[AMPS] Tetrode Amp Help

[Michael McCarthy, W1NR]

Here are a couple of sources you may find at the library:

	Radio Handbook, 22nd Edition, 1981 page 22.52-22.61 has
something that may be very close.  It uses a directly grounded screen
that floats the cathode negative with respect to chassis to provide
screen voltage.  It appears to be designed to go along with a 5W output
transmitter in another section of the book.

	Radio Handbook, 16th Edition, 1962 page 654-661 has another
using a 4CX1000A.  This one uses the screen bypass cap built into the
SK800 socket.  This uses a grid swamping resistor for 75W drive.  I have
often thought about building this one!

	Then, there is the Collins 30S-1.  You can probably get a manual
from one of the manual reprint vendors.

Mike, W1NR

BTW: The 4CX1000A and 4CX1500B are virtually interchangeable.

Leigh wrote:
> 
> Hello Amp People,
> 
> I acquired a very nice home-brew amplifier recently and I am in
> the process of figuring out what I need to do to get it on the
> air.  Unfortunately, it came with no documentation, ugh!  It is a
> grid-driven tetrode design using a 4CX1500B tube.  It has a
> filement supply and an adjustable bias supply built into the RF
> deck.  It is built like a battleship, uses vacuum variables, a
> manly band switch, and is fully metered.  It appears to only
> require HV + screen voltage to operate.  Unfortunately, my
> limited amp experience is with grounded-grid amps and I have a
> few questions for anyone on the list here with significant
> experience with such a beast.
> 
> I guess the biggest question I have is in regards to the
> requirements of the screen supply.  There appears to be no screen
> by-pass resistor in the RF deck so I'll assume the builder (have
> no idea who it was) included that in his screen supply.  The
> Eimac data sheet states 70mA for this resistor so I guess its
> value should be around 5k ohms?  What is the recommended size of
> this component.  I would guess 5 watt would be large enough but
> maybe I am not considering possible failure modes?  Some
> references I have seen state that HV should be applied before the
> screen voltage so I'll assume it is a good idea to apply screen
> voltage with the TR relay activated.  Any thoughts on a
> recommended screen supply circuit.  I wouldn't think with the
> screen bleeder that regulation is required and I was thinking of
> using a choke input filter (anyone have a ~4-5 HY 350mA 400VDC
> filter choke lying around?).
> 
> None of my references have any constructed amps described using a
> grid-driven 4CX1500B design (or any grid-driven tetrode for that
> matter).  Anyone out there have a good reference of a successful
> design that I could use for my reference.  I will be using a 3000
> VDC 1 amp supply that I already have built up for high voltage.
> The HV xmfr in this supply has a 375V tap that I will use to
> power the screen supply so that is no problem.
> 
> Any other words of wisdom to help me out here.
> 
> Thanks for your time reading this and hopefully you won't spend
> too much time helping me out here (time is a precious
> commodity).
> 
> 73 de Mike
> K7PI
> Mercer Island, WA
> 
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-- 
**************** Give Every Man His Dew **************
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Everest Engineering Corporation, Consultants
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