As a long time Drake owner, I would offer a loud "Amen" to Ron's
comments. In the best of all worlds, use Sylvania tubes if you can
obtain them, and they usually will not need neutralization. As a young
man going to Ohio State University in the 70's, I worked at the Drake
dealership in Columbus, Ohio. Any T4 or TR series which did not at
least meet minimum output into a calibrated dummy load/wattmeter got new
6JB6A's and the "old" tubes got tossed. Who knew?
73,
Chuck AC7GZ
Ron Baker wrote:
Carl, first of all it would be a sin to modify a nice piece
of Drake equipment. With that said I do not like any
Drake modifications, I like it the way it was, back when.
The problem is finding the 6JB6 tubes, and if you know where
to look new tubes are still available. We know lately
there are several opportunities to buy those on eBay, both
new and used. The problem is you really never know what
your getting until they arrive, but then its probably to
late if it was misrepresented. Those tubes just because
they are in a nice looking box and/or labeled as a match
pair, mean they are really new. In most cases the seller
may not know for sure especially if it is part of an estate
sale. All those are still "buyer beware" Also watch out,
some of those deals maybe manufacturer 2nd's, those not
quite meeting manufacturer specifications, and those
probably will not work at transmitting tubes on the upper
brands.
Also, do not go for the less expensive 6JB6 substitutes. I
have tested several, none of which preformed well in the
Drake radios. Some do well on the lower bands and even
put out more power, but on 15 and 10 meters oscillate and
will not neutralize. So stick with the 6JB6 tube. I have
found staying with the Sylvania, GE or RCA tubes work well
in the Drake. Other brands floating around like
International (blue box) are nothing but garbage, even new
out of the box. Match pairs if you can get them that way
is nice, but having a match pair is not necessary if you
follow a few basic rules. Always make sure all the tubes
are the same manufacturer and are roughly the same age or
have the same manufacture date code. If all that is
unknown simply test each tube in the transmitter one at a
time but removing the plate caps on all but one tube at a
time. Note you need to keep all the tubes in the
transmitter because the filaments are in series. Test each
tube by measuring the idle current of each tube
individually. Do not adjust the bias while testing the
tubes, but one at a time record the idle current of each
tube under test. Then just match the tubes that had the
same idle current reading. Basically test all the tubes
under the same test condition and then match the tubes with
the same idle current for match pairs or triples.
Testing the 6JB6 tube for performance is not too difficult.
Sure signs of weak and bad tubes is the power output. The
first sign tubes are getting weak is a fall off of power on
10 meters. A good set of tubes in a 4-line transmitter
should put out 100 watts or more at 10 meters. As the tubes
get weak you will no longer obtain that power level. As the
tubes get weak lack of power output becomes noticeable
starting at the highest frequency or bands and works towards
the lower bands. Another test for tube performance is how
well the handle the bias adjustment. A good set of tubes
the bias adjustment should have plenty of adjustment room on
both sides of the 60MA set point. Old weak tubes the bias
setting is near or at the end of the pot rotation. A good
set of tubes you should be able to turn the bias up to 120
to 150 MA of current. However, do that quickly and not
more that a second, you don't want to ruin the tubes. Good
tubes with good conductivity have the capacity to idle at
much higher current levels. With that said, the normal
bias setting for a pair of tubes is 60 to 80MA max and for
three tubes 125MA in the TR4 series transceivers. I like
setting the bias to 60MA for new tubes and around 80MA for
the older tubes.
Where to buy tubes, There are several tube vendors that
still have the 6JB6 tube. Typically you can buy new NOS
tubes in the 22 to 30 dollar range. You can check out my
website under the "Parts & Service" for a few tube vendors I
deal with. I know one of those vendor has a quantity of
NOS GE tubes at $22 each. I just bought 50 from him and was
well pleased with what I received.
Ron / WB4HFN
-----Original Message-----
From: drakelist-boun...@zerobeat.net
[mailto:drakelist-boun...@zerobeat.net] On Behalf Of Hulett,
Russell
Sent: Saturday, August 22, 2009 9:52 AM
To: drakelist@zerobeat.net
Subject: [Drakelist] Sweep Tube frustration
Of four pair 6JB6 I own, only one will load on 15M and 10M.
Only two will load above 40M. I'm using my T-4XB as the
test rig ( the best pair (Sylvanias) are now in my T-4X ).
All of the pair were "matched" by the vendors.
I'm beginning to reluctantly think about doing the 6146
conversion. I hate to modify a nice rig, but expense of
buying non-performing sweep tubes is becoming an issue for
me. Have folks found the 6146 to be less problematic than
the 6JB6 sweep tubes? In my younger days, I always found the
6146 to be pretty bullet-proof.
All advice appreciated.
73, Curt KB5JO
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