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

[Richard Knoppow]

     I tried to find the industrial version of the 6C4, which is 
supposed to be less microphonic and can't find it. However, 
having a few 6C4s to choose from may find one that is better than 
the others. They are very commonly used as local oscillators for 
both main tuning and second conversion oscillators as well as 
BFOs. I have not had to buy one for a long time so don't know 
what prices are like now.

On 11/8/2019 12:37 PM, Fernan Bolando wrote:
> thanks again to all
> 
> i was planning to refresh my stock of parts for my other projects and was thinking
> i should also buy a few spare parts for my hammarlund. i was thinking the following
> 
> 1pc 6BE6
> 1pc 6C4
> 1pc 12AX7
> 1pc OB2
> 
> are there other parts i should also include?
> 
> regards
> fernan ve4feb
> 
>> Sent: Friday, November 08, 2019 at 1:27 PM
>> From: "Bill Cromwell" <wrcromwell at gmail.com>
>> To: hammarlund at mailman.qth.net
>> Subject: Re: [Hammarlund] hq 145a tone chirp/blip when tapping on the table. normal?
>>
>> 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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>>>
>>
>> -- 
>> bark less - wag more
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL