[Amps] Commander VHF-1200 questions

gudguyham at aol.com gudguyham at aol.com
Sat Jul 18 18:31:26 EDT 2020

You may never find a schematic that fits your particular build.  It was typical for the original Command Technology to make undocumented changes.  You’d be lucky if the original manual that came with it had the “as built” schematic.  Originally grid trip overload was not available but as the tubes became more expensive it was an added feature.  If you want to install grid overload protection I have a PC board i sell with instructions for that amp.  Contact me off list.  At this point in time there is no support for any Commander amps.  Good luck.

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 On Saturday, July 18, 2020, Jeff DePolo <jd0 at broadsci.com> wrote:

I have some questions on these amplifiers regarding their history and
changes made to them over the years.  I know they were originally made by
Command, and then sold to Palstar, and then back to Command (?), and then to
AN Wireless?  This one appears to be a very early Command model.  It is
serial #105, which is presumably #5 off the line.  The lexan front panel
doesn't have the usual Command Technologies "flag" logo, it just has the
word "Command" in a plain black font.  None of the documentation I can find
online, either with Command or Palstar branding on it, seems to match what I
have.  Some differences I've found between what I have and what I've found
in the schematics online include:

- There is no two-speed blower operation on this one.  There is a resistor
in one leg of the AC to slow the blower, but no relay to jump across it to
speed it up when transmitting.

- There is no grid over-current protection circuitry.  Did that come later?

- One manual I found shows one side of the filament grounded (like this
one), and a later manual shows it floating. 

- A few component value differences (not RF-related), differences in wire
color codes, etc., nothing major but would be nice to have accurate prints.

Any history on revisions that were made to these amplifiers over the years
(and why), or a source for schematics that match this presumably-early unit,
would be helpful.  While I have it open, I may as well incorporate whatever
improvements I can, especially adding grid protection.  And while I have it
open, given its age, shotgunning the HV rectifier/filter board would
probably be wise; is there a better way to get to it that I'm not seeing, or
does the socket sub-chassis need to be disconnected from everything else and
removed from the chassis?

On a somewhat related note, has anyone bought tubes from eBay seller "Nevada
Endeavor"?  They have a listing for "Pre-Order Thomson CSF 3CX800A7".

                    --- Jeff WN3A

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