[Johnson] Johnson Valiant question

[Dave Maples]

All: I managed to uncover the problem with the SSB adapter and now have it
working, at least as far as I can tell.  The 12BY7 final in the adapter puts
8 WATTS into a 50-ohm load at max output.  That's certainly plenty to drive
the socks off the Valiant.  All well and good, but in order to move from AM
to SSB and back I have to disconnect the antenna relay from one box and move
it to the other.  Ditto the mike connection.  Very much a kluge.

As this thing is designed in SSB the Valiant HV supply stays keyed basically
forever and the finals are activated by switching bias on and off.  The VFO
is keyed through a ground in the SSB adapter.  The adapter tubes stay on all
the time.

Here's my question: Why couldn't I rearrange the PTT circuitry in the
Valiant to (a) shift the modulator bias from the normal level to about -250
VDC (all I have to do to do this is lift the ground on the MOD BIAS pot),
(b) shift the final bias in the CW and AM modes as is done in SSB today, and
(c) key the antenna relay?  This would require that the HV stay on in AM and
CW just like it does in SSB, but with solid-state diode stacks like I have,
so what?  If I do this then I can use the same basic methodology to key the
rig in either AM or SSB (basically just take a contact closure from the SSB
adapter to key the PTT in the Valiant).  This will do two things:  (1) It
avoids having to switch the antenna relay and mike back and forth, (2) It
avoids the large CHUNNNG! every time I key the Valiant in AM mode, and (3)
it sets the stage for me to do semi-breakin in CW without the need for a TR
switch.

Positive / negative thoughts here?  There's probably a dozen things I am not
seeing with this...

Thanks,
Dave Maples

-----Original Message-----
From: johnson-bounces at mailman.qth.net
[mailto:johnson-bounces at mailman.qth.net]On Behalf Of Gary Schafer
Sent: Tuesday, October 05, 2004 10:23 PM
To: Dave Maples
Cc: johnson at mailman.qth.net
Subject: Re: [Johnson] Johnson ssb adapter help


Dave,

First check to see what kind of a load that 2 watts is supposed to be
feeding. I believe it fed directly to the final grids at a fairly high
impedance and not at 50 ohms. I may be wrong about the impedance??
But if you are trying to measure it at 50 ohms and it wants to see a
higher impedance that may be part of the problem.

73
Gary  K4FMX

Dave Maples wrote:
> All: I have a non-working Johnson SSB adapter I am restoring.  Symptoms
are
> very low output on all bands (a few milliwatts vs. the 2 watts called for
in
> the manual.  So far I have changed out one bad tube, but no correction.
Can
> anyone who has one of these pass along (a) the Peak-to-peak VFO injection
> voltage and (b) the most likely places to check for failure?
>
> Thanks,
> Dave WB4FUR


Johnson mailing list
Home: http://mailman.qth.net/mailman/listinfo/johnson
Help: http://mailman.qth.net/mmfaq.html
Post: mailto:Johnson at mailman.qth.net