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Frequency Counter on a 38-116 - Printable Version

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Frequency Counter on a 38-116 - quick573 - 12-26-2021

I have two dead bands on my 38-116  code 125, 3 and 5. Not 100% sure about 3. Where would I hook a frequency counter to see if the oscillator is running or should I use a scope. 
Thanks, Frank

RE: Frequency Counter on a 38-116 - John Bartley - 12-26-2021

Use a digital SW portable, tune it to "a frequency in the dead band + I.F." and set it near the set being serviced.  Slowly scan back and forth across "the frequency" and listen for the swishing in and out on the digital set as you cross the frequency.

RE: Frequency Counter on a 38-116 - quick573 - 12-27-2021

I don't have a portable SW radio but I do have a frequency counter and a scope.

RE: Frequency Counter on a 38-116 - Radioroslyn - 12-27-2021

If your counter is sensitive you can inductivity couple it. This can be achieved by rapping several turns of hookup wire around the glass portion of the 6A8 osc tube. One end of your coil connects to the counters input the other is left unconnected.

RE: Frequency Counter on a 38-116 - quick573 - 12-27-2021

i'll give it a try...Thanks

RE: Frequency Counter on a 38-116 - quick573 - 12-28-2021

Nope...not sensitive enough or its just a Chinese POS

RE: Frequency Counter on a 38-116 - Greg - 12-28-2021

Just some thoughts...

Did you try the counter on a working band or just the non-working bands? If it's going to work at all it seems like it should work on a working band. So I'd test it there first.

Otherwise, I never did this but, I might consider using an RF signal generator as a stand in for the oscillator. That's assuming the oscillator isn't working.

Comments anybody? Would either of these work?

1) A somewhat "indirect approach". I would try wrapping a wire around the 6L6 mixer and connecting it to the generator.

2) Or a more "direct" approach. Looks like pin 5 of the 6L6 is the oscillator input to the mixer. I would  connect the signal generator to pin 5 through a smallish capacitor and see what happens as I tune in the range of the band of interest.

In either case, tuning the signal generator should tune the radio.

You're probably most likely to hear something on band 3, 4-7 MHz.

You could also have a bad antenna or oscillator coil in these bands OR simply dirty band switches?

RE: Frequency Counter on a 38-116 - quick573 - 12-28-2021

I tried it on all bands.Nope. It has 6A8 mixer and another one for oscillator. 6L6's push pull out put.

RE: Frequency Counter on a 38-116 - Mondial - 12-28-2021

If your scope has a bandwidth of 20 MHz or greater, you should be able to see the oscillator signal. Take the tube shield off and try wrapping the coil of wire around the 6A8 oscillator tube in the area around the plate as Terry suggested. If you connect your scope probe to the end of the wire, you should see the oscillator signal if you turn up the vertical sensitivity.

Try the broadcast band first as its the lowest frequency and you know its working.

RE: Frequency Counter on a 38-116 - quick573 - 12-29-2021

Yes it's 100 MHz. I will try that. I really hope it's not a coil that failed.

RE: Frequency Counter on a 38-116 - quick573 - 01-01-2022

I get a sine wave on the scope. The higher the frequency the tighter the display which is good. On the top band however. the amplitude of the display is very, very low. Also on that band there is almost no background noise. I can barley hear only one station. Any ideas what's going on or should I say not going on. New caps, tubes and band switch cleaned with deoxit. And Happy New Year!