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Philco 620 question - Printable Version

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Philco 620 question - Danny - 10-11-2011

Just picked it up this weekend. Case in great shape but it's been electronically molested by someone. Powered it up and it sounds like I've got a signal tracer on it. Volume control has no effect, very loud always. Tone control changes pitch. Planning to start on it tomorrow by looking for short in 6A7. Can anyone give me a heads up on this anomily? Any help would be appreciated
http://www.nostalgiaair.org/PagesByModel/804/M0013804.pdf

Re: Philco 620 question - Arran - 10-12-2011

My first suspect would be an open cap on the center lug (wiper arm) of the volume control, or at least something realted to that control, I see three capacitors and two resistors connected to it. I guess the first question that I should ask, does the radio still have the molded bakelite condenser blocks in it? What often happened with these sets is that the bakelite blocks would go bad and someone would connect a replacement cap to the terminals of the old block. If someone has messed with it the first thing you need to do is take an inventory of the parts that are supposed to be there according to the factory service info, it looks like N.A has it all there. It would be best to tear all the mods out and go back to the factory diagram if possible, it is never worth trying to trace out what someone else did.
Regards
Arran

Re: Philco 620 question - Danny - 10-12-2011

I've replaced the caps on all 3 VC connectors, but I will replace the one on the center tap again. I lifted 3 of the condenser blocks and found they have been restored. Maybe I'll check the rest just to be sure. Taking an inventory sounds like good advice to me, never thought of that. Arran, thanks for the help and I'll keep you posted.

Re: Philco 620 question - Arran - 10-12-2011

I would also check the resitors related to that volume control, one may be open or have drifted in value. Has the volume control itself been replaced at some point? Sometimes people grab any old potentiameter and install it in a radio but if it doesn't have an audio taper or is the wrong value it won't work properly.
Regards
Arran

Re: Philco 620 question - Danny - 10-12-2011

Arran....the volume control tab was not grounded. You lead me right too the fix, thank you. Now I need to find out why the osc is not oscillating. Touching the top cap of the 6a7 does nothing. Placed transistor radio close to the osc coil of the 620, then ran the variable condenser on the 620 full up then full down and I got no signal indication on the transistor radio. It's the same on all three bands, no osc. I've got a few hours free tomorrow that's dedicated to looking into this. Thanks again for your assistance.

Re: Philco 620 question - TA Forbes - 10-12-2011

If the radio has been previously "worked on" I would review the "repairs" and see if they were done correctly.

Also, have you tested the 6A7?

Re: Philco 620 question - Danny - 10-13-2011

Yep....tested the 6A7 it was week but not dead. I replaced this 6A7 with one that was in a working radio. No change....Thanks for the help guy's. I'll keep all posted.

Re: Philco 620 question - codefox1 - 10-13-2011

I feel your pain. No matter how bad, I like to see original work. Occasionally I see restored sections that I would be proud of if I were that good, and later problems that I need to fix. This does not happen often, unless a great restorer dies at the bench and his (radio) remains fall into your hands.

So get yourself a good schematic, check off item by item with a yellow marker that connection is correct and component are correct and good, and you'll get there. That is unless you have a better nose than me, which is quite probable.

Bear in mind that repairs 30 years ago are different than restorations today. Different mentality entirely.

Re: Philco 620 question - Glenn Roberts - 10-13-2011

I hear you. The 118 on the bench now was butchered in the distant past. I found an electrolytic that was installed backwards. If it wasn't for a past posting by Ron I would have followed right along, It just didn't look right vs the schematic. I've found two other issues since. Good Luck and take your time.

Glenn

Re: Philco 620 question - Danny - 10-14-2011

Had to be recently molested, elect caps are of the newer type. I've
Started at the 42 and am working backwards on the schematic line by
line.
Beginning to regret this purchase.