[TMC] VOX-3 question

[Chris Bolkan]

Hi Meir!
Thank you for that restoration link. I completely missed that. There is
so much on John's site! I will check it out.
It is unfortunate that the frequency multipliers have no calibration
procedure. I'm not as troubled about fiddling with the multipliers as I am
by further messing up the tracking and endpoints of the master oscillator.
Best regards,
Chris

On Tue, Apr 12, 2022 at 4:19 AM Meir Ben-Dror WF2U <wf2u at ws19ops.com> wrote:

> Chris,
>
> The only procedure for disassembling and repairing/calibrating the MO is
> in the link
>
> https://www.tmchistory.org/tmc_restoration/paul_spivak_docs/gpt_750_mo_repair.htm
> .
> The GPT-750 MO is identical to that of the VOX and PMO series master
> oscillators.
> In the procedure covered there is no mention of how to align the
> multiplier/output stages.
>
> Good luck with the VOX-3.
>
> 73, Meir WF2U
> Landrum, SC
>
> On Apr 11, 2022, at 7:27 PM, Chris Bolkan <bolkyboats at gmail.com> wrote:
>>
>> Hi TMC lovers!
>>
>> I now have the VOX-3 back together and working. Everything seems to
>> function more or less. The master oscillator works very well putting out a
>> nice sinewave throughout its frequency range.
>>
>> Unfortunately, I lost track of the exact relationship of the tuning shaft
>> to the counter dial, and of exactly where within the almost inch travel of
>> the calibration slug, the movement limits are established by the control
>> mechanism for it.
>>
>> So, even though I set the counter dial to be correct at 3Mhz, it is off a
>> bit at each end and I am not sure if placing the calibration slug in
>> another segment of its travel will help.
>>
>> I did not mess with the fancy eccentric calibration tracking mechanism
>> built into the master oscillator capacitor. All I did there was carefully
>> clean and lube everything so it all worked again. I think if there was a
>> way to calibrate the end points, it might be pretty close in the middle,
>> but I am not sure.
>>
>> The other thing that doesn't seem exactly right are the frequency
>> multipliers. They all work...sort of.....with reduced amplitude and a funky
>> relationship to the output control, where the output control "peaks" the
>> output rather than just acting like a level control. The output waveforms
>> are not super clean either with differing amplitudes over many cycles
>> probably indicating they need to be tuned up.
>>
>> I am only starting to dive into this, but thought I would ask if anyone is
>> aware of a factory calibration or setup procedure for the VOX when it was
>> originally being built. I think if one exists it would be very useful to
>> me. The VOX-5 manual I have is very helpful but does not dive into the
>> areas I took this thing apart so does not provide what I am looking for
>> unless I have somehow overlooked it.
>>
>> Thanks in advance if you can point me in the right direction!
>>
>> Best regards,
>>
>> Chris Bolkan
>> KI7NXY
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