HW-101 mic amp questions - another weirdness.

[Kenneth G. Gordon]

Since my last post, I have done some more measuring of values, and 
other checks and have discovered a strange phenomenon:

the "Anti-Trip" adjustment doesn't work as it is supposed to, and, even 
worse, adversely effects the mic gain.

Presetting the "VOX Sensitivity", and "Anti-Trip" controls to about 1/3 
open, followed by adjusting the VOX Sensitivity and VOX delay controls 
to my liking, then, after turning the AF gain up a bit to adjust the "Anti-
Trip" control, I find that the "Anti-Trip" control does absolutely nothing 
to keep the speaker audio from tripping the VOX, no matter where it is 
set.

HOWEVER, the higher I set the "Anti-Trip" pot, the LOWER the mic 
gain, no matter where I set both the gain control on the mic (I am using 
a Turner Plus 3), or the CW/MIC Level control.

In fact, if the "Anti-Trip" pot is cranked all the way to the clockwise stop, 
mic gain is extremely low, and as I crank it back towards the counter-
clockwise stop, the mic gain increases drastically to what I consider to 
be "normal".

With the "Anti-Trip" pot set to its counter-clockwise stop, both VOX and 
mic gain are almost perfect, except for the fact that I must keep the AF 
output down to a reasonable level, and not hold the mic up to the 
speaker. :-)

I use the HW-101 for various 75 and 40 meter net operations, and 
reports are that it sounds excellent on the air.

So, it appears obvious to me that there is a mis-wiring error in the rig, 
and possibly a failed component, in the anti-trip circuit.

All tubes check out just fine. I substituted known new tubes for 
suspected ones, with no change in symptoms. All voltages and 
resistances now appear to be within tolerances.

Thinking about V-1's 130 VDC screen voltage vs its ~40 VDC plate 
voltage, in that stage, I don't think it matters, although, to me, it seems 
rather odd.

In any case, even with only 8 VDC on the plate, it worked just fine 
before I changed R-1, and now it works even better.

As I mentioned before, I have substituted a 6GH8A for the original 
6EA8 at V-1, and both the CW/MIC LEVEL control, and the 
microphone's gain control are set to about the 10:00 o'clock position for 
best sounding audio. At these settings the ALC kicks to S-9 only on 
strong peaks, and averages S-7 to S-8, while the VOX works perfectly.

It seems like there is always something different about every one of 
these rigs I work on to keep me interested in learning what the next 
mystery might be! :-)

Ken Gordon W7EKB 

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