Hi!
Yes, you are absolutely correct. I was assuming that the driver cannot swing the voltage needed. If it is as you describe, just a matter of gain, I see the only disadvantage the reduced reachable output power.
I do like such tubes (well maybe except the 6C45Pi which I yet have to hear in a amp or preamp which convinces me). But only for purposes where they are strong, amplifying small signals for example in a phono stage.
I have heard combinations of low output impedance sources, driving a TVC or input transformer which resulted in poor sound. Some combinations work though. <just a low output impedance on paper, does not mean it will sound good when loaded inductively.
Best regards
Thomas
Yes, you are absolutely correct. I was assuming that the driver cannot swing the voltage needed. If it is as you describe, just a matter of gain, I see the only disadvantage the reduced reachable output power.
I do like such tubes (well maybe except the 6C45Pi which I yet have to hear in a amp or preamp which convinces me). But only for purposes where they are strong, amplifying small signals for example in a phono stage.
I have heard combinations of low output impedance sources, driving a TVC or input transformer which resulted in poor sound. Some combinations work though. <just a low output impedance on paper, does not mean it will sound good when loaded inductively.
Best regards
Thomas
Tell me why, Thomas !
So what do you recommend for this case ?
I personally prefer 6J5-6BX7 in driver for some DHTs like 2A3, 300B.
Rgds,
Hi!
Just my observation, that doesn't mean it is true for all combinations.
I have not tried for example the Tribute TVCs for high impedances which work well for many.
Best regards
Thomas
Just my observation, that doesn't mean it is true for all combinations.
I have not tried for example the Tribute TVCs for high impedances which work well for many.
Best regards
Thomas
Without feedback you need about 30 to 40x gain so I would go for a single stage, using a triode straped pentode, something like 6J43 (you can buy for $1) or C3g or many other incredible tubes. I would not go for a 6C45pi as it works with quite low voltages, not giving the headroom you'll need. Also sounds a bit dry.
If you use 2A3 to drive 2A3, then you get distortion cancellation and don't have to worry about gain or voltage swing. 5842 -> 2A3 -> 2A3 should perform very well.
True but I think any modern DAC could drive a 1:2 input transformer. Or even use the balanced outs from the DAC and use a 1:1+1 to double voltage, then a DHT driver could be used with a gain around 10 like the 4p1Le.
I guess for a 2A3 I would want to avoid a "super" late 60' triode/pentode strapped triode while keeping it two stage. Cause really I would be listening to the D3A or whatever late 60's technology sound instead of classic DHT sound?
I wouldn't want a three stage 2A3 either. If I was going that far it would be for a 300B or maybe further to a Gu70.
I'm just on the fence with it cause I have a little 5842/D3A amp and I know how those tubes "sound", they just tend to have a different harmonic distortion spectrum than I want from a DHT amp. Would rather just go 6L6 or EL34 SET if I wanted the late 60's SET sound ( and save a lot of money.)
I am sort of go all DHT or go home when it comes the the 45 and 2A3 but I'm just looking at it from a design perspective and don't have the hands-on eperience with DHT's like most here.
Hi!
This distortion cancellation scheme pops up every now and then. But I don't really see how this could work well. Both tubes would amplify different levels of signals. Distortion rises to the square of the signal level. So how can it cancel? Propbably second order distortion cancels most but that would leave 3rd order dominating. Is that really what you would want?
It also does not work necessarily with intertage transformer coupling. Some intertage transformers like the tango NC20F are very sensitive to the polarity. If you wire it to get the distortion cancellation, HF response will suffer.
Best regards
Thomas
This distortion cancellation scheme pops up every now and then. But I don't really see how this could work well. Both tubes would amplify different levels of signals. Distortion rises to the square of the signal level. So how can it cancel? Propbably second order distortion cancels most but that would leave 3rd order dominating. Is that really what you would want?
It also does not work necessarily with intertage transformer coupling. Some intertage transformers like the tango NC20F are very sensitive to the polarity. If you wire it to get the distortion cancellation, HF response will suffer.
Best regards
Thomas
Hi!
I can only restate my experience. There are cases where it works well and there are combinations which sound poor. Especially watch out any DCoff set and how the input transformer can handle it.
Best regards
Thomas
I can only restate my experience. There are cases where it works well and there are combinations which sound poor. Especially watch out any DCoff set and how the input transformer can handle it.
Best regards
Thomas
you may find my thread on 6av5 distortion useful.
Take a look at the spectrum of 6j52p's driving 6av5 triodes in pp, 6av5 are said to be near equivilents of 2a3s when triode connected. The 52p's are in a diff pair so 2nd harmonic should cancel but they are loaded by 12k5 so SE with a ccs you perhaps could get lower distortion. And we're talking 0.065% at 1 W here folks.
Take a look at the spectrum of 6j52p's driving 6av5 triodes in pp, 6av5 are said to be near equivilents of 2a3s when triode connected. The 52p's are in a diff pair so 2nd harmonic should cancel but they are loaded by 12k5 so SE with a ccs you perhaps could get lower distortion. And we're talking 0.065% at 1 W here folks.
Thomas, "Cancellation" is probably a poor choice of terminology. It would be better described as distortion "Reduction" or "Partial Cancellation".
In my experience it is rather sensitive to bias condition, and requires tweaking to achieve optimal results.
I have achieved over 20dB reduction in 3rd harmonic (with other odd harmonics reduced as well), and George reported over 30dB reduction.
http://www.diyaudio.com/forums/tubes-valves/200384-closed-loop-stability-help-needed-5.html
While it is possible to adjust the bias to achieve a lot of upper harmonic reduction (at the expense of increased 2nd Harmonic production) I don't think it would be stable over time and would require periodic adjustment.
In my experience it is rather sensitive to bias condition, and requires tweaking to achieve optimal results.
I have achieved over 20dB reduction in 3rd harmonic (with other odd harmonics reduced as well), and George reported over 30dB reduction.
http://www.diyaudio.com/forums/tubes-valves/200384-closed-loop-stability-help-needed-5.html
While it is possible to adjust the bias to achieve a lot of upper harmonic reduction (at the expense of increased 2nd Harmonic production) I don't think it would be stable over time and would require periodic adjustment.
For driving the 2A3, I like the 12AX7 family direct coupled. I've tried several tubes over the years and this for me is my favorite, and very easy to implement, no coupling cap, not expensive IT. It may be a boring tube to some but in this application, it gives the right amount of dynamics, detail, and of course, drives the DHT just fine.
I'm working on my second amp with this configuration now.
Jim
I'm working on my second amp with this configuration now.
Jim
For my last amp based on 6C4C DHT I used triode connected E180F with cascode CCS. That is the best line stage/driver so far.
Hi!
That's what I would expect and that is something I try to avoid in amplifier designs. I want the amp to sound stable over a wide range of bias points and from tube to tube and as tubes age.
In your case, if I read correctly, you used different tube types with different a,plification factors. That might be easier possible to find a combination which provides some cancellation or reduction. But at cost of the mentioned instable sound. With the same tube type cascaded as suggested above I don't see how this is reachable.
Best regards
Thomas
That's what I would expect and that is something I try to avoid in amplifier designs. I want the amp to sound stable over a wide range of bias points and from tube to tube and as tubes age.
In your case, if I read correctly, you used different tube types with different a,plification factors. That might be easier possible to find a combination which provides some cancellation or reduction. But at cost of the mentioned instable sound. With the same tube type cascaded as suggested above I don't see how this is reachable.
Best regards
Thomas
Hi!
An interesting tube!
VinylSavor: Tube of the Month: The 843
Would require some means to get the gain up though. Either by use of an input transformer or another stage
Thomas
An interesting tube!
VinylSavor: Tube of the Month: The 843
Would require some means to get the gain up though. Either by use of an input transformer or another stage
Thomas
Hi Thomas,
Seems you like 801A/VT62 very much. Do you compare sound quality between these tubes and 45 tubes when they are power tube ?
Seems you like 801A/VT62 very much. Do you compare sound quality between these tubes and 45 tubes when they are power tube ?
Hi!
If you read my blog, you will realize that I would never assign the sound qualities of an amp to the output tube only. Too much depends on many other things of the amp. This is especially true for the 801A family of tubes. These react very sensitively to the filament supply, output transformers and matching to the speakers. Not implemented properly a 801A can sound thin and wiry, almost screechy, especially in preamps. If properly taken care of, it will sound very detailed and neutral, preserving all the colors. Tubes like the 45 or 2A3 (or 26 in preamps) are much more forgiving to the filament supply.
For some the 801 can be almost too neutral and they prefer the euphonics of a 45. I'm also torn between 45 and 801A amps. I like both for their strenghts
Best regards
Thomas
If you read my blog, you will realize that I would never assign the sound qualities of an amp to the output tube only. Too much depends on many other things of the amp. This is especially true for the 801A family of tubes. These react very sensitively to the filament supply, output transformers and matching to the speakers. Not implemented properly a 801A can sound thin and wiry, almost screechy, especially in preamps. If properly taken care of, it will sound very detailed and neutral, preserving all the colors. Tubes like the 45 or 2A3 (or 26 in preamps) are much more forgiving to the filament supply.
For some the 801 can be almost too neutral and they prefer the euphonics of a 45. I'm also torn between 45 and 801A amps. I like both for their strenghts
Best regards
Thomas
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ECC99 datasheet mu is 22. I'd guess real-world mu would be about 18 or 19.
A 2A3 with plate-cathode voltage of 250V and plate current of 60mA (15W plate dissipation) will have a grid-cathode voltage of -44V (approximate).
So with 2.5V peak input, you could drive the 2A3 to full output with an ECC99, but with not much headroom.
Use of a line amp with gain may be desirable, in which case, why not integrate that into a 3-stage amp with input selector and volume control? The two driver stages could then be operated well within their max limits under all operating conditions.
PS - What's wrong with using a higher mu tube into a cathode follower, driving the 2A3?
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