An EIMAC tetrode 4CX800A was never fabricated.
73
Peter, DJ7WW
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
Herbert Schoenbohm
Sent: Samstag, 11. Februar 2017 21:35
To: towertalk@contesting.com
Subject: Re: [TowerTalk] 3CX800A7 vs. GU-74B
Thanks to all that responded to my inquiry about using the GU-74B's (a
tetrode) in triode socket configuration as a replacement for the
increasingly expensive and affordable 3CX800A7's. All agree it could
not be done or should not be done especially in the case of Alpha 87A
which has a very extensive firmware protocol. Now here comes the good
news, at least for some of you....Many recently newly manufactured QRO
amps are using the GU-74B's (tetrode) and they are still going at a
reasonable price. In fact there are 10 of them on eBay today for a
reduced price of $195.00 each from one vendor.
Herb Schoenbohm, KV4FZ
On 2/5/2017 6:09 PM, Herbert Schoenbohm wrote:
I have been trying to buy just one single triode 3CX800A7 to fix a
problem with a sick Alpha 87A. Several match pair are available but
used and will only be sold in pairs. The new Eimac version of this
tube are still available but cost as much as the amplifier did years
ago! The less expensive Machlette (Chinese) version of this tube,
although advertised on eBay, are reportedly not in stock and a 60-90
day waiting period. However, Svetlana (Russian Federation) made many
thousands of the GU-74B which is there version of the Eimac tetrode
4CX800A. The GU-74B's are plentiful on eBay for a third the price of
a 3CX800A7. I have successfully before used spare tetrodes (4-400's)
as substitutes for 3-500Z's in several amplifiers by merely making
sure the screen grid was connected to the grounded grid at the
socket. My question is if the GU-74B's could be successfully operated
as a triode. I have not found a print of the socket for the GU-74B
and if there is a difference requiring a socket change this idea would
be a non-starter. Many EU hams are using the GU-74B in home built
amps and now more and more commercial amps have chosen them as their
PA tubes. Please let me know if the idea of using a GU-74B is even
feasible. A single 3CXP800A7 (medical version used in MRI's) if good,
would also solve my problem if I could only find a source.
Thanks,
Herb Schoenbohm, KV4FZ
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