Does anyone know of a good tested schematic for a push pull 813 tube ultra linear design amp. I was thinking of 250 watts from two 813 tubes with ultra linear output transformer taps.
Also, is there any reason not to use separate transformers for each needed voltage. The power supply will be a separate unit mounted under the main chassis. Many of the components for this project will be salvaged from various items I can acquire cheaply. A multi-tapped power transformer is more complex than several individual units. It is also easier to calculate power demands on only one secondary voltage/load.
This may possible be my last amp project. The eyes and hands are not what they used to be.
Any suggestions on this project will be much appreciated.
Thanks Tad
Also, is there any reason not to use separate transformers for each needed voltage. The power supply will be a separate unit mounted under the main chassis. Many of the components for this project will be salvaged from various items I can acquire cheaply. A multi-tapped power transformer is more complex than several individual units. It is also easier to calculate power demands on only one secondary voltage/load.
This may possible be my last amp project. The eyes and hands are not what they used to be.
Any suggestions on this project will be much appreciated.
Thanks Tad
Wavebourn,
Is there any advantage or disadvantage to having separate transformers for each needed voltage? What would be the optimum area to tap the output for the ultra linear voltage? There is very little 813 information on the net. Most tube amps are using the KT series tubes. I see nothing wrong with the old 813 item. It has many really good characteristics. It also is one hulking monster!!!!
Tad
Is there any advantage or disadvantage to having separate transformers for each needed voltage? What would be the optimum area to tap the output for the ultra linear voltage? There is very little 813 information on the net. Most tube amps are using the KT series tubes. I see nothing wrong with the old 813 item. It has many really good characteristics. It also is one hulking monster!!!!
Tad
I would not use them: too dangerous, inconvenient, and PITA to get good OT. I currently plan to build 200W amp prototype based on 4xGU-50 tubes.
Here is a good design for an 813 amp:
Champ 1000 Watt Tube Amp
Notice its for PA use not HiFi.
If you want to go with UL then it limits your supply voltage to around 1100V because the screens wont take much more. Even this is pretty high especially with top caps IMHO.
Getting some output trannys large enough with such a high primary impedence and also good bandwidth is almost impossible.
Cheers Matt.
Champ 1000 Watt Tube Amp
Notice its for PA use not HiFi.
If you want to go with UL then it limits your supply voltage to around 1100V because the screens wont take much more. Even this is pretty high especially with top caps IMHO.
Getting some output trannys large enough with such a high primary impedence and also good bandwidth is almost impossible.
Cheers Matt.
Hi there,
With the 813 there are 2 routes you can go with, in ultralinear:
Use a B+ of 750 volts and figure out the loadlines to get your output transformer impedance. I am thinking it will be a low value, like 5-6K, but you will have to figure it out to be more exact. In this case the output transformer will not be too exotic and most likely an off the shelf item will work.
The other scenario will get you more power because of the higher B+ voltage; 2KV. You will have to have a custom built output transformer with 2 windings; one for the plates @ 2KV with an impedance of about 12-15K and another winding for the screens with the voltage at 750 volts. The 2 windings will probably have to be wound side by side so there is adequate coupling, but it still will not be as good as traditional ultra linear where the same winding is used, with taps for the screens. This will cost a lot as many parts will be custom made for your project.
The 3rd scenario would be to go traditional pentode mode with 1.5-2 KV at the plates and 750 volts for the screens. Output transformer impedance would be 10-16K. I have been thinking about going this route for a Super PA / Guitar Amplifier which I know is impractical but would like to see how well it would work. I have some UTC CVP-5 output transformers that are rated at 10 or 14K, 300 watts and hi-potted for 3.5KV. I would run them with 1.5KV B+ as I am reluctant to push them any harder. I am expecting , which is what the RCA handbook says, 250 watts for a pair of 813's.
I love the 813.... To me it looks like a 6550 on steroids.
Daniel
With the 813 there are 2 routes you can go with, in ultralinear:
Use a B+ of 750 volts and figure out the loadlines to get your output transformer impedance. I am thinking it will be a low value, like 5-6K, but you will have to figure it out to be more exact. In this case the output transformer will not be too exotic and most likely an off the shelf item will work.
The other scenario will get you more power because of the higher B+ voltage; 2KV. You will have to have a custom built output transformer with 2 windings; one for the plates @ 2KV with an impedance of about 12-15K and another winding for the screens with the voltage at 750 volts. The 2 windings will probably have to be wound side by side so there is adequate coupling, but it still will not be as good as traditional ultra linear where the same winding is used, with taps for the screens. This will cost a lot as many parts will be custom made for your project.
The 3rd scenario would be to go traditional pentode mode with 1.5-2 KV at the plates and 750 volts for the screens. Output transformer impedance would be 10-16K. I have been thinking about going this route for a Super PA / Guitar Amplifier which I know is impractical but would like to see how well it would work. I have some UTC CVP-5 output transformers that are rated at 10 or 14K, 300 watts and hi-potted for 3.5KV. I would run them with 1.5KV B+ as I am reluctant to push them any harder. I am expecting , which is what the RCA handbook says, 250 watts for a pair of 813's.
I love the 813.... To me it looks like a 6550 on steroids.
Daniel
Actually two 813 tubes need only 1,5 KV on plates and 750 V on g2 to made Amp with made 260 W of out power,Raa is 9,3 Kohm.
