[Amps] Tube choice for SB-200 on 6 meters

[Jeff Blaine AC0C]

Larry,

I don't want to dispute Carl's experience in the 572b 6m conversion 
category.  But I cay say that if you are interested in digimodes or RTTY, 
the 572b is going to be one seriously suffering set of birds.  I think I 
have 6 in a box below my desk sacrificed to the gods in a test to see how 
they would hold up...

The problem with the conversion using the SB200 is not the transformer per 
se, it's a real workhorse.  It's the voltage.  Loaded it runs around 2100w 
and that will get you up to about 700-800w at max grid drive into a pair of 
GI7b under rtty service.  If you have enough cooling.  Depending on the 
frequency (and a lot of other things), the net efficiency will be in the 
45-63% range.  Which is a pretty large amount of plate disipation in RTTY 
service hence the need for 2x.  For CW or SSB, a single GI7B is a FB match. 
It has about 350w plate disipation vs. 160w ea for the 572b.

If you would like to take a look at a SB200 using 2xGI7B with RTTY service 
in mind, you may like to check out the presentation link on my qrz web page. 
There is quite a lengthy presentation there that goes into great detail the 
various mods.  Hope it helps.

73/jeff/ac0c


--------------------------------------------------
From: "Larry" <n1miw at cox.net>
Sent: Friday, July 10, 2009 11:34 PM
To: <Amps at contesting.com>
Subject: [Amps] Tube choice for SB-200 on 6 meters

> Hello group,
>
>   I'm looking for some information on converting an SB-200 to 6 meters. I
> originally thought about using the Russian GI-7B tube, but now I'm not 
> sure.
> It looks like I can only use one tube due to power supply limitations. 
> What
> have you guys seen in real-world conditions if you used this tube? Will I
> see about 500 CLEAN watts out from the single GI-7b (someone said in the
> archives that one of these tubes equals 2 572B's)? Can I use 2 GI-7b's
> without letting the smoke out of the transformer or PS? There's also the 
> mod
> for the GLA-1000 where the output watts is ~750 which I'm using for
> comparison, but I don't know what the current was at that limit. The spec
> sheet for the GI-7b might put the current for 2 tubes at close to 1A, 
> which
> the SB-200 can't supply as far as I know.
>
>   If the single or dual GI-7b can't give me 500 watts+ out from the SB-200
> PS, is there another tube (or tubes) of choice you would recommend for the
> SB-200? Obviously I do not want to use the 572B's because of the 
> controversy
> surrounding them at this frequency. TIA... Larry N1MIW
>
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