Question about Music Man Rd50 Cap mods

[Stevem]

The last two MM Amps I did over I used Sylvina 6BG6ga tubes and the needed adapters from SND tubes, these tubes are a super killer value and there plate cap set up is just what's needed in these MM amps and there plate voltage!

[ToneMerc]

Current issue JJ 6L6, EL34 or 6CA7 no problem, Sovtek 5881 not a problem as well.
TM

Thanks ToneMerc, for the suggestions on the caps. Regarding the tubes you listed, would rebiasing be needed on these? I currently have the original Sylvania 6l6's in it. By the way I sent you a pm. Please let me know if you received it. I'm having some trouble with the website and I wondered if my pm's are also not getting received. Thanks![/quote]

YW....Yes I responded, hopefully it helps.

TM

[cyclone_cj]

Stevem, thx for the hookup on the 6bg6, I have boxes of them from the tube caddies I bought on ebay:) TV sweep tubes:))

I concur on the MM amps running the output tubes to death, my 65 watt had 6ca7's and ran them ragged. Very reliable clean amp, sounded great with a boss od1 in front playing punk rock in Detroit in '78:)

[JMFahey]

Regarding the tubes you listed, would rebiasing be needed on these?

In these amps, biasing takes a new meaning.
Tubes are biased *positive* 16 or 24V at the grids so they will tear down to the last electron from the cathodes with a pry bar if needed , that's why they "run tubes down to the last drop" .

So they work in a reverse way: the transistors are the actual current feeders and the tubes just pass it through, while at the same time dropping most of +V through them and letting transistors handle some 60 to 70V max.

So biasing applies, but you are biasing the transistors, not the tubes.

Cathodes will comply and sit at whatever voltage is needed to pass whatever current is fed them.

Reverse logic, here you set cathode current , and cathode to grid voltage (tube bias) takes any value needed to pass that current.

Of course, typical transistor bias current in any standard SS amp is very low by Tube standards, a few mA, so that's what tubes will also pass at idle.

So in a nutshell, tube type or age isn't *that* important here, as long as there is some emission left, I doubt you'll have to rebias even if you use TV sweep tubes or any unconventional type.

[vibratoking]

FWIW, in the 'old' days I used a green MXR Distortion + with an almost dead battery into an HD100 with matching 4x12. Prolly the best rig I ever had. That was a very very good amp. Fat, natural, controllable sustain at will. The RD is a very good amp as well. Not too much transistor in those amps for me.