• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

211 output transformer suggestion

Jump to Latest
#43
smoking-amp said:
6197 with gm of 11000 and internal Mu of 22 would give an Rp of 2000 Ohm at 30 mA idle. 7.5 Watt Pdiss.

The 7x 6197 was just a napkin scribble guess for how many tubes to get 25 Watts out in pentode mode, class AB.

For 25 Watts in triode mode, and class A, that would take more like 16x 6197 tubes. 16 tubes in parallel would give 125 Ohms Rp equivalent for the bunch. Figuring 5X that for triode operation with low distortion would require a 625 Ohm primary SE OT. A rough estimate anyway for continuous operation. (class A)

So, I guess 300 Watts in class A would take around 192 tubes. $63 of tubes. $400 of sockets. Whew! At least you won't need an OT with 19.2 peak Amps available. Forget that idea.

Well, I guess that could be scaled down considerably if taking audio crest factor into account in class AB. Maybe 50 tubes would work for peak power intermittently in class AB. Just not for continuous sinewave.

The $0.33 price comes from a tube sale at Bangy-Bang tubes (on Ebay) early this year of military surplus stock in high quantity. 200 tubes per box. Normally that place is hideously expensive for single tubes, so I guess they do some volume sales occasionally (of overstock) to keep people checking their website or Ebay store. When an Ebay sale says "serious tubes" I figure a SERIOUS $$$ price goes with it.

I have seen some prices on 6197 tubes on Ebay recently in the $0.50 (60 quantity) up to $2 range lately.
Click to expand...

Thanks, I'll have in mind for future project, know I have to see what I can do with these big baby's 🙂
 
#44
It's very difficult to make transformers for 1000:1 frequency range, and even harder with DC biasing the core. Yet another option is to use two different transformers per channel, one optimized for low frequencies, one for high. Only the low frequency one needs to carry DC. Paul Klipsch built an amplifier like this (mono! of course) in about 1946. On his the output transformers were mounted at the speaker, with high voltages running between amp and speaker - don't! of course.


All good fortune,
Chris
 
#47
alexanderfa said:
Does anyone knows any old amplifier using 211?
I want to compare how they use this tube.
In the RCA datasheet recommend at 1250v Rload=9600
Click to expand...


What is "old" for you in that context? Sound Practices era old? Or RCA-still-producing-211-tubes old? If the latter is the case you will have a hard time to find a schematic for a hifi amplifier, as the 211 is a transmitting, not a receiving tube.
Check the schematic for the Western Electric 43A amplifier; it used 211s for sound reproduction.
 
#49
Chris Hornbeck said:
It's very difficult to make transformers for 1000:1 frequency range, and even harder with DC biasing the core. Yet another option is to use two different transformers per channel, one optimized for low frequencies, one for high. Only the low frequency one needs to carry DC. Paul Klipsch built an amplifier like this (mono! of course) in about 1946. On his the output transformers were mounted at the speaker, with high voltages running between amp and speaker - don't! of course.

All good fortune,
Chris
Click to expand...

Hi, Chris this sounds little complicated
why not use a bi amplifier, 2a3 for mid and high range and a class D for Low range?
 
#50
schiirrn said:
What is "old" for you in that context? Sound Practices era old? Or RCA-still-producing-211-tubes old? If the latter is the case you will have a hard time to find a schematic for a hifi amplifier, as the 211 is a transmitting, not a receiving tube.
Check the schematic for the Western Electric 43A amplifier; it used 211s for sound reproduction.
Click to expand...

Western Electric 43A use 211 in PP, it would be interested to know what is the impedance of the output and the frequency response..
 
You must log in or register to reply here.
Top Bottom