[Kenradio]

Hello everyone, I have a Philco 37-650B that has a very odd problem. When I got it from Ebay I had to first replace the shadowmeter that was missing (I had a spare from a junked 37-650 chassis) then rebuild the capacitor blocks/replace paper caps and replace any resistors out of tolerance. When I fired it up it would work but sensitivity was weak and there was no deflection of the shadowmeter (the meter is good). I was using a 30' piece of wire for the antenna for my testing. If I connected the wire to the grid cap of the 6K7 RF tube the signal was much stronger but then the signal dropped off a few seconds after connecting the antenna (I checked the RF and Ant. coils and all are good). It gets much weirder--when the antenna is connected to the proper terminals the stations are still weak but goes to full sensitivity if you turn the power on/off quickly but as soon as you move off the station the sensitivity drops again!!! The oscillator section is good as the stations are right on frequency. I connected the radio to my outdoor 110' antenna and it pulls in many stations and the radio is extremely loud at low volume with occasional dropouts in sensitivity---It sounds like possibly an AVC issue and I replaced all components on the AVC bus but it still doesn't work like it should. I did sub the 6A8 & 6K7 tubes in the RF deck just in case but no change. I collect and restore Philcos--I have a 37-610B, 37-9, (2) 38-643B, 37-84 & model 16B in my collection but this 37-650 is driving me crazy. Any suggestions are greatly appreciated. Ken

[Ron Ramirez]

Hi

First suggestion: You have too many 38-643B sets. You should immediately send one of them to me.

This seems to be a fairly common problem with 1937 Philco sets. I suggest you not only check the AVC, but also suspect the AM band antenna coil. Hopefully you still have that 37-650 junker? You may need the AM antenna coil from it. This is the usual culprit when you get stronger reception using the antenna on the grid cap of the 6K7 RF amp instead of the antenna terminal on back.

Also, be sure the jumper on back is connected between terminals 2 and 3 on the four-screw terminal block (the screws labeled BLK and GND).

[Kenradio]

Hi Ron, I forgot to mention that it affects all 3 bands but on the AM band it is more noticeable. I did check the primary/secondary windings of the antenna coils and they are ok (I checked them when I had the antenna coil assembly out to change the caps). I do have the donor chassis just in case. I didn't change the 51,000 ohm resistor in the antenna section--it reads about 50k. I do have the link across term. 2 & 3. The B- voltage in the AVC section varies to around -13 V when it is working to around -.6v when the signal gets weak. Thanks, Ken

[Kenradio]

Hi Ron, what would cause the signal to drop when tuning off a station? Then I would have to turn the radio on/off quickly and it would play again till I tune it again. It is very strange as I haven't had a radio do that. The 38-643 radios ---I bought off of you a few years ago when you had them for sale on Ebay. I restored one and I'm using an ARBE III to power it and I haven't done anything to the other one yet. Ken

[Ron Ramirez]

what would cause the signal to drop when tuning off a station? Then I would have to turn the radio on/off quickly and it would play again till I tune it again. It is very strange as I haven't had a radio do that.

OK, that is very odd. That has me baffled for now.

Sounds like your AVC is working correctly. How are the B+ voltages? Do they vary when the signal drops off?

You might check for any loose/bad solder joints, especially if you removed the RF unit.

I have three 37-650 chassis out in the garage. Maybe I should restore one of them, get it playing right, and one of those 38-643 sets could come back home to me? Divorce can make a guy do some dumb things sometimes, like selling radios that he regrets selling later.

[Guest]

Hi Ron, I'll check the voltages and also check the wiring out on the RF unit. I wouldn't mind getting another 37-650 chassis that is in good shape and not rusty. I could trade you the working 38-643 for one (the dial is in very good shape). I want to get this radio working properly as I had one back in 1978 and it got me started in collecting Philco radios and this one has the instruction manual and original tag that described the features of the 37-650. Thanks, Ken

[Kenradio]

I wouldn't mind getting another 37-650 chassis that is in good shape and not rusty. I could trade you the working 38-643 for one (the dial is in very good shape). I want to get this radio working properly as I had one back in 1978 and it got me started in collecting Philco radios and this one has the instruction manual and original tag that described the features of the 37-650.

Cool! Thank YOU!

I'll take a look at the three I have here and get back to you...

[exray]

Hi Ron, what would cause the signal to drop when tuning off a station? Then I would have to turn the radio on/off quickly and it would play again till I tune it again.

Sounds like a partially open coil or bad solder joint. Or bad bandswitch switch contacts.

The *idea* here is that the connection is high resistance or partially open. Voltage from your meter may make it across or the 'surge' from off/on restores the connection. Dropping off when tuning away could be the result of the dropping AVC voltage. A bad detector tube will also do this if there is a high resistance connection at the grid cap. Sometimes resoldering the cap on the tube is a cure.

A good DMM or VTVM will often reveal these problems. A VOM will put enough voltage across the connection so as to mask it.

Good luck - its difficult to find these things sometimes.

[Kenradio]

Hi exray, that is a good idea on the bandswitch---I do have a spare 37-650 bandswitch from the antenna section of the RF unit w/coils that is good. I will sub it out tomorrow and see what happens. Thanks, Ken

[Ron Ramirez]

Hi Ken

Turns out I have two, not three, 37-650 chassis. One of them will fit your needs; the other one needs a lot of work.

More details forthcoming via email. Thanks!

[Kenradio]

Hi, I swapped out the antenna section of the RF unit a few days ago and it appeared to fix the fading issue but it came back. I checked the service tips on the Philco Repair Bench website and noticed that one of the tips was for fading issue with the 37-650 and said to check part #8 a 40 Pf capacitor that developes an intermittent short. I noticed on my radio the AVC voltage fluctuates when the signal is going in and out so this may be something for me to check out. I don't look forward to removing the RF section as the cap is underneath the switch wafers.

[Joe Rossi]

Ken, I replaced this cap when I restored my 37-650. If you got the schematic and service notes from Chuck Schwark, it gives the instructions on how to get the RF section out. It was easier than it looked. I thought for sure that I would make a mess of it, but Philco knew what they were doing when they published the instructions. Just label where the wires come out of there and where they go on the chassis. This will also give you a chance to replace the rest of the caps in the RF. Believe me, the performance enhancement is worth it!