A question: does the H&K incorporate an input tank circuit. If not adding
one will improve the gain. Grounded grid tubes are known to have
comparatively low gain, so that every improvement in matching is worthwhile.
Besides, remember that a gain of about 8-9 dB is about reasonable for such a
setup- even the 4-1000 is about that figure- more than that requires a high
level of elaboration. On the other hand keep in mind that a sizeable portion
of these 120 watts are transferred to the output, so it's not a total loss.
Alex 4Z6KS
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Edward Swynar
Sent: Saturday, September 05, 2009 5:32 PM
To: amps@contesting.com
Subject: [Amps] The H&K 304H
Many thanks to all who took the time to respond to my query about the old
Heintz & Kaufmann 304H (their version of the Eimac 304TH, per Lud's note to
me)...
Well, research into my radio shack library here revealed that the 304H is
most certainly NOT a good candidate for grounded-grid service: a piece in a
1954(?) issue of QST described just such an arrangement, & stated that for a
kilowatt (approx.) input, a single g-g 304H would need 120-watts of drive!
Hardly promising.
However, I did take heart when thumbing through my 1980 edition of the ARRL
HANDBOOK: there's an interesting low-band "junker" design listed therein
that incorporates a grid-driven 833A. The article makes mention of the
possibility of using a 304TH in its stead, & published specs say that such
an arrangement would need but 30, or so, watts of drive...ideal.
As I mentioned to Lud, I could lash together a robust enough filament
voltage provider that would easily power up either an 833A, or a 304H: then,
with the filament "sockets" paralleled, and allowances made for room, I
could run either tube in the circuit, as dictated by availability &
interest...
...One tube at a time, of course!
~73~ Eddy VE3CUI - VE3XZ
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