amplifiers with 3 power tubes

[Jammin'John]

1 x Transformer - Hammond, Output, Single-Ended, 30 W - $152.31
SKU: P-T1640SEA https://www.tubesandmore.com/products/P-T1640SEA

1 x Transformer - Hammond, Power,
SKU: P-T272JX https://www.tubesandmore.com/products/P-T272JX

It's still being modded. I got a larger choke,a Triad 4 henry,100 ohm,250ma.
Variable cathode bias rheostat I will change out as well as the fixed cathode resistor.
Right now I can run 3 x 6v6,2 x 6l6/KT66,1 x KT88,KT90.
With the bias mods:
3 x 6v6,2 or 3 6l6/KT66,1 or 2 KT88,1 x KT120,1 x KT150,2 x 6v6 with one 6l6/KT66,etc.

I have a bunch of old american tubes that I have been mixing & matching. Combinations that I can never use in my Tweed Fender clones !

JJ

[jpfamps]

Stephenson amps in Canada make an amp with 3 ouput valves (tubes).

Standard Tube Amplifier by Stephenson Amplification

It looks like the amp is indeed push pull, and that the "extra" valve (an EL84) can be switched in an out.

These amps seem to be inspired by many of Kevin O'Connor's ideas in TUT series (co-incidentally also Canadian...).

In addition to mixing output valves, the Stephenson amp doesn't label the impedance selector switch with the nominal impedance tap, the idea being that you should use the setting you like the sound of best, and not worry about employing the "correct" tap on the secondary, another one of Kevin's ideas.

I can't comment of the sound of these amps as I haven't heard one.

Laney have also had a 5 EL34 output valve parallel single-ended amp in production for a while now.

[Chuck H]

I think that sunn drone's inquiry can only be confounded at this point. I'll go out on a limb and say that what the average musician is going to encounter in instrument amplifiers isn't likely to demonstrate even one three power tube amp. Let alone "some". It took a thread full of nerds just to find a few. Most amps perceived as having three tubes are likely cases of mistaken identity. As far as I know Fender, Marshall, Vox, Selmer, Mesa, Sears/Silvertone, Supro, Watkins, Hiwatt, Sunn, etc, never made one.

[sunn drone]

I think that sunn drone's inquiry can only be confounded at this point. I'll go out on a limb and say that what the average musician is going to encounter in instrument amplifiers isn't likely to demonstrate even one three power tube amp. Let alone "some". It took a thread full of nerds just to find a few. Most amps perceived as having three tubes are likely cases of mistaken identity. As far as I know Fender, Marshall, Vox, Selmer, Mesa, Sears/Silvertone, Supro, Watkins, Hiwatt, Sunn, etc, never made one.

Thought you were pickin at me till I googled confounded. Then I caught a smile. I didn't mean ta do that ta anyone. Honest engine. Ahm just an old person who tinkers with old amps, been doing the collecting part for a long time. I just about feel like my collection is complete. So I was peelin thru ebay and it came to me, what kinda amp is it that I don't have? I had remembered seeing so many odd configuations on ebay thru the years and I never paid much notice to em because thats not what I was collecting at the time.. I just assumed when I posted at the forum that everyone else had spent years at ebay looking at amplifiers getting ideas to what they needed as I had. If readers saw the stream they would know what I was getting at. I was reluctant at not mentioning ebay. Sorry folks. Confounded, hadn't heard that expression since my algebra teacher used it back in the seventys.........

[Tage]

randall satan power tube test right at the end of the you tube mixes 6l6 and kt88. You could do a mix with 50 watter since it has adjustible bias for each tube but thats only 2 tubes. With a 6550 I'd worry bout screwin up a nice amp. And then again It wouldn't quite be a tweed thing runnin randall. They have phase inverter and not a rectifier like tweed amps do ta get get the sag,or lag......

The statement about one amp having a rectifier vs. a phase inverter indicates sunn drone might not understand why amps, push pull amps, cannot have an uneven set of tubes. also more rectifier tubes are not required in relation to the number of power tubes in an output stage.

The randall referred to uses mis matched pairs to make up the halves of an output stage. long story short, yeah you could have an amp with 3 power tubes. i've fixed a few amps that got used this way for a while, gigged, not sounding great though...

[J M Fahey]

FWIW I felt curious and found the Beacon, NY 3 tube amp referred to above.

And it's a single ended amp, so any number of tubes, odd or even, can be used there.

Powered by a trio of NOS Philips Mil Spec 6V6GTY’s wired in parallel.

home

[Dave H]

$1599 for a 10W guitar amp? but it is "Pure class"

[J M Fahey]

And that's without front panel markings at all.

Silkscreening/engraving/Sharpie writing labels must probably double the price

[Leo_Gnardo]

The randall referred to uses mis matched pairs to make up the halves of an output stage. long story short, yeah you could have an amp with 3 power tubes. i've fixed a few amps that got used this way for a while, gigged, not sounding great though...

On mis-matched pairs, one of my customers got a THD Flexi-50 some years back, was advised by the staff at THD (maybe Andy Marshall?) to run it with one 6550 and one EL34. Even when biased properly, it never did sound very good to me, and scoping it showed a very unbalanced output waveform. I thought the amp had a lot more promise, had a great front end and built like the proverbial brick s#!t house, tough as hell. One day I slugged a pair of KT88 in there, and that's all she wrote - THERE's the tone! That customer heard it too, went with the 88's, and bought 2 more Flexies. So, why would anybody want an unbalanced output tube pair unless they wanted a lame sound? OK, granted there are some who do, takes all kinds I guess.

Juan, nice find on the beacon amp. I live 10 miles away & can't find him, you're about 6000 miles and you can. Funny none of the buttons work on his page, you think he could rope a web-adept friend into getting his web presence more user friendly. Only thing I know about him, he bought a house last year. Had no money, had to borrow from a friend for the down payment. Walking on very thin ice he is, I say good luck pal and don't quit your day job.

[Jammin'John]

SE Parallel

I generally run 3 x 6v6,2 or 3 x 6l6,2 or 3 x kt66,1 or 2 x kt88.
Some day I will run 1 x kt120 or 1 x kt150
It's not my schematic or design so I don't want to show "others" work.
I'm a player,not a tech. Adjustable cathode bias SE Class A.
12 - 28 watts. 4 & 8 ohm output.

JJ

[Chris - CMW amps]

3 powertubes can be something like a Fender 300PS or 400PS amplifier;
one single ended 6V6 or 6L6 transformer-coupled driver to the (push-pull) output-section....

Great and ballsy amps btw.....

[Chuck H]

3 powertubes can be something like a Fender 300PS or 400PS amplifier;
one single ended 6V6 or 6L6 transformer-coupled driver to the (push-pull) output-section....

Great and ballsy amps btw.....

Yes. Justin mentioned this above in post #2 as well as the use of a power tube to drive the reverb pan in some amps.

[rathmann]

Haven't seen it in a guitar amp per se, but a number of vintage hifi systems bi-amped using a single ended 6v6 to run the highs and a push-pull pair for the lows.

[Wombaticus]

There were one or two amps from the 60s that had three power tubes. They used one as a Voltage regulator for the screen grids.

The Sho-Bud Compactra 100 was one such amp, using a 6L6 just as a voltage regulator. I've seen Deke Dickerson play the hell out of one of these - it sounded great in a loud and clean kind of way.