ferrite beads

Posted by Lew (A) on February 27, 2014 at 08:15:58

In Reply to: RE: Klyne, Beveridge system posted by AJ on February 26, 2014 at 16:42:00:

Good idea. Bill Thalmann actually did that already on my Bev amps. There are four resistors that link the solid state input stage to the tube output stage. Two 1K resistors go respectively to the grids of two of the 4 output tubes (grid-stoppers). The other two are 7.5M and go to the cathodes, I think, of the bottom tubes in the totem pole arrangement. Bill put ferrite beads on the afferent leads (where the resistor leads solder to the input board and before the body of the resistors) of all 4 resistors, early on, in our attempt to quell oscillation. It definitely helped. Then I installed a shield made with TI Shield (Texas Instruments), between the input/driver board and the output stage board, in each amplifier. I really think that what may have happened with the one amp that is giving trouble is that I installed four new output tubes in that amp, which probably brings up the transconductance and enhances the tendency to oscillate. So, something more is now needed. Like I said, the other amp, still on its original tubes, does not oscillate and sounds excellent. The other thing I did that probably does not help was to bypass a 10uF electrolytic that is used as a coupling cap with a 0.1 uF teflon film cap. Possibly the electrolytic was deliberately chosen to limit bandwidth and reduce the tendency to oscillate, until I "tweaked" the circuit and thereby created problems of wide bandwidth. But as a true audiophool, I could not tolerate an electrolytic coupling cap.

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Follow Ups Full Thread

Topic - Klyne, Beveridge system - airheadair 09:20:46 02/25/14 (20)

RE: Klyne, Beveridge system - Michael Samra 01:52:50 03/01/14 (12)

Your model 3s - Lew 08:06:36 03/03/14 (11)

RE: Your model 3s - AJ 14:19:20 03/03/14 (10)

RE: Your model 3s - Lew 16:45:40 03/03/14 (9)

RE: Your model 3s - Michael Samra 17:10:10 03/04/14 (0)

RE: Your model 3s - kentaja 08:05:59 03/04/14 (4)

RE: Your model 3s - Lew 08:38:18 03/04/14 (3)

RE: Your model 3s - kentaja 11:09:07 03/04/14 (2)

RE: Your model 3s - Lew 18:56:59 03/04/14 (1)

RE: Your model 3s - kentaja 06:48:08 03/05/14 (0)

RE: Your model 3s - c1ferrari 20:05:48 03/03/14 (2)

RE: Your model 3s - Michael Samra 11:22:31 03/12/14 (1)

RE: Your model 3s - c1ferrari 17:32:44 03/12/14 (0)

RE: Klyne, Beveridge system - AJ 16:42:00 02/26/14 (3)

ferrite beads - Lew 08:15:58 02/27/14 (2)

RE: ferrite beads - AJ 11:52:31 02/27/14 (1)

RE: ferrite beads - Lew 14:35:19 02/27/14 (0)

Sorry I missed your earlier post. - Lew 11:46:25 02/25/14 (2)

RE: Sorry I missed your earlier post. - airheadair 08:37:21 02/26/14 (1)

RE: Sorry I missed your earlier post. - Lew 10:50:55 02/26/14 (0)

Follow Ups

ferrite beads - Lew 08:15:58 02/27/14 (2)

RE: ferrite beads - AJ 11:52:31 02/27/14 (1)

RE: ferrite beads - Lew 14:35:19 02/27/14 (0)

ferrite beads

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