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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