dot to my schematic. The radio is now playing quite nicely. All I need to do now is get a new grille cloth and put the chassis back in the cabinet.

Dan

RE: Philco 45 ECaps - dconant - 11-12-2025

Well I guess I spoke too soon. I noticed this morning when I first turned on the radio it played well, after about several seconds the volume started to go down. Thought maybe a tube problem so I replaced each tube one by one. As I did the radio played normal and then shortly volume decreased. Not a whole lot but quite noticeable on weaker stations. Seems like an AVC problem but I don't know how to identify the AVC circuit. Does someone have a suggestion? All paper caps, e-caps and resistors have been changed.

Dan

RE: Philco 45 ECaps - RodB - 11-12-2025

Dan, the AVC is generally sourced from the detector. So, if you look at the diagram above for the detector diode connected to the second IF secondary winding then down to the volume control there's a 2 meg resistor (#26) going to the left that feeds the signal grids of the IF and RF tubes. That's the AVC, which will be a negative 2-3 volts with low or no signal input and up to 10-15 volts when a station is tuned in. At the top of the volume control where the 2 meg resistor connects you should see this voltage vary with the strength of the rf signal. If you measure the other side of the resistor the meter will load the circuit and give you a false reading.

RE: Philco 45 ECaps - dconant - 11-12-2025

Rod, I follow you up to where you say the 2 meg connects to the left IFs and RF tubes screen grids. I don't see that connection. The 2 meg connects to the secondary of IF 1 and IF 2. Am I reading this wrong or is there another tiedot missing somewhere? I measure -.5 off station to -6 on station. Never goes positive. Using a DMM, negative connected to ground and positive at junction of 2 meg and volume.

Dan

RE: Philco 45 ECaps - RodB - 11-12-2025

The AVC should always be a negative voltage. It is fed through the 2 meg resistor to the signal grids of the IF and RF tubes (the grid caps) not the screen grids. The stronger the received signal the more negative the AVC voltage thus reducing the gain in the tubes, automatically. Your AVC seems to be acting normal.

RE: Philco 45 ECaps - dconant - 11-13-2025

I see now. I was thinking when you said 10-15 volts you were saying positive 10-15 volts. I seem to always get signal grid and screen grid mixed up. Thank you.

I noticed in the riders schematic changes that R21 was changed from 500 ohms to 400 ohms to prevent variation of the 6A7 tube. My set had the 400 ohm resistor. I tried a third 6A7 and that solved my fading volume when set first turned on. So I guess the 500 ohm to 400 ohm didn't quite do the trick.

My filter choke was open so I replaced with a 200 ohm 5 watt resistor. I also changed e-cap (#59) from 6 mf to 16 mf to cut down on the hum. There is still some hum, but didn't think I should go any higher. Maybe I should get a new choke.

Those two circuit boards in this radio made working on this radio quite difficult. I think working on my 37-116 was easier.

Dan

RE: Philco 45 ECaps - RodB - 11-13-2025

Power supply filter caps for the 80 rectifier can be increased considerably when not using a filter choke. If you experiment with 22mfd caps and temporarily connect them across the installed ones you might be able to cut the hum. Indeed, this is the circuit to use until the correct choke comes along. Buying a new choke will be very expensive(copper). I will check my stash for one that is close. If the rectifier tube was one with a cathode the tube specs would tell you the maximum capacitance for the input filter cap. If you have a voltage chart you can also experiment with the 200 ohm resistor to get the correct B+.

Edit: I don't have the choke you need.

RE: Philco 45 ECaps - morzh - 11-13-2025

I would add that increasing the caps' values is possible but should only be done to the cap after the choke / field coil.
Significantly increasing the value of the cap right after the rectifier will increase B+ voltage and, at least, will decrease unnecessarily the tubes' useful life as they will run hotter (the power increases linearly vs the voltage as the tubes act as current sources and not passive resistances; still in crease is increase and should be avoided if not needed).

After the choke/FC increasing caps does work well and causes no increase in B+.

RE: Philco 45 ECaps - dconant - 11-13-2025

I increased the cap after the choke but since there is no choke now, replaced with 2K resistor, is this the same as increasing right after the rectifier?

RE: Philco 45 ECaps - RodB - 11-13-2025

No, first filter cap is right after the rectifier. Increasing the cap after the choke is the second filter cap or cap after the filter resistor (it's 2k now).

RE: Philco 45 ECaps - morzh - 11-13-2025

Caps that can be increased are the 58 and 63.