The AM Forum

I have been thinking about drilling a hole in the plate cap for a screw for a good connection since I don't have a plate cap for it. would you use a brass screw?

I picked this tube up for $5.00 at a yard sale and it looks like it would make a good project amplifier.

Just us an aviation hose clamp!

I'd rather silver plate a strap and fasten it to the anode connection

Al

Yard sale...... ::)  ;D

fuse clip on center post or hose clamp around the anode. Light it up and ground the grid and see if it draws any current. That's almost as cool as the 7- 4CX3000As I bought for $100

Wow, that's the best tube you could get for a linear amp. They are selling for about ~ $300 used. It appears to be in great shape. The Eimac lettering is still red and it's heat sensitive paint. Post a pic of the underside fil structure. It may look a little tarnished, but have no black signs of heat abuse. My guess is it's a good tube that was well taken care of. (Probably professional MRI service)

Be sure to run it for at least 16 hours with filament on only to getter the gas. Being an indirectly heated tube, that's the way it's done.

The real test will be when you apply HV to it.  That's when many will short out if gassy.  Be sure to use heavy cooling - especially on the underside filament structure. If starved for air and abused, the fil seals can pop after one OB transmission, otherwise.

T

Well Tom there seems to be some dark area but it's more a silver color than black. I have seen some YC-156 tube that were black from top to bottom and reports where it was said that people ran these at 40 KW for days and they turned black.

Very little is published about the YC-179. One area different between the YC-156 & the YC179 is the filament current which in the case of the 179 draws one amp more.

Here's a couple shots of the bottom.

I had the filament on for 7 minutes three times. No blower but the temperature never got up to endanger the seal. In a couple weeks when I get back from up north, I'll see if can do more with it.  


Tom you may find this interesting about gettering the tube.

Glomed from someones notes.

I visited the Eimac factory in San Carlos circa 1989-1990 for the purpose of
witnessing the manufacture of the YC-156 tubes, which my employer was using in
production at that time. If your YC-156 has PEM nuts in the grid ring, it was
built for us.

IIRC, Eimac's procedure for final de-gas and de-barnacling the tube was to
immerse it in oil (so it would not arc externally) and run the cathode/anode
potential up to 20kV with a current-limiting resistor and an energy storage
capacitor. They ran them this way for some number of days, with no heater
power.

At the factory, our procedure was to run them in the amp, with heater and HV
applied, for 72 hours. They'd arc a half dozen times the first day, then
settle down. Our HVPS had a very fast shut-down but no crowbar.

Were I to do it in the home shack, I'd string up enough resistors to get a few
Meg ohms at 100 watts, feed them into a few uF worth of capacitance at high
enough voltage, and run the whole thing at about 15kV. The Joule storage
capacity of the caps would ensure that enough energy is transferred during an
"event" to adsorb the gas into the copper anode (the heated copper anode is the
getter in the YC-156: no amount of heater operation will getter the tube), or
melt off the barnacle, whichever condition causes the arc. In a used YC-156,
it's more likely gas; what we witnessed in young tubes was proposed by Eimac to
be the barnacle issue (aka Rocky Point Effect).

Also, bear in mind that it is not possible to guarantee that a tube won't arc,
so a responsible amplifier design is one that won't get damaged when an arc
occurs.

This goes straight back to the 40's Machlett technique I mentioned a few months back:  De-gassing tubes via HV AC.  

Slam them with HV across the widest elements, no filament power for some hours.  It drives the gas into inert ions, works about 75% of the time.

Can tame cranky MV rectifiers, too.  I'll be happy to send the scans to anyone interested via E-mail.

Better than throwing things in the trash...  :'(

DG

"At the factory, our procedure was to run them in the amp, with heater and HV
applied, for 72 hours. They'd arc a half dozen times the first day, then
settle down. Our HVPS had a very fast shut-down but no crowbar."


Terry,

Thanks for the info. Looks like the author is credible and knows what he's talking about based on professional experience with the factory.

Interesting info about using current limited high voltage to de-gas them.  I've had a few experiences where these techniques would have helped.   The key is the fast shut down and current limiting to avoid damage and meltdown. 

Unforntunately, for most of us, this "break-in" period usually takes place in the amp under full power and sometimes takes out the tube, if gassy.



T

Thus method would be very easy to duplicate with a variac and furnace ignition transformer, diode stack, charging a cap. I rebuilt a high voltage power supply in our lightning generator with a furnace transformer and a string of 1n40007s half wave rectifier. They are rated for 10 ma output current so it is just a matter of charging the right cap value to do the deed inside the tube.  10KV ac should make around 14KV DC peak charged.
A friend worked on some HV stuff that used 3-400s and new tubes arrived with holes blown in the plates. They worked fine.
I would stand a tube in a vertical position.

I wish I had them kind of yard sales here lol.  I guess I could allways hit up the local Superbowl guys for there used tubes but then were looking at 3cx10,000's .  ::)
Good luck on your project, you found a good starting point.

Ive heard of hi potting with AC but never degassing.

John posted his comments several times over the years and they are well worth following....and scrapping the myths running around forever.

I use a 13.5KV AC neon sign transformer along with a rectifier and filter caps for the degassing of tubes with handles and hipotting the average TX tube for AM use.

For large glass jugs its a matter of running low DC of around 800-1000V with enough positive bias to get the plates a nice orange. The idea here is to prevent arcing. Forced air cooling required. This was gleaned from a BC engineer 5 decades ago and has salvaged many a jug from the trash.

Carl

The WOR technique does NOT use DC.  Nor filament emission at all. 

It does it via the same thing that neon signs use, just high voltage AC, acting on whatever conductive gas exists. 

I guess if it didn't conduct, it wouldn't be a problem anyway.

This is where it differs from all the traditional "cooking" methods.

73DG

It doesnt say anything in that single page you posted.

To whom are you addressing this to?

That was meant for me.  You probably ought to get me to send the dope to you on this technique, too. ;)

73DG