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Guess That Tube

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SY

SY

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Joined 2002
SYclotron.com
Wow, there's some pretty esoteric guesses!

But the winner is bigwill, with a VERY mundane choice- 12AX7. Despite the knocks, if that tube is run using the lightest possible load, it is impressively linear. Taking it up to the measurement levels up to the 19.8VRMS used in my 5692 (heavy duty 6SN7) tests, the second was still better than -65dB, third and higher below -100dB. That's better than a 6SN7 can do.

The circuit was a single red LED in the cathode and a bipolar current source for a plate load. Test current was 0.8mA. Using my resistor trick to increase LED current had no effect on distortion or gain- the CCS works as advertised.

Show me a DHT with this sort of linearity and kind harmonic distribution and I'll start taking them seriously.
 
Globulator

Globulator

Member
Joined 2004
cutestudio.net
SY said:
The circuit was a single red LED in the cathode and a bipolar current source for a plate load. Test current was 0.8mA. Using my resistor trick to increase LED current had no effect on distortion or gain- the CCS works as advertised.
Click to expand...

So I'm listening to this phono amp with 12AX7s in two stages, each with 270k anode and 4.7k cathode resistors - if I soup this up to a red led and CCS should it sound better? (I.e. should the distortion fall?).

If so - please provide the exact details of the CCS you measured with please, ideally with a diagram for the ignorant, as someone may want to implement it :)
 
SY

SY

Ex-Moderator
Joined 2002
SYclotron.com
rdf said:
Boooo, that was my first guess but because it went without reply I went the next closest octal equiv based on the 'class' hint. It'll take a CCS on the plate and CF on the output to make a 12ax7 run that sweet. Booooo.
Click to expand...

Ahhhh, you're just jealous of bigwill.:D The "class" hint was supposed to drive people toward DHTs, but that didn't work.

Actually, these results point to use as a voltage amplifier to drive a split load inverter for pp EL84. I'm thinking of rebuilding the RLD to use a 12AX7 to a 6DJ8. A bit more open loop gain will drop the source impedance.
 
Wavebourn

Wavebourn

Member
Joined 2006
wavebourn.com
Globulator said:
So I'm listening to this phono amp with 12AX7s in two stages, each with 270k anode and 4.7k cathode resistors - if I soup this up to a red led and CCS should it sound better? (I.e. should the distortion fall?).

If so - please provide the exact details of the CCS you measured with please, ideally with a diagram for the ignorant, as someone may want to implement it :)
Click to expand...

CCS would not help if you don't have a light load.
 
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