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Latest on the 37-650 - Robbie Roberts - 02-13-2006

Here's the latest update...

I have checked through almost all tha capacitors, and all are good.(The only ones I haven't checked are inaccessible withough pulling the RF subchassis again- a last ditch maneuver) I even checked the rebuilt bakelites. (The micas and the one picaf. rated bakelite were too small value to check...) Also, all the resistors, except for the one which was dead wrong, are correct. The dead wrong one has been replaced temporarily with a composite totaling proper ohmage.

I replaced the test volume control with the original, and it seems to be dead, no real volume increase or decrease, and would absolutely not test for continuity. It is supposed to be 2 meg total, with a tap at 1 meg ohm. The test unit is a 1 meg, with tap, and it actually ohms out at 750k ohms total, so I think replacement is in order in any case. Where can I get a proper volume control? Also, is it possible the dead wrong resistor blew out the volume control? Cooked it perhaps?

I think my two problems are:
1. Volume control shot- I think the amp section is otherwise fine. With the test VC in place, it does increase/decrease volume.

2. Totally out of correct alignment. I think I whacked everything out of kilter trying to adjust away the resistor isue before I found it. Hey- this is my first project set, so I'm allowed... lol

I still have to figure out the problems causing the motorboating on certain freq's, and the squeal on others. I think it is all related to the VC and alignment. Everything else checks out.

Anybody in South Jersey/ Philadelphia area wanna stop by and play with this radio?

Scott

- Bill Hutchinson - 02-13-2006

Scott,

From your description, it sounds like scenario #2 is your most likely problem. You've probably whacked it out of alignment enough to cause a multitude of problems (I'm trying to be kind here, trust me Icon_smile ). Also, #1 is also a likely issue as well. Put your temporary volume control back in for now - it'll do in the short run.

Since it's motorboating, this is a good indication the alignment is way off. Go through the procedure step by step, and keep repeating it until you get some satisfactory results.

Keep at it - you can do this! We're all pulling for you!

Bill

- Robbie Roberts - 02-13-2006

Thanks, Bill! I keep telling myself I'm having fun... ;) I was wondering if there was a way to add 1 meg ohm of resistance to the test unit volume control, but realized it would probably make it either unlowerable or unraisable past a certain point... So I guess that wouldn't be an answer... lol

One other thing, my shadow meter is inoperative- it is connected, etc, but whatever the magnetic field affects to create the shadow is not there at all, so I can't judge signal strength by that meter! Is there a way to rig in a temporary needle type meter to gauge the signal strength? I understand now why the shadow meter needs to be set up first!

Scott

- Bill Hutchinson - 02-13-2006

Check out this procedure from Chuck's website on shadow meter servicing.

http://www.philcorepairbench.com/tips/svctip01.htm

It may not work too good if the set is out of alignment - I think I'd do that first. Icon_wink

Good luck!

Bill

- Chuck Schwark - 02-13-2006

As long as the Shadow Meter coil has continuity and is providing B+ to the DET-OSC and RF tubes, you're fine. It does not need to make a shadow to allow the front end of the set to operate. The Shadow Meter is the least of your worries at this point.

If, by chance, the coil is open, then sub in a 1.5K, 1/2 w. resistor during this phase of your repairs.

- Robbie Roberts - 02-14-2006

The shadow meter has continuity through the coil, and I recall getting close B+ voltage as discussed previously. From my understanding there should be a small metal piece, which is affected by electro-magnetic force of the coil, in turn resulting in the changing of the shadow dimension. Mine has no such flap. (It is the later style) Therefore, I am under the impression the shadow meter is not working, other than as resistance in the line. Ohms out about 1.5k ohms.

So, looking at the adjustment needs, is there a common start point I can use for all the variable caps which need adjusting?(The Ant., RF, and Osc. compensators) Sort of like when you tune a carb. on a car, you make bench settings, and go from there? Should I turn them all the way in and then back 3 turns, and then start tuning? I just keep going round and round with this...

Thanks!
Scott

- Robbie Roberts - 02-14-2006

OK...I've gone through and done everything the best I can figure out... I spent a good few hours tonight aligning, aligning and aligning... I first set up the two cans, tuned them to 470kc, as indicated by the schematic.

I went through the best I could following the directions. I basically tuned each tuning condensor until I found the signal, and then tweaked for loudest/best tone, until I had that nice tone loud, clear, and strong, on each. (I did not have the variable capacitor of 350 ohm to jumper in for one step) Still nothing much. SO I swap a few tubes. AM(Broadcast) still rewards me with pops, shrieks, and whistles to blow the ear drums out. SW 1 gives me nothing. I am cursing it, its parents, etc.

SW 2 gives me something! The very first thing I receive is around 6mc. I tune it in, and bring up the volume. It is a church program about perserverance and faith. Ok. Very funny. Very apropos. World Harvest Radio strikes again... lol... About the only other thing I managed to get was the word "communist" and I lost that signal(was around 10mc)

I'm running out of ideas here!

Anybody want to stop by? I'll give you a free truckload of genuine "Storm of '06" snow! I just want it to work right....(whimper)

Ideas?
Scott

- Steve Chambers - 02-14-2006

Robbie Roberts Wrote:I'm running out of ideas here!

Anybody want to stop by? I'll give you a free truckload of genuine "Storm of '06" snow! I just want it to work right....(whimper)

Ideas?
Scott

Scott:

Miswired band switch? Open coils? If you replaced all the wiring, I'd still bet on a wiring error. Band switches are hard to figure out (at least for me) from a schematic. Keep at it.

Steve Chambers

- Robbie Roberts - 02-14-2006

Thanks Steve- I've been through the band switches three or four times, and I'm pretty certain they're in right... Too blasted many of them, if you ask me!
But I went through them, manually cleaned them, and reassembled completely. It took a while, the pictures look upside down, but once I reversed the schematic, and understod the shaded/solid areas, I got them figured out. So I'm pretty confident with the RF section... And the tone of the RF generator is coming through as it should. Also, there is that one SW station coming through, I think if the switches were in wrong, it wouldn't even give me that.

Scott