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37-650 Saga continues... - Printable Version

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37-650 Saga continues... - Robbie Roberts - 02-27-2006

re: The 37-650 Saga

I just pulled the 2nd IF coil can for a look-see, and
to clean up the trimmers, in case they are dirty.

While doing so, I took the following readings:
(#28 on the schematic, for those following the
proceedings here)
Readings made with all wires disconnected from
trimmers: trimmer number given for coil reference
only, ohmed circuit is the coil shown for each
trimmer. I made sure to clean ends of coil leads, in
case they had varnish, rosin, etc., throwing reading
off.

Trimmer 28P coil should have 12 ohms resistance. Reads
14 ohms

Trimmer 28S coil should read 8 ohms total, and 4 ohms
at tap. Actually reads 14 ohms total, with 10 ohms at
tap.

These sound high to me.

How may these readings be contributing to the
misery...er, mystery...

Scott

- Chuck Schwark - 02-27-2006

Actual resistance is immaterial - you have continuity on both windings.. You're good.

I'm still fighting... - Robbie Roberts - 02-28-2006

Ok- Here's the latest, boiled down:
I have reasonably good reception on both SW bands, could use more adjustment, but gets the point across well. I can pick up lots of stuff, depending on the time of day, so I think thats ok.

The BC band is still the issue. I have trimmed and tuned and adjusted until I can do it in my sleep. Here is the final result:
Everything above 900 is fine, maybe a little off freq, but quite acceptable. Everything below is pure crap- buzz and whistle and blatt and squeal, etc.

If I attach the antenna lead directly to the top of the 6A8G Det. Osc. tube, all magically works wonderfully- again, a need for more precise adjustment, but otherwise, I get almost full range(a little messy at the 540 end, but negligable.) If I touch the antenna lead with my finger, it improves even more. I remember there being a troubleshooting step being done this way but forget what this indicates as the problem!

Help?

Thanks!
Scott
So close....

- Steve Chambers - 02-28-2006

Open antenna coil on broadcast band? Antenna coil not properly wired into band switch? Something along these lines.

Steve Chambers

- Chuck Schwark - 02-28-2006

An open winding on RF transformer coils 1 and 10.

Primary to sec. shorts/leakage in these RF transformers.

Bad bandswitch contacts (or sneak shorts/leakage) for these coils; contacts F10, F11, D10, D11, C12, B10, B11, A1, A11.

Two RF transformers and switches are all that stand in the way from the antenna connector to the grid cap of the 6A8 in BC band position.

Try changing the 6A8 tube.

BC band OSC coil 17 is probably ok, since you get the upper half of the BC band. Check resistor 23, cap 22. Check for leakage/shorts in the OSC coil 17.

Don't suspect the RF tube since both SW bands are fine. If that 6K7 is working at SW freqs, then it should also work in MW as well.

Try changing the 6K7 tube. Clrean the RF tube socket contacts. Looks for bad/loose/rusty/corroded grounding rivets.

- Robbie Roberts - 02-28-2006

Thanks, Chuck- I'll start the "laundry list" with the tube swaps, and go from there...

Thanks again,
Scott

- Robbie Roberts - 02-28-2006

Chuck- Quick question: RF coil 10?

Scott

- Chuck Schwark - 02-28-2006

Robbie Roberts Wrote:Chuck- Quick question: RF coil 10?

Scott

Ok, part number 9 (the other 10). Icon_confused

Mea Typo

- Robbie Roberts - 02-28-2006

Cool- Thanks Chuck!
Scott