[Heath] Concerning the SB-200 and tubes...

[Wilson]

Has anyone looked at the 4CX tubes triode connected?
4-125A and 4-400A work great that way.
Wilson
W4BOH

-----Original Message----- 
From: Kenneth G. Gordon
Sent: Sunday, May 18, 2014 10:49 PM
To: George Collins
Cc: Heath at puck.nether.net
Subject: Re: [Heath] Concerning the SB-200 and tubes...

On 18 May 2014 at 21:44, George Collins wrote:

> Hi Ken,
>
> What a neat project!  I would appreciate information on the fan you used 
> and any
> photos or other info you have available in electronic form.

I have taken a number of photos with the idea of writing an article for 
Electric
Radio Magazine on it. I can send you the photos I have, and a .JPG of the
chassis, but I have not written anything on it yet. The fan is a fairly 
common
one. I'll get that info to you too.

>  I have an SB-200
> that I was planning on selling, but this sounds like something I would 
> like to
> try.

The first thing you want to do with the SB-200 is replace all the caps and
diodes, especially in the power supply. If the filter capacitor in the bias 
supply
is bad, all kinds of really strange things can happen if you attempt to use 
any
form of "soft-key" unit with the SB-200.

The SB-200 is a very, very relible and robust amplifier in my experience. If 
it
weren't for the 572Bs, it would be completely reliable.

>  Have you any information on the IMD performance to expect from the
> conversion?

That was one thing I specifically investigated. Although I have forgotten 
the
exact figures, in SSB service (either AB1 or AB2), 4CX250B's IMD is low and
that is one reason I chose it.

The 4X150A is not particularly good in that regard, so although I have a
number of NIB ones, I chose not to use those. BTW, that tube fits the exact
same socket and chimeny as the 4CX250B.

I'll try to find the URL where I found the IMD figures for that tube and for
several others and will send that to you as soon as I find it.

BTW, many years ago, I used first one, then a pair of 304TLs in grid-driven
class AB-2 service as an SSB linear amp for AFMARS work. I only learned
recently that the IMD of a 304TL is NOT suitable, i.e. good enough, for
modern SSB work.

I was very disappointed to learn this. They are one of my favorite tubes.

Ken W7EKB
_______________________________________________
Heath mailing list
Heath at puck.nether.net
https://puck.nether.net/mailman/listinfo/heath