High Plate Voltage

[jon]

I'm thinking about a 5f6a circuit with 750 plate and 350 screens. Am I nuts. My ot is a 5.2k into 4,8,16.

[ToneMerc]

At 750V, you will need an OT around 10 to 11.5K. Thus, you could run it at 10.4K, 8-16-32, in theory. Personally, I would modifying the laminate stack as well.

TM

[jon]

What do you think it will do to the overall tone of the amp

[xtian]

At 750V, you will need an OT around 10 to 11.5K. Thus, you could run it at 10.4K, 8-16-32, in theory. Personally, I would modifying the laminate stack as well.

TM

Your answer reminds me that I'm always wondering how to figure OT primary impedance. I'm daunted by the idea of load lines, because I've read this stuff half a dozen times, and it's not sticking. Any rules of thumb, or a list of common output sections with OT specs available? How do I get a grip on this important topic?

[ToneMerc]

What do you think it will do to the overall tone of the amp

I've only done this several times in Dumble 100W Skyliner TS topologies, which is far from a Tweed Bassman. A good tweed Bassman should already be fairly touch sensitive and I'm not so sure if the slight mid accent would be present in the 5f6a circuit. IMHO, these early circuits sound better with less voltage not more.

I guess a question for you is, what is your ultimate goal?

TM

[jon]

I'm calling it a 5f6a but it really is a octal rocket. So far I have fixed the bias, changed the 50pF coupling cap to 250pF. My plate voltage is 392 and my screens are at 382, and I installed 6l6wgb's

[jelle]

I'm thinking about a 5f6a circuit with 750 plate and 350 screens. Am I nuts. My ot is a 5.2k into 4,8,16.

Yes.

[jon]

So is nuts good or bad or just nuts

[ToneMerc]

So is nuts good or bad or just nuts

Octal rocket....freakin nuts

TM

[rp]

Some random thoughts:

Wasn't it one of the complaints about the reissue Fender Bassman that it had too high voltages?

Some old Marshalls ran over 500V, given the wall voltage you'll often be at 550V or more. Some people love the high voltage Marshalls some prefer the lower voltage ones. Old Marshalls are just Bassmans, right?

There were several guitar amps in the power war 70s that had very high plate voltages with low or regulated screens or ultralinear taps hifi style - no one is really too crazy about any of those, except maybe for bass.

70s Ampegs ran pretty high voltages. Listen to the Stones live from that era, they sound great.

There you go 1/2 dozen of one 1/2 dozen of the other...

edit: BTW even with the screens in check I don't think you can put anywhere near 750 on any 6L6, certainly no modern one.

Musicmans put over 500V on their tubes. They were good amps - and damn loud.

[roberto]

Old Marshalls are just Bassmans, right?

Well, no. Old Bassman's B+ is around 430V, and you won't obtain that sound if you have 750V B+ (and of course less voltage on screens).

[Gaz]

Make sure you have some 1000v wire

[ToneMerc]

edit: BTW even with the screens in check I don't think you can put anywhere near 750 on any 6L6, certainly no modern one.

Musicmans put over 500V on their tubes. They were good amps - and damn loud.

Modern JJ 6L6, SED winged C's and Sovtek 5881 can handle 720+ VDC in the MusicMan config just fine and FWIW, most of the higher power MM amps had just over 700V on the plates.

TM

[rdjones]

edit: BTW even with the screens in check I don't think you can put anywhere near 750 on any 6L6, certainly no modern one.

Musicmans put over 500V on their tubes. They were good amps - and damn loud.

Modern JJ 6L6, SED winged C's and Sovtek 5881 can handle 720+ VDC in the MusicMan config just fine and FWIW, most of the higher power MM amps had just over 700V on the plates.

TM

50W MusicMan models have 525V on the plates, I'm pretty sure all 65W and up models have a 715V B+ with either 6L6s or 6CA7s.
Screens are at half the plate voltage.
Another part of the secret to tube reliability and longevity is class B operation.

The "high plate" sound is a bit more glassy or brittle than what you would expect from a tweed Bassman.

rd

[jon]

edit: BTW even with the screens in check I don't think you can put anywhere near 750 on any 6L6, certainly no modern one.

Musicmans put over 500V on their tubes. They were good amps - and damn loud.

Modern JJ 6L6, SED winged C's and Sovtek 5881 can handle 720+ VDC in the MusicMan config just fine and FWIW, most of the higher power MM amps had just over 700V on the plates.

TM

50W MusicMan models have 525V on the plates, I'm pretty sure all 65W and up models have a 715V B+ with either 6L6s or 6CA7s.
Screens are at half the plate voltage.
Another part of the secret to tube reliability and longevity is class B operation.

The "high plate" sound is a bit more glassy or brittle than what you would expect from a tweed Bassman.

rd

Thanks guys I think I am going to give it a try. This amp is kinda a test bed for ideas.