Yes it can...
just so we know what sort of record is, that amp works better with a low input impedance. Your pre can't tolerate it. Your pre can only tolerate input impedances around 2 orders of magnitude higher.
I await your discovery that a solid, low output impedance, valve design that allows you to return it to low input impedance configuration sounds better.
cheers,
Douglas
...well, feel free to make some practical design suggestions and post some resulting schematics...
That is has near zero chance of success. That 12AX7 has *NO* business in such a circuit. Find a set of 12-20k plate to plate to 600R CT secondary OPT. A watt or three should be sufficient. Load a 6C54Pi LTP with them. Ground one grid, apply SE signal to the other. You will need several 6C45's for matching stock...as Match is critical.
Chicago BOH-2, or Peerless S-217-D should do well for the OPT's.
cheers,
Douglas
Interesting that you are going with a push-pull drive primary winding.
My concern would be with the need for proper layout (RF) within the build to limit possible oscillations from the high Gm tube.
I still like 6922 or 5687 step down LL1660 4.5:1 as an option. Probably 6922 at 10mA and 90V plate, which would run from a 100V B supply, better match for the LL1660 Rp wise IME as well. Single tube, no matching of multiples, shielded sections, lower Gm, high enough gain and current drive, low Zout.. but taking nothing away from your concept/design/reality - that is one ballsy line drive stage.
Tigerscent, if you were needing a single 6922 or 5687 - let me know, I can also throw in a nice mcmurdo 9pin teflon socket.. my shout, postage included.
Hanze.
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My father once told me that at some point I would run into a build that made me want to put the stopper right inside the glass bottle. Even with 6C45's it has not happened yet...
cheers,
Douglas
Well, what I could come up with is that the Russian 6C45 is regarded as a 'super-tube' by some and has the following characteristics:
High Mu single triode
Low plate resistance
High transconductance
High linearity
Very low input/output capacitance
Low noise
Very quiet
Low gain
High current
Very Low impedance
Comparison with 12AX7
15 12AX7 dual tubes would need to be paralleled to get the noise voltage down to one single 6C45
High gain in comparison
6C45 specs: http://frank.pocnet.net/sheets/112/6/6S45PE.pdf
12AX7 specs: http://www.mif.pg.gda.pl/homepages/frank/sheets/093/1/12AX7.pdf
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... it plays well with other tubes.
Obviously the 12AX7 isn't designed for low impedance output. It is designed for gain, like the first stage of an amplifier. Just the same as asking a signal tube to compete with a 6BQ5A. I was thinking of comparing it to a 6L6GC, but that is too far removed.
The 12AX7A is designed for high impedance circuits and these days we are used to thinking more lower impedances - hence the popularity of the 6922 and later darlings of audio design. A different design philosophy entirely. But like anything, it's just a part. Each part has strengths and weaknesses and isn't a "bad" part compared to another that has different characteristics. Something like the 12AX7A compared to a 6922 (or whatever).
In other words, I wouldn't use a 12AX7A to drive an output that was low impedance.
When I was growing up, we used the 12AX7A. Later people began using the 6DJ8 (cheap UHF tuner tube, microphonic as heck). At some point they smartened up and began using the 6922. But this happened after tube design for audio had pretty much died, then restarted again. Only this time, the engineers and techs were in a low impedance frame of mind and new 12AX7A designs weren't that successful. They were using them for low impedance circuits (from the point of view of the 12AX7A tube). It wasn't until the use of a lower voltage, higher current tube (6DJ8 / 6922) was used were they able to get positive results. Since then "we" have pursued tubes that operate in ever lowering impedance environments. Of course now, many sneer at the 12AX7A tube - but only because they don't know how to use it. Especially true of low to no feedback designs. This was as unnatural for audio circuit design as was using a 6DJ8 was in earlier times. Yes, the 6DJ8 was considered a "garbage tube" back in early days of audio design.
No matter your viewpoint, the 12AX7A was a highly engineered tube, the same can be said for the 6EU7 (a 12AX7A further engineered for lower noise, etc.). The same can be said for the 6922 as far as overall quality is concerned. I still think the 6DJ8 is a "garbage tube" designed for UHF service in consumer television sets. It did it's job just well and cheaply enough for it's widespread use in TV tuners. Who remembers channel 13?
Instead of arguing against the 12AX7A, why not simply concentrate on the positive attributes of your choice of tube? Don't make examples by mis-using the 12AX7A, which is really silly.
