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In Reply to: RE: 20B posted by Ralph on January 17, 2017 at 10:32:54
Yes, Ralph, this is fun and educational at the same time. I think?
Mostly fun.
Follow Ups:
Hi Pat,
It can be fun to just throw money at stuff - try stuff out...
But at some point soon, you will find it more rewarding to do some basic learning (theory) of how tube circuits work so you can work some of this stuff out yourself. You can simply apply someone's advice, or you can try and work out the "why"and "how" yourself, seeking guidance along the way. I reckon the second approach will be more rewarding and better for your learning.
What requirements are needed from your triode driver? What restrictions do you have in its implementation. What sonics are looking for - what would you like to be different from your pentode? You will find it helpful - and waste less of others freely-given time - if you know why these questions should be asked and how to start answering them, even if you can't work all the way to the solution.
The approach I take before a build to ask myself *honestly* what the purpose of the build is: Reliability? Nice looking? What sonic presentation? Do I want it to be "special"? What would I like to learn? Then I plan (too much planning, it must be said), design, build, and check it... If it works, great. Sounds great - even better. If not, I troubleshoot and learn some more. But I will try to work it out and understand what is going on - what I need to know.
I don't have much free time to invest in this stuff - I wish I had more - but you apparently do. I'd love in a few months to be coming to you for advice!
Enjoy,
91.
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein
91, yes you are correct. I am trying to learn as I go along. I have been experimenting with several modifications of the amp over the past 8 months. Some mods I understand why/what/how and others I am at a loss and ask many questions. I do read quite a bit, but in the end I do rely upon the good folks at AA for much of the learning experience.
It is fun to learn electronics and apply it.
The purpose of my build is quite simple: I want the best sound possible, to my ears at least. With regards to the current situation, the amp has great dynamics/transients and texture. However, I want to smooth out the sound with a bit of warmth and fullness. So, Dave Slagle was kind enough to point me in the direction of modifying the current 6C6 driver and making it a triode. This was a first step to see if the triode driver moved me in the right direction. Yes, it did indeed. The only issue with the 6C6 driver is that the output is too low, but otherwise I enjoy the sonics. So, I posted this latest post to see what triode driver tubes would do well with the 2A3. It appears that the 20B might be in the right direction. I like the 20B as it would require few modifications from the current schematic and I "might" be able to supply the filament with battery (5V, 1.4A). So, I am learning bits and pieces. Doing research on my own and asking many questions.
I appreciate your response. Keep the good stuff coming.
Pat
Hi Pat,Glad you took my post in the spirit intended - sometimes when rushed I can come off a little abrasive!
Considering your objectives, the 20B would not be my first choice. The 20B should be as clear as a bell, transparent, and direct... probably without etch. But it won't provide that intimate, smooth, tonally dense sound you are are seeking.
The 6C6 should be the ideal tube (gain aside). My system, which also runs a 6C6 driving a 2A3, has a lovely alive, flowing, and textured and natural presentation from the bass and midrange, although there is some high-frequency emphasis (but not etch, ringing or graininess): sibilants seem emphasised on some poorly produced music. But, it is pretty recent and coincides with some other system changes (several actually) - I don't think it is due to the 6C6.
Added later:
I'm curious, can you explain what changes moved you closer to warm and fuller and those that moved you away from it?
Currently, you have some pretty funky stuff going on with the design. I reckon it may have sounded initially appealing/impressive, but may become tiresome with extended listening. I often read of people trying LED and battery bias then returning to more traditional biasing because it sounds more natural. The lack of output tube cathode bypassing greatly increases plate resistance and suggests a much higher tube load is warranted; running a too low a load (like in your current design) can create a rather high distortion, strained, etched sound. The output tubes of both channels is supplied from a single 50uF DC Link capacitor - that seems a little low, even for LSES - I have not used a DC Link, but I'd guess that is not helping your cause either... and the PS might be ringing, which might fake clarity but may become fatiguing with extended listening. But I have not heard these things as a system or independently, so I can't be sure.
My guess is that the sound you are hearing is caused by a few significant issues and layered-on compensation. It is important to make changes progressively and listen to each critically, then relax and listen for an extended period non-critically. Then make a decision as to whether you like the change. Basically, apply reductionist thinking then system thinking.
Looking at the over-all design shown (with 6C6 as pentode) I'd suggest:
Output: trying the Hashimoto at 3.5k load (if it has multiple primary windings) and bypassing the output stage cathode with a balanced-sounding metalised poly cap (NOT Mundorf, except maybe the plain Supreme).
Input/driver: using a larger PIO on the screen bypass (at least 4uF), and trying a traditional cathode 5W R (Mills WW/Kiwame/KOA Speer - if the correct values are avail.) bypassed with a balanced-sounding metalised poly cap.
PS: without some modelling, I can't say. I'd be looking at it though.
I guess what I am suggesting is that you return the amp to "known good" state - one that should satisfy your preferences - then experiment carefully.
All that said, I do wonder about your system's gain structure. If your preamp is outputting circa 17v (that sounds like the max - whether you achieve this depends on the source output and the preamp's gain), then you could drive your 2A3 with a 45 or 2A3! Or just build a different amp specifically designed to meet your needs and wants...
Cheers,
91.
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein
Edits: 01/18/17 01/18/17 01/18/17 01/18/17
91. Thanks for the additional input. You inspired me to re-listen to the 6C6 in pentode mode with a few mods. The link below is an update of where I stand. Your input would be appreciated, if so desired.
Thanks,
Pat
Thanks Pat.
I won't post to the other thread - I am tight for time at the moment.
One last thing though. Your comparo of 6C6 as pentode versus triode should be taken in context of your current build and system only - don't draw absolute conclusions from it. I suspect the pentode is highlighting deficincies in implementation. For example, pentode have low (no!) power supply ripple rejection; if your PS in noisy - and i suspect it could be - the pentode will sound as you have described. A triode has better PSRR. Also, pentodes are sensitive to screen voltage variation and bypassing quality, which will not be ideal in your design. Not trying to defend pentodes or suggest they are better... only that triodes are more tolerant of implementation and that is what you may be hearing.
Continue to enjoy!
Cheers,
91.
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein
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