Re: Stereo 70 /removal HF Network - Steve O - Tubes Asylum

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Re: Stereo 70 /removal HF Network

In Reply to: Re: Stereo 70 /removal HF Network posted by chopper87 on July 20, 2002 at 15:15:24:

Regarding feedback about the removal of the feedback/phase comp resistors, I've heard both positive and negative comments with the positive slightly outweighing the negative (but sample size is small). I for one tried the mod using stock circuit but modern parts. Used Dyna A25s and JBL L100s for speakers, POOGED CDB560 was source feeding home made 100K ohm, 24 step passive attenuator. To my ears the amp lost it's smooth, mellow forgiving sound and became somewhat etched with unatural "detail" in the upper registers...clinical may be the word. I changed it back to stock after a few days. Obviously, tastes differ and you may like the sound.
Note that you have something other than a full fledged ST70 on your hands since it is not stock with triode output and decreased overall feedback (I assume by your description of the "larger" feedback resistor which = less overall feedback). Both changes increase the tendency towards stability. Therefore you may well be just fine with your proposed changes. If it were my setup I'd use a scope to take a look at the amp driving the speakers just to be sure there was no serious instability. If everything seems OK, and you like the sound, leave everything in place. If not, put it back.
Two final points: I've never seen a GOOD discusion regarding what to do with the overall feedback values and phase comp caps when using triode outputs. Theory indicates that the values should change but to what? Also, is the 7199 really up to driving the added capacitance of triode connected 6CA7s??? I's a marginal circuit to begin with.
Lastly, the color code for the 18K resistor is Brn, Gray, Or, Silver not Brn,Blk,Or as in my original post. Brain fade strikes every 30 sec...

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Follow Ups Full Thread

Topic - Stereo 70 /removal HF Network - chopper87 13:53:26 07/20/02 (12)

Re: Stereo 70 /removal HF Network - Flyquail56 17:30:46 07/20/02 (4)

Where is JOE ROSEN? - chopper87 06:24:16 07/21/02 (1)

He was quiet for a long period but did post recently (nt) - Metralla 08:07:02 07/21/02 (0)

Re: Stereo 70 /removal HF Network - chopper87 18:25:42 07/20/02 (1)

Re: Stereo 70 /removal HF Network - Flyquail56 06:39:52 07/21/02 (0)

Re: Stereo 70 /removal HF Network - Jim Carlon 16:59:35 07/20/02 (0)

Re: Stereo 70 /removal HF Network - Steve O 14:38:00 07/20/02 (2)

Re: Stereo 70 /removal HF Network - chopper87 15:15:24 07/20/02 (1)

Re: Stereo 70 /removal HF Network - Steve O 18:49:45 07/20/02 (0)

Re: Stereo 70 /removal HF Network - Kico 14:21:34 07/20/02 (2)

Re: Stereo 70 /removal HF Network - chopper87 15:18:57 07/20/02 (1)

Re: Stereo 70 /removal HF Network - Kico 17:08:56 07/20/02 (0)

Follow Ups

Re: Stereo 70 /removal HF Network - Steve O 18:49:45 07/20/02 (0)

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