6G2 Princeton transformer-YET AGAIN!!

Discussion in 'Shock Brother's DIY Amps' started by