On testing transmitting tubes

[w1vtp]

I've heard a few comments on wanting to test transmitting tubes.  Here's an excellent article on that subject.  I borrowed a tester for the 813 from Steve, W2TRH.  All 13 of my 813 collection were tested.  I had one "sparkler" - some sort of inter-electrode failure.  That one has been set aside for a future night light  .  The filament still works, I have a 10 volt transformer (or two - three) that will light it.

Al

[DMOD]

Good practical info Al.

Thanks

Phil - AC0OB

[MikeKE0ZUinkcmo]

Thank You Al, I appreciate the information as well.

Mike

[WB5IRI]

Cool! Just what I needed. Now, if there was only a way to test that 3CX5000 a guy has for sale for a hundred bucks . . .

[w1vtp]

Cool! Just what I needed. Now, if there was only a way to test that 3CX5000 a guy has for sale for a hundred bucks . . .

Start with a pig pole transformer (4200 volt variety will do) and go from there.

I'm sort of kidding folks

Al

[KA0HCP]

Al, can you post a photo of the tester Steve loaned you?  bill

[WA2SQQ]

I have two "NOS" Eimac 3-500Z's that have been sitting in their original box's for about 15 years. I suspect these may be gassy. Anyone know of any testing services? My SB-220 would like a new set, but I'm reluctant to plug them in and try them.

[Jim, W5JO]

I have two "NOS" Eimac 3-500Z's that have been sitting in their original box's for about 15 years. I suspect these may be gassy. Anyone know of any testing services? My SB-220 would like a new set, but I'm reluctant to plug them in and try them.

If they are reputable brands I wouldn't be that concerned.  I've replaced 4-400s, 4-1000s and others in BC transmitters without incident with older spare tubes.  There is always a minuscule amount of gas in any tube but the amount should not be enough to cause problems and the getter will cure that. 

If you tried them when you bought them without problems, they should be good.  Since there is a short warranty period on transmitting tubes, I check them in circuit when I purchase in case there is a manufacturing problem.  If not they go on the shelf for future use.

[W2VW]

The 3-500Zs should be fine unless they have late 80s date codes.

Internet folklore.

Make sure you dissipate them hard enough to produce orange glow on the anodes once in a while.

[w1vtp]

Al, can you post a photo of the tester Steve loaned you?  bill

Unfortunately, I do not have it any more.  It is ~12 x 3 x 8"  with a meter, two knobs.  We should get the schematic from Steve sometime.  I imagine one could make a voltage tripler DC supply out of an old TV PS.  One would also need a bias DC circuit for the control grid.  Dunno if Steve's tied the SG to the CG or what but that voltage needs to be variable a well as the HV circuit.

I think that article from GE news should suffice.

[W3RSW]

There is a very simple circuit that came up on another site not too long ago specifically for testing 572-B's and 811a's.

Basically a 6.3 volt @ 4 amp filament transformer with center tap feeding the tube filament.
A variable power supply,  positive to the plate which is also tied to the grid.
 Fil. Xfor Center tap to supply negative. A 0 to 500 ma meter is placed between the plate cap of the tube and the supply positive or between the negative supply and the Fil. Xfor CT.
A volt meter needed across the supply of course, and a switch in the primary winding for "HV".
Let the filament warm up for a few minutes.

According to the note for all good 572B's, The. Meter will show 250 ma at 44vdc. Apparently the writer found numerous good 572-b's to be close to that reading as verified later in a loaded amp at RF.

I built one up with a supply made from standard 220 split winding to 110 utility transformer, a radio shack bridge rectifier, 25k min. Load / bleeder resistor and 40uf/160v filter cap. Used resistors in primary with a combination with various tap arrangements to come up with the following values found for a good Cetron 572b supplied by Derb

34v. 160ma. Ser. No. 147-8-2 as marked with ink internally on the base element structure.
54v. 290ma.      
62v. 370ma

Plot was reasonably linear with some roll-off on upper end.

Another Cetron only yielded 160 ma at 66 vDC, ser. No 147-7841.
A third on hand had an open filament.

So I tried two supposedly NOS Westinghouse 811-A's , looked brand new in new boxes.
One had open filament.
The. Other yielded 155ma at 33.7 volts which fit on the same plotted slope as the one good 572b.

This method should work for other triode transmitting tubes using correct Fil Xfor and known good tubes for calibration. Thought of trying it on tetrodes like an 813 with both grids tied to plate and beam plates grounded but haven't gotten around to it.  May have to tie the beam plates to others, but looks interesting.

[W3RSW]

Meant to add pix of 572-B tester.
Lash up sans meters in line.

    Not complicated.
All junk box and old fester parts.

** See the old 2x4 sanding block that I spied nearby for the base. **

[W2PFY]

Good information Al!

On a display tube its fun to hook them up to a PS and see what they will do.

Attached is a link to and 805 triode that I am running some unscientific tests on. Enjoy..

https://www.youtube.com/watch?v=Dfh2I8wmm5w