Low mu triode as DI?

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Blue Jinn

Blue Jinn

Rider of the ARPocalypse
I was wasting time (I know, hard to believe) and came across some cheap (although with shipping not quite as cheap) 6AS7's. They are a low mu (appr 2) high current triode. Using the Plate resistor || plate resistance (I think and I can't offhand remember the abbr.) I'm getting ~200-500ohm Z from the plate follower. I know these are used in headphone amps. Also, with just one stage would be inverting, but don't really see that as a drawback, or otherwise easily remedied. thoughts. I'm looking for a use for some 80v/100mA transformers i have....
 
I was wasting time (I know, hard to believe) and came across some cheap (although with shipping not quite as cheap) 6AS7's. They are a low mu (appr 2) high current triode. Using the Plate resistor || plate resistance (I think and I can't offhand remember the abbr.) I'm getting ~200-500ohm Z from the plate follower. I know these are used in headphone amps. Also, with just one stage would be inverting, but don't really see that as a drawback, or otherwise easily remedied. thoughts. I'm looking for a use for some 80v/100mA transformers i have....

Can't see any point to those valves at all, sorry! I doubt they will have any sonic advantage over the far more heater current friendly 12AU7 (ECC82).

If you want a really low noise valve front end use the 82 with the two sections paralleled and use a low anode load, C: 5k. This would give a gain of 10dB or less I would think. No need for followers to get a 1meg input Z.

I would use a simple voltage doubler circuit to get about 200V HT supply.

I strongly advise Merlin Blencowe's "Designing Tube Preamps for Guitar and Bass". And his later book on power supplies.

Dave.
 
Can't see any point to those valves at all, sorry! I doubt they will have any sonic advantage over the far more heater current friendly 12AU7 (ECC82).

If you want a really low noise valve front end use the 82 with the two sections paralleled and use a low anode load, C: 5k. This would give a gain of 10dB or less I would think. No need for followers to get a 1meg input Z.

I would use a simple voltage doubler circuit to get about 200V HT supply.

I strongly advise Merlin Blencowe's "Designing Tube Preamps for Guitar and Bass". And his later book on power supplies.

Dave.

You're not kidding about the heater current. That's a huge drawback. Tends to offset the really cheap price. They are pretty tubes though. ;-)

The Z out does seem insanely low though and that from a plate out, which is why I thought the DI. With parts I have on hand cheaper than the Hansen Hansn Audio Gothenburg, .

I'll put the book on my birthday list. His website is definitely a go-to!
 
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