Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders.

---

[ Follow Ups ] Thread: [ Display  All  Email ] [ Tube DIY Asylum ]

---

[ Alert Moderator ]

---

Re: Diferential EL84 (ala John Swenson) strange findings

Posted by John Swenson (A) on November 24, 2005 at 23:39:21

In Reply to: Diferential EL84 (ala John Swenson) strange findings posted by kenev on November 24, 2005 at 07:46:40:

Hi Evangelos, that level of audio peaking sounds very unusual. I had mine oscilate at 77MHz when I didn't have screen stoppers in place, but that seems a little bit out of the range of what you are talking about.

My guess is that its related to some resonance with either the input or output transformer, my first guess would be the input transformer. Are you using the 124B? If yes try taking it out of the circuit and see what happens. My guess is the impedance or capacitance of whatever is driving the amp is not working well with the transformer. If your preamp has enough gain you don't need the transformer, its just there because I was using a passive preamp and a DAC that had a lower than usual output.

BTW I hope you are using a bit more negative voltage than what is used in the V2 schematic. With the BBMCCS (or the selfbias CCS which is what I use) I use a -30V supply. The V3 schematic shows the self bias CCS.

If that doesn't work let me know and we can do some serious debug here.

John S.

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

VH Audio

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2025, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---