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Old 3rd February 2011, 11:15 PM   #11
AJT is offline AJT  Philippines
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operating in triode mode at B+ of about 900volts, you can still get a lot of output power...
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Old 3rd February 2011, 11:51 PM   #12
banat is offline banat  Serbia
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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
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Old 4th February 2011, 10:27 AM   #13
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hey-Hey!!!,
I am running 813's at 580V with a 10k a-a output trans. 30% U-L taps at 110 mA/tube idle. I'll try the 20% taps soon; with the 40% taps I lost too much power. These OPT's are wound by Heyboer, with coils copied from S-265-Q.
cheers,
Douglas
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Old 4th February 2011, 11:24 AM   #14
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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
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Old 4th February 2011, 12:16 PM   #15
banat is offline banat  Serbia
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Originally Posted by Bandersnatch View Post
hey-Hey!!!,
I am running 813's at 580V with a 10k a-a output trans. 30% U-L taps at 110 mA/tube idle. I'll try the 20% taps soon; with the 40% taps I lost too much power. These OPT's are wound by Heyboer, with coils copied from S-265-Q.
cheers,
Douglas
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
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Old 4th February 2011, 12:22 PM   #16
AJT is offline AJT  Philippines
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Default look for sparky813

hey Tad, you may want to touch bases with this guy from this thread: transmitter tube amp
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Old 4th February 2011, 12:26 PM   #17
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i have a quad of these 813's but one of them is clearly used up.......do you have a source of those we can get cheap? thanks
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Old 4th February 2011, 03:26 PM   #18
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Quote:
Originally Posted by tryonziess View Post
Wavebourn what are you using in your current large tube amps as output tubes. You seem to always produce really nice projects.
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.
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Old 4th February 2011, 03:34 PM   #19
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Quote:
Originally Posted by banat View Post
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.
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
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Old 4th February 2011, 11:46 PM   #20
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Has there been in new high power tubes manufactured in the last 20 years which would make a nice 250 - 300 watt amp.
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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