|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
50.80.146.114
In Reply to: RE: You can do it with a 6C6... posted by Ralph on January 17, 2017 at 09:20:16
Hi Ralph,
Thanks for the input. I am currently using a 6C6 and want to move away from it. I want to use a triode (not a pentode wired for triode).
WHile the battery bias is ideal, I would certainly forego it if necessary to get a triode driver.
Any thoughts on a 4-pin triode such as a 20B?
Pat
Follow Ups:
~!
The Mind has No Firewall~ U.S. Army War College.
The type 841 is fairly low gm, resulting in high plate resistance. The 20B has a lot of gm for a single element( as opposed to a TL304 ). The HY40 comes close, and the 65 Watt cousin HY51 eclipses it.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Don't rule out pentodes just yet. The type EL84 is a fine signal pentode. Gain is determined by delivered gm at your operating point and the load resistance. Output impedance is approximately the load resistance, but with available gm in that tube, a reasonable gain can be acquired without exceeding 10kOhm...:)
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Hm- complications.
The mu is sufficient... I'd give it a shot- just remember you're having fun, right?
for my latest build I wanted an all DHT front end. I thought
about EML's 20B, but I just couldn't see paying that cost...
My solution was to use the Type 26 DHT. ..........
A single 26 can drive a 2A3 or a 45......caveats are 1) you must use
DC filaments to lower hum. and 2) the gain from a single Type 26 is not
much.
I use 2 stages of Type 26's cap coupled and both 26's on a common filament supply. This arrangement allow 1) Twice the gain for the output
tube and 2) provides Humbucking noise canceling for the filaments..
My amp has all AC filament heating.
Have fun
Willie
HY40 is very comparable. Mu is a bit higher, and gm a bit lower. Thoriated cathode instead of coated...:)
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
... with the hi plate voltage and filament requirements the HY40 sounds more like an output tube than a input/driver tube.
I think I'll stick with the Type 26..
Willie
I suppose it pays to collect such stuff as it becomes available...and the only reason I'd worry about the 'power tube' flavor is in its cathode heating requirement. That it will tolerate HV, and substantial plate dissipation is of little consequence. Besides, it is only about 30% bigger than the 20B which was put up as a potential signal tube solution.
Along with the HY40, there is its bigger, higher gm cousin the HY51A and HY51B which are also not easy to find...:)
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
I am going to have to agree here with Jeff-Dennis
If you have a low-mu tube you will never get the dynamic quality (dymanic contrasts) it will sound like all other SE amplifiers limp whet noodle?
I discovered this 16 years ago with my then WE 300b tubes and tube amplifier these low-mu 6sn7 tubes just dont have the getup and go like a higher mu 6sl7! or other higher mu tubes.
once you discover this for yourself you will never look back
I am speaking from experience here just like jeff and Dennis
my current SE amplifier uses a very hi mu tube 300!! LED biased and the gm70 final tube is also biased with LEDS!!!
Now there is nothing wrong with LED Bias actually if you look into why you will see several advantages one i will mention here is when you LED bias you get to full mu of the tube! and you remove rk bypasses and the rk!!!
Have a blast i am
Lawrence
"when you LED bias you get to full mu of the tube! "
You do? How?
The gain of a stage can only reach the mu of the tube when the total load impedance is infinite. A very high total plate load will get you close to the mu. A CCS plate load, either direct coupled to the following stage or RC coupled with a very high grid resistor, will get you close.
So back to my question, what does LED bias have to do with the gain of the stage?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
That tube, likely a 6HV5 or one of its cousins has a ridiculous amount of gm; 65 mA/V which for a mu of 300 delivers a plate resistance of around 5kOhm. compared to the 60kOhm plate resistance of a 12AX7...it is quite small.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Lawrence,
Good to hear that others are using LEDs to bias the tubes. Please tell me, how and what specific LED parts are you using the bias the final tubes? Curious how you get enough current for the finals using the LEDs.
Pat
Hey Pat, just like you did on your driver tube, you needed 4v bias and since some of the the red led's are 2v VF you can get your bias the current will fall into place but if you want to know for sure your trusty DVM in series measuring the Current this will tell you exactly what you need to know and that is the cathode currentIn mine I put 55 LED's in series and there is 5 in parallel to bring the slope resistance down, each of these red led's should have a slope resistance of 2ohms or so. even though my added slope resistance is around 20ohms it sounds really good, now i can parallel more say 20 to bring it down around 5ohms and i may try that but you have to be careful if there is not enough current running through the led you can have differing slope resistance (higher) so at or around 7-10 ma each Led is good
I bought my led's for .02$ each so 1000 leds for like 20 bucks!!! very cheap to make very good bias, cheaper then good quality dale or whatever resistor
if you want to know where i got them contact me privately
Lawrence
Edits: 01/20/17 01/20/17 01/20/17
And this has what to do with a very fine, thoriated tungsten triode?
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Yes, Ralph, this is fun and educational at the same time. I think?
Mostly fun.
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
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: