Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Dick -
You have it right. Try and get three (or two) of the same brand
together. Preferred tubes are Sylvania, Zenith, RCA and GE in that
order. All Zenith branded tubes were manufactured by Sylvania. There
are "some" that will not work without modification of the neutralization
circuitry in the transmitter, but these are not always "brand specific"
since many tubes were cross branded. I have had specific problems with
Westinghouse and Raytheon branded tubes. The "generic" brands that came
late in tube production are suspect since there is no way to know who
made them, almost certainly NOT the name on the tube.
The 6KM6 is not a particularly good sub. It has considerably different
interelement capacitances, Plate resistance and Transconductance, each
of which "could" be a problem for stability. Certainly not in the TR-4
series, since the filament current for the 'KM is 1.6A vs the 1.2A for
the 'JB, and the filaments of the TR-4 are a series/parallel
combination. There are a lot of "recommendations" on the auction sites
that serve no-one except the seller.!
The best substitute I have found to work consistently, following the
same brand limitations above, is the 6GJ5/A. It is an _identical_
tube with the single exception that the Suppressor grid is connected to
the cathode internally rather than being brought out to Pin 8 as in the
'JB. Since the Drake transmitter finals are operated in Class AB1,
grounded cathode; and Pin 8 of the socket is grounded, the 'GJ is a
drop-in replacement.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B & C-Line Service Supplement CDs
<www.k4oah.com>
Donley wrote:
I have seen some comment on power amplifier tubes for the above Drake
transmitters, but I would like some definitive information. My T-4XB
uses 6JB6 and the T-4XC and TR-4C use 6JB6A's. I do not know the brand
names on the current tubes as I have had no need to open the cases.
1. The 6JB6-6JB6A should be interchangeable as long as all tubes are
the same in one transmitter?
2. I believe I remember that Sylvania was the tube of choice? Are
there any other manufacturers' tubes that will work satisfactorily?
Are there any that absolutely will not work?
3. Are there any substitutes (6KM6) that will work? I have seen 6KM6's
on the auction site that are claimed to be excellent substitutes.
4. If this has been hashed out before, please tell me and point me to
the archives.
Thanks.
Dick
KC9UB
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