Bill (Wa4Lav) is looking to improving a T'bolt. I just went through
ours (at work) and got it back on the air for some experimental work
(as it can tune anywhere in the HF spectrum). Quickly I found how
limited it is, and as someone stated, wasteful of a pair of 4-400As.
With the low plate voltage (1950 under load) the thing naturally runs
to AB2 class, as you kick up the drive. 600 Watts output on the low
end was about normal. The variable L gets really hot. With VSWR I saw
sparks in the output network, but it was recoverable. (HV clearance
isn't too great in that packed amplifier).
I would raise the HV to at least 2500 or more. Then you better look
at the HV clearances again. I was going to use an L4B power supply
which I found at work, (Minus the RF half). Cut out the HV components
in the T'bolt, and bring cable out and back in, from the L4B PS
chassis. You can really reduce the mass of the Tbolt that way too.
Disconnect the 866 filament power, but recheck the 4-400A filaments
as you do this to verify that it didn't rise above nominal. After you
get it working, you might consider removing all the iron and the Hg
rectifiers to install the components of the new C input HV section.
You might have to install a step start relay for this to prevent
blown fuses and/or power switch on the T'bolt.
Another thing, get rid of the funky connector for the bias switching,
and install a small 12 or 24 VDC coil relay in a minibox, mounted on
the apron of the chassis where the connector was. I had to nibble out
the cutout on the outer cover a little to clear the box when i slid
the amp back into its skin. This relay can be wired to your PTT
circuit and ant relay. The T'bolt of course doesn't have an antenna
relay system, but there isn't much room for one anyhow.
I put a muffin fan on the side to cool, pulling air across the tank L
and helping the tiny fan on the plate connector heatsinks for the
4-400A. If you really push them for a kW or more, you might consider
a better cooling system. The lower fan underneath the input circuit
seems fine for the seals so far.
I gave up on ours when I got the 8877 based RF Plasma Prod HFS1000G
amplifier working for my application at work, as the poor T'bolt
needed so much TLC and the RFPP was 1 kW output easily.
John
K5PRO
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