[kadulazarini]

Dear All,

I`m finishing the restoration of 3 Philcos 70 with the lower numbers chassis. For all of them, I rewound the primary of the oscillator coil, replaced all internal caps of the block and metal case condensers, re-stuffed the electrolytics, and replaced the tone control cap. For two of them the pots were still OK, and the radios are playing great after the alignment. However, for the third one, the original pot was bad and I bought a 5K 4W wirewound pot from ebay (they come from China) to replace the original. I put a 220 ohms 2W resistor between F and G (see schematics at http://www.nostalgiaair.org/PagesByModel...013833.pdf) and connected the RF cathode to F. The 5k pot connections I kept according to the original schematics. A former owner replaced the 250 ohms DC choke to a 150 ohms DC one. The new electrolytics are 10 µF.
It worked, but the sound is very low only at the end of the pot. Is there alternative connections that will get the radio back to the right track?

Thank you.
Kadulazarini

[morzh]

Kadulazarini


1. It is always nice when asking people to look at something to provide the l;ink to the sch; it is a simple courtesy so one does not have to go on some website and start searching.
2. It is also a nice gesture to tell what exact model you have and what code. Lower number chassis does not mean much to me, though it may to someone.
3. It is also nice to show exact position of the part (the number) on the exact version of the schematic as Rider manuals often times are confusing as heck or simply lack information.



Having said that, if you are talking of the volume pot, your trouble may be because wirewound resistors are mostly linear and you need a taper, that is a log scale pot where the resistance changes not proportionally to the angle but slower at first and faster thereafter.

[kadulazarini]

OK, morzh, thank you for the tips

1) Philco model 70 no code, Chassis # below B22,000 that has a pot with 2 wirewounds, one with 250 ohms and the other with 5K ohms, 4-5 Watts. Chassis # above B22,000 has only one wirewound. Model 70 schematics are on http://www.nostalgiaair.org/PagesByModel...013833.pdf

2) I am referring to the Volume pot part number 5039, part number 1 in the schematics.

3) I have been told that we can add some resistors/caps and the radio works normally without the 250 ohms wirewound. Does anybody know how to do this modification?

Thank you very much for your attention.

[morzh]

Well

Same exact resistor, 250/5000 Ohm is in Philco 20.
Now I suspect the points F and G on that resistive divider, where the missing pot section used to be, are shorted together or maybe there is the sub resistor of 250 Ohm in between them. Otherwise nothing would work, that thing completes the Field coil circuit.
I also suspect that the first two tubes' cathodes that used to go to the wiper of that section are wired to the ground (chassis) somehow or maybe to that E-F connection point. Otherwise they would not work either.

Right?