Krakatoa - venturing into A2 with SE amp

[Bigun]

A colleague kindly gifted me his prized stereo with the idea that I'll take some of the bits off it and build myself an amp.

What did I get? - two pairs of SV811-10 triodes, a pair of Hammond 1629SE output transformers, a Hammond 714 power transformer, lots of other chokes, power transformers, caps and two chassis to hold this monster - you'll find it here (Paravoz) Customer Examples - Hammond Mfg.

I've heard the amp on several occassions and it sounds good and looks even more impressive. But the point here is to start over, the existing amp has had a good life and now it will be reborn in my hands as a far simpler amplifier.

Although the SV811-10 is now extinct, there are other tubes that could be used in the future with very little modification such as the 845. At the end, I'm not aiming for maximum output power.

Most of my projects remain half-finished for years so don't expect daily updates

 

[Wavebourn]

Here you go:

I even have boards for A2 drive.

 

[Bigun]

That looks good.

How about choke loaded source follower to avoid need for a -Ve supply (output tube can use a little cathode bias) ?

 

[Wavebourn]

Sure, you can do that. Either choke load, or interstage transformer.

 

[Bigun]

Great. Do I need a slow start on the Th-W filament ? And do I need to delay B+ (400Vak) until the filament is hot ?

no experienced Th-W builders out here these days ?

 

[Radiola]

Some useful considerations from the world of transmitting tubes (which SV811 was before genetically modified):

https://www.cpii.com/docs/related/23/Tube Maintenance.pdf
https://www.w8ji.com/Vacuum Tubes/CPI AB-18 New v2.pdf

Quote from the first link: 'Power tubes should not be operated in the emission-limited mode'

 

[Wavebourn]

No need for slow starts nor delays. It is not a magnetron with cathode current density that can heat it up.

 

[6A3sUMMER]

Bigun,

Darn, you made me have to send my mind all the way back to my 1963 chemistry class. But I guess that was just 'Elemental'. I will try and 'Table' that thought.

 

[indra1]

... Although the SV811-10 is now extinct, there are other tubes that could be used in the future with very little modification such as the 845. At the end, I'm not aiming for maximum output power....

You may want to check https://www.vivatubes.com/brand-new-factory-matched-pair-2-svetlana-sed-sv-811-10-vacuum-tubes/, and also include the 211 into consideration for future upgrades.

 

[Bigun]

Thanks everyone !

No need for slow starts nor delays. It is not a magnetron with cathode current density that can heat it up.

talking of big tubes...I just happen to have a tube with a high cathode current density in my collection - here's a photo comparison against the SV811. The big tube is actually a Tetrode.

 

[Tubelab_com]

I had a pair of good 4-1000's and several 4-400's. These are BIG glass tetrodes with 1000 watt and 400 watt plate dissipation ratings......Reality finally won the battle in my mind and I sold them all along with most of my 833A's and all the other transmitting tubes.

I still have three good 833A's and ONE OPT and power transformer set capable of extracting 200 watts out of one tube in SE. The frequency response if only "guitar amp" quality, so I doubt I'll ever build it.

Insanity still rules my mind in the quest for a 1KW (500 WPC) HiFi quality amp. Again I have the parts, but the output tubes will be TV sweep tubes. That one keeps inching closer to reality. I need to build it before I get too old to be capable of moving it.

 

[w5jag]

Great.

Do I need a slow start on the Th-W filament ?
And do I need to delay B+ (400Vak) until the filament is hot ?

No, AFAIK, the 811 / 572 type tubes are instant on.

I was getting 9 watts out of SV-811-10 with an inadequate power supply. I bet 15 can be had pretty easy.

I think I was using a 10K load, possibly 5K - don't have my notes here at the office.

Win W5JAG

 

[Bigun]

If I remember correctly, that big tube I pictured uses a multi-KW plate supply.

Back to sanity - I have been dismantling the old amp to recover parts for this project (credit: it was superbly built by 'Radiola' who has now moved on to SITs). So I now have a pair of Hammond 1629SE output transformers, providing a 6k5 load (with 500 Ohm DCR) for each tube. They are heavy beasts.

I'm still trying to figure out what the chassis needs to look like so I can get something on order.

 

[6A3sUMMER]

Eimac has a 1500W plate dissipation VHF RF triode that is intended for class A TV transmitter service.

I remember that someone posted the 200 Watt SE mono-block amplifiers he created.
The pair of amps filled a 19 Inch rack from top to bottom.

 

[PRR]

...These are BIG glass tetrodes with 1000 watt and 400 watt plate dissipation ratings........

Bah. Bigun's tube is rated 30KW plate dissipation. (Using all the water my well-pump can supply; though only a few PSI drop so I could use the exhaust for hot water, if I needed that much hot water.)

Rated 40 Amps emission, 1KW filament power, 14KV. Can do >50KW <50MHz.
http://www.mif.pg.gda.pl/homepages/frank/sheets/065/r/RS2048CJ.pdf

 

[Tubelab_com]

Bah. Bigun's tube is rated 30KW plate dissipation.

Yeah, but a big glass tube almost a foot tall with a 150+ watt filament that lights up the room looks way cooler. Either way the plate voltage requirement and resulting high impedance OPT makes either of these rather impractical for an audio amp. Even the "little" 833A LOOKS good. I voted the pair of 4CX350's off the island early on for that reason. Sold them and their sockets / chimneys to a guy who built a 6 Meter RF amp.

As for extracting 200 watts from an 833A in A2 on 1500 volts.........don't try this at home.......Note the 1/4 inch Lexan "blast shield" in place when actually playing this thing. It only existed for about a week over 10 years ago to "prove the concept." Will I ever actually build it?????

 

[Bigun]

Bah. Bigun's tube is rated 30KW plate dissipation.

True to my screen name

 

[Magz]

C'mon people, what's the big deal? 200WPC in a single chassis SET mono amp, 180lbs each, 2300V on the plates. Still cranking and sounding great!! No electrocutions yet, 6 years later.

The Midlife Crisis - My 833C Amp Build

 

[hpeter]

Funny story-833 has better curves than kt88 in triode

 

[Wavebourn]

Nothing is funny; so called "audio tubes" were just cheap tubes in mass production. Consumer audio never was considered as more critical application than military radio and electronics, when everything was made with tubes.