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[Amps] Re: [Amps] Changing 3-500z to 8877

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Subject: [Amps] Re: [Amps] Changing 3-500z to 8877
From: (
Date: Wed, 21 Aug 2002 14:54:20 +0200
Not the greatest idea.
Adding to the already notices made by others, I like to point out also:

1) As is, the HVPS in an SB220 is too low and small for an 8877.
2) Replacing the internal HVPS with an external one (better a full 
bridge without doubler) would increase the power to the point that 
plate variable will start to arc even with the old 3-500z pair.
3) The switch wafer on the output PI of the SB220 is not really 
reliable at high power unles one has very delicate hands and uncommon 
talent to tune up.
4) The 8877 is a ceramic tube and its cooling requires not only air, 
but air with a certain amount of pressure. This can't be done with the 
simple side blower existing.
5) Etc. etc.

Mauri I4JMY

> >Hi all
> >    I can get an 8877 & socket for a very inexpensive price from a fr
> >My question is can I convert my SB220 over to the 8877 ??? Aside from
> >mechanical aspect of the blower, mounting platform for the tube, Time
r delay
> >& so on .. I assume the tuned input will have to be modified .. But w
ill the
> >pi output be OK ??? I want to do this because I have the tube & I hav
e NO
> >love for 3-
500z with all there parasitic problems & standby heat !! I know
> >the output would be the same or maybe a hair better ,but the drive po
> >will be lower ..and that is nice.. Richard or Tom can you give me any
> >pointers ....
> >
> It's a big job.  No one at the Rx-end will see the 1/6 S-
unit increase.  
> Keep the filament choke.  It can be used as the heater-choke for the 
> 8877. (Don't ground one side of the heater.   Connect the cathode to t
> heater to prevent heater/cathode arcs.)
> -    The tuned input should be reworked for a Q of 2 -
 3.   Drive power 
> will be about half.  However, an 8877 has almost as much feedback-
C as a 
> 3-
500Z and it has way more VHF amplification, so I wouldn't assume that 
> its going to be less squirrelly.
> have fun, John. 
> -  R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K, 
> end
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