251 schematic with 6S6B-v triode, launching the project.
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rock soderstrom
Tour de France
That's good to know, thanks for sharing your experiences. What about distortion, do you have a comparison to a transformer with a higher step down factor?
Yes, with 200K anode load a transformer => 10:1 would probably be more suitable
rock soderstrom
Tour de France
I have just had another look at the data sheets. The 6S6B and also the 5718 are pretty current potent little beasts. The 6072 and especially the AC701 don't quite come close...
I've got another pair of tube mics with 6S6B and 10:1 transformers but the circuit is slightly different (higher plate and cathode resistors) and the transformers are quite smaller compared to the Bv11. So I don't know how fair this comparison would be... But will check.
Seems like using a 200K anode load a transformer is a good inquiry.
I'm just trying here to cross informations
A friend of mine sold me a old stock of old Russian OTK 6ZH45B-V (pentode)
they can be connected as triodes and have a very low self noise.
He advised me:
- 6.3v heater tubes
- 125V K/cathode
- Ri is low = ~5K
- Just fine tune it to low voltage one ple (use larger plate resistor - maybe 200k or more) - after the resistor should be about 30-40v or less
- Preferable transformer ratio for 6Zh45B-V is 5:1 or 6:1 \ 7:1 10:1 will work, but gain will be lower,
- 6Zh45B-V - amplification factor is relatively low (mu
is about ~23-25), with low Rp, so low ratio transformer is preferable.
- It is about Rp \ Ri in triode mode
so you can use lower ratio transformer,
They will work fine with the usual ratio transformers because they are quiet.
Generally RL should be higher than Ri at least 5 times to get full gain, some say 10 times, but over 5 is actually close to full gain,
Best way to adjust the operating point - including voltage drop - is to measure the actual mic
For 6S6B you can also use 6:1 or 7:1 transformer, it's Ri is also quite low,
Here is an approx formula for triode: Ri = mu×(1/gm) mu25×(1/5gm)= ~5-6k
Seems like the 6Zh45B-V in triode mod works pretty much the same way as the 6S6B-V
These informations are in some ways, out over my curent knowledge.
Maybe you guys make sens out of this?
Best
I'm just trying here to cross informations
A friend of mine sold me a old stock of old Russian OTK 6ZH45B-V (pentode)
they can be connected as triodes and have a very low self noise.
He advised me:
- 6.3v heater tubes
- 125V K/cathode
- Ri is low = ~5K
- Just fine tune it to low voltage one ple (use larger plate resistor - maybe 200k or more) - after the resistor should be about 30-40v or less
- Preferable transformer ratio for 6Zh45B-V is 5:1 or 6:1 \ 7:1 10:1 will work, but gain will be lower,
- 6Zh45B-V - amplification factor is relatively low (mu
is about ~23-25), with low Rp, so low ratio transformer is preferable.
- It is about Rp \ Ri in triode mode
so you can use lower ratio transformer,They will work fine with the usual ratio transformers because they are quiet.
Generally RL should be higher than Ri at least 5 times to get full gain, some say 10 times, but over 5 is actually close to full gain,
Best way to adjust the operating point - including voltage drop - is to measure the actual mic
For 6S6B you can also use 6:1 or 7:1 transformer, it's Ri is also quite low,
Here is an approx formula for triode: Ri = mu×(1/gm) mu25×(1/5gm)= ~5-6k
Seems like the 6Zh45B-V in triode mod works pretty much the same way as the 6S6B-V
These informations are in some ways, out over my curent knowledge.
Maybe you guys make sens out of this?
Best
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