251 schematic with 6S6B-v triode, launching the project.

[Murdock]

I got a 7:1 Bv11 in my M49c clone with 6s6b and the output impedance is around 200 ohm and has great bass response. So it works.
A 10:1 transformer would be more suitable for higher plate resistor and lower current.

 

[rock soderstrom]

I got a 7:1 Bv11 in my M49c clone with 6s6b and the output impedance is around 200 ohm and has great bass response. So it works.

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?

A 10:1 transformer would be more suitable for higher plate resistor and lower current.

Yes, with 200K anode load a transformer => 10:1 would probably be more suitable

 

[rock soderstrom]

A 10:1 transformer would be more suitable for higher plate resistor and lower current.

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...

 

[Murdock]

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

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.

 

[Papa Tango Charly]

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

 

[Papa Tango Charly]

If you can't notice, you placed that capacitor between R6 and ground (in series with R6 - have i said anything about that, anywhere?).

Do you see / have any connection to R5 and R5, from the non-grounded terminal of that capacitor?

And please, read through that article i linked:


Spoilers: R4 and R6 are supposed to form a (DC) voltage divider...

Ok, here it is, hope is good now, Thank you for your advise Khron. Best

 

[ZHOUJUN]

If you like full, detailed low frequencies, 5718 is a good choice. In the M49 structure, I feel that its tone is very close to AC701, and 5718 also works well with T14. I will try building my M251 with the 5718.