Posts: 1,106
Threads: 88
Joined: Jun 2011
City: Tacoma
State, Province, Country: Washington
I have one of these radios. It sounds great and works fine using the pushbuttons on the AMBCB. However, all the tunable bands act like they are bandspread tuning. If I set the LO to be spot on at 1400 KHz, tuning down the dial, I get about 10-15 KHz for every 200-300 KHz I go down the dial. I've looked and looked at the schematic, but for some reason I'm just not seeing it. There must be some significant series L or C that's keeping it from tracking properly. It's also off in a similar way on the SW bands.
If anyone has any experience with this particular problem, I would appreciate any help you can give.
TIA
Brenda Ann
Posts: 7,300
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
On the osc section of the tuning condenser does the rotor and stator have the same number of plates? Was thinking maybe someone pulled some of the rotor plates out. Short of that perhaps a mechanical problem, the dial is moving faster than the cap.
Terry
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
Posts: 1,106
Threads: 88
Joined: Jun 2011
City: Tacoma
State, Province, Country: Washington
Everything mechanical is sound and functioning properly. Tuner is complete, it just acts more like a trimmer, like there's a series capacitance to ground that's not right, but the schematic shows no such capacitance.
Posts: 893
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Joined: Mar 2008
City: Vieques, PR USA
State, Province, Country: PR
Hi Brenda,
Double-check to confirm that the LO is actually functioning in the non-PB mode by monitoring its frequency.
-Bill
Posts: 7,300
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
Probably wouldn't hurt to give the P/B and bandswitch a good cleaning.
Terry
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
Posts: 1,106
Threads: 88
Joined: Jun 2011
City: Tacoma
State, Province, Country: Washington
Eureka! The problem ended up being a well-disguised broken ground strap from the tuner to the chassis. I should have gotten a clue earlier when I noted that getting my hand or a tool anywhere near the tuner caused frequency changes, but one doesn't think of broken ground braids..
It tracks a lot better now, but still won't drop in perfectly. It's up to 20 KHz off in the middle of the AMBCB if I align it to be spot on at 600 and 1440 (and it's way off at the top: 1600 comes in at 1660).
Posts: 2,128
Threads: 18
Joined: Oct 2008
City: Merrick, Long Island, NY
Time to repeat the alignment procedure from the top. Assume the padders have been cleaned out, dried and restored to approximately the original positons for a start. Old trick, count turns in, disassemble, clean, dry, assemble, turns out for a start.
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