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Best way to reduce gain in this circuit?
Best way to reduce gain in this circuit?
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Old 28th October 2019, 11:15 PM   #11
chede is offline chede  Germany
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Best way to reduce gain in this circuit?
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
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Old 28th October 2019, 11:52 PM   #12
rayma is offline rayma  United States
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Quote:
Originally Posted by chede View Post
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.
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Old 29th October 2019, 12:22 AM   #13
kodabmx is online now kodabmx  Canada
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Best way to reduce gain in this circuit?
Quote:
Originally Posted by Ketje View Post
Before you make a nice oscillator with Jon's proposal , try it this way.
Mona
I thought the FB would be positive (too good to be true?).

Really though? Simply returning the 1M to output instead of ground? I'll gladly try it...
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Old 29th October 2019, 12:24 AM   #14
kodabmx is online now kodabmx  Canada
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Best way to reduce gain in this circuit?
Quote:
Originally Posted by rayma View Post
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.
In this case, you simply strap the grid to ground and B+ each through 1M resistors.
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Old 29th October 2019, 12:33 AM   #15
TonyTecson is offline TonyTecson  Philippines
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Best way to reduce gain in this circuit?
use a lower mu triode for the gain stage, 12au7, 6gu7, or even 6080....
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Old 29th October 2019, 01:15 AM   #16
kodabmx is online now kodabmx  Canada
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Best way to reduce gain in this circuit?
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.

Last edited by kodabmx; 29th October 2019 at 01:17 AM.
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Old 29th October 2019, 03:04 AM   #17
Tjj226 is online now Tjj226
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Quote:
Originally Posted by kodabmx View Post
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.
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Old 29th October 2019, 04:13 AM   #18
TonyTecson is offline TonyTecson  Philippines
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Best way to reduce gain in this circuit?
Quote:
Originally Posted by kodabmx View Post
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,

you can check this out.....Low-mu preamp
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Old 29th October 2019, 09:11 AM   #19
chede is offline chede  Germany
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Best way to reduce gain in this circuit?
Quote:
Originally Posted by kodabmx View Post
In this case, you simply strap the grid to ground and B+ each through 1M resistors.

Right, sorry ... didn't look at the schematic in post #1 closely enough to see that this was not there yet. In the Aikido, John Broskie had put it in ...


Regards, Claas
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Old 29th October 2019, 03:15 PM   #20
Lampie519 is offline Lampie519  Netherlands
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Put the volume control between the gain stage and the buffer (Floating DC). It does not reduce the gain but it does not ruin your buffer stage.
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