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Re: [Amps] 3CX1500A7/8877 vs el cheapo GS-35B

To: "Leigh Turner" <invertech@frontierisp.net.au>, <amps@contesting.com>
Subject: Re: [Amps] 3CX1500A7/8877 vs el cheapo GS-35B
From: "Carl" <km1h@jeremy.mv.com>
Date: Tue, 31 Jul 2012 06:43:47 -0400
List-post: <amps@contesting.com">mailto:amps@contesting.com>
So the gain and efficiency go up but so does the cost of the PS and tank 
components.

Use a good tube to start with, learn how to build fault circuits and enjoy 
life. I wouldnt want to be in the same room with the blower for one or two 
GS-35B's.

Carl
KM1H



----- Original Message ----- 
From: "Leigh Turner" <invertech@frontierisp.net.au>
To: <amps@contesting.com>
Sent: Tuesday, July 31, 2012 4:29 AM
Subject: Re: [Amps] 3CX1500A7/8877 vs el cheapo GS-35B


>
> Hi Bill,
>
> But my point here was that if you design the tank circuit for a higher 
> plate
> voltage and plate load impedance then you won't have to take a hit on the
> efficiency.
>
> As Jim reported in his reply to my post, he obtained 61% efficiency from a
> pair of GS-35B tubes in GG on 6m with 4100 Volts plate potential under 
> load
> and a tuned Pi-input network of proper Q factor. This result is consistent
> with what other folk achieve from amps using this very cheap tube.
>
> When the input circuit Q and the tank Z are optimized then the efficiency
> and the requisite drive power will compare favourably.
>
> Is the GS-35B tube a drop-in replacement for the 8877?  Hell no; but with
> appropriate circuit design changes it will / can be made to work superbly 
> at
> very low cost...which is what ham radio amp homebrewing is all about; its
> even more satisfying when you can build an amp from junk box parts and 
> make
> it really sing with a cheap tube that some misguided folk regard as a sows
> ear piece of crap :-)
>
> Cheers,
>
> Leigh
> VK5KLT
>
>
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of Bill, W6WRT
> Sent: Tuesday, 31 July 2012 1:42 AM
> To: AMPS
> Subject: Re: [Amps] 3CX1500A7/8877 vs el cheapo GS-35B
>
> ORIGINAL MESSAGE:
> On Mon, 30 Jul 2012 06:32:14 -0700, VK5KLT wrote:
>
>> complaining about achieving circa "only" 55% efficiency and a few extra
>> watts of exciter drive is splitting hairs; particularly in a GG AB2 SSB
>> linear.
>
> REPLY:
>
> "Splitting hairs"?
>
> If you call an extra 500 watts DC in to get the same RF out and almost
> double the drive "splitting hairs", then I guess so.
>
> 73, Bill W6WRT
>
>
> Good comments here Bob; you've nailed some relevant points here.
>
> The GS35B does indeed need a higher plate voltage / plate load impedance 
> to
> achieve parity in efficiency with the 8877; complaining about achieving
> circa "only" 55% efficiency and a few extra watts of exciter drive is
> splitting hairs; particularly in a GG AB2 SSB linear.
>
> At circa $120 the NOS GS-35B represents the best bang for buck in the 
> 1500W
> plate dissipation triode tube class; costing a meagre 10% of that of a new
> 8877 from CPI/Eimac, or 15% of the cost of an excellent Chinese clone.
>
> Most affordable key RF components for building QRO amps like tubes, vacuum
> capacitors, vacuum relays, doorknob capacitors, roller inductors, etc are
> all made by non-USA countries. If it weren't for the China tube companies
> producing affordable clones of the popular ham-radio tubes and Russian NOS
> surplus parts, then readily available tube amplifier components would be a
> thing of the past...or the exclusive domain of the wealthy ham.
>
> Cheers,
>
> Leigh
> VK5KLT
>
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