[TMC] VOX-3 question

Wed Apr 13 16:29:44 EDT 2022

There's another resource on tmchistory.org that seems to be
under-utilized,, namely the entire rest of the drawings section.  You can
sometimes glean useful information about parts within a TMC rig, in cases
where you need to replace them, or just figure out how they work.

For example:  let's say you're working on a PAL-350 RFA-1 amplifier, and
you think the filament transformer in the rig is not working correctly.
>From the schematic, you'll find that its ref designator is T210.  The parts
list in the manual says that it's a "Transformer: Power (Filament)" with
TMC part number TF-180.  That part number is *also the drawing number*!
Now go to the drawings page, and scroll down to the "TF" section, then
traverse that section down to "180"; a click on the link (if there is one);
that'll takes you to the drawing.  In this case, the drawing tells you the
physical size, some info about how to wire the transformer for 120 and 240V
operation, and a discussion of the MIL spec for the 'former.  For RF
transformers, the drawing usually shows turns counts, inductances, and
other possibly useful info, if you're trying to make a replacement.

I've scanned all of the A- and B-size drawings that I have, which covers
most small parts.  Some drawings are missing, and probably gone forever.  I
still need to work on the C-size drawings and up, which may happen in the
next "while" thanks to some excellent help from Nick K4NYW, who figured out
how to get my elderly wide-format scanner going!

As ever, if there's a drawing that you need to look at, let me know, and
I'll do my best to make it happen.

73, John K4OZY

On Wed, Apr 13, 2022 at 11:53 AM Chris Bolkan <bolkyboats at gmail.com> wrote:

> I dove a bit into the "S Documents" doing a word search on VOX. There are
> 22 related documents! Many of them are very interesting and applicable. I'm
> just starting to dig in, but have found a document on mechanical setup of
> the capacitors in the master oscillator and how to align the control
> shafts, a calibration procedure for the VOX-5, an interesting doc on
> applicable crystals, the one Nick provided the link to and many others.
> This "S" file is a gold mine!
>
> One thing to look out for is that the titles of the documents
> sometimes seem completely unrelated to the actual content. It's weird to
> me, but they must have had reasons for naming some of them the way they
> did. The important takeaway for me is to do the word search and look at
> everything! There are gems hidden in documents whose titles seem completely
> unrelated to what I am looking for.
>
> Thanks again for pointing this file out. It is awesome!
>
> Chris
>
> On Tue, Apr 12, 2022 at 2:33 PM Nick England <navy.radio at gmail.com> wrote:
>
>> Yep - I figured there was an S but I couldn't remember where they were
>> squirreled away.
>> See page & of S-110 for RF section alignment....
>> https://tmchistory.org/tmc_drawings/drawings_db/s/s-docs_100_199/s_110.pdf
>>
>> Have fun, Chris.....
>> Nick England K4NYW
>> www.navy-radio.com
>>
>>
>> On Tue, Apr 12, 2022 at 4:50 PM John Poulton <jp at cs.unc.edu> wrote:
>>
>>> I haven't had time to research this, but it's possible that one of the
>>> S-documents (Specifications, located under "S" in the Drawings part of
>>> tmchistory.org) may include a document that outlines the factory
>>> procedure
>>> for VOX alignment.  They exist for some TMC products, but not all...
>>>
>>> And, I'm assuming you guys already checked the various manuals for the
>>> VOX..
>>>
>>> Sorry not to be more help!  This week has turned into a bit of a
>>> nightmare,
>>> time-wise.
>>>
>>> 73, John K4OZY
>>>
>>>
>>>
>>> On Tue, Apr 12, 2022 at 11:38 AM Chris Bolkan <bolkyboats at gmail.com>
>>> wrote:
>>>
>>> > 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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