The 805 and 833 don't need huge voltages to run. Nobu k Shishido found they are best run at about 800 volts and 100-135 ma. Nobu used a 3.5k out put transformer in his amps for the 805.
I have made both Se And PP using the 805; I used 5k for the PP
If you can't afford inter-stage transformers you can use a Cathode follower such as a 6BL7.
The ming Da uses only 750 volts for 40-50 watts.
Phil
I have made both Se And PP using the 805; I used 5k for the PP
If you can't afford inter-stage transformers you can use a Cathode follower such as a 6BL7.
The ming Da uses only 750 volts for 40-50 watts.
Phil
Nobu. K. Shishido 805
Nobu design for the 805 SE; he claims 45 watts for the 805 and 35 watts for the 838 {no top cap} with driver transformers.
Out put transformer 3.5K.
I have built 805's using about 800 volts, but driving them using 6BL7's as cathode followers, for the voltage amps I used Mu followers running at 750 volts, using 6AQ8's. A friend of mine has built the amps using driver transformers and Cathode followers, he prefers the sound of the Cathode followers.
Phil
Nobu design for the 805 SE; he claims 45 watts for the 805 and 35 watts for the 838 {no top cap} with driver transformers.
Out put transformer 3.5K.
I have built 805's using about 800 volts, but driving them using 6BL7's as cathode followers, for the voltage amps I used Mu followers running at 750 volts, using 6AQ8's. A friend of mine has built the amps using driver transformers and Cathode followers, he prefers the sound of the Cathode followers.
Phil
Attachments
I built mine using Hammond 1642SE output transformers to drive Magnepans. This output transformer is pot tested to at least 3500 Volts and I only put 1000 Volts on the plates of the 833As. In that configuration they only draw about 120 ma at zero grid bias. They will be linear by the current change proportional to applying battery voltages to the grid. Running them that gently produces more than enough power for loud passages even on Magnepans. The 1000Volt pi network should use polypropylene filter capacitors rated at over 2000 Volts and the choke of a10 Henries should be on the negative side to ground because Hammond chokes are only rated at 800 Volts and there is no need to have them live by putting them between positive terminals of the filter capacitors. You need to ground the frames of the output transformers and the negative speaker wires and properly fuse the power supply. Running the wires that carry 1000 Volts can be threaded through plastic tubing for added safety and the anode caps need to have plastic guards to prevent being able to touch them. The 10 Volt 10 Amps for the heaters is tricky but it can be done. You could use a car battery and a dropping resistor to to start, but eventually you will want to build something that will use use a 4.5 Farad final output filter capacitor which will need to be pre-charged with a 9 Volt wall wart through a 100 Ohm resistor. Once you have it running it makes Magnepan speakers sound better by far than they did when I auditioned them with a respectable solid state amplifier.
I drive the grids of my 833As with 45 SET through a headphone output transformer which goes from 5 k to 600 Ohms between 833A grid and ground with spectacular results.
If you go for it and your experience is limited find someone to help you and keep you safe.
I drive the grids of my 833As with 45 SET through a headphone output transformer which goes from 5 k to 600 Ohms between 833A grid and ground with spectacular results.
If you go for it and your experience is limited find someone to help you and keep you safe.
I'm interested in the sound of your 45/833 amp as I've heard that the 833 can sound "steely". How does the 833 change the tone of the 45?
It is hard to say because it depends on speakers and how you drive the 833A makes big differences in sound. I tried parallel feed and it sounded thin and watery to me but a Lundahl LL2765 30 ma single ended transformer sounds full bodied. A Sowter transformer might sound different. If possible the best way is to visit someone who has done it and try whether the sound is to your liking. Unfortunately, so few people have 833A stereos that one would have to travel far to hear one I doubt any two people have the same exact preferences. To me an 833A with Magnepans sounds more like a live orchestra in the Wilmington, DE opera house than $50 k speakers I heard at a seminar given by a high end A/V store.
I did a youtube presentation The 833A Single Ended Triode Amplfier - YouTube. If you travel to Delaware you can audition what I built and see how to make everything safe. Reply on youtube comments because I don't think we are allowed to put email addresses in these posts.
The idea of a TB3-2000 triode is entertaining; 2500 Volts, an output transformer that is pot tested to hold that voltage, but realistically, my 833A with 1000 Volts drawing 120 ma puts out more than enough current through a Hammond 1642SE can effortlessly make Magnepans too loud.
Still, I love to witness spectacles and it would be fun to witness a T3-2000 or a GM-100 in action.
Still, I love to witness spectacles and it would be fun to witness a T3-2000 or a GM-100 in action.
I just did. Someone was running GM 100's so hard the anodes were red hot with some yellow, making more power than anything I or most people would find practical. It reminds me of a stunt at an airshow I saw years ago where someone put an airliner jet engine on a truck and raced it down a long runway.
The Bulgarians build GM 100 SETs which run at 5000 Volts and announce 833As are for wimps. If you fall in love with the 833A sound driven by a 45, you have to be a good sport about it because the sheer joke of it all is hilarious.
Still, I read that the GM 100 has a beautiful sound. But 5000 Volts is more than I want to get involved with for audio.
The Bulgarians build GM 100 SETs which run at 5000 Volts and announce 833As are for wimps. If you fall in love with the 833A sound driven by a 45, you have to be a good sport about it because the sheer joke of it all is hilarious.
Still, I read that the GM 100 has a beautiful sound. But 5000 Volts is more than I want to get involved with for audio.
GM100
Did you mean this pictere?
It runs on 1900Volts at 350 mA, so it runs not that red hot as in the picture.
It a sort of modular system, i can run many different radar end or tranmitter tube's.
Think of the TB3-1000, TB3-2000, 6C21, GMI30,TB5-1250, TB-1500, TB5-2500, 833, SRS326, T3-800
It is a pity that uploading a few videos does not work, that might have been fun.
You also can visit Thomas Mayer @ vinylsaver, he has a number of pictures of the 2018 ETF event.
Did you mean this pictere?
It runs on 1900Volts at 350 mA, so it runs not that red hot as in the picture.
It a sort of modular system, i can run many different radar end or tranmitter tube's.
Think of the TB3-1000, TB3-2000, 6C21, GMI30,TB5-1250, TB-1500, TB5-2500, 833, SRS326, T3-800
It is a pity that uploading a few videos does not work, that might have been fun.
You also can visit Thomas Mayer @ vinylsaver, he has a number of pictures of the 2018 ETF event.
Attachments
Hey, it makes a good guitar amp
A 45 buffered by a mosfet (the second prototype Tubelab TSE board ever built, before Tubelab existed) is driving an 833A well into the red zone for 200 watts of SE terror. Drive the whole thing with an old ADA guitar preamp using a preset named "Jimi." It could be heard two blocks away.
For all but a few pictures there was a 1/4 inch thick Lexan shield between me and the pile of deadly electricity. The plate supply came from an old Motorola radio transmitter. it was rated for 1500 volts at 1/5 amp. I was using about 280 mA.
This was a test of a custom made OPT which worked great for guitar, but wasn't quite good enough for HiFi. This test amp only existed for about a week, and the stuff in the picture tells you that it was nearly 20 years ago.
