Help ID'ing Homebrew Amp.

[Larry Kirkland]

I remember from the "old days" a construction project where you modified 
the base of 1625 tubes to allow grounded grid operation.  I think you 
had to cut the wire from the suppressor grid to the cathode.  They are 7 
pin and were cathode driven. 

The voltage sounds too high for 1625's, though.  You could get away with 
1000 volts on the plates if you had plenty of spare 1625's.  They were 
plentiful, because they were used in the popular ARC-5 series of army 
surplus transmitters.  Check and see if the filament transformers were 
12 volts.  Also, two of the 7 pins were slightly larger than the other 5.

73's
Larry W4LK


Dennis Wade wrote:
> No, not 8...7 pin.
>
> Are you suggesting that any input tuning might have been on another
> chassis?  Interesting...
>
>          Dennis
>
> On 5/27/06, Rick Brashear <rickbras at airmail.net> wrote:
>> Are they 8 pin sockets?  It sounds to me like a grounded grid of some
>> kind and likely it is only the final and supply of a larger setup.
>> Obviously, the tuned circuits were in another portion of the
>> amplifier.   Of course, that's just my two cents worth.
>>
>> Rick/K5IZ
>>
>>
>> Dennis Wade wrote:
>>
>> > Please excuse me...somehow this got sent before I was done....to
>> > continue...
>> >
>> > On 5/27/06, Dennis Wade <sacramento.cyclist at gmail.com> wrote:
>> >
>> >> Good Evening,
>> >>
>> >>        At a recent hamfest, I found what appears to be a homebrew RF
>> >> power amp.  There is a choke input power supply, and by the ratings
>> >> I'm expecting about 1.5 KV at around 300-400 ma.  There is a tank
>> >> assembly, and a plate choke on the top of the chassis that is pi
>> >> wound, appears commercial.  The power supply uses 2 816's.  The final
>> >> tubes, are..of course missing.
>> >
>> >
>> >         There are 4 positions for the final tubes.  The input comes
>> > from the UHF coax connector and goes right to each of the 4 sockets
>> > with an RFC to ground.  No filament choke, no input tuning of any
>> > kind.
>> >
>> >         There are 3 pins of each socket tied together and grounded on
>> > each socket.  Filiment power appears to be 12.6 volts fed directly
>> > from a transformer in the power supply end of the chassis.  A cathode
>> > driven amp?
>> >
>> >         Power output is taken from topside plate network and fed back
>> > under the chassis and a loading cap to another SO-239 (can this
>> > arrangement be stable..output and input both under chassis?).
>> >
>> >         I can take pics of whatever someone wants to see if it would
>> > help.  Any thoughts?
>> >
>> >           Thanks,
>> >
>> >                Dennis
>> >
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>>
>>
>>
>
>

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