[BC] Re: CE transmitter

[Lamar Owen]

On Tuesday 17 May 2005 22:24, DHultsman5 at aol.com wrote:
> If it had transistors it was the 316F.  The transistors drove two
> 4CX15,000A tubes in the final amplifier.  This was the FIRST  two-tube 10
> kW. transmitter and predated the Gates MW-5 and MW-10 series transmitters.
> Agreed the direct coupled transistors would all avalance every now & then.

I worked on a 316F for a long time.  The exciter could very easily be 
overloaded, and while the original transistors used might have worked OK, 
there were never any real direct replacements.  And pity the guy who has to 
clean up from a plate to grid short in the peak tube!

The two-tube Doherty amplifier takes some getting used to, and can be a pain 
to tune if you're not set up to measure the things you need to measure.  The 
whole Doherty linear amplifier design is brilliantly elegant, though, and I 
really enjoyed the beast overall.  But getting good sound out of it was not 
easy, and predominantly due to the exciter.

Owners of 316F's would do well to replace the whole exciter with an LPB or 
similar 100W transmitter and couple into the Doherty from there.  You'd have 
an easier to maintain beast, thanks to the complete unavailability of an 
exact replacement for the transistors used, which, in the six-transistor 
modulator in particular, are very critical as to voltage ratings and hfe 
curves.  That is, the modulator transistors really need to be a matched 
sextet.  The PA quad isn't quite so critical, but having four matched 
transistors is a help.  Of course, doing the exciter replacement relegates 
the transmitter to aux status due to the loss of type-acceptance, and 
wouldn't work for most. (At least I think I have that correct; correct me if 
I'm wrong on the type acceptance issue).
-- 
Lamar Owen
Director of Information Technology
Pisgah Astronomical Research Institute
1 PARI Drive
Rosman, NC  28772
(828)862-5554
www.pari.edu