EAR Yoshino V20 Amplifier

[poynton]

Hi.

Has anyone a circuit diagram of this amplifier?

Or a similar one using multiple small triodes?

Thanks

Andy

[poynton]

[andrew_whitham]

I'll second this request. but I'd guess if anyone has these lurking anywhere they'd have been posted already

It IS an interesting way of doing things and I'm intrigued by it
Isn't "conventional wisdom" that lots of parallel tubes is naughty?Had it been any other designer....

so I've been a thinkin'

The website lists the tube complement as 26 (!) ecc83's and 4 ecc82's. Given is 5 ecc83's per side of each push pull output channel

Ok thats 20 tubes 10 triodes per half of the PP. But Ri for that combo is still around 6.5K, implying a transformer with a large turns ratio, another no, no

Oddly there's a review there that tells us that the Output tubes are set up to deliver 2.5watts each - huh? my datasheet says 1 watt max per section...

Then to quote the same online review elsewhere "A further five tubes per channel complete the line-up, including three more ECC83s for the input stages and a pair of ECC82 driver tubes."

ecc82's presumably as cathode followers to drive the input capacitance of the output stage

Then to take a complete flyer a mu follower (or similar) input stage and "differential" phase splitter.

Sound plausible?

I have a feeling that the OPT requirements effectively kill this approach for DIY, not sure though. 10 triodes ought to swing enough juice - 50-60ma at 300v for sure, but I'm figuring an OPT of the order of 40k - 50k here?!

Not quite similar but one of the tubecad journal's circuits fo the month is a headphone amp with multiple triodes. It is OTL though

Andy

[andrew_whitham]

no sooner than I hit the button - I had a brainwave...

Could the output tubes be out of phase? one triode for each half of the transformer, you might be able to tap more power then. 2.5w from a "2w" tube?

Andy

[EC8010]

You probably need to think near enough pure Class B, too. Possibly even B2 (that would lower the required output transformer impedance requirement).

[pinkmouse]

I remember seeing it in a hifi shop in Hanover. Didn't get to hear it, but a very pretty piece of design.

[Brian Beck]

The website lists the tube complement as 26 (!) ecc83's and 4 ecc82's. Given is 5 ecc83's per side of each push pull output channel

Can someone please tell me why Tim De Paravicini used ECC83s as output tubes? Just to prove it could be done? Among common tubes, I can't think of a less likely candidate for an output stage than the ECC83.

But wait, why not take this concept further and use 100 nuvistors per channel?

[andrew_whitham]

Doesn't make any sense to me either. Could be a typo/misinformation, I guess.

If you were picking tubes to do this with surely you end up with low Ri types (of course the ECC88 would be a favourite...)

I think I'll sketch this - it looks sufficiently like work I think

Andy

[andrew_whitham]

YEP! would love to see the schematic... wonder if its anything like the attached, probably not if theres 20 watts available...

I've run the numbers through TCJ's push-pull calculator and all I can come up with quickly is 10 watts for the 12AU7 (ECC82) thats at 300Va / 9ma / 1750 load

I guess that the ECC82 / ECC83 are reversed. I couldnt get any sensible figures for the ECC83 - not enough current.

And its at this point I'd drift towards bigger tubes - a similar number of 12SN7 gets around 16-17w straight away (400Va / 9ma / 2250 load)

I don't doubt that these could be improved, particularly if you're smarter than the average bear.

Actually there's a project right there, tough to beat that output with 0.7% third harmonic. Kind of makes a indirectly heated 300b

like I said Hmmmm

Andy

[poynton]

Originally posted by andrew_whitham


............. I couldnt get any sensible figures for the ECC83 - not enough current.



...........like I said Hmmmm

The reason I asked in the first place is that I have a box of twin-triodes at home (cannot remember the type but not ECC83/82/88 ) and I thought it would possibly make a good project.

Andy, Care to flesh out your schematic with some more numbers ?

Where is the TX available from ?/

Andy