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34-87 weak on low end of band - Printable Version

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34-87 weak on low end of band - Guest - 02-17-2007

Hey all,
I am new to the hobby and I have a 34-87 that I recieved a few years ago and I am just now starting to go through it. I have noticed that the volune needs to be turned all the way up to hear the low end of the band. The high end of the band is great. You can tune in a station between 1000kc and 1700kc with the volume almost off and you can hear stations. I am using a long wire antenna that is about 25' with a loading coil so it should be resonant for 80 meters, so it should be long enough. The caps are new, resistors are new and the tubes check out fine.
Any ideas.

Thanks

Perhaps a 37-84?? - AI2V - 02-17-2007

I have noticed that the volune needs to be turned all the way up to hear the low end of the band.

**I haven't had a 37-84 in about 40 years but in looking at the schematic there appears to be only one component that would cause your problem- of course I could be wrong.

It would appear that what you are seeing is weak capacitive coupling which would make it frequency sensitive. The lower the freq, the poorer the coupling. The schematic shows part #3- "Capacity obtained by twisting the ends of two wires" on the grid of the input tube- this is the only part that sees all of the input freqs and is not part of a resonant or feedback circuit. I would look closely at this twisted pair of wires- maybe they have been unwound or run too closely to ground. You could probably replace the twisted wires with perhaps 10 or 20pF of fixed capacitance.



'

- Guest - 02-17-2007

Thank you. I will check it out.

- Chuck Schwark - 02-17-2007

Also see the SERVICE TIPS section of my site for additional info on the 80, 81, 84, 37-84. The 37-84 is essentially the same as a Model 84. See these Tips as well.