|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
In Reply to: Re: triode EL34 and true triodes posted by Richard CWY on August 13, 2002 at 19:53:56:
Hi,Pardon me for popping in.
In a pentode most of the performance is determined by cathode, control grid and screen grid. It is the voltage at screen grid that gives ampl. factor and current for a given voltage at control grid.
One may vary the plate voltage quite a lot without having any significant difference in performance (known as high internal resistance).
So when using tetrodes, beam tetrodes or pentodes it is the DC supply for the screen grid that is the important part. [If one looks inside an radio set the output pentode most often has a very raw DC supply for the anode, but more filtered for the screen. And so quite little hum though the PSU is basic or less.] Good news is that screen grid draws little current and so are easy and cheap to filter well (YMMV).
Follow Ups:
The BRUTE the president of an audiophile club I belong to uses for an amp is a good illustration of Pär's point. The man uses a 250 WPC ARC amp. There are 20 6550s in beast. 8 tubes per channel are the O/P devices; the remaining 4 tubes serve as voltage regulators for the O/P tubes' screen grids.
Eli D.
That's what you have to get right. As you say luckily it's fairly easy. Some designs use a series regulator tube for the screen supply, and I bet the sound great. Might even try it one day.
Hi,Do by all means try a series regulator tube :-)
I only have one such an amp (an ARC D-51 (?)) but I don't really like it. But it is probably not due to regulation...
This post is made possible by the generous support of people like you and our sponsors: