Apache help needed

[MATTHEW ERICKSON]

Bill Coleman N2BC wrote:
>
> I should have known the refurb was going too clean....
>
> Symptom: modulation level control has no effect what-so-ever....   I have
> audio, plenty of it. Might be a bit on the 'thin' side (no lows) but haven't
> given it a critical listen yet.  Just wanted to determine what's with the
> modulation level control.
>
> What I found:  It looks like I've found either a wiring error and/or a mod.
>
> 1) the modulation level control (R3) is hanging on the Low B+ and going
> noplace! Supposed to take the AF from the second section of V8, thru a
> blockling cap, thru the pot to the grid of the driver.  What I have is a
> blocking cap straight to the grid of the driver and a 100K resistor to ground.
>
> 2) plate voltage has been removed from V8 and the grid of the first section
> jumpered straight to the plate of the section. This has the effect of jumpering
> out the clipper.
>
> This looks like a mod(s) - but for the live of me I can see no reason for the
> wiring of the modulation level pot other than a 30 year old mistake.
>
> My questions:  Anybody recognize any of this?  Should I restore it to original?

First of all, all this sounds like a self-styled and
lacking-in-knowledge
"engineer" thought he could do better than the Heathkit engineers and
things
just got worse and worse.

First step I suggest is connect the pot like you know it to be. (#1
above).
Next: TEST THE POT ACTION.
NOTE: the audio may not be so thin now. Then "thin-ness" may be a result
of over-driving the next stage at the present time.

Second step I suggest is remove the jumper that short around the clipper
and give V8 its B+. I don't know value of plate resistor; something
around
100K may work fine. Check clipper wiring. Does it look reasonable? Early
ARRL Handbooks show circuit ideas.

Please note that my attitude is to restore original circuit, THEN worry
about
remaining possible "thin=ness".

Should you restore this thing? Oh, Yea! It's worth it!!

Best regards,

Allen, KJ6XH
http://www.speedlink.com/mattall
email:    mattall at speedlink.com