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[RMoore]

Larrchild wrote on Tue, 30 March 2010 16:43

Svetlana once took a 4CX250 external anode tetrode (forced-air all-metal transmitting tube) tube die and built it as a triode with a desired load of about 700 ohms. Dunno if it's still around, but that had promise. (if you put it in another room to overcome the blower!)

Bizarre!

I found an internets thread from '99 discussing 'London Power Amps' using 4CX250B in some models

http://archive.ampage.org/threads/0/ampgen2/014942/4CX250_tu bes_in_London_Power_amps-1.html

6/1/1999 6:15 PM
Pascal
   4CX250 tubes in London Power ampsThis company uses these unusual tubes in the power section of certain amps and seem to get quite a good amount of wattage from them when compared to the usual tubes we see in amps (6L6, EL-34 and company). Is London Power the only amp maker to use these tubes for guitar amps and does anyone have playing experience with these tubes and/or amps? How do they hold up tone wise. The canadian amps are very pricey so I was wondering if the money is worth it. Also, has anyone homebrewed with these tubes??

6/1/1999 7:04 PM
Dave Chun
   If I remember correctly, the 4CX250s are triodes more suited for RF applications (they can dissipate over 250W each.) There's lots more info at the Svetlana website, www.svetlana.com.

6/2/1999 12:57 AM
Bruce
   A pair of 4CX250s in push pull class AB1 at audio frequencies will put out way over 600 watts with the right power supply!  
Try and find an OT for them though! $$$$  
Bruce

6/2/1999 5:16 AM
Dave Chun
   The London Power Bass Amp does just that - a pair of 4CX250s for 700w. I emailed them about the OT and it's a custom Hammond type that weighs *35 lbs.*




http://www.londonpower.com/spectext.htm



If you really need more power, check out our SUPER SCALER models. The SUPER SCALER v700 uses the same 4CX250 power tubes the legendary SPECTRUM 700 used. Half the size of a 6L6 but capable of outputting over 800W per pair. Utter reliability, as witnessed by their aviation and military uses in radars and transmitters in tanks, ships, planes, and anywhere microphonics or failure could not be tolerated.

The SPECTRUM integrated amps are built like our other head-style amps, in a steel Hammond chassis, with venilated cover and wooden ends with flip-uphandles. A custom ToroidTech toroidal power transformer with dual primaries assures world-wide mains compatibility. Our custom Hammond output transformer, PEC sealed military pots and Switchcraft open-frame jacks are all chassis mounted. Solen polypropylene filter caps, Wima and Philips signal caps, metal-film and flame-proof metal-oxide resistors mounted on Teflon circuit cards are hand-wired for a lifetime of service. The usual Twenty Year Warranty applies to everything except the tubes and reverb tank.

[Larrchild]

A generic 4CX250 doesn't have a low-z load like this special triode version. They used less distance from other elements to the plate to lower the Z. This prohibits higher operating voltages for obvious reasons.

[RMoore]

Jim Williams wrote on Tue, 30 March 2010 17:38

For those interested in mondo power tube amp design, Electro Harmonix has released the new KT120 power tube. 60 watts each and you can do some severe damage with those. Maybe I'll replace the GE6550's in my 1966 Deluxe Reverb with a pair of those. It could win the mighty small amp award. Great for small clubs when no one suspects the little amp as the offender.

Nice!

http://www.univalve.net/vbulletin/showthread.php?p=22758

[RMoore]

With these absurdly high voltage tubes I'd be a little worried about the amp turning into a Tesla coil... what do you guys think?

[bruno putzeys]

Larrchild wrote on Tue, 30 March 2010 14:56

In his circuits with rows of tv tubes or KT-88's, the load is reasonable as you say, but with 4 transmitting tubes, it's still pretty high. (9500 ohms) I'm saying transmitting tubes like 813's operating at higher voltages seem to want a fairly hi-Z load. Looks like a pair of 813's in AB1 want 19 k load resistance @2500 vdc.      http://faculty.frostburg.edu/phys/latta/ee/wing813amp/813dat asheet1.jpg

Ah right. I should've done my homework there (I only looked at the posted pic which showed 8 smaller tubes). 9500 is high.

Jim Williams wrote on Tue, 30 March 2010 17:38

It could win the mighty small amp award.

I'm afraid I'll always win that one.

[Larrchild]

Slightly off-topic.. Great finally meeting you at AES!

[Larrchild]

RMoore wrote on Tue, 30 March 2010 10:04

Apparently there is the possibility of arcing with these 813's if there is a failure mode..

He's running this thing at Max rated plate voltage and is totally asking for trouble. I never ran 813's above 2250 vdc.

[John Monforte]

At 2500 volts, won't it generate x-rays?

[Larrchild]

Hence the term "more transparent".
Seriously, just barely.
> 10kV they become an issue.

[Moby (Mike Diack)]

Sometimes 2 output tubes is enough.
Here is a Mullard design using MZ2-200 bottles (sorta like a 212 with a bowler hat)
http://www.r-type.org/static/mz2200.htm
And a locally made version of it that I inherited
(Used to power dozens of Vitavox horns at religious rallies in the '60s). 58 on stand is for scale.

M

[Larrchild]

Mike, I suspect a classified ad in Jamaica's "Gleaner" would provide a very healthy sum from one of the many thermionically-faithful denizens.
Very Nice!

[foreignlove]

Love the amp!
Does any one know anyone in USA who is able to build 500- 1000 watt tube amps. Cant seem to find anyone. Thanks

[Mike Cleaver]

Stephen Sank used to have a picture of a one off RCA power amp that delivered either 500 or 1000 watts IIRC.
He had it up for sale.
Don't see it on his site anymore.

[Jim Williams]

bruno putzeys wrote on Thu, 01 April 2010 04:06

Larrchild wrote on Tue, 30 March 2010 14:56 In his circuits with rows of tv tubes or KT-88's, the load is reasonable as you say, but with 4 transmitting tubes, it's still pretty high. (9500 ohms) I'm saying transmitting tubes like 813's operating at higher voltages seem to want a fairly hi-Z load. Looks like a pair of 813's in AB1 want 19 k load resistance @2500 vdc.       http://faculty.frostburg.edu/phys/latta/ee/wing813amp/813dat asheet1.jpg Ah right. I should've done my homework there (I only looked at the posted pic which showed 8 smaller tubes). 9500 is high. Jim Williams wrote on Tue, 30 March 2010 17:38 It could win the mighty small amp award. I'm afraid I'll always win that one.

Yea, Hypex. Did you ever finish that 2k watt module?

Back in 1977, there was a tweed Fender Champ done up by Red Rhodes. It was used in a booth at Namm. He gutted it, built two chassis, one on top, one on the bottom. He fitted 6 kt-88's in it with 2 massive transformers.

This was a 200 watt Champ! Every 10 minutes they would crank it up. By the time the SPL meter man came by, it was off. They never found the source of that volume, no one ever suspected it was "The Champ".

[bruno putzeys]

The 2k module has been is in production for a year now. A higher performance one is slated for Q3 of this year or so.