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Re: [TowerTalk] 3CX800A7 vs. GU-74B

To: electric911inc@hotmail.com, dj7ww@t-online.de
Subject: Re: [TowerTalk] 3CX800A7 vs. GU-74B
From: mike repinski via TowerTalk <towertalk@contesting.com>
Reply-to: mikflathead@aol.com
Date: Sun, 12 Feb 2017 10:03:50 -0500
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
 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@hotmail.com>
To: Peter Voelpel <dj7ww@t-online.de>
Cc: towertalk <towertalk@contesting.com>; Herbert Schoenbohm 
<herbert.schoenbohm@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@t-online.de> wrote:
> 
> 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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