[BC] Gates BC-5 and 10H

[chuckg@chartermi.net]

The 5H had a pair of 3CX2500F3's(with filament leads)  for modulators and a
single 3CX2500F3 for a final. 
The 10H and the 5HA had  pair of 3CX2500F3's for finals. 
All versions used a 4-400 as an IPA, noted for rather short life in the 5HA
and 10H versions.  Positive peaks required a lot of grid drive to the
final(s).
The only other tube in the transmitter was a 12BY7A in the VSWR overload
circuit. 

The original solid state audio driver was a nasty push pull design, with 12
discrete darlington pairs per half. 
It was completely DC coupled from the input transformer right to the grids
of the modulators, generating bias voltage along with the audio drive- with
only a diode pair for arc supression. 
An arc in the modulators most always meant replacing every transistor. 
In the early '70,s Harris redesigned the audio drivers using a handful of
GM DTS-series transistors resulting in better positive capability and more
rugged construction. 

Likewise, the single-output device RF driver was redesigned with a parallel
output pair, for the same reasons. 
Also added was a BNC external exciter input, making later addition of Cquam
nearly a plug n play affair. 

If one managed to tune the 3'rd harmonic resonators in the PA circuit
perfectly, a difficult feat at the low end of the band- PA efficiency could
hit 90%. 

One of our stations still has one in daily service, with the "HA"
modification. 
They've long ago pulled the positives back, symmetrical with the Negs, lol.
Flamethrower days are over. 


Chuck G. 
Quicksilver Broadcasting





Original Message:
-----------------
From: Dave Hultsman reader at oldradio.com
Date: Thu, 19 May 2005 14:22:46 -0700
To: broadcast at radiolists.net
Subject: [BC] Gates BC-5 and 10H


In a message dated 5/18/05 12:05:10 PM Central Daylight Time, 
broadcast-request at radiolists.net writes:
ISTR the Gates BC-5H and BC-10H were fully transistorized except for
modulators
and finals just like the MW-5 and MW-10. The difference was they were plain
old high level plate modulation also like the MW-5 and MW-10 and, naturally,
had a pair of modualtors (3CX3000's IIRC) and a pair of finals because two
were less expensive than one (believe these were 3F2500's). ISTR that the
"H" designation meant "hybrid" IOW tubes with solid state drivers

Didn't the  BC5H and BC-10H had an RF Driver tube?

Dave 


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