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Re: [Amps] multi-tube amplifiers

To: amps@contesting.com
Subject: Re: [Amps] multi-tube amplifiers
From: Steve Thompson <g8gsq@eltac.co.uk>
Date: Fri, 26 May 2006 22:10:29 +0100
List-post: <mailto:amps@contesting.com>

Colin Lamb wrote:
> I am familiar with solid state amplifiers using combiners - somewhat common.  
> Were there any commercial tube amplifiers using combiners?  Any precautions, 
> notes or advice - beside using a lot of extra hardware?  But, if you have 
> extra tubes, you might have extra variables and switches. 

To get most of the combined power out in the right direction, the 
amplitude and phase of the two inputs to the combiner have to be 
reasonably well matched. Solid state amps tend to manage this by 
default, as they are inherently wideband. With valve amps being 
relatively narrow band, and with multiple variables on each, there's 
more latitude for imbalance which leads to power going into the combiner 
termination rather than up the spout. That need not be a killer, 
provided that the combiner load can take the full output from both 
amplifiers (if only for a short while). I've heard of it being done on 
vhf and uhf.
> It would also be a way to avoid running tubes in parallel - something like 
> keeping wives in separate houses but combining the fun.

A delicate touch is needed to get double the fun - it's all to easy to 
get 75% even though you're making double the effort. Worst case is that 
all the fun goes somewhere else (but each wife gets 100% of her fun all 
the time).

Steve

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