Alternate tubes for Peavey Roadmaster

[glebert]

I've been working on a project Peavey Roadmaster that is designed to run with six 6L6GC tubes. I don't have a sextet of 6L6GCs on hand, but have a number of 6550 and KT88 pairs and quads. I was thinking of running a pair of 6550s or KT88s and running double the output load (8 ohm cab on 4 ohm tap) as it seems like 6550s and KT88s should lower output impedance than the 6L6GCs. Putting in four of the big bottle tubes might be too much filament current for the PT. My KT88s have N/C on pin 1, FWIW.

Plate voltage is about 500V, screen voltage is about 475V. Bias voltage is between -74 and -37V (ish).

https://www.thetubestore.com/lib/the...-Schematic.pdf

Thoughts?

[Jazz P Bass]

I would go with the 6550's.

[Enzo]

And I would remind you that Peavey never installed matched sets of power tubes. (Nor did Fender or Marshall, or most anyone else)

[glebert]

And I would remind you that Peavey never installed matched sets of power tubes. (Nor did Fender or Marshall, or most anyone else)

Sure, but at this point I don't have more than a pair of any brand of 6L6, and I don't really have a use for these big bottles.

[Enzo]

Oh nothing wrong with experimenting. Just saying you can install a mishmash of 6L6s and the amp will still work. And remember too this is not a hifi. Mismatched tubes might make for a pleasing tone.

[tedmich]

Just pair the tubes up for the push pull and compromise a bit on the bias setting, should be super LOUD! Some sweat 2 different adjustable bias circuits but its likely overkill.

I'd forgotten but there was another version of Peavey's Roadmaster called a "Super Festival Series" which had a complex SS preamp and 4 x 6550, yours is preferred.

[glebert]

I'd forgotten but there was another version of Peavey's Roadmaster called a "Super Festival Series" which had a complex SS preamp and 4 x 6550, yours is preferred.

You know, I got this amp just because it was a project to work on, figuring to flip it for a little profit. In researching it I've found quite a few threads where people said how much they loved the all tube Road Master and wish they had never sold it. I certainly don't need 160 watts of tube power (not even for bass!) but maybe this one will have to stay a while anyway...don't tell my wife...

[tedmich]

most musicians realize they don't need 18 watts, much less 100-160! But there are still a generation of people who think they need an SLO through a 412 to sound good or (in an extreme case) Randy Holden's Sunn setup off of the Population 2 album * (LOL)...

so I'd probably sell the Roadmaster once fixed up...

* cool interview here

[glebert]

so I'd probably sell the Roadmaster once fixed up...

Oh, I'm sure I will, I sell pretty much all of them eventually. Some doom guy will want to plug this into an 8x15 cabinet or something.

[nosaj]

Just pair the tubes up for the push pull and compromise a bit on the bias setting, should be super LOUD! Some sweat 2 different adjustable bias circuits but its likely overkill.

I'd forgotten but there was another version of Peavey's Roadmaster called a "Super Festival Series" which had a complex SS preamp and 4 x 6550, yours is preferred.

I believe Thurston Moore from Sonic Youth uses one for his art prog noise rock.
nosaj

[tedmich]

yes Thurston Moore has used them for several decades!


many pictures here

LOL many have black gaffers tape over the Peavey emblem, since coolness is easily lost...

[glebert]

I did try a couple of vintage 6550s in this amp. Can't say it sounded much different than with a couple of 6L6, and then there is the problem of the tube retainer clips no longer being usable and actually pushing the tubes out of the socket. I bit the bullet and ordered up bunch of 6L6GCs for this and some other amps that need them.

[Enzo]

In general, PV designed their tube power amps to be strong and clean, and generally they ran fairly cool. They were not intended to color the sound much, that was the job of the preamp.

[catalin gramada]

6P3S-E

[catalin gramada]

I just took a glance to Roadmaster schematic, which have lot of similarities to a point with the Alphabass I working now. Be aware of C32 filter cap to driver stage rated at 450v for 445v on the rail. You may want to replace with a 500v rated,or rising 1K, R60 a bit maybe, or both.The PT have 10 percent "regularisation" around. With 6x5881 the plate voltage slide from 505v idle to 465v onset clipping. With 6l6 instaled will be more 425-450v may suppose.
in my opinion changig the tubes with a more current heaters rated type request for an additional heater transformer. The PT get hot as hell as it is.