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

[Bill Cromwell]

Hi,

When my HQ145X was acting badly (when I acquired it) I checked all the 
tubes. They all checked very good. But the rascal 6C4 was NOT so good 
and all the "artifacts" including microphonics and gross drift problems 
disappeared when I subbed another 6C4. Thereafter it was a really good 
radio and I relied on it when my "pretty" radio went down for repairs.

On 11/8/19 1:23 PM, Richard Knoppow wrote:
>     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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> 

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