Renovation of fifty years old tube amplifier - Page 2

Wavebourn · 2nd June 2009, 09:29 PM

So, no reason, just "after"....

McGyver · 2nd June 2009, 10:06 PM

I heard several times Dynaco ST35 and I liked it very much. It was good enaugh reason for me to do it that way.

Wavebourn · 2nd June 2009, 10:08 PM

Quote:

Originally posted by McGyver
I heard several times Dynaco ST35 and I liked it very much. It was good enaugh reason for me to do it that way.

But it had also a local feedback, from an output tranny to screen grids, it is very significant. More deep global feedback could cause instability on high frequencies.

cheap-Jack · 3rd June 2009, 04:00 PM

Quote:

Originally posted by McGyver
I heard several times Dynaco ST35 and I liked it very much. It was good enaugh reason for me to do it that way.

Hi.

Yes, it is a very good approach to bypass the entire tone-control stages as they surely render the sound "horrible". Likewise, I bypassed the entire line+tone-control stages of my 50-year young stock Dynaco PS-2 preamp.

You have done everything right. But you can still make it sound better by converting the PP powerstage from pentode to triode by simply connect the G2 of each EL-84 to its plate with a 100R resistor. I guarantee you will find it sound more transparent, more airy & more musical.

This is what I have done with my 50-year young stock Dynaco ST-70 which sounded "horrible", "fat" & "slow" like what you just described. Like you, I hate vintage sounds.

I triode-strapped the EL-34 Ultra-Linear PP with a more complex Vg2 level shifter, switchable from triode-UL. Yet I've left it triode-strapped mode for ever since day one of its upgrade. I've also reduced the 20dB global loop NFB to 10dB. This offsets somewhat the reduced O/P power after triode convertion.

Listening is believing. Triode sounds so much more musical than pe tode.

c-J

Wavebourn · 3rd June 2009, 04:30 PM

Sure, if to tie screen grids to anodes less global feedback may be needed.

McGyver · 3rd June 2009, 04:45 PM

Yes, I LOVE triode sound. But REAL triode, and not triode-strapped pentode. Especially direct heated triodes are magical. I'm using upgraded ukrainian monoblocks based on 6B4G DHT in PSE, and I love it. And Braun amplifier goes to one of my friends. Maybe I'll install triode-pentode switch. No need to drill, becaude there are 3 unused switches on the frontpanel.

WBS · 4th June 2009, 04:52 AM

Nice work. It is a very clean looking amp.

I would never have guessed it was 50 years old! 50 year old American equipment looks 50 years old.

planet10 · 4th June 2009, 05:22 AM

Nice looking amp...

dave

Miles Prower · 4th June 2009, 05:52 AM

Quote:

Originally posted by Wavebourn
Congratulations!
Everything is fine, except what for did you lower feedback?

May be because he doesn't like that "solid statey" sound you get from too much gNFB?

Wavebourn · 4th June 2009, 05:53 AM

Quote:

Originally posted by Miles Prower

May be because he doesn't like that "solid statey" sound you get from too much gNFB?

2nd June 2009, 09:29 PM	#11
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	So, no reason, just "after".... __________________ If I disappear suddenly, that means I finally created a time machine and pushed wrong button that brought me to Stalin's Russia. In any experiment any result is the result. Even if it is negative.

2nd June 2009, 10:06 PM	#12
McGyver diyAudio Member Join Date: Nov 2004 Location: Poland	I heard several times Dynaco ST35 and I liked it very much. It was good enaugh reason for me to do it that way. __________________ http://www.audiosurgery.beepworld.pl/dacki.htm

3rd June 2009, 04:30 PM	#15
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	Sure, if to tie screen grids to anodes less global feedback may be needed. __________________ If I disappear suddenly, that means I finally created a time machine and pushed wrong button that brought me to Stalin's Russia. In any experiment any result is the result. Even if it is negative.

3rd June 2009, 04:45 PM	#16
McGyver diyAudio Member Join Date: Nov 2004 Location: Poland	Yes, I LOVE triode sound. But REAL triode, and not triode-strapped pentode. Especially direct heated triodes are magical. I'm using upgraded ukrainian monoblocks based on 6B4G DHT in PSE, and I love it. And Braun amplifier goes to one of my friends. Maybe I'll install triode-pentode switch. No need to drill, becaude there are 3 unused switches on the frontpanel. __________________ http://www.audiosurgery.beepworld.pl/dacki.htm

4th June 2009, 05:22 AM	#18
planet10 frugal-phile(tm) diyAudio Moderator Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III Blog Entries: 5	Nice looking amp... dave __________________ community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA


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4th June 2009, 04:52 AM	#17
WBS diyAudio Member Join Date: Jan 2007	Nice work. It is a very clean looking amp. I would never have guessed it was 50 years old! 50 year old American equipment looks 50 years old.

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