-Chris
Obviously the 12AX7 isn't designed for low impedance output. It is designed for gain, like the first stage of an amplifier. Just the same as asking a signal tube to compete with a 6BQ5A. I was thinking of comparing it to a 6L6GC, but that is too far removed.
The 12AX7A is designed for high impedance circuits and these days we are used to thinking more lower impedances - hence the popularity of the 6922 and later darlings of audio design. A different design philosophy entirely. But like anything, it's just a part. Each part has strengths and weaknesses and isn't a "bad" part compared to another that has different characteristics. Something like the 12AX7A compared to a 6922 (or whatever).
In other words, I wouldn't use a 12AX7A to drive an output that was low impedance.
When I was growing up, we used the 12AX7A. Later people began using the 6DJ8 (cheap UHF tuner tube, microphonic as heck). At some point they smartened up and began using the 6922. But this happened after tube design for audio had pretty much died, then restarted again. Only this time, the engineers and techs were in a low impedance frame of mind and new 12AX7A designs weren't that successful. They were using them for low impedance circuits (from the point of view of the 12AX7A tube). It wasn't until the use of a lower voltage, higher current tube (6DJ8 / 6922) was used were they able to get positive results. Since then "we" have pursued tubes that operate in ever lowering impedance environments. Of course now, many sneer at the 12AX7A tube - but only because they don't know how to use it. Especially true of low to no feedback designs. This was as unnatural for audio circuit design as was using a 6DJ8 was in earlier times. Yes, the 6DJ8 was considered a "garbage tube" back in early days of audio design.
No matter your viewpoint, the 12AX7A was a highly engineered tube, the same can be said for the 6EU7 (a 12AX7A further engineered for lower noise, etc.). The same can be said for the 6922 as far as overall quality is concerned. I still think the 6DJ8 is a "garbage tube" designed for UHF service in consumer television sets. It did it's job just well and cheaply enough for it's widespread use in TV tuners. Who remembers channel 13?
Instead of arguing against the 12AX7A, why not simply concentrate on the positive attributes of your choice of tube? Don't make examples by mis-using the 12AX7A, which is really silly.
-Chris
My father once told me that at some point I would run into a build that made me want to put the stopper right inside the glass bottle. Even with 6C45's it has not happened yet...
cheers,
Douglas
Sounds like you were fortunate to have a good mentor.
I've struggled to get D3a stable at VHF, I needed to go to some considerable effort to have it clean on the scope up to several MHz.
To Anatech;
I think the real question comes down to gain structure, how much voltage gain does the OP need ? - what is the input sensitivity of the amplifier to full power, and what is the voltage output of the source component?
No sense in driving a motor vehicle open throttle and then adjusting 'speed' by applying the brake.
I lived with the ME850 for some years with various tube front ends.
Cheers,
Hanze.
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I cant bare it any longer, it's not right to embarrass someone like this. The OP does not understand, but then he never asked to learn anything except an answer to the original question. Which was met with some objection (rightfully), and other suggestions which may or may not have been ignored. Alternate input from 'a certain other' is counter intuitive, self biased, and fails to take the actual application into account.
TigerScent - there is no credible answer to this question, it is akin to asking the number 5 if it is pregnant.
You have been given the best advice, if you go with the PP design as per Douglas, there is no reason to not use a PP to PP transformer and drive the balanced inputs on the ME550 directly - this makes sense.
Having lived with the bigger brother of the same amplifier, I can say that a certain 2H does help (PP action cancels this, and feedback will increase higher order harmonic distortion to achieve lower output impedance, which is a moot point - use a linear tube and forget feedback), and if with line level source, you do not need much voltage gain.
Firstly, is the output of your source balanced?. If not, use a single ended drive stage to a step down transformer. If you use something like LL1660S, you can decide to drive your amplifier through its SE inputs, or configure the transformer to drive the amplifier through its balanced inputs, using the transformer as the phase inverter instead.
Hanze.
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Hanze, I must respectfully disagree with you. TS has asked for a schematic...if I am going to go to that effort, it is going to cost him learning something. IMO, that is a remarkably equitable arrangement.
We are not talking about 5, we are talking about a low output impedance, balanced output linestage. The 12AX7 has no business in that sort of use.
cheers,
Douglas
We are not talking about 5, we are talking about a low output impedance, balanced output linestage. The 12AX7 has no business in that sort of use.
cheers,
Douglas
Thanks Hanze,
Yes, I know the 12AX7 has a high impedance in comparison. I initially thought he made a mistake and meant to say the 6C45...however on further searching I came across this article: Designing Common-Cathode Triode Amplifiers ... which mentions using the 12AX7 and a high input impedance and low output impedance...
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