[AMPS] 6154/6155 Question

[Roger Rehr]

I recently got unmodified 6154 and 6155 amps, and have been
modifying them to work on 2m and 432 respectively.

I have completed the mods on the 6154 and it works great on 2m.

Last evening I started the non-cavity part of the mods on the 6155.
Of the two amps, the 6155 appears more "untouched", whereas the 6154
had obviously been worked on before (missing screws here and there, etc).
As I went to remove the control grid/thermal control module (bias supply)
in the 6155, I found that it has only one large board; the 6154 has a
smaller board mounted on top of the larger board that contains a slide
switch with the labels "S1",  "Normal", and "Set PA Current".  The board
is labeled: "NSN 5998-01-298-2106 AM-6154/GRT-21 & AM-6155/GRT-22".
This small board also contains 4 resistors, a 6 pin IC, a transistor,
and a capacitor.  I do not see it on my schematics.  The 6154 is working
fine with this board.  There is no evidence that this board was ever in the
6155.  In the 6154 it attaches to pin 13 of "P1" of this assembly and to a
point at or near E1 on the underside of the main board.  These locations
look untouched on the 6155, not as though something was removed.

I guess/hope the board was a upgrade that is not necessary.  I don't know
its purpose, though it clearly relates somehow to setting the bias level.
The fact that the more "mint" amp didn't have the board makes me wonder
if on one of its trips to the repair shop the 6154 had the upgrade added.

Any thoughts would be appreciated so I know what to expect when I turn
the amp on, and if I need to do some scrounging/building...

P.S. a second question: can I exchange the RF modules from the two units
to verify operation of all the control circuitry before I complete the 432
mods, etc??


73 from
Roger Rehr  W3SZ ex-AA3QK ex-WA3JYM
mailto:rrehr@epix.net        FN20ah
http://www.epix.net/~rrehr
2 Merrymount Road, Reading, PA  19609
610.670.8687



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