[Hammarlund] hq 145a tone chirp/blip when tapping on the table. normal?

[Richard Knoppow]

    Probably microphonics. Can come from the oscillator tube or 
just physical vibration of the tuning condenser or anything else 
in the oscillator circuits. Most, if not all, receivers using 
conventional variable capacitors for varying the oscillator 
frequency suffer from some microphonics. The oscillator tubes can 
also cause it, particularly the popular 6C4. There is actually a 
special low microphonic version of this tube, can't remember the 
type number.
     You may be able to localize the source by tapping around 
with the eraser end of a pencil. Some receivers are much more 
microphonic than others, I don't know how the 145 is for this. My 
HQ-129-X is not too bad. My R-388 (51J-3) is pretty much free of 
microphonics but does not use a variable capacitor for tuning.

On 11/8/2019 9:23 AM, Fernan Bolando wrote:
> Hi all
> 
> me again. ive noticed something new :)
> 
> when i listen to a steady cw tone/signal and a relatively strong tap on the table
> will cause the the tone to chirp or blip. it does not drift though, just a
> sudden blip blip thing. i just wanted to know if its normally for the old
> tech.
> 
> stability seem good after warm up. i can zero beat on a cw tone, just fine.
> 
> regards
> fernan ve4feb
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL