Some valve pron

[lurcher]

We just had another get together of like minded DIY folk. We (myself and Paul Barker) decided that something over the top was called for, so between the two of us we decided a 75w SET would be fun. So here is a picture of the output stage running at 1450v @ 160ma a side. Thought folk here might at least take pity on us :-)

http://i57.photobucket.com/albums/g201/simon2a3/Owston%2018-06-11/12cCustom.jpg

[Spectral Morn]

Interesting.

What kind of valves are those?

Regards D S D L

[Reid Malenfant]

That's some dissipation :eek: 232W per side...

Is that per channel? I'm not a valve guy but i'm assuming you might get a bit more efficiency from valves due to the transformer? Theoretical maximum efficiency from solid state is only 25% for an SE :eyebrows:

[Ali Tait]

Yes that's per channel! The valves are 833's, and the picture doesn't do justice to the size, they are almost the size of your head...

[Ali Tait]

....and the sound was amazing. One of the very best amps I've ever heard.

[Yomanze]

More importantly how did this amp sound?!

[Marco]

We just had another get together of like minded DIY folk. We (myself and Paul Barker) decided that something over the top was called for, so between the two of us we decided a 75w SET would be fun. So here is a picture of the output stage running at 1450v @ 160ma a side. Thought folk here might at least take pity on us :-)

http://i57.photobucket.com/albums/g201/simon2a3/Owston%2018-06-11/12cCustom.jpg

Lol, Nick - madness!! :eyebrows: What's the protection circuitry like? ;)

Marco.

[Reid Malenfant]

What's the protection circuitry like? ;)

Marco.
I think it's called a transformer :eyebrows: No DC allowed or supported :)

[Ali Tait]

The protection is you stand well back!

[Ali Tait]

A link to some pics on Audio-Talk-

http://www.audio-talk.co.uk/phpBB2/viewtopic.php?t=3262&postdays=0&postorder=asc&start=150

[Marco]

The protection is you stand well back!

Stand well back before lighting the blue touch paper, eh? ;)

Looks like you guys had another interesting meeting - nice one :cool:

Marco.

[Jonboy]

The protection is you stand well back!


Great stuff Ali, probing fingers are not invited:eek:

Its all about the sound and not the asthetics

[Ali Tait]

Jon, yes, though there were some nice looking diy efforts if you look through the pics.

Marco, yes, it was a great meet. I bought myself a 401!

[anthonyTD]

brilliant!
no need for a radiator in that room then ?:eyebrows::lolsign:
Anthony,TD...

[MartinT]

The protection is you stand well back!

Not half - that's scary voltage and dissipation. Did people lean back as you were increasing the anode current?

[Ali Tait]

Aye, to get away from the smell of ozone. :lol:

[Ali Tait]

Scary voltage indeed, but nothing for 833's. It was interesting hearing them sound better and better as more current was fed through them.

[Ali Tait]

Nick and Paul are talking about running them at 3kV next time!

[Reid Malenfant]

It was interesting hearing them sound better and better as more current was fed through them.
I guess triodes sound best in class A ;)

[Ali Tait]

AFAIK they were always running in class A. The soundstage opened out more and the sense of acoustic and air and space just kept getting larger as the wick was turned up. They really sounded amazing.

[lurcher]

Yep, single ended, so always A. They were running at about -7v on the grid when idling, so the challenge is to find a driver stage that will handle the 80v P/P signal, but also the grid current of 50ma or so as the grid goes positive (A2) for half the signal and negative (A1) for the other half.

It was just a lash up for the day, so no protection built into it specifically, but a lot of monitoring at startup. Paul built the output stage and heater supply (10A @ 10V), I built the driver stage, ECC40 to augmented cathode follower (12AX7, 12BZ7, 6BX7). The two parts had never met each other before the day (we just agreed on the plug and socket to connect the two. The power supply and driver is aimed at a big SE project, but not 833. There was a 5A fuse in the 1500v power supply, does that count? In fact, it was a expensive gold plated one, it was the only 5A 20ma fuse I could put my hands on at the time :-). Oh, and I did put a old perspex turntable cover over the HT supply to protect from fingers on the cap terminals.

As for efficiency, yes thats 220W per side, + 100W for the heater. As you say max efficiency for SE is 25%, but thats only true for A1 operation. As A2 can get you closer to the diode line, max efficiency is closer to 40%. Just dependent on how far the driver can push towards the diode line. I dont think the is a solid state equivalent of 2 (because of course you can have B2 and AB2 push pull amps). Thats why I can get 32W out of my 211 Set, though thats a much easier valve to drive into A2.

[SPS]

Nick and Paul are talking about running them at 3kV next time!

don't post that over on audiotalk Ali... you may have phil may be planning to go even higher...

we didn't just have this 833...another member brought one too which also sounded very good...

i was very impressed

most of us stood well back... just to be on the safe side.

not the sort of amp for the lounge (nick may not agree ?)... but would look just right on the set of an old horror film

[RochaCullen]

Glad to see you were making use of our latest discovery the Belkin PureAV interconnects.

There was some scary looking stuff at that show and a heck of a lot of chip board.

And I did spot some very fancy isolation being used for your amp, a tea cup.

But the thing I loved most was the sign stating, "Do Not Touch. Not only will this kill you, but it will hurt the whole time you are dying"

Genius.

[lurcher]

They were specially shaped ceramic stand off insulators. They may have looked to the untrained eye like tea cups :-)

The heater supply inside the chassis overheated without the extra air flow.

[Ali Tait]

Yes, the warning signs were great!

[shane]

There was a 5A fuse in the 1500v power supply

That's relief. For a minute I thought it might be a bit dangerous.

[lurcher]

It was on the 240v side though :-)

[Reid Malenfant]

Actually i was talking cobblers the other day :doh: Theoretical maximum power efficiency of SE class A is 50% if it's choke loaded rather than constant current load. It'd also be nearly 200% voltage efficient.

I do like the look of these monster valve amps though, i'm just not sure i like the voltages involved. Low voltage DC isn't too bad, 240V AC can give a nasty shock, but 1500V DC will lock you onto it due to muscle contraction :eek:

Very sensible putting up warning signs :eyebrows:

[WOStantonCS100]

You guys are flippin' crazy! I luv that! :eyebrows: But, my life insurance policy clearly states I'm not to go near or even think about building such a beast or the family gets nothing should I be discharged into another life!

[Ali Tait]

Ah, but you should hear how it sounds...

[activexp]

Madness, total madness :mental: but impressive! :)