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Confirm that the bias switch is working and in the 6l6 position the resistance is 750/570 in parallel (324 ohms) , and all the connections are solid. For some reason, the 6l6 are drawing too much current. That's the only thing that is not common to the 6v6.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Yes, with amp off, unplugged, tubes removed and all caps drained, I clamped probe leads to the -/ground/negative junction of 570R/750R and pin #8 of the octal. I jostled/wiggled all connections and even the handle of the switch and got a steady 323 ohms and 750 ohms with the switch in it's respective positions. No intermittence or fluctuation. I will research these tubes to see if they are specced differently than a standard 6L6. Again, they are Sovtek 5881/6L6 WGC. I seem to recall reading once, that certain 5881 models can be replaced by any 6L6 but not necessarily the other way around? While this issue is puzzling, I am not displeased with the whole process. Its actually kind of good that I'm experiencing some problems, as it will be helpful for future builds to be armed with good troubleshooting skills. This has been and continues to be a wonderful learning experience and I truly appreciate your holding my hand through it all.
Thanks,
Gene

I can't see any reason for it not to work. All the data says it is compatible. Although max plate voltage is supposed to be 350, it can handle twice that. The only thing I can guess is some limitation due to the heater voltage being bit high? Try the two back to back diodes and see if you can drop it and try again.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Stephen,
For heater voltage reduction, would a 1N5408 or 1N5404 work as well as the 1N5401? They are both 3.0A at 1000v and 400v, respectively and are readily available, locally.
Thank You,
Gene

Yes, either one. Get 2.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

So I guess the next step, after taming the heater voltage, and acquiring another new, known to be good 6L6, will be to measure the current draw. It seems the simplest/safest way to do this is to install a 1 ohm 1% resistor in series between the wire coming from the cathode bias resistor switch and pin #8 of the octal and then measure the voltage drop from one side of the resistor to the other? How do I convert this voltage reading to current? And what is an acceptable level of current draw in this case? Even though the 6V6 appears to function properly, it seems a good idea to check the draw of both a 6L6 & a 6V6?
Thanx,
Gene

Snowy described how to calculate the power dissapation of the Tramp tube in a previous post. You can use that method. A 1 ohm resistor is not required, just some good voltage measurements. see below


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For other builders reference here's some voltages I measured today with a JJ 6L6GC tube fitted.
I also did the calculations to check the dissipation, which turned out to be perfect.

B+ at C12 (VRM set at Max) = 400 Volts

Measured resistance of Cathode resistors (switch in 6L6 position) = 321 Ohms
6L6 pin voltages:
Pin 3 = 393 VDC
Pin 4 = 390 VDC
Pin 8 = 27 VDC

Voltage across 1k screen resistor = 3.48 Volts
Measured resistance of screen resistor = 987 Ohms

I obtained the following values:
Voltage across Cathode resistors (27 volts) / Measured resistance (321 Ohms) = 0.084 Amps (Cathode Current)
Voltage across screen resistor (3.48 volts) / Measured resistance (987 Ohms) = .0035 Amps (Screen Current)
Subtract .0035 (Screen Current) from 0.084 (Cathode Current) = .0805 Amps (Plate Currrent)
Pin 3 to Pin 8 voltage = 365 volts

Calclating the dissipation:
Pin 3 to Pin 8 voltage (365 volts) X Plate Current (.0805 Amps) = 29.4 watts dissipation


For a Cathode Biased amp this puts me right where I need to be for the JJ 6L6GC tube's published 100% dissipation of 30 Watts

Hopefully those numbers will provide some ballpark reference to other builders when using a 6L6GC

Snowy

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thank you sir,
I will take some measurements and post my findings.
Thanks Again,
Gene

I installed diodes (1N5401 cross referenced to NTE5801, same specs) and I now have 6.18-VAC across the heater circuit, the leg with the diodes is 2.73-VAC and the leg without the diodes is 3.52-VAC. Would it have not been better to trim the voltage on each leg? The way it is now, it seems like an unbalanced load on the transformer. Is that 6.18-VAC in our ballpark for proper operation?
Gene

Stephen,
I made an executive decision/judgement call (I AM, after all president and CEO of my own world) and decided that the heater voltage was close enough to take some current readings and it is really beginning to seem like I've made much to do about nothing! I'm making an educated guess that all the 6L6 issues are going to boil down to a matched pair of crappy/faulty tubes. the current draw on both the provided 6V6 and the one SOVTEK 5881/6L6WGC that did not fry seem well within expected limits and are even a tad lower than snowy's testing.
6V6
Cathode Current) .0401-A
Screen Current) .0016-A
Dissipation) 15.3-watts (a little high)

5881/6L6WGC
Cathode Current) .0824-A
Screen Current) .0034-A
Dissipation) 28.993-watts

I will NOT try to run the amp with this SOVTEK tube but just used it for testing and will wait for a new JJ to arrive. FWIW, while gradually bring up the VRM, the amp sounded fantastic even with this apparently bad tube until I got the VRM above 90% and that's when all HE double hockey sticks broke loose.I'll let you know how it goes once I get a good tube here.
Thanks,
Gene

A new JJ-6L6 arrived and it appears that all is well. It even works with the SOVTEK 5881/6L6 that gave me a lightning show. I seems that it was NOT a bad tube but indeed simply the consequences of too high heater voltage. A nice and knowledgeable tech at TubeDepot,Robert Hull, explained what he assumed was happening and why. He said with the high heater voltage, combined with the close physical proximity (inside the tube) of the heater filament and the cathode, I was likely experiencing "arcing" between the 2. I pounded the crap out of this amp, cranked, with my Les Paul long enough to make my fingers sore and this amp sounds amazing for what it is. In standard gain mode, with 6L6, it's very "Princeton-esque" (although a bit quieter) and with the gain in "Tude" mode it sounds much like a silver faced Princeton with a good boost pedal at mild to medium boost. The bottom end is amazingly tight/clear, even with full on distortion. With a 6V6, the bottom is a bit mushier (like I would expect) and sounds "OK" but nothing like the way it sounds with the 6L6. I really learned a lot and am seriously looking forward to my next build. This is likely a new addiction for me and I'm glad it won't require a needle or a pipe! This amp is not quite what I'm looking for, but was chosen for it's simplicity and ease of build and it certainly accomplished that. It got my feet successfully wet and I'm stoked. My thanks to you for your thoughts, comments and advice.
Thanks Again,
Gene