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Well, then I'll live up to your expectations by leaving this forum. I write a lot of posts in here that have nothing to do with anything I do for a living. I do it because I enjoy helping other people. A number of other members here have suggested a number of my posts be "stickied". A large...

The output section is straightforward other than where the U/L taps are in the OPTS. It's not the output section, it's the front end that is so different. You did not make my head explode - I just wanted to caution you that what you were thinking of wasn't a good idea - and that I had a lot...

Hi Alex, Thanks for clarifying what your board is all about. Much appreciated. However the cathode stripping phenomenon plain and simple does NOT occur "IMHO" at typical audio amp voltages. Here's a very good explanation of why - and pay careful attention to the author's remarks about tube...

Thank you for the very kind words. I sincerely appreciate them. :yes:

Depending on where it was installed it can make a difference. Remember - if you fire up the amp when the power supply caps are fully discharged those caps are in essence a dead short to ground for a very short time (until they begin to build a charge). If the caps are fully discharged then...

Tom, Nice work! I've seen a few where solder strips riveted to the chassis had poor grounds too. Corrosion over the years snuck in. Watch for that as well - IIRC the last one I had left the bus bar with a high resistance ground that you could cure (temporarily) by wiggling the bus wire...

Change 'em all! Don't even waste time trying to save them. They are 50 years old and have had a hard life. Change every wire too, 50 year old PVC insulation is tired . Change the AC pots. CAREFULLY disassemble the dual bias pots and clean/lube them thoroughly - and re-tension the wipers while...

Hi Bob! You have a tremendous advantage over the typical user - not just because you have the skills and knowledge base to deal with tube electronics, but also because you KNOW your amp can handle the extra heater current draw these tubes could be presenting. Plug these in a vintage (or...

Smart man! :yes:

Pardon the minor rant here... In the last few years especially many US tube users have developed a "fetish" about tubes - if it isn't European (or at least European designated - "E90Fs are WAY better than 6BH6s" - yeah, right!) then it isn't any good. Do some searching around this and other...

This only applies to mercury vapor tubes such as an 83. It does NOT apply to typical audio tubes. When a mercury filled tube cools some of the mercury condenses on the glass and gives it a soiled sort of look. Also - if you want to see what healthy tubes look like, look at Vic's pictures. The...

It's necessary!! :yes: Wow - that is VERY kind. Thank you so much. :D

While some will disagree with the amount of time and the % involved, bringing the current UP to bias spec is always a good idea. Might I suggest it be lowered even more... If the old tubes are tired, then it's likely that the amp's owner has been adjusting the bias to compensate for a while...

I'm not a Williamson fan either, but a Mullard circuit using the EF86 is a different story.

I agree on the switches, etc. But the business about eliminating pentodes is off base. The EF86 especially can provide superb performance, as can the 5879 and if you move up the current scale - the 12BY7A.

Thank you so much for your kind words. :yes: And what you posted is one of them I'm afraid. Old stock tubes were no better matched or tighter tolerance than current production. As an example, I matched over 500 GE 6550As, a tube most all agree was a truly FINE quality, well made tube...

First off, it is not possible to accurately match power tubes for plate or cathode current with any Hickok (or all but a small handful of other specialized units) tube tester. The voltage applied during testing is simply too low for it to be a meaningful exercise. It also lacks the current...

How about we do a bit of analysis? With about 410 volts on the plate - and essentially zero on the cathode - 28 ma. would give you .028 times 410, or about 11.5 watts. That's pretty cool for a 19 watt dissipation rated tube like a 7868 or 7591. If you were to run the tube at 40 ma, you'd...

Yep, and I must say the published data is not promising. First off, as you've already suggested, this tube doesn't look like it'll drop into much. Indeed - look at the heater current requirements. 1.7 to 1.95 amps per tube! That's 6% to 22% above a KT-88. Four of those could end up needing as...

Install resistors in the cathodes of the power tubes. Use metal oxide films (they used to be called "flameproof" resistors), 10 Ohms or so is perfect. Don't use carbon comps - they can actually catch fire. And for those worried about it - the inductance of a 10 Ohm resistor is extremely low - it...

Yes - it's fair to say that under the right conditions an OPT can act like a car's ignition coil - the OPT can generate brief but quite high voltages that can breakdown insulation on the magnet wire.

Nope, not Triode... Try Gary Brown at xfrmrs@roadrunner.com - he's done some work for me. Heyboer is another possibility of course... Also Audio Transformers (Doc Hoyer) - autrans@aol.com. Doc ain't cheap, but he's good! He's the only guy I recommend to rewind iron for the Cit II.

Let me just expand on this a bit: 1. Do just what Cademan said. 2. (If equipped) measure the primary from plate tap to screen tap on each side of the trafo center tap/point. You should have low resistance. 3. Measure primary to trafo case - infinity should be the result. 4. Measure...

Often it's just old age! The insulation breaks down after 100s/1000s of thermal cycles and arcing between the windings finishes the job. Any uninsulated wire then has the potential to short against anything else in the neighborhood. What's shorted BTW?

No, not even close. It's a completely different tube.