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Old 31st August 2004, 02:02 AM   #1
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Default question about 811A and 572B

HI

I plan to possibly use the 811A in an amplifier.

I didn`t find the 811A datasheet but the svetlana is suppose to be a direct remplacement of the original 811A.

On the 572B detasheet, they didn`t mention the amplification factor, the Rp and Vmax (continus).

They say that the tube can handle 2750Volts in ICAS. But do a derating factor of about 75% could be fine for a Continus service (around 2000V)

If the 811A cannot accept a 2000V continus, do wou know a tube (possibly a DHT) that can handle this with a 30-40Watts dissipation minimum.

572B datasheet
http://www.svetlana.com/graphics/products/pdf/572B.pdf


Thanks a Lot.
Martin
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Old 31st August 2004, 04:25 AM   #2
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Default 811a

High Martin.

The 811A is good for 1250 volts, 45 watt plate dissapation max CCS, with 1500 volts, 65 watt plate dissapation, -4.5 volts grid bias, ICAS typical. Mu is approx 160.

Hope this helps.
Steve
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Old 31st August 2004, 04:26 AM   #3
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Martin,

Votre English c'est bon! Mon Francais est crappy.

The 572B is a much higher power triode than the 811A. 2000 volts will likely melt an 811A with the turn of the switch.

I suggest you look at the 845, 211, or even 805 and run it at reduced ratings. Note that even these tubes cannot handle 2000 volts reliably. I suggest that you re-design your power supply and use a maximum of say 1100 volts. My 805 SET amp achieves full plate dissipation of 120 watts easily and makes 40 watts RMS output on 1050 volts plate supply.

If you must run 2 kV on the plate I recommend 810. That is 175 watt PD and 2500 volts max anode. 833A is another that will handle the high voltage but at 450 watts PD it is only necessary for giant class-A SE amps (makes ~125-150 watts in SET).

I trust you know that these voltages are extremely lethal and special care is needed in design and servicing such circuits. Such tubes must be enclosed to keep curious hands away while proper ventillation is also supplied.
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Old 31st August 2004, 06:55 AM   #4
billr is offline billr  New Zealand
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Hello,

if you are interested i have quite a few diagrams of 811 amps, and i have a few datasheets on the same.

If you want to contact me on b i l l dot ramsay at clear dot net dot nz i would be happy to send them to you.

kind regards

bill
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