6G4B SE Amp.

[PRR]

> if I connect EL34, 6550 or KT88 in triode mode SE

I've done 6L6 (1938 vintage), 6L6GC (1970s) and 6550 (unknown vintage) in a very high impedance SET.

You can use essentially the same bias condition and load for all three, and swap tubes any time. The original 6L6 (collectors' item) is only rated 19 watts plate dissipation; the other two are both rated 35 watts. Some 6L6GC are feeling weak at 35 watts, most 6550 are happy at 40 watts if you don't need industrial reliability. 400 volt supply, a cathode resistor to give 50mA to 80 mA plate current is safe in either 6L6GC or 6550. Use 5K load for "clean", 2.5K may give more power.

The 6550 is a beautiful SET. Good looking too.

Nothing wrong with 6L6GC, and they are the second most available tube on the planet today.

Don't abuse vintage 6L6 this way. Mine is gassy and tends to run-away if I don't bring it up to temperature slowly. The metals are not as good as recent tubes. And many of the vintage 6L6 you find have been used in hard service until they gave trouble. Keep them down to 250V 50mA, which is really not enough power for most loudspeaker users.

I have not tried 2A3/6B4, or EL34-SET.

My real preference is two 6550 in SET parallel, sticking with the hi-Z load. Some people say there is a loss of detail when paralleled- I don't hear that on my vintage speaker (RCA DuoCone). With the hi-Z load, the tube really loafs along linearly. Worth a try.

This is a very different sound than the same 6550 or 6L6GC in a Dynaco or Carlson push-pull AB output.

[fdegrove]

Hi,

Paul,

I've now got old enough that my PX4's will outlive me, so I feel OK about using them.

Beautiful valve...PX25 or DA60 are marvelous too.

Secondly the 6a5g sounds for all the world to me exactly like a 6b4g.

And it should...

I haven't heard an R120.

You even surprise me that you know that one.
I heard it only once at a get together with the L'Audiophile crowd in a small theater in Paris on enormous Klangfilm open baffles.

Kind of makes you realise how little progress has really been made in audio.

It was a jaw dropper as were most others like the AD1s and other unobtainable valves from the past.

PRR (other Paul),

Some people say there is a loss of detail when paralleled- I don't hear that on my vintage speaker (RCA DuoCone). With the hi-Z load, the tube really loafs along linearly. Worth a try.

The effect is most pronounced on high gain stages but can be overcome by careful matching and/or individual fixed bias.
Good idea on keeping Zprim high.

Cheers,

[James D.]

I have an very ancient friend (so he says - he's 92 and proud of it) who has an R120 audio amplifier. He runs it into a Tannoy GRF. Glorious mono. The amp is second word war vintage and absolutely wonderful. He has an EMT turnatable with Ortofon arm and SPU mono cartridge. This feeds a Leak preamplifier. We play old mono records into the night whilst sipping a Grappa or two. He's Italian and speaks a little rusty english. I'm English and speak a little italian - but boy do we communicate about audio!!!

My favourite mono record is an EMI box set of Pablo Casals playing Bach Chello Suites recorded in 1948. Fantastic playing that just sends me. Closely followed by some of the Hot Club sessions. Jazz as it should be performed and heard!

best regards

James

[cominup]

Hi,

Where did this project go to?

Could you show your completed schema and amplifier?

I like sound of 6C4C/6B4G, but it's not enough power so PSE could be a very good solution.

Lookforward to your infor.