C3M 300B mono block project.

Discussion in 'Tube Gear' started by Tleung, Jun 18, 2018.

  1. @billfort they are on the bench. :)

    This is another project I promised Bill that we will do it together 8 years ago. Finally I got the bug to build. I order all the filament transformers and power transformers today. I am going to mount the filaments trans on a L shape aluminium. Using the double turn on switch method by J-rob.

    I am going to build this based on the GA Italian C3M 300B all credit go to Fabrizio Cappelleti.
    I am thinking of adding a switch for Triode and Pentode. I hate drilling on stainless steel. I need to dill another hole at the back plate to accommodate the extra switch. I just put the rubber layer in between the two top plate. I will be bolting it down tomorrow. The transformers will take a week to 10 days to arrive. At the mean time I am shopping for parts online.
    Couple of small items form PartConnexions.
    20180618_230148.jpg 20180618_230118.jpg

    Attached Files:

    guiller, marantzfan and Redboy like this.
  2. marantzfan

    marantzfan Administrator Staff Member

  3. Hi marantzfan you are more than welcome to jump in. I am not an expert in electronic like the rest of the guru. I am the best a copy cat. I was going to build the first mono block and adjust it to my liking and Bill will come by my house and we will build his mono block.
    TubeHiFiNut and marantzfan like this.
  4. billfort

    billfort Administrator Staff Member

    Oh oh, I have no more excuses; guess I better dust off my pile of parts and get started on this.
    Redboy likes this.
  5. Well guess what Bill. I just got a call form the store I order the tranny. They all arrived :). Going to pick them up this afternoon. Also need to buy some Hammertone spray paint to repaint the bell ends. I guess I will start the build sooner than I planned.

    This is the colour I am thinking.

    TubeHiFiNut likes this.
  6. TubeHiFiNut

    TubeHiFiNut Administrator Staff Member

    Time to get busy..... ;)
  7. billfort

    billfort Administrator Staff Member

    That should look good with the brushed stainless. I'm going to stick with black for the iron and caps on mine - existing bits are still in reasonable shape under the dust (I think!).

    Like the plan to add a second switch for filament warming - never worried about it with the indirectly-heated CV378 rectifiers we used first time around but for flexibility and given the price of the 300Bs we'll be plugging in this thing, it makes much sense. Looks like it will be easy enough to put the 2 switches in the existing punched plate holes and to drill another for the fuse on the other side of the cord socket.

    Are those our original brass binding posts? Think I'll go with something all copper this time around.

    Aside from drilling the fuse hole, the main issue I have with my existing chassis is enlarging the driver tube hole which would require a large ($ :) ) stepped bit that I don't have - think I better bring my chassis down to your shop sooner than later. :D

    I have our original Hammond 159P chokes for the PS but also have a pair of 193Js, which might fit under there but will be a bitch to squeeze in - think they are worth the trouble?

    I bought a pair of Hammond 182H9s for the C3m filaments way back - will these still fit the plan?

    (now you got me started...)
  8. I need to paint the bell ends because mine was dented.

    How about these binding post. and matching RCA

    You can come down anytime this weekend. I should be free.

    The 159P will be a better option. 193J too big to go under.

    The 20V filaments will be fine.

    Do you also use a seperate 5V filament trans for the 300B?

    Attached Files:

  9. billfort

    billfort Administrator Staff Member

    Posts are still brass though. I think I have a pair of the Cardas solid coppers here but not sure about input jacks - better check.

    I have separate 5v CT trans - Hammond 166MS
  10. I changed my mind. I am going to leave the transformer stock color. My second pair OPT do not have dents. Save me some time. I am ordering some end bells to replace the dented one. Just order the Cathode resistors, trying out a new kind. Need to order 2 DPST form Partsconnextion. Going to go thru my collection see what resistor I have and what is missing. I am using solid core cloth wire like my last built. Just pickup 4 pieces X2 supressor .01uf caps also.
  11. billfort

    billfort Administrator Staff Member

    May I suggest you just X2 everything you need to get? I'm good for it, promise. :)
    marantzfan likes this.
  12. Sure Bill no problem.
  13. marantzfan

    marantzfan Administrator Staff Member

    If it wasn’t for a national border, I’d say X3. ;)
  14. I can collect some smaller part for you also. like 4 pieces X2 supressor .01uf caps. Or some chicken head nobs for the hum pot. I assume that you already have most of the parts right?
  15. billfort

    billfort Administrator Staff Member

    If these sound the way the first pair of C3m>300Bs sounded that Tony built to this formula, it might be good to try rolling a pair of these Anthony.
  16. billfort

    billfort Administrator Staff Member

    My parts box is pretty much set by where we ended up with that 300B build way back when - and since we went through so many driver tube iterations, I might be in reasonable shape.

    I completely forgot I built a pair of those mahogany & stainless chassis for you - I'm actually further along than you are I guess. :)


    Looks like you are upping the PS filter capacitance though.
  17. Yeah you are way ahead. I am still cutting holes from the insulation. Next will be adding grommets to the holes.
    I just grab what I have on hand as the PS caps. They are 15uf and 2x 70uf. On the first C3M 300B build I use double chokes. One on the +V and one on the -V. I am not going to do that for this build. I can add it on later. based on the last build seem to be using double choke give me a better bass performance.
  18. Redboy

    Redboy Knobophobe

    Woo hoo, a build thread! :)
  19. marantzfan

    marantzfan Administrator Staff Member

    Bill, do you mind sharing with me the size/shape of the chassis you guys are using?

    I know you both used steel, but I’ll likely go with aluminum as I’ll be hacking up mine in my garage with hand tools. :)
  20. Redboy

    Redboy Knobophobe

    Looks like the same basic layout as those partially finished plates I sent you awhile back, Anthony. :)

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