Mesa Lone Star Special - no 15 and 5 watt power

[Randall]

Man, did I luck out on this one! Customer describes on phone that the 15w and 5w settings do not work, so I do some research while I wait for him to arrive. Searches here and the Gear Page point to the lower settings running off a 5Y3GT, while the 30w setting is SS rectifier, and that these amps tend to smoke the 5Y3. Sure enough, that's what it was. Good thing, because it appears the schem is unavailable, and I really don't like dealing with Mesas.

So... my question is really about rectifier tubes. It came with a Mesa branded 5Y3GT, and all I have in house are RCA's, and I don't want to put one of them in a Mesa for religious reasons. So a new one it is. What is the difference or preference between a JJ 5Y3S that is advertised as "an octal rectifier diode with a true directly heated cathode." Or a Sovtek 5Y3GT that is "An indirectly heated diode intended for rectification of commercial-frequency alternating current."? And are these both full wave rectifiers?

Thanks.

[Leo_Gnardo]

"For religious reasons" heh heh .... In any case I expect any of those 5Y3 will work better than the probably MIC one that was Mesa factory install. What are they thinking, "Let's chintz out on parts?" Time was Mesa was proud of their amps' toughness. No more of that I guess.

I wonder what it is that makes 5Y3 prone to failure in that amp. Too many microfarads in the filter? Draws too much current? Generally 5Y3's are tough and put up with all kinds of abuse. But I can see you don't want to sacrifice the premium made in USA RCA's. If it becomes a recurring problem might try one of the small bottle 5U4 currently available, or even an old one. 5R4 another choice. Prices on NOS rectifiers are still reasonable, not all have rocketed to the stratosphere like Mullard or Amperex GZ34.

[Randall]

Is the direct vs. indirect heating an issue?

[Leo_Gnardo]

Is the direct vs. indirect heating an issue?

I doubt direct vs indirect is an issue. 5AR4/GZ34 are definitely indirect, that's how they get their intentional slow warmup. AFAIK all "real" 5Y3 are directly heated EXCEPT Sovtek and/or other brands sold by New Sensor which seem to be re-labeled Russian GZ34-like rectifiers that deliver unexpectedly high voltages. Well their literature actually says "indirectly", gotta give 'em that much credit, but people that are looking for the expected 5Y3 "sag" are disappointed with the Russkies. OTOH there's an NOS 5Y3GTB variant that's super saggy, a bit rare now as guitarists looking for natural compression seem to have scoured the market dry.

[The Dude]

I will guess they are prone to failure because Mesa tubes and/or tube QC are/is abysmal. I wouldn't use one unless I had to. My $.02.

[Randall]

Thanks guys, I went with the JJs.

[TimmyP1955]

Schematic shows directly heated, which the JJ is. AC to 4 and 6, heater 2, heater 8 = B+.

The indirectly heated Sovtec is as above, plus cathode tied to 8. 5V heater.