Re: Gary Pimm - a question....

Posted by Gary P (A) on August 31, 2001 at 15:37:32

In Reply to: Gary Pimm - a question.... posted by JeffreyJ on August 31, 2001 at 14:22:06:

It took 2 things to make it stable.

1. RF grounding. I used 2 .01uf 1500V ceremic caps right at the C4S. One goes between the ground wire and the B+ wire from the power supply. The other goes from the ground wire to chassis ground. This provides a low impedance to ground in the RF range but doesen't mess up the semi single point ground scheme (in theory ;-}).

2. A 27pf 500V ceremic disk cap between the base and collector of the upper MJE350 transistor (the one that conects to the 2N2907). This slows down the transistor a bit. Value may need to be adjusted for each circuit layout.

I had listened to mine for over a week before I realized that it was oscilating. It was putting about 300mv p-p on the plate of the 45's. About the only thing I noticed after controlling it was the background was a little quieter.

Hope this helps. I'll try to get some photos of the new version of output C4S's on my website this weekend.

Gary

My crude little web page ;-} (Open in New Window)

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Follow Ups Full Thread

Topic - cheap amp w/ line txs from RS - larry moore 07:21:54 08/28/01 (16)

Active load instead of plate chokes - JeffreyJ 15:25:32 08/30/01 (0)

Re: cheap amp w/ line txs from RS - Scholl 05:42:40 08/30/01 (0)

Anyone? - uW 08:34:28 08/29/01 (13)

Re: Anyone? - Gary P 15:24:55 08/30/01 (5)

Gary Pimm - a question.... - JeffreyJ 14:22:06 08/31/01 (4)

Re: Gary Pimm - a question.... - Gary P 08/31/0115:37:32 08/31/01 (3)

Re: Gary Pimm - a question.... - JeffreyJ 23:22:15 08/31/01 (2)

Re: Gary Pimm - a question.... - Gary P 09:58:40 09/1/01 (1)

Thanks, Gary (nt) - JeffreyJ 14:51:59 09/4/01 (0)

I've been thinking about this too.... - Pete Millett 10:20:01 08/30/01 (4)

And now for the math... - uW 11:14:23 08/30/01 (3)

I'll try and descibe the circuit... (long) - Pete Millett 14:01:06 08/30/01 (2)

Good grief! - uW 14:16:09 08/30/01 (1)

Looks like I have a project for the weekend.... - Pete Millett 15:51:52 08/30/01 (0)

Re: Anyone? - larry moore 09:46:41 08/29/01 (1)

Mmmm Interesting. - Anthony Dockrill 22:42:15 08/29/01 (0)

Follow Ups

Re: Gary Pimm - a question.... - Gary P 08/31/0115:37:32 08/31/01 (3)

Re: Gary Pimm - a question.... - JeffreyJ 23:22:15 08/31/01 (2)

Re: Gary Pimm - a question.... - Gary P 09:58:40 09/1/01 (1)

Thanks, Gary (nt) - JeffreyJ 14:51:59 09/4/01 (0)

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