C3M 300B mono block project.

Beautiful work. I'll be interested in how you get on with keeping your 300B's quiet. That's something I need to work on myself.
 
Looking good Tony! Been away on business and it looks like I have some catching up to do.

Are you still thinking those big old H-P 4 MFD/1000VDC caps will work well on the c3m screen? Good to know now before I cut holes. :)

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@billfort they are also very good. I just trying a different cap. I have an extra pair of Alfa cap for you if you wish top use them instead.
 
Took me a bit longer because I did not realize that these are mirror image top plate.

That's funny. I guess you forgot all those 'discussions' we had around mirror-imaging 15yrs ago when we laid these things out - the great debate around 'aesthetics' vs. repeatable practicality when we all built 12 pairs of these. Yeah, 'aesthetics' (mirror-imaging) won out and I made it even harder with that (and my) particular chassis pair when I reduced the overall height because I thought them kind of awkward and over-the-top with those big high cocobolo bases. :)

I think that was right before you and I decided to start doing this ourselves and leaving behind the 'design by committee' aspect of group scratch building - too many cooks and all that.

These are looking good by the way!
 
Well it had been awhile since I post the progress on the Mono block. One is completed tonight. I still need to do the adjustment on the Filament voltage and fine tune the B+ but all wires and components are done. Take me a lot longer this build mainly because we have such a beautiful summer I end up spending more time out door. Also I was trying to run all the wire without crossing signal and power. When I finish the second amp I will post a detail explanation on my component selections.
 

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This is looking good Tony! I really like the way you've kept the AC away from signal and I bet if there is half a chance of getting this thing quiet on AC heated filaments, you are heading that way.

Going to copy your layout mercilessly and really look forward to reading your listening impressions, then of coarse hearing these in the flesh-and-blood (yeah I know, that's a different circuit, but certainly related :) ).
 
Last night I finish the smoke test. Nothing blow up :). After some minor adjustment, B+ is at 430V and Cathode is at 63V. with a 1K cathode resistor.

But the C3M Plate voltage is a bit low at 196v instead of 215v. Will get some new dropping resistors and adjust it. Filament at the rectifier is 5.1V and the 300B 5.2V and C3M 21V. all AC.

Measure the output hum with shorting the input give me 5mv I am okay with that. Now I will be finishing the second unit and start my burn in.
 
just me 2 cents (Canadian) .
I'm running C3M-300B for almost 10 years now. Initially I did a lot of tests with C3M driver, ending up with "textbook" mode: 220V Ua, 16mA Ia, 150V Ug2. Sound-wise tube is very sensitive to G2 arrangements. With one resistor from HT to the G2 and cap to the ground, sound was not the best IMO. Much better results I've got with the relatively high current G2 setup.
Currently I'm running G2 network at 7.5mA : 33K from HT to G2 and 33K to the ground, G2 current is 3ma. This config. also allows safely use 250v cap form g2 to the ground (without any tubes (HT load) in place, voltage is not exciting 250v. )
Cap is 22uF/ 250V film. 66K g2 networks double as a shunt for a HT.
 
Thanks @Alexz for sharing your experience. I am still in the middle of adjusting the amp. Trying to get to 220v at the plate of C3m. I am currently running at 20ma at cathode and 3ma at g2.
 
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i wish I could have a listen to your build. If it sounds half as sweet as it looks, it will sound heavenly!
 
Thanks @Alexz for sharing your experience. I am still in the middle of adjusting the amp. Trying to get to 220v at the plate of C3m. I am currently running at 20ma at cathode and 3ma at g2.
20mA is OK, if you have enough HT to load anode 10-12K, otherwise it will be not enough gain, c3m has S 6.5mA/V
I'm loading it with 12K, gives enough gain to drive amplifier direct from CD or phono stage. With 16ma RA(12k) drops 192V + 220v Ua = 412v HT and about 20v for additional RC filtering.
 
Thanks @Alexz for sharing your experience. I am still in the middle of adjusting the amp. Trying to get to 220v at the plate of C3m. I am currently running at 20ma at cathode and 3ma at g2.
oops... just realized that it is 20ma CATHODE... (Ia+Ig2), so you run Ia at about 17ma.
 
Well it is done. Finished the project last night. Well after many tweaking I am finally happy with all the voltage.
B+ on 300B around 420v, 68V cathode with 1K cathode resistor. 215 at the C3M plate 5.5V at cathode with 3ma at G2. I am running around 20ma total. Hum at one amp is 3.7mv and one at 4.8mv.

First impression last night. I love it. The amps are fast with deep and wide sound stage. I cannot judge the tonality yet until they burn in. But the bass and high are more extended than my 310A/300B which is more dreamy like in the mid range. Well time will tell. I will list my part selection on my next post, need to work on it since I had changed many parts before settle into the final amps.

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Well it is done. Finished the project last night. Well after many tweaking I am finally happy with all the voltage.
B+ on 300B around 420v, 68V cathode with 1K cathode resistor. 215 at the C3M plate 5.5V at cathode with 3ma at G2. I am running around 20ma total. Hum at one amp is 3.7mv and one at 4.8mv.

First impression last night. I love it. The amps are fast with deep and wide sound stage. I cannot judge the tonality yet until they burn in. But the bass and high are more extended than my 310A/300B which is more dreamy like in the mid range. Well time will tell. I will list my part selection on my next post, need to work on it since I had changed many parts before settle into the final amps.

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Beautiful amps, Tony. :)

You should be very proud of these. :)

And I'll bet they sound wonderful. :)
 
Ok Tony, that is motivation enough; I'll tell the family that the kid's extra-curriculars are on hold until I spend a few days at the bench in the basement.

Have to drop around for a listen after they cook for a while!
 
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