UL operation is not necesary for this tubes to obtain low max distortion(2,5 %)since this tubes is beam power tetrodes(pentode)
CT (550V~) of main Tr. Uba secondary 1100 V~ /0,4A is good for Ug2/750 V suplly.
QB2/250 or 813 or GU 13 is the same tube, I prefer Russian GU13 tube,is the Best One !
All the Best
UL operation is not necesary for this tubes to obtain low max distortion(2,5 %)since this tubes is beam power tetrodes(pentode)
CT (550V~) of main Tr. Uba secondary 1100 V~ /0,4A is good for Ug2/750 V suplly.
QB2/250 or 813 or GU 13 is the same tube, I prefer Russian GU13 tube,is the Best One !
All the Best
Attachments
The awesome one thousand watt amp that Champ constructed in the U.K. is what led me to this project. Using the ultra linear circuit with push/pull should make for a nice high quality amp. I can not use the SE amp output for my speaker setup and have also read many negative things about SE.
To the best of my ability I am going to wind the transformers myself. There is an abundance of good material on the web and with all of this groups help may get something that works. There is no way I can afford commercial trannies, if I could find them in this high of an output.
Has there been in new high power tubes manufactured in the last 20 years which would make a nice 250 - 300 watt amp. I suspect most are just clones of 1940's designs.
I like the nostalgia of tubes and think a nice tube amp would be nice with the rest of my toys.
Now off to research those tubes Tony suggested.
Wavebourn what are you using in your current large tube amps as output tubes. You seem to always produce really nice projects.
Thanks Tad
To the best of my ability I am going to wind the transformers myself. There is an abundance of good material on the web and with all of this groups help may get something that works. There is no way I can afford commercial trannies, if I could find them in this high of an output.
Has there been in new high power tubes manufactured in the last 20 years which would make a nice 250 - 300 watt amp. I suspect most are just clones of 1940's designs.
I like the nostalgia of tubes and think a nice tube amp would be nice with the rest of my toys.
Now off to research those tubes Tony suggested.
Wavebourn what are you using in your current large tube amps as output tubes. You seem to always produce really nice projects.
Thanks Tad
Not say it is imposible but I never try to run GU13(813) tube with such of low Plate voltage,but on 1,5 KV to 3 KV Uba,this higher -up to 3KV- I use for DIY RF AM transmitter and 1,5KV for RF DIY modulator stage.
With 1,5KV on 2x GU13( 813) plates and 750 V on G2 of this RF(audio) class AB modulator this tubes realy sonicaly `shine`, and they normaly last for decades long under this Voltage condition.
I tested this RF modulator on two 500W/8 ohm(1KW) HI FI DIY speaker kabinets,conected speakers on 4ohm auxiliary output tap of output modulation trans.That was the incredible sound presure in the house
,think that average SS amps need at least double or more RMS power to perform the same sound quality like this simple 2xGU13 RF modulator Amp does.I made this equipment for my friend AM Pirate radio station on early 90` and this equipment work fine even today!
Best Regards
look for sparky813
hey Tad, you may want to touch bases with this guy from this thread: http://www.diyaudio.com/forums/tubes-valves/89057-transmitter-tube-amp.html
hey Tad, you may want to touch bases with this guy from this thread: http://www.diyaudio.com/forums/tubes-valves/89057-transmitter-tube-amp.html
I use Gu-50 output tubes. 800V B+, 275V G2, with parallel feedback around them. To drive them I use pentode part of ECF200 directly coupled through DC voltage divider with Concertina phase splitter using triode part of it. For higher sensitivity I use 6F12P. I plan to try 6F1P, it is nice, cheap, and available. Then Concertina is directly coupled with LTP using either 6J51P in triode with additional resistors in cathode for degradation, or 6P15P in pentode.
I plan to build monoblocks with 4K output transformers, 4XGu-50 output tubes driven by a pair of 12L6GT as cathode followers. Output power will be limited by optical compressor on 200W per channel level. Compressor senses screen grid current, it is my proprietary anti-clipping arrangement.
However, I considered GU-13, but found Gu-50 more convenient.
It is not impossible at all...
The amp can also run 257B and I think this one is a bit better at low B+ than 813. I'll probably put it back to the Tantalum anode sooner than later.cheers,
Douglas
The larger TV sweep tubes from the end of the vacuum tube era can do it. I got about 45 35LR6's at a hamfest for $4 each. I put 4 of them in Petes red board and got 250 WPC on 650 Volts of B+. Both channels paralleled into a 1250 ohm OPT made 504 watts at 5% distortion and over 525 watts at the edge of clipping. A quad of any of the big sweep tubes with a 35 or 40 watt plate dissipation rating would make 300 watts in pentode mode PPP easy.
The 813 in pentode mode would also make plenty of power but there are some issues. The plate and screen voltages need to be quite high to get away from the "tetrode kink" in the curves. The plate to plate impedances (OPT primary impedance) needed at these voltages is also high, ranging from 10,000 to 16,000 ohms. Finding (or winding) a quality OPT to cover the entire audio range at these impedances and power level is nearly impossible. It is far easier to make an OPT that handles 500 watts from 20 Hz to 20 KHz at 1250 ohms than it is at 12,500 ohms.
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