|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
96.227.141.114
In Reply to: RE: Too low plate R value for a triode ? and CCS substitution? posted by Eric Chan on March 22, 2017 at 08:53:34
"You mean 1250 ohm just enough for the job ?"
Eli means 1250 ohm is good enough for the job.
Follow Ups:
If you want to try a CCS plate load a cascode MOSFET would be a good choice (K&K Audio sells a convenient kit). This CCS works best with about 30V across it. That would leave 28V for signal swing. A CCS load should result in lower distortion. My only caveat here is that my experience with 6N30s is they like more voltage on the plate; 80V seems kind of low. In my preamp (differential with CCS "tail") the OP is 150V@25mA.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
To the point I made that 80V seems kind of low, I have a Sun 2A3 amp that I modded with CCS loads for the input and driver stages. I kept the input tube 6SN7 but changed the driver to a 6BX7. Because of voltage constraints I had to run the BX7 at 120V p/k instead of the more usual 250V - 300V. Still, with the CCS load the amp sounded very good; much better that stock. One caveat: as the tube ages the plate voltage will increase (bias current fixed by the CCS and thus the bias voltage across the cathode resistor too). As emission falls plate voltage must increase to maintain bias current. This will "eat" into the signal voltage headroom. This can be compensated for by small tweaks to the CCS (decreasing the current). In my case this is critical, in yours maybe not so much if you have lots of extra headroom to begin with.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
Hi JKT, What kind of CCS do you use?
Depends on the application. For plate loads it's hard to beat the simplicity of the cascode MOSFET. K&K Audio's kits are very convenient and cheap. Highly recommended. The IXYS MOSFETs that Kevin uses sound better in this application than DN2540s. Do note that these CCSs work best with currents in excess of 10mA and voltages greater than 30V across them. Although I have had good results using them as plate loads for 6SN7s with only 4.5mA. As to the voltage, in addition to the 30V for the CCS you will need to allow for the signal swing. E.g. if you require 20V peak to peak signal swing then you would need 50V across the CCS.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: