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Best way to reduce gain in this circuit?

kodabmx

Member
Paid Member
2011-10-31 1:00 am
Toronto
The input is capacitor coupled (not shown).

I'm thinking NFB, but I'm used to driving NFB into a cathode, and this circuit inverts... What about using the unused grid or the cathode of the same triode?

Any idea are appreciated. And yes, I know 2 cents for a 2 resistor divider is also a solution...
 

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Tjj226

Member
2012-12-02 2:49 am
I wouldn't use NFB on a preamp. It just seems like an unnecessary complication when all you really need to do is tweak the circuit to accept an input tube with a lower amplification factor. 5687s for instance are cheap and have an amplification factor of 15 compared to 22 on the 6N14P.
 
I use a choice of 6N6P, 5687, E182CC, E80CC, ... in my Aikido as the first stage to vary gain.

No rewiring, I use adapters I bought off the big auction site (used to build my own adapters, but there are nice ones available).

Look for example for "E182CC to 6H30 Vacuum tube adapter socket". The seller I bought from also did some custom adapters for me at my request.

Need only to change cathode resistors for the first valve to re-set the bias curent to the desired value. I have socketed the cathode resistors ... ;)

I can also easily re-configure the Aikido as buffer / ACF if I need no gain by just taking out the first valve and inserting a small MKP capacitor into the socket to route the input signal directly to the buffer stage. In your circuit in post #1, that would be inserting a cap between pin 7 and pin 6 of the socket for the first valve. :)


Regards, Claas
 

rayma

Member
2011-04-29 8:37 pm
I can also easily re-configure the Aikido as buffer / ACF if I need no gain by just taking out the first valve and inserting a small MKP capacitor into the socket to route the input signal directly to the buffer stage.

That would remove the bias DC voltage from the upper grid, which is
normally provided by the input stage, and the buffer would not work.
 

kodabmx

Member
Paid Member
2011-10-31 1:00 am
Toronto
12AU7 would result in virtually the same gain though... 6080 is silly because it has crap linearity, and it's heater requirements... 6GU7 is slightly better (never heard of it before, thank you.) but still almost as out of touch as using a step down transformer. Voltage divider seemingly for a low cost solution. The rest are past the point of diminishing returns IMO.
 
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Tjj226

Member
2012-12-02 2:49 am
Different pinout though... And they weren't cheap the last time I bought them (which is why I switched to 6N6P)

I'd rather use a 2 resistor divider on the input that rewire the sockets.

I don't know what prices are like in canada, but here in the US I can find them for ~20 bucks on ebay.

But in any case, I am sure there has to be some tube out there that you can pretty much plop in and cut the gain down without rewiring the sockets.
 

TonyTecson

diyAudio Moderator Emeritus
2003-05-29 2:57 am
Maybunga, Pasig City
12AU7 would result in virtually the same gain though... 6080 is silly because it has crap linearity, and it's heater requirements... 6GU7 is slightly better (never heard of it before, thank you.) but still almost as out of touch as using a step down transformer. Voltage divider seemingly for a low cost solution. The rest are past the point of diminishing returns IMO.

silly 6080? tell that to Peter Millette, :D

you can check this out.....Low-mu preamp