[Amps] 572B AMP PLANS

[Roger (K8RI)]

On 12/26/2010 11:06 PM, Jeff Blaine wrote:
> Hsu,
>
> The 813 looks nice.

Wayyy back in another life, I beat the snot out of a pair of 813s for a 
couple years, running the legal limit which back then was 1KW average or 
2KW PEP. I probably ran about 60% CW and the other 40% SSB back then. 
Cooling was convection.   At 1KW out PEP they might need a bit of air.As 
they can be found for around $25USD each they make a very economical 
tube.  Some places are calling them rare and antique with huge prices.  
There are just too  many places selling them for much less for that kind 
of price to hold up.

>    But I am very impressed with the GI7B.  I really work that tube hard - both in the RTTY contesting and on the
> bench (one time, I ran the pair for 20 minutes key down at rated power) for simple endurance test on the amp.  Finally had to stop
> out of worry the DL was going to explode.  hi hi.
>
If you have the transformer, I think you could run 4 GI-7Bs well beyond 
1500 out, so they should loaf along at the US legal limit.  You'd still 
have less than the cost of one imported 3-500Z in tubes.  With 4 the 
load resistance would be low enough for the tank to be fairly broad band.

Tube lifetime?  They are rated at 1000 hours, but that is military use. 
I'd expect them to last much longer in amateur service, but I have 
nothing to back that up.

> If I am needing to use glass, I think I prefer the 3500Z if you have high enough plate voltage available.  I'm not sure what the
> 3-500z looks like at 2500V.
>
As I've said before, I'd stay away from 811As unless running a pair at 
500 watts or less and I'm not sure how they'd do then.

73

Roger (K8RI)