[TowerTalk] 3CX800A7 vs. GU-74B

[Herbert Schoenbohm]

The best solution I have found is to use Matchlette 3CX800A7's from 
China for $400 each.  Matchlette used to be made in the USA but was 
bought out by a Chinese. K5SVC sells them after buying them in larger 
quantities direct from China but he has had them on back order for 
several months and doesn't know when he will get any.  The people in 
Colorado even sold them as a lower priced substitute until RKR Design 
was sold to another company that only supports the later  Alpha amps.  
The second best option is to look for some medical pulls of the 
3CXP800A7's which Ii used here for over a year.


Herb, KV4FZ


On 2/12/2017 11:03 AM, mikflathead at aol.com wrote:
> An 8877 needs more voltage than a 3CX800 for one. The socket is 
> different also. Plus it is a lot larger if space is an issue.
>
>
> -----Original Message-----
> From: john nistico <electric911inc at hotmail.com>
> To: Peter Voelpel <dj7ww at t-online.de>
> Cc: towertalk <towertalk at contesting.com>; Herbert Schoenbohm 
> <herbert.schoenbohm at gmail.com>
> Sent: Sun, Feb 12, 2017 9:12 am
> Subject: Re: [TowerTalk] 3CX800A7 vs. GU-74B
>
> Can you replace 3cx800 with 8877?
>
> Sent from my iPhone
>
> > On Feb 11, 2017, at 8:34 PM, Peter Voelpel <dj7ww at t-online.de> wrote:
> >
> > An EIMAC tetrode 4CX800A was never fabricated.
> >
> > 73
> > Peter, DJ7WW
> >
> > -----Original Message-----
> > From: TowerTalk [mailto:towertalk-bounces at contesting.com 
> <mailto:towertalk-bounces at contesting.com?>] On Behalf Of
> > Herbert Schoenbohm
> > Sent: Samstag, 11. Februar 2017 21:35
> > To: towertalk at contesting.com <mailto:towertalk at 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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