[Amps] Any new tube research?

Carl km1h at jeremy.mv.com
Sat Aug 20 06:23:11 PDT 2011

----- Original Message ----- 
From: "Roger (sub1)" <sub1 at rogerhalstead.com>
To: <amps at contesting.com>
Sent: Friday, August 19, 2011 7:05 PM
Subject: Re: [Amps] Any new tube research?

> My experience with the 728F's has been mixed.  I've used new ones and
> also NOS.  I've had several fail within the first 50 hours. The ones I'm
> using (rotating) through my one amp at present appear to be good ones.
> However I'm planning on building up 3 amps using the 4CX3000A7 running
> class A with the legal limit out. (HF, 6-meters, and 2-meters)  My only
> complaint about the tube is the size. It's just too big for a compact
> desk top amp. With the tube being over 9" tall, I'll end up with an RF
> deck about 14" tall and fan noise is likely to be a problem. I may have
> to either remote a large fan or remote the amp with a control head
> mounted in a compact desktop cabinet that appears like a compact amp.
> Still running the legal limit out in Class A means the tube will be
> close to it's dissipation limits and I won't need much additional heat
> in the winter. <:-))  OTOH I have a couple of tested 4-1000As I'd like
> to build into HF amps just for (as you say) nostalgia. I also have some
> of the RUSSIAN GU81M which is also a large glass bottle (Pentode)
> although its performance fall off rapidly with frequency compared to the
> 4-1000A.

Aww, you poor fella, I feel your pain (-;

The 6C21's (pulse rated 450T family) in one of my AM amps are 12.625" tall 
not counting the heat radiating plate cap. At least the 304TL modulators are 
Real amps belong in racks and not on the desk....


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