Richard -
That is an excellent book. All those terms are just fancy names for
what we call GAIN. Simply put, it refers to what happens if we put
filament, plate, (screen) and grid potentials on a tube, and then
"wiggle" the voltage on the grid, what happens to the current through
the tube.
Go easy with the DeoxIT, don't spray it around, and preferably put the
liquid ON switch contacts and no where else. As for the relay, take a
narrow strip of good paper, wet it with DeoxIT, and then put it between
a pair of closed relay contacts and draw it out. Hold the relay closed
with your finger to do the Normally Open sets.
Drake was not always consistent with the Voltage and Resistance charts!
There were eight (8) versions of the TR-4, and often they would just
change the schematic, but not always the photos and V & R charts. So if
I use them at all, I use them as guides only. If a reading is way out
of what the chart says it should be, check the schematic for YOUR unit.
I have seen instances where the cathode of a tube is connected directly
to the chassis, and the resistance chart shows 470 ohms. A check of
schematics shows that once upon a time, there WAS a cathode resistor in
this stage, but not any more in this version! Aside from that, ALL
TR-4(any) versions had 20 tubes.! VR20 is the 0A2, kinda "out of order"
on the schematics.
Nah, I don't know of anyone who can determine a bad tube just by
looking... :-) Unless the glass is broken or there are metal parts
rattling around inside! Generally speaking, if a tube gets hot when
turned on, it's working. It may not be great, but it's probably
working. Aside from an open filament, the main failures in tubes
(unless broken glass or metal pieces are loose!) are the cathode coating
has had all the electrons wrung out of it, or the glass seals (where
pins go through the glass) have leaked allowing air inside.
Generally speaking, Drake designed their circuits to work over a wide
range of tube characteristics, and good quality tubes were originally
manufactured with characteristics very close to specifications. So the
equipment will continue to work, often within specifications, over a
wide range of tube degradation.
One exception, of course, is the 6JB6 PA tubes. They are being pushed
to their limit, and DO degrade with use. IF you ALWAYS keep the plate
current dipped, with only a second or two of "off resonance" operation,
these tubes will last for years. My "daily driver" B-Line has tubes
that are over ten years old, and they still have full output. I can
change bands in less than 5-10 seconds with "muscle memory"! :-) What
kills finals are the guys that key the transmitter, then look for their
glasses so they can see the meter AND find the manual, and THEN dip the
PLATE. The very characteristic of these tubes that made them desirable
in the first place, i.e., LARGE plate current with low voltages, is what
kills them IF operated off resonance. One tube can draw as much as 1
AMP of current off resonance, and since if the plate circuit is not at
resonance, all that POWER has to be dissipated by the plate, which very
quickly becomes red, then yellow, then white hot, just before the glass
melts enough to suck a hole in it! Very quickly, defined as _seconds_.
So don't sweat it so much. If all the tubes get hot when turned on,
they're probably good enough to "work". The only tube I've seen that
was DEAD operationally but still hot, was a few 6JB6s that probably had
all their cathode material evaporated, melted or blown off.!
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:
Gary,
I don't think I'm the only one that's gonna hang onto this for future
reference!
One of the things I have read is "Getting The Most Out Of Vacuum
Tubes" by Robert B. Tomer. So I have a reference for what you are
saying regarding testing in circuit, re-tubing ect. I know that if you
read one thing on Emission testing, you have read everything about it.
I have spent considerable time covering transconductance, mutual
conductance, Dynamic conductance and maybe others.
I am going to start cleaning my TR-4 after the "eagle flies" this
week. This is a new to me radio and it needs to be cleaned and
aligned. After I clean it with deoxit I want to check the tubes. (I
should probably be more concerned with cleaning the relay but that
will happen on it's own.) I can't afford to buy a set of tubes to try
and see what will happen with tube substitution after cleaning it.
This sorta leads to something else that I don't understand. The
resistance chart for the tubes goes from V-1 - V20. The schematic
shows tubes V-19A and V-19b but not a V-20.
Just something I noticed in preparing to do this. I'm sure there are
those here who can look at a tube and win a bet as to weather or not
it is good. They might want to over look my posts. I believe that I
can get a piece of mind from testing my tubes in a tester. Which for
me goes a long way in sussing things out. And I do have a couple of
issues that I don't think cleaning will clear up. Hopefully I'll be
wrong.
Thanks to all.
I'm done.
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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