What I am looking for is a recommended NOS twin triode in the "standard" noval pinout (12AU7 etc.) for a cathode follower.
I know about the standard forum recommended 6N6P (not NOS) and 5687 (different pinout). I know 12AU7 is often called an "OK" CF tube but I was wondering if there was something better. Larger heater draw or different voltage is no problem.
I know about the standard forum recommended 6N6P (not NOS) and 5687 (different pinout). I know 12AU7 is often called an "OK" CF tube but I was wondering if there was something better. Larger heater draw or different voltage is no problem.
The figure of merit is gm, but you also have to consider desired drive current- a tube with 1mA of plate current won't drive a 1k load very well no matter how high the gm. For general purpose applications, it's tough to do significantly better than the ECC88 if you're limited to a dual package.
Hi Stuart,
Indeed.
If more Pa and/or more Ia and/or more Ea-k is necessary than ECC88 could stand, the noval dual triode ECC99 might be of interest.
Regards,
Tom
SY said:For general purpose applications, it's tough to do significantly better than the ECC88 if you're limited to a dual package.
Indeed.
If more Pa and/or more Ia and/or more Ea-k is necessary than ECC88 could stand, the noval dual triode ECC99 might be of interest.
Regards,
Tom
Hi,
Totem pole an ECC88 into a White CF and drive nails.
This modified White CF (mWCF) has an output Z of 100 ohms
(though repeatedly with various brands, it's about 120 ohms)
You heard it last year at Dave's I believe (back porch).
Cheers!
Totem pole an ECC88 into a White CF and drive nails.
This modified White CF (mWCF) has an output Z of 100 ohms
(though repeatedly with various brands, it's about 120 ohms)
You heard it last year at Dave's I believe (back porch).
Cheers!
oldeurope said:Good moring,
I recommend the ECC83 12AX7.
Kind regards,
Darius
It is generally not a good choice for a CF. Besides the low gm, the current is low which means available drive current is very low- try to swing more than 0.1mA and distortion will rise precipitously.
oldeurope said:I think the input impedance of the next stage is 50KÙ.
Thus the ECC83 has the lowest loss in gain. (0,98 @2mA)
This is why I like the ECC83 here.
Kind regards,
Darius
At 2mA, you'll have some grid current issues with actual 12AX7s.
The gain for an ECC88 in this position is 0.97. The difference between that and a tube with a mu of 100 is less than 0.1dB.
SY said:
At 2mA, you'll have some grid current issues with actual 12AX7s.
The gain for an ECC88 in this position is 0.97. The difference between that and a tube with a mu of 100 is less than 0.1dB.
Hello,
for 2mA at 240VDC you have -1,5V. Where is the problem?
Kind regards,
Darius
Hello SYOriginally #15 posted by SY
Put one on the bench and do some measurement with non-zero source impedance.
The source has a high impedance this is why I use a cathode follower.
Scroll down here:
http://radio-darius.blogspot.com/
V10 is the cathode follower V9 is its constant current draw.
Kind regards,
Darius
The source has a high impedance this is why I use a cathode follower.
Exactly. That's why you want bench tests of the CF to be taken with the CF being driven by a high source Z. The distortion spectrum will be illuminating, and the source of the distortion will be evident as you look at the spectrum while reducing the driving source Z.
thanks
whow yes, the D3a looks good. µ(g2)=80 and high transconductance.
Kind regards,
Darius
Hello panos29,Originally #18 posted by panos29
Not exactly cheap and not even double triode, but D3a and E280F are definitely excellent (maybe the best?) for cathode followers when triode strapped and even better in pentode mode CF.
whow yes, the D3a looks good. µ(g2)=80 and high transconductance.
Kind regards,
Darius
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