Grant Youngman wrote:
Is there any truth (or significant value in performance) to
this concept that it does matter which plate lead connects to
each modulator tube? Appreciate any advice the list
membership might have. Bill, w0ng.
Yes.
The male voice waveform tends to be very asymmetrical. If the phase is
incorrect the radio will likely hit 100% negative modulation before getting
to 100% positive.
There is more than one way to skin the cat. You can (1) just reverse the
mic leads -- thus reversing the phase. Or you can (2) swap the phase by
changing plate leads on the modulator (or by swapping the leads on the
driver transformer, etc.). Or you can use an all pass filter in the audio
chain which will remove the asymmetry altogether.
In any case, the objective (and you should have a scope to check which is
which) is to get highest possible positive peaks before you hit 100% on the
negative peaks.
Another way would be to check the 'phase' of the audio on an o'scope and
follow it all throughout the audio chain until it gets to the grids of
the modulators.
Most important, observe that the proper 'phase' is being applied after
the phase-splitter process.
This discussion came up this morning, on 75m AM on 3.880.
We do tend to have some rather 'technical' discussions in South Texas,
on 3.880.
Another place you might want to look Bill, is an article written by AM
Reflector list participants WA5BXO, K4KYV and WA3WDR at
www.qsl.net/*wa5bxo*/asyam/aam3.html
--
73 = Best Regards,
-Geoff/W5OMR
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