Gassy tubes

[W9RAN]

Tube in question is the 4D32 from the HT-20 I've been restoring.  The condition of the original final was unknown, so when I saw purple discharge and arcing inside the envelope I figured it was bad and got another from my stock (also unknown).  The 2nd tube did the same thing, even with only 350 V screen voltage applied.  (This was with -80 on the grid and no excitation).    The third one I tried works fine.

The 4D32 isn't expensive ($20 at SSN) and I've got at least one that's good, but I was surprised to find two in a row that were gassy and/or internally defective.   Wonder if anyone knows if this was a known problem, or if I've just got some old tubes that may have been abused.

Any way to re-getter a gassy glass tube?

73, Bob W9RAN

[W3RSW]

Of the 4D32's I've had, none have shown this.  I think your second thought is probably what's happened; tube seals opened by careless handling of the pins.  Generally I've found the 4D32's to be one of the most rugged tubes, under stressed in normal operation.  Kind of like 1/2 of an 813; they're rugged too.

[Todd, KA1KAQ]

I agree with Rick's assessment of this tube. Thought I've heard similar stories from 32V owners, more often it's a case of a soft/tired tube vs new/gassy. Raytheon cranked out the last batch of these I'm aware of, 70s or 80s date codes. Haven't heard of any duds with that batch but they'd still be fairly new in comparison without as much time for the elements inside to contaminate.

As far as reactivating the getter, one way I'm aware of is to apply heat to the shiny patch on the side of the tube. Several OTs (generally ex-military) have told me that they would use this method on smaller tubes like the 7-9pin miniatures with some success. Heat as applied to the area by passing a Zippo lighter to and fro beneath the spot. The brand of lighter is no doubt of vital importance here, Bob.

An indirect method that has worked for me on other tubes is to run them at a higher heater voltage for some period of time, for example on a tube tester with the voltage cranked up. Not generally a good idea, but if the tube is already headed for the trash otherwise, why not? I noticed it as a side effect of trying to rejuvenate cathode emission, completely unintentional and no doubt unreliable as far as results go.

I moved this to the Tech forum Bob to get input from folks who might not read the QSO section.

[W3RSW]

We read all the sections. 

Hey, didn't we see a poll somewhere before or at least a rundown of how many hits each section gets?

Steve?  Gary?
Data available?  be kind of neat to see a breakdown and summary.

[WQ9E]

Bob,

I think you just hit a run of bad luck with previously abused 4D32's.  I have a couple of Viking 1's and a 32V-1 and have never run in to a gassy tube problem with one.  Keep in mind that Johnson had a 1 page modification to use an 829B in place of the 4D32 due to shortages during the Korean conflict.  The 829B and its various pulse rated versions are cheap and available at almost any hamfest and it only requires a very slight power reduction from the normal V-1 rating.

On the tube front, I recently finished replacing relays and general repairs on an FT-102.  One of the 6146B tubes has a hole/split in the plate running about 3/4 of the length of the plate (visible above the E in Electronic).  The previous owner did put a question mark on the tube base as to its usefulness.  Did I forget to mention I also had to convert the two lower ranges of 10 meters back to 10 meters?  Despite spending some time in CB use the radio is in surprisingly nice shape with none of the usual heat darkening on the plate choke or in the final compartment.

Rodger WQ9E

[Pete, WA2CWA]

We read all the sections. 

Hey, didn't we see a poll somewhere before or at least a rundown of how many hits each section gets?

Steve?  Gary?
Data available?  be kind of neat to see a breakdown and summary.

No mystery. Go to the Home Page http://amfone.net/Amforum/index.php
Scroll down to the bottom and under Info Center and "Forum Stats"; click on "More Stats"
You must be logged in.

[W3RSW]

Thanks Pete.
"Your a better man than I, Gunga Din."

I knew I'd seen some stats somewhere before.
Great info and I especially like the bar graphs.
Great job by the site administrators too.

[Steve - WB3HUZ]

Been using the same 4D32 in my 32V since the 80's. If I ever put a new one in there, I'll burn the filament in for a few days before applying the high voltage.

[ka3zlr]

I wonder how many guys don't do that...warm'em up a'lil before putten'em under load..

[W1RKW]

An indirect method that has worked for me on other tubes is to run them at a higher heater voltage for some period of time, for example on a tube tester with the voltage cranked up. Not generally a good idea, but if the tube is already headed for the trash otherwise, why not? I noticed it as a side effect of trying to rejuvenate cathode emission, completely unintentional and no doubt unreliable as far as results go.

I wonder if wrapping a tube up in foil and some sort of insulation to keep the innards above normal operating temp help rejuvenate it??

[Todd, KA1KAQ]

I wonder if wrapping a tube up in foil and some sort of insulation to keep the innards above normal operating temp help rejuvenate it??

I do recall someone suggesting something similar back in the 90s, placing the tube(s) on a baking tray in the oven for some period of time at 200 degrees or so. This prompted some newb to put tubes on a glass plate in his microwave to save time, resulting in fireworks and his complaints about the method. No, really! 

Some guys have made special test jigs for testing and burning in transmitting tubes. Steve's approach is probably the easiest and best for time and simplicity. This is the method used by many users of the 100TH, 250TH, and other surplus tubes made during WWII with marginal materials at times. No guarantee, but a whole lot better than just stuffing it into the socket and throwing the juice at it.

[w3jn]

The issue may not be a gassy 4D32.  I scored an almost mint HT-20 and it had a fried parasitic suppressor resistor.  Replaced the resistor, tuned 'er up into a dummy load, and copiuous amounts of smoke came out the top.  As I recall there wasn't an abnormal indication on the plate current meter.

Yep, the stupid parasitic resistor fried again.  I concluded that the original design was screwed up.  I copied the parasitic choke design from a 32V and it worked FB after that.

So the blue flashing might be some parasitic oscillation rather than gas.  I suggest you re-do the parasitic suppressor so as to copy the Collins design.

[W9RAN]

Thanks JN, there's something to this because my parasitic suppressor was fried too.  But I'd already replaced it before I ran into the gassy/bad tube problem.  I'll check the Collins for comparison, as I was surprised that the original HT-20 choke was 15 turns.  Had to dig up one of those extra long comp resistors to have enough space to hold it all.

The crusty-rusty HT-20 is looking pretty good now.  Last night I finally found the source of a really crazy oscillation in the modulator, turned out to be a defective 6K6 driver tube, even though it tested OK.   Thankfully the driver and mod iron wasn't the problem as I first feared and AF sounds good.

Just proves those who say "the only tube tester that matters is the actual circuit" - are right!

73, Bob W9RAN