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Lingwendil 5th June 2009 06:34 AM

Breaking in your tubes?
Hey everybody, when working with new tubes, does anybody here break them in without a complete amp to run them in? I've got four el84 and two 12at7 strung up in series/parallel at 25.6v AC to cook the heaters right now, as I'm waiting on output and power transformers, as well as other parts. Would it be worth running a 250~ 300v b+ and throwing together a few parts to let the tubes idle at their typical working currents for a few hours a day?

SY 5th June 2009 09:19 AM

Running the heaters for long periods without current flowing through the cathode will be a detriment. I would definitely use a B+ supply here.

Alastair E 5th June 2009 06:34 PM

Fo rBig tubes that have so-called bias-driftissues like 6C33C-B etc I run these at normal heaters for 24-48 hours only.

After that cool down and then heat up again with no +B for half-hour. Then pull rated cathode-current (600mA for 6C33C-B) at below max Pd for 2-3 hours--They get good and HOT, but no 'plate-glow'...

Then B+ off, leave to cool. Fit to amp, bias up and job's a good un....

(After this treatment the bias setting doesnt drift much over months/years of service--and Thats with a known 'drifty' tube type, and no arcing/flash-over issues)

Really No point in leaving any tube with heaters only for more than a couple of days, as this could cause 'cathode-interface' (A sort of cathode 'poisoning') issues etc....

Again, No point in running a tube for more than a few hours with B+ applied, without it actually being used--Just a waste of life....

It only takes a couple of hours at max cathode-current with a good tube to 'burn-it-in'--Bias drift after that, and I would suspect a problem tube...

Small tubes like EL84 and sig tubes, I really wouldnt bother. Just build amp and fit tubes, set up and leave on for say, 6 hours. re-check bias and away to go...
IMHO, not much point in doing anything else to 'em, as they are a pretty stable tube.

Lingwendil 6th June 2009 04:48 AM

I left them with heaters running overnight, and then unhooked them this morning. I'll rig up a B+ supply tommorow morning and run them at 75% dissipation each for an afternoon then. I was actually thinking of building up a dirt simple big beef preamp with them even, 12at7 parallelled input buffers, with triode connected el84 grounded cathode, into an el84 cathode follower, and then run that as my preamp for the time untill my other parts come.

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