WOT Preamp

[alexg]

I just finalized the design of my WOT (with output transformer) preamp.

It uses 407a/2c51/396a/5670 tube, paralleled triode into Edrel's experimental 10K:600 preamp OPT.

It rocks!

Pix to follow.

[kabubi]

congratulations, Alex!

i'm quite sure it sounds sweet. read your thread on the LSA1 being substituted by the OB and i was thinking of suggesting the crazy idea to combine the 2 instead with the OB handling the lower registers...

[tony]

hi alex, is the topology like that of the ultrapath?


broskies' here: http://www.tubecad.com/2008/08/blog0147.htm

[alexg]

@Kabubs, OB is in the works.

@Tony, not quite like the ultrapath. simple cathode bias, I paralleled the two 2c51 triodes, one tube per channel. the 417a version also sound very sweet!

[edrel sison]

i would like to do this tony, very soon. uses 10K for the pot and diode biased..
now if i can get some cheap 5842s i will also sample a preamp like alex did!

[tony]

6n1p, 6922, 6dj8, are nice sounding triodes....

parang menakita ako sa southern radio na 5842 the other day....

btw, in lieu of the silicon diodes, you can try 2 red led's....you can even use the 6H6 or 6AL5 dual diodes although i haven't tried....

although half the transconductance, type 6BC4 if you can find it will make a nice preamp...they are available at the Rogalski's for a dollar each....

[tony]

@Kabubs, OB is in the works.

@Tony, not quite like the ultrapath. simple cathode bias, I paralleled the two 2c51 triodes, one tube per channel. the 417a version also sound very sweet!

ok, maybe you should try it not paralleled.....

[alexg]

@Kabubs, OB is in the works.

@Tony, not quite like the ultrapath. simple cathode bias, I paralleled the two 2c51 triodes, one tube per channel. the 417a version also sound very sweet!

ok, maybe you should try it not paralleled.....

I need the current to drive the OPT.

Tried it with single triode, too screechy and forward.

Anyway, I am using it now with my 5842/4a7a, sounds a bit better than the 2c51.

[alexg]

congratulations, Alex!

i'm quite sure it sounds sweet. read your thread on the LSA1 being substituted by the OB and i was thinking of suggesting the crazy idea to combine the 2 instead with the OB handling the lower registers...

Hi Kabubi,

I really like the LSA1, though I miss my 2a3 SE, my EL84 SE and my flea powered 12b4 amp. These amps cannot drive the LSA1. I have a small listening room and very limited funds, so the thought of swapping my LSA1 with Zu, Omega or other high sensitivity and easy to drive speakers, has been popping on my mind.

[tony]

@Kabubs, OB is in the works.

@Tony, not quite like the ultrapath. simple cathode bias, I paralleled the two 2c51 triodes, one tube per channel. the 417a version also sound very sweet!

ok, maybe you should try it not paralleled.....

I need the current to drive the OPT.

Tried it with single triode, too screechy and forward.

Anyway, I am using it now with my 5842/4a7a, sounds a bit better than the 2c51.

may i know what was your operating point?

[alexg]

may i know what was your operating point?

On the 5670/2c51, 150V on the plate, 7 ma per triode. If the B+ is slightly higher, both on parallel and unparalleled, then it becomes quite sibilant and bright.

[tony]

alex, i have ahunch that the 5687 will be better at that plate voltage.... been looking at that tube, largish cathodes than the others.....capable of more current....like the 6H30 russian tube...

[alexg]

alex, i have ahunch that the 5687 will be better at that plate voltage.... been looking at that tube, largish cathodes than the others.....capable of more current....like the 6H30 russian tube...

5687 and its nicer brother, the 7119, is one of my favorite drivers. works well between 150 to 180 plate voltage, only problem is the lower mu. But I have used it on a single input/driver for a 2a3 SE, sounds really nice, but it will need a preamp with a bit of gain. I built a PP EL84 with 5687/7119 driver into a lundahl interstage, and it sounds excellent (the 5687/7119 into Edrel's autoformer phase splitter also sounds excellent).

I have a 2a3 SE on the works right now, tried the 5842 with lundahl interstage, works great. Next iteration will be a two stage of 5687 triode to drive the 2a3, should work great, will let you know.