|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
72.211.153.103
In Reply to: RE: 20B fun without Nreaking the Bank... posted by PakProtector on January 19, 2017 at 09:27:34
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
Follow Ups:
"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.
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: