• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

is this possible?

firefart_1st said:
I had forgotten this schematic but...

i do have a pair of 211's and I was wondering...

with those schematics is it possible do crank 80W :bigeyes: out that amp like it says on the bottom ?

if someone know how to explain it do me... please do! :D

From a 211 with a Pd= 100W, no way. The best you could theoretically hope for is Po= 50W, and practically, you'll get less than that.

Furthermore, there is the SE OPT problem. Take a look at the OPT specified: 6K5 : 8R. It is very difficult to wind an OPT that can handle the DC magnetization, match those impedances, handle the power, and do it all while preserving sonic performance, especially at the extremes. If you want a monster SET, it's doable, but the sonics will probably relegate it to guitar use where sonic performance isn't so demanding as HiFi.

I dropped a SET project based on the 812 that worked at a lower power level than this since Jack at Electraprint couldn't guarantee he could design an OPT for it that was up to HiFi standards. No one else offered a SE OPT that came close to what this project needed. Since I don't play, I didn't need a SET guitar amp.

If you want more than 20W from a SE design, then go for something like a MOSFET source follower parafeed, and remember to include a really big heat sink. You ain't gonna get it from hollow state. :whazzat:
firefart_1st said:

p.s.: my tubes are 311T but they should be the same...

Actually they are not interchangable. The 311 has a higher plate resistance owing to a greater physical distance between grid and plate structures. This requires higher plate voltage to get the same current draw. You would porbably need to go positive voltage on the grid to get them to work. 311Ts were often used as diathermy oscillator tubes. (I own both types)

I agree!

with both repplys ^^

I don't intend to make that amp.

I'm looking forward to make a 7 to 15W SE amp with them.

since they are 311T and have that "problem" I'm not sure how to get them blowing the good tube sound

and still I don't have PT and OT for them.

just have the filament transformer for both.

If you can help me to get on the right track I would appreciate that :D

( since the transformer feeds both tubes at the same time... it is going to be a problem for stereo application right?

firefart_1st said:

I'm looking forward to make a 7 to 15W SE amp with them.
since they are 311T and have that "problem" I'm not sure how to get them blowing the good tube sound

People make 805s work as outputs, and they are even worse as far as Rp and voltage requirements go. So your 311Ts, if good, can be used. Depending on Vp available, low negative or zero bias might work. Choke loading and parafeeding the output to a 10K ohm PP transformer is a possible way to go.
I order my PT and OT customized from a local manufacturer

they can do whatever I ask so.

my 311T's are good and tested for.

they had been tested with 300V and a simple Class A design.
and sounded pretty good! no distortion on my scope...
but the output was less than 300mW :smash:

so. i will post a schematic that I would be getting to practice. later on...

since I don't want to buy a bigger power transformer... and use the one I already have... I will have both tubes with cathode to ground...

so. negative bias needed.

it does sound worse doesn't it?
for the PSU I was wondering about 1Kv. not to difficult to achieve. although. dangerous

I'm posting the details from SE tube CAD program.

if you please, tell me if it is in a good track...

I don't have the driver circuit made yet.

if I 'push it harder' on the input signal it will have positive grid current.

anyway. it is a 311T and 10W of power is pretty good for me ^^

p.s.: on the picture is does not have the negative bias on the 200k grid resistor. it is suposed to be -51V


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