Thanks to all for the advice and expertise. Anyone who has looked at
tube testers know that "the" one to get is high dollar. You would think
that for the amount the design gets that it would also repair a bad or
questionable tube. :-)
Dollar for dollar I might be ahead on this just to buy a new set of tube
types for my TR-4 and go from there. I feel relatively curtain I have a
hinky tube because after the set warms up there is often a change in
audio that goes from a low pitch to high pitch or vise a versa sound on
my back ground noise. If I change over to X-CW and back the audio
returns to normal. Maybe a good cleaning will help. I'll find out.
Thanks again,
Richard Palmer
Garey Barrell wrote:
Richard -
First, there are two major types of tube testers. The least expensive
is the "Emission" type which merely applies power to the filament and
plate of a tube and measures the current on a "Good-?-Bad" meter
scale. They are slightly better than using an ohmmeter on the
filament pins to see if the filament is intact! The more expensive
type, the "Mutual Conductance" type, applies filament and plate
voltage and then applies a known AC signal to the grid to measure the
actual "gain" of the tube.
The Emission tester will tell you if the cathode is still emitting
electrons, and the Mutual Conductance tester will tell you how the
tube amplifies _at the single test point and level_ chosen by the
tester manufacturer. Neither tells you much of anything about
operation at RF.
Typically only the "latest" tube testers will test the "Compactron"
type of tubes (6JB6) without some sort of adapter.
One of the better tube testers available is the military TV-7/U
family. It doesn't have sockets to test the Compactrons, but someone
has made a set of adapters for it to allow it to test the common sweep
tubes, like the 6JB6.
All the rest of the tubes in the Drake gear are 7 and 9 pin
"miniature" types, which just about any tester made after about 1940
will test. These tubes are all the same size pins and pin circle.
All that said, a tube tester isn't all that much help anyway. The
only REAL test for a tube is in the circuit you want it to work in.
Your best approach to maintaining your Drake gear is to get a couple
of each tube type, "test" them by plugging into a working radio and if
they work, put them in a safe place!
This is especially true for 6JB6 tubes used at RF frequencies. These
tubes were designed for use as horizontal output tubes for TV sets.
They operated at almost 16 kHz in that service!! Sylvania, in the
early 60's, characterized (tested) some of their "TV Sweep" tubes such
as the 6JB6 for linear amplifier service from 2-30 MHz. The resulting
data was used by Drake and several other Amateur equipment makers to
develop transmitters that would run considerably more power than those
using the 6146, and do it at a lower plate voltage! Add that the
sweep tubes were about 1/3 to 1/2 the cost of the 6146, and that a
lower plate voltage could be used for higher power output and it was a
done deal. The pertinent characteristic was a high "perveance", or
high currents at lower plate voltages. They were designed to operate
24/7, inside a TV set with 25 other tubes and keep working, so they
were able to serve in CW or SSB service at considerably higher power
levels than their published specifications..
The catch here is that since the tube was designed to operate at 16
kHz, NOT 30 MHz, not all brands of the same tube type were
interchangeable. Operation at 30 MHz requires considerably more
attention to internal tube structure such as lead lengths,
interelement capacitance, etc. The result was that one manufacturer
might make a 6JB6 with considerably higher reactances that worked just
fine at 16 kHz, but would make it impossible to neutralize in an HF
transmitter without changes in the neutralization circuitry. Add the
fact the some of the smaller, even well known companies that put their
name on a tube may well have had that tube made by more than one
manufacturer, and it gets difficult to say which tubes will work in a
T-4X and those that won't.
Further complicating the situation is that the RF gain of a tube falls
off with decreasing emission, and falls off first at the higher
frequencies. 6JB6 tubes in T-4X service will fall off first on 10M,
then 15, then 20, then ... Most will continue to put out SOME power
on 80 and 40M after 10M output is just about zero.
My experience has shown that Sylvania, Zenith, RCA and GE are the ONLY
brands of 6JB6 that I have found to work _consistently_. Raytheon,
Westinghouse, Standard, and most others are potential trouble. Some
work, some don't, depending upon who _really_ made them.
By the way, it is NOT a good idea to replace ALL the tubes in a radio
at once. "Retubing" is somehow seen as similar to "replacing all your
tires". This is not only wasteful of a finite source of vacuum tubes,
but can turn a working radio into one that doesn't! Even New Old
Stock tubes, all manufactured over 30 years ago, are not all "good".
So get a few spares for each type, _check them in a currently working
radio_, and if they are "good" put them in your tube stash for a rainy
day.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line& TR-4/C Service Supplement CDs
<www.k4oah.com>
Richard Palmer wrote:
I hope this is not off topic. With the use of "vintage" being used
for all Drakes and tube testers, many from the 1940's and before, up
to the last ones made, it has become impossible for me to determine
what will service my early TR-4.
I have spent hours and hours looking up tube testers by type, make
and model. I have spent hours squinting at pictures trying to count
socket pins. I am burnt out and am looking for help in finding just
where to look. I have no idea if post WWII testers even test 9 pins,
or if all 7 pins are of the same size.
Richard Palmer
KB8NXO
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