Western Electric 421A Arcing On Startup - lost cause?

[L0rdGwyn]

Hey there - having an issue with a new tube on my Crack + SB.  Just purchased Western Electric 421A.  On startup of the Crack, the tube arcs after about 10-15 seconds of hitting the on switch.  Arcing continues for about 3-4 seconds, then the tube works fine.  This is the first time I've come across any arcing in my power tubes.  Crack + SB is/was within spec when it was built 3-4 months ago, have had no other issues with the 7 or 8 other power tubes I have rolled through it (6080, TS 5998, another WE 421A, TS 6AS7G).

The tube otherwise is in great cosmetic condition, getter flash is intact, pins look to have minimal to no wear, however, the base is loose.  It is from 1957.

Is this an issue that could potentially go away, or am I better off cutting my losses and attempting a return?

Thanks for the help 

Edit: just a thought, is it possible the tube has some residual gas from either a) sitting around for 60 years or b) being almost completely unused?  Hoping this is the case and letting it burn in will solve my issue.

 

[Doc B]

The loose base could mean the seals are bad.

 

[L0rdGwyn]

The loose base could mean the seals are bad.

Thanks, Doc.  I'm gonna let it run for a couple hours, see if it comes back.  I would think if the seals were bad, the getter flash would be affected to some extent?

 

[Doc B]

That is true. If the getter looks new there could be a clearance issue between the grid and heater.

 

[L0rdGwyn]

Yeah, that may be the case.  Seller refunded me and told me to keep the defective tube.  As much as it hurts my soul to throw a 421A out, probably only a matter of time before it shorts and takes my Crack with it.  Too bad, as after the initial sparking on startup, it sounds phenomenal.  Oh well!

Thanks for your two cents, Doc.

 

[Doc B]

There is one last thing you can try. Rap the tube against the palm of your hand a couple times. Sometimes that can move stuff inside enough to clear the short. I saw my old bud Crazy Eric do that with an RCA 50 he picked up at a swap meet for a couple bucks because you could see the structure was tilted inside. He says "here goes nothin'", a couple of smacks against his palm, instant $100 tube.

Speaking of Crazy Eric, he has just completed restoration of an amazing Western Electric rack system including 43A amps. I'm talking to him about shooting some stills and doing a video of his WE collection.

 

[fullheadofnothing]

Does the arcing happen every time you apply power to the tube, or did it just happen the first time?

A minor leak can leave the getter intact and just have a tiny bit of gas that burns off the first time you use it after its been sitting for a while. Meanwhile a short should continue to spark constantly and not go away with use.

 

[L0rdGwyn]

Ahh, the old "whack it against something and see if it works" technique.  I gave it a shot, free tube that is broken at this point anyway, resulted in a piece of glass from the interior of the tube (where the wires are sealed into the glass) breaking off on the inside, HA!  Must have been splintered already.

So, the arcing was worst when I first turned the tube on and improved with subsequent attempts.  After several, the arcing/popping stopped, but there were would be a glow that seemed to move up and down the heater filament/grid on both triodes 10s after turning on, then would stop.

I had to work over the weekend, so to test your small leak theory, just popped the tube back and did a couple on off cycles, letting it run for 10-15 minutes in between.  Absolutely nothing happened on the first turn on, then seeing blue sparks on both triodes on the second and third cycles, so it doesn't seem to be improving.  Again, its only when the amp is first turned on, then the tube settles down and works fine.  If I wasn't concerned that one of these arcs wasn't going to harm the amp, I would say it it is still usable.

One more tidbit - the pops with the blue sparks/arcs are audible through my phones with the pot all the way down.  Found this out by accident - first time I turned it on today, nothing happened, no arcing, sparking glowing.  I got hopeful, plugged in some headphones, turned the pot down and turned the amp off and on again, this time a large spark and an ear splitting pop in the right channel, scared the bejesus out of me!

 

[Doc B]

Yes the volume control would not have any effect. The tube is after the volume control in the signal path of the circuit.

 

[L0rdGwyn]

Ah yes, duh, I should have known that.

Well thank you both for your help.  I am giving up on this tube, going to lay it to rest.

I've picked up this oddity in its place, a Tung Sol 421A, can't be many of these around  ;D subjective listening tells me this is a 421A, not a 5998.  To new beginnings!

 

[JamieMcC]

One of the things that distinguishes the 421a variants from the more regular 5998s is they normally have they clear tops.  If you do see tubes labelled 5998 with domino clear tops they will be early ones around the 1950's fwiw I think these are the best of the bunch . While they all have the domino plates there are a number of variations of the internal structures and getter positions that have changed over time.

 

[L0rdGwyn]

I have seen the clear top 5998's but have never owned one myself.  I have owned five different 5998's, they all sounded similar to me, but one stood out, had a slightly different internal structure (thicker, longer copper colored rods on the sides of the heater filament, as opposed to thinner, shorter silver rods on other 5998's I've owned) and sounded closer to a 421A.  The TS 421A pictured has both top and bottom getters and it does sound on par with my Western Electric 421A.  I'll have to keep my eyes out for a clear top could pair with my incoming Crackatwoa, planning to jump in on the sale and will likely do a build log as well.