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How to get more drive out of an 01A DHT?

2P29L I found to be fairly neutral, quite smooth. I found the treble unexciting, and generally I was rather bored by it. I'm sure this is doing it a disservice, because smooth and neutral are positive virtues. I can't remember everything about it and I should audition it again. I don't remember many negatives, but nothing that made me want to go further with it. I remember thinking it was about 90% of a 10Y or 01A. That may not be such a bad thing!
 
Input capacitance rises when you triode strap a penthode. Why not use a penthode connected EL12 to drive your final? So you have a three stage amp but the 01 should easily drive the EL12 which in turn can drive a big load. Perhaps the like-drive-like principle could be of interest.
 
2P29L I found to be fairly neutral, quite smooth. I found the treble unexciting, and generally I was rather bored by it. I'm sure this is doing it a disservice, because smooth and neutral are positive virtues. I can't remember everything about it and I should audition it again. I don't remember many negatives, but nothing that made me want to go further with it. I remember thinking it was about 90% of a 10Y or 01A. That may not be such a bad thing!

I have the 01a Amplifier built with source follower & it really doesn't detract from the sound I was getting before, in fact it improved dynamics & bass control the only reason I'm not using it now is microphonics, I get no hum either, it would obviously have to be powered from your existing B+ but then so would the other methods mentioned here. I think from memory I have been running them at 15mA each & Ale mentioned that He runs them at 10mA. They aren't that difficult to implement either.
 
andyjevans, I understand that 01A is a nice sounding tube. But, if you add a cathode follower after it, will it not degrade the sound? Would it not be better to use a slightly less nice sounding tube with a bit better drive capabilities and do without the cathode follower? Or, is a cathode follower such a benign circuit?
 
I agree Ale, source followers IMO take nothing away. They do give an added benefit of the possibility of A2 and hence no blocking distortion at higher levels.

Of course with a cathode follower using an indirectly heated valve even if it is a high Gm pentode triode connected you are also driving the the heater-cathode capacitance. Which to a small degree is also slightly diode like due to the high temperature of the ceramic coating between the heater and cathode.

How about Rod Colman's shunt cascode with the 01A?

Cheers
Matt.
 
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I agree Ale, source followers IMO take nothing away. They do give an added benefit of the possibility of A2 and hence no blocking distortion at higher levels.

Of course with a cathode follower using an indirectly heated valve even if it is a high Gm pentode triode connected you are also driving the the heater-cathode capacitance. Which to a small degree is also slightly diode like due to the high temperature of the ceramic coating between the heater and cathode.

How about Rod Colman's shunt cascode with the 01A?

Cheers
Matt.


01a hasn’t got enough gm to work in a folded cascode topology am afraid:

DHT Folded Cascode Experiments – Bartola(R) Valves
 
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Some years ago I measured CCS loaded 01a (201a) with SIC follower.
 

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I've been getting on with other things, though still using 01A into EL12n (mostly).

I haven't yet put in a cathode follower - sounds pretty OK at lowish volumes without. But I really should try something out. I was thinking something simple and generic with an ECC99. Does this draft idea look OK? Any useful tweaks I should make? The maximum h-k voltage is 200v. Ideally I ought to raise the heaters. I chose 8mA to give adequate current and keep a 20K resistor to ground. Reading Morgan Jones it seemed important to make this resistor as large as possible.
 

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I've been getting on with other things, though still using 01A into EL12n (mostly).
I read your earlier comments about wanting to get more drive from the 01A. And it seems that more drive = more current. Please forgive my technical ignorance but . . .

I've heard people say that a particular output tube needs a certain amount of voltage from the input tube in order to provide full power output. But I've never heard anyone say that an output tube needs a certain amount of current from the input tube to produce full power.

Since your preferred input tube, the 01A, has a mu of 8 and you're using a 2v source, does that mean it can only supply 16v to the output tube? If not, how much voltage can it provide?

How much input voltage does the EL12N need to produce full power?

If the EL12N needs more voltage than the 01A can deliver, and your priority is to use the 01A, why not try a different, more sensitive, output tube instead of switching to a different input tube?

I might be able to offer a suggestion but I want to make sure I understand the concept of drive requirements first.
 
Thanks for the post. To be clear - the 01A is working fine at lower voltages into the EL12n, since I don't listen loud. A more sensitive output tube isn't necessary. A mu of 15-20 is enough for my system and I know of no power tubes of minimum 18W dissipation that have a higher mu in triode.

So what I'm doing is researching performance at higher volumes where slew rate may come into it. Now, to be frank I know very little of slew rate. Also it was my understanding that more current was needed to cope with the input capacitance of the output tube.