[Johnson] valiant audio problems

[Gary Schafer]

Ronnie,

I had the exact same problem with a heathkit ssb transmitter one time. I
bought 3 new D104 cartridges before I figured out the problem. The first
audio stage had a leaky grid. With a dynamic mike hooked to it it worked
fine as the coil in the mike shorted the grid to ground so the voltage
could not creep up. But with the D104 there was only the grid resistor and
the grid voltage would go up an bias the tube wrong.

Check the first audio tube again and check that the grid resistor is good.

73
Gary  K4FMX


w5sum@glowbugs.com wrote:

> howdy men
> This will be somewhat long. Put on your thinking caps :)
>
> My valiant has some quirky problems with the audio. I can use an
> astatic 10DA and I get PLENTY of audio. In fact I only have to turn
> the gain up to about the 10 or 11 o'clock position to get all the
> audio I need. BUT when I use the D104 I have to turn the audio gain
> up nearly all the way and it sounds like poop.
>
> Now, this is my original Valiant I have had since I was a yonker. I
> had loaned it out three years ago and the fellow I loaned it too
> prompty traded it to another ham for a rice box! That ham traded it
> to someone else, who traded it to another ham that I happened to
> know, so I got it back by trading off my Apache for it. Somewhere
> along this path, it had its microphone chassis connector changed
> out to a CB type 4 pin plug.  When examining it, it looked like it
> had been wired up by a drunk monkey with a blow torch! I found a
> PAIR of cermet 474K resistors in parallel, in place of the 1 Meg
> Resistor that was supposed to be there ( grid input of first audio
> stage)   This pair of resistors in parallel were reading real squirrely
> with my DVM and in fact, ranged up and down from 5 Meg ohm to
> 25 megohm!!!  Anyway, put a nice Allen Bradley 1M 1% in there
> and put in a regular two pin mic connector that was supposed to be
> there. I also changed out the two .005's and the 300pf caps that
> are hooked to the mic connector ( the 300 was hooked to pin 2 of
> first audio)
>
> On the air tests this morning got me an A+ for audio when using
> the 10DA but the D104 still has to have way too much audio gain
> to 100% modulate and still sounds like crap.  This D104 is used
> daily with a Ranger and gets glowing reports so I know its good.
>
> I have changed out the 12AX7, and the 6C4 in the audio, as well
> as the 12AU7 ( the clipper circuit is bypassed)
>
> So, I can't imagine why a D104 would not have enough drive for this
> rig, or WHY it sounds so darned bad.
>
> any suggestions?
>
> thanks in advance
>
> Ronnie
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