Home OTL Asylum

OTL, Output Transformerless Amplifier User Group.

[ Follow Ups ] [ Post Followup ] Thread: [ Display  All  Email ] [ OTL Asylum ] [ Return to Search Results ]
[ Alert Moderator ]

The Beveridge amps are so fussy as is....

that I have stuck to every single element of the original schematic, which I was lucky to have obtained from Roger Modjeski a couple of years ago. There are no modifications, except new parts and better capacitors in some cases. I finally got out one of my oscilloscopes and did the dangling coil of wire trick to see if I can detect oscillation. By this criterion there is no oscillation, now. (I fixed one more iffy looking solder joint before that.) So, I am thinking maybe the very low voltage, high frequency AC I am picking up with my Fluke frequency counter is of such low magnitude that it won't be audible. Also, it may always have been there, since I have never used the Fluke in this way before.

What I might do is to move the 1K grid stop closer to the grids they serve. Beveridge built them sitting in space about half way from the input board to the grid pin of the output tube, about 1" to 1.5" from the grid of the driven output tube. I have seen many photos of other Beveridge direct-drive amplifiers; they were all built like that. Even the schematic depicts a distance between the 1K and the output tube grid. (But no distance is stipulated in the detailed schematic.) In this one of my two amplifiers, they are perhaps closer than normal to the input side, which leaves maybe 2" to the output tube. Back when Bill Thalmann did work on these, right after I bought them, he added some ferrite beads between the body of the 1K resistor and the input board, to suppress oscillation. Bill did the same on the 7.5M resistor lead. I haven't messed with that.

This post is made possible by the generous support of people like you and our sponsors:
  Crux Audio  

Follow Ups Full Thread
Follow Ups
FAQ

Post a Message!

 Forgot Password?
Moniker (Username):
Password (Optional):
  Remember my Moniker & Password  (What's this?)    Eat Me
E-Mail (Optional):
Subject:
Message:   (Posts are subject to Content Rules)
Optional Link URL:
Optional Link Title:
Optional Image URL:
Upload Image:
E-mail Replies:  Automagically notify you when someone responds.

[ Top Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]
[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]