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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