I'm working on yet another Valiant I. This one has the Johnson SSB
adaptor wiring modification kit installed (if that is an issue?). All
appears to be well, RF out, etc. but I have a question regarding one of
the meter readings. In the oscillator position (6CL6 buffer cath.
current), I get a continuous 10ma reading, key up (idle current, if you
will). Key down, I get an expected swing upward, the keyer circuit
appears to work OK, and the unit transmits with nothing untoward
happening. On the other two Valiants I have, there is no measurable
current in the osc. meter position, key up. I've checked virtually all
components in/around the buffer and keyer circuits with no problems
detected. The only issue is that the derived grid bias on the buffer is
-3v vice the -5v called for in the book. That may be the reason the
buffer is idling at a higher current... but why? What is not provided
by Johnson is a re-drawn schematic after the somewhat extensive re-wire
job for the SSB adaptor. I could just ignore the issue as the 6CL6 is
still well within its operating range. Maybe someone else has had this
come up and/or its normal after the mod has been done? The mod book
makes no mention.
Thanks for any insights. de K3HVG

Hi Jeep:

I am responding from a dark hole - guessing. A shot in the dark, so to
speak.

I am guessing that the 6CL6 was converted to a class A stage for use with
the ssb adapter. The basis for this is my vague recollection from an early
Single Side Band ARRL publication by Father Morrison, who was a teacher of
one of my friends. He converted a Viking II for use with a Central
Electronics 10A sideband rig and basically did the same thing to a driver
stage (maybe a 6AQ5), using it as a class A stage.

So, what is good for the Viking II ought to be good vor the Valiant. I
think the article may have been in a 1955 or 1956 QST.

How is that for pulling out trivia from way back and applying it to a
different set of facts?

73, Colin K7FM

"COLIN LAMB" ) writes:
Hi Jeep:

I am responding from a dark hole - guessing. A shot in the dark, so to
speak.

I am guessing that the 6CL6 was converted to a class A stage for use with
the ssb adapter. The basis for this is my vague recollection from an early
Single Side Band ARRL publication by Father Morrison, who was a teacher of
one of my friends. He converted a Viking II for use with a Central
Electronics 10A sideband rig and basically did the same thing to a driver
stage (maybe a 6AQ5), using it as a class A stage.

But I thought a lot of those things had enough oomph to drive the output
stage directly.

The 10A was classified as an exciter, and the schematic in the CQ SSB book
shows a 6AG7 in the output of the 10B (and the ad in the back says it's good
for 10watts). The SB-10 adaptor schematic in the same book has a 6BQ5, and
the text even says you'd basically break the connection between the driver
and the output stage, and connect the adapter there.

Given that these have actual output stages that use driver type tubes,
I would have thought it was simpler to just drive the output stage directly.

Michael VE2BVW

k

The 10 uses a single 6AG7 in the output. I recall tht the 6AG7 has 11 watts
plate dissipation and the stage runs class A. Class A runs about 33%
efficiency - and the circuit is poorly laid out and resistors are across the
coils to prevent parasitics. I measured 3 watts output with my 10A.

Although the power output ought to be able to drive a pair of 6146 tubes, I
do not think that was the way they did it.

Hopefully the manual for the adapter will answer the question.

73, Colin K7FM

Guys.... Thanks for the replies. Colin's reply falls in with what I
thought of. The modification sheets tell you what to do, a la Heathkit,
but make no explanation of the results of same nor an updated
schematic. I may have to re-draw the beast...maybe. I came close to
buttoning the thing up and "dealing" with the buffer idle current
(apparently benign) but decided to plug in a mic and have a look-see.
No modulation. I discovered two, absolutely new-looking 47K resistors
in the audio chain were dead open. No heat damage, nothing! They looked
like NIB AB's out of the package (as does everything in this unit).
Bottom line, I changed out the four green plastic Sangamo .1uf caps, two
of which were associated with the bad resistors. I've not have bad
experiences with these type of Sangamo's, up to now. So, it ain't just
the BB's and the paper/wax jobs that go bad. Now we're good to go. 150
watts and 100% modulation. Doesn't look bad on the scope, too! Again,
tnx for the comments.

Next projects: another NC-183D and a Lysco 5-bander. Urrah!

Jeep/K3HVG