[TenTec] another amp question

[Ed]

jerome schatten wrote:
> Learned gentlemen...
> 
> Excuse me if this is somewhat off-topic, but I've been following the  
> 811 amp discussion with much interest and have a related question:
> 
> I'm currently doing some work my pair of 813's and was thinking about  
> the 'parasitic' problem as discussed on this list.
> 
> My fear is not blowing the tubes or the band switch, but rather in  
> blowing the front end of a modern transceiver driving it.  The  
> configuration is a pair of 813's truly running zero bias GG (grids all  
> tied together and connected directly to ground ~ 50 ma. idle current  
> at 2200v). No band switch (rotary inductor pi-network). Manual  
> switching tx/rx avoids hot switching. Input to the amp is grounded in  
> Rx. Works 80 thru 20 only.
> 
> Should I be worried about the parasitic problem taking out what's  
> driving it?  If so, how to prevent (minimize) that?  In the 40 years  
> I've been running this beast (still the same set of tubes) I've driven  
> it with everything from a Viking Ranger, to a Jupiter and never had so  
> much as burp. But one never knows.
> 
> Getting nervous in Vancouver,
> va7vv


What a great amp.....I could kick myself for ever selling the pair of 
813's I built. For you "new" hams, 2 813's in GG with 2200 to 2700 on 
the plates was hard to beat. They didn't like 15 and they definitely 
didn't like 10. But from 20 on.....what an amp. If I had some tube 
sockets and a filament transformer, I would build a 813 amp in a heartbeat.

I liked the idea that Ameritron uses, instead of floating the B- with a 
5 to 10 ohm resistor, they used a diode. So you have B- above ground 
enough to run the meter circuit, but the diode doubles as a fuse.

I've been building, repairing, and using amps for 30 years. 99.9% of the 
time, any catastrophic event has been operator error or component failure.

I would suggest thinking about using a diode in the B- return and let it 
act as a fuse.

Ed W3NR