EF86 when used as a triode

[microx]

When an EF86 is strapped as a triode which double triode half is it most similar to.
From what I can see it would be ECC83/12AX7. I want to make a stereo G7 but use only one tube.
Steve

 

[mcs]

The gain of a EF86 triode stage is typically about 20-30 times, which is lower than the 12AX7. So I don't think they are that close.

I think a 2C51 or ECC85 would be closer - or perhaps the ECC40?

Best regards,

Mikkel C. Simonsen

 

[PRR]

There isn't any triode quite like the EF86's triode mode.

But the circuit isn't real fussy.

You do need a low plate resistance. That rules out 12AX7.

Offhand, 12AU7 will work. If you have octal space, I'd use 6SN7. 6DJ8 or other tuner twin-triode should work too.

Watch heater power and case heat on the larger tuner twin-triodes.

Any different tube will need some trim of the cathode resistor. Jakob may have a better idea how it should bias, but I'd aim for plate voltage about 1/2 to 2/3 of supply voltage.

 

[NewYorkDave]

The 12AV7 has a low plate resistance and about enough gain. It could be worth a try.

 

[microx]

Thanks for that guys.
I guess I will try the 12AU7 (ECC82) the 12AV7 has no European eqivalent although there are plenty in the surplus shops in the USA.
Transport will be more than the tube.
Steve

 

[gyraf]

The only dual-triode that I know of being suited for a condenser microphone is the 12AY7/6072 as used in AKG C12 and ELAM 250.

Jakob E.

 

[microx]

How is it used in the C12, cascade, strapped or just one section, or point me to a schematic,
Steve

 

[gyraf]

AKG mic Schematics, incl. C12:

http://www.geocities.com/SiliconValley/Peaks/5212/start.htm

Jakob E.

 

[microx]

Perfect ,it even uses a higher ratio transformer (looking at the .5mfd coupler) just like I want to use. Looks like I building a stereo C12.
Thanks to all,
Steve

 

[Gus]

IIRC the AKG C24? uses a 6072a cathode biased.

 

[microx]

Nope!
Looks like I am building a C24.
Steve

 

[Guest]

[quote author="microx"] an EF86 is strapped as a triode [/quote]
at 1,1 mA anode current:
2 mA/V transconductance
2,25 kOhm noise resistance.
Source: Pfeifer, Electronisches rauschen

xvlk

 

[CJ]

Most EF86's will protest having the screen that high.
So for triode, you would have to run a pretty low B+.
This is especially true of the Sevetlana version.
cj