This can kill you.
Has anyboidy had any experience with an 833-A single-ended triode amplifier?
One weakness of the SET is you are limited to sensitive speakers because of low power. Some people have experimented with using radio station transmitting tubes, especially the 833-A. Once you know how to do it, it is not difficult to build an 833-A final amplification stage which will work with low sensitivity speakers such as Magnepans if you prefer the sound of planar transducers to cone in box speakers and you can still have the purity of SET.
I have had success with only 1000 Volts through Hammond 1642SE output transformers. At this voltage the 833-A only draws 120 ma with zero grid bias so you can drive the grid with a 45 SET through a Lundahl LL2756 step-down transformer. The 10 Volt 10 Amp DC needed to heat the 833-A cathode is slightly tricky to build and I use 4.5 Farads in the final filter stage to do this.
Building your own, with help from someone who had experience with how to do this safely if you need it is much less expensive than buying one from a factory.
I have had success with only 1000 Volts through Hammond 1642SE output transformers. At this voltage the 833-A only draws 120 ma with zero grid bias so you can drive the grid with a 45 SET through a Lundahl LL2756 step-down transformer. The 10 Volt 10 Amp DC needed to heat the 833-A cathode is slightly tricky to build and I use 4.5 Farads in the final filter stage to do this.
Building your own, with help from someone who had experience with how to do this safely if you need it is much less expensive than buying one from a factory.
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Definitely one of the more exotic builds I’ve ever seen hereabouts, to put it mildly. Congratulations! A couple of things I’m wondering: 1) Looking at the curves shown on page 10 of this 833-A datasheet the performance of the tube with 1000 volts on the plate and 0 volts on the grid doesn’t look particularly linear. Have you measured the amp’s distortion characteristics? 2) Given the 75 watt rating of the output transformer, and how close to cutoff the tube appears to be operating, I’m guessing that the maximum power capability of the amp is probably no more than around 50 watts, and perhaps less. I suppose that’s enough to drive Maggies in a small listening space such as yours, as shown in your system description thread, but is much less power than most people seem to find necessary with Maggies in more typical spaces. In any event, congratulations again on some very impressive work. Regards, -- Al |
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@gregdude: I pulled up Will's ad. I believe they are PP mono using pairs of 811A transmitter tubes and big output trannies. Also 4 (!) 5R4GY rectifiers per chassis. Some serious plate voltage here (1200+). Looks like a nice restoration job by Will. Definitely worth the money! Imagine what you could get for them in Japan! |
https://www.audiogon.com/listings/lis8fgf9-dynaco-st-70-by-will-vincent-as-good-as-it-gets-sold-tube. This is an expired agon listing but it has his phone number and stuff... |
Building your own, with help from someone who had experience with how to do this safely if you need it is much less expensive than buying one from a factory.Yes this sort of thing can be deadly. A while back I built these 50kg each 805 monoblock monsters that used 900v top cap anodes, I got 50w out of them in the end but I had to use an interstage transformer between the 300B and 805 to get the best sound. https://ibb.co/0yf1fKP But in the end I stood back and look at what I was doing, and said "YOU WILL DIE ONE DAY" playing around with these things, so I got rid of them and have a longer life for it I’m sure. Cheers George |
I need help in how to put photographs in these answers. The picture of the curves on the 833-A at 1kV have near equal spacing for grid voltages vs plate current so it looks linear. I do not have distortion measuring equipment but I understand second order harmonics are not easy to hear in music and it sounds very clear. Of course all 1kV wires must have thick insulation and the anode cap is modified with a collar to prevent the danger of anyone touching the anode, unlike a 3-500Z or a GM-100 which requires an air cooled finned anode cap. You do need to know how to make the power supply with a cage to prevent any access to the power supply parts and you need to ground the output transformer frame which is rated at 4kV. Here is a link to some pictures of it before I connected it to Magnepan 0.7s and replaced the driver transformers with Lundahl LL2765 driver transformers. |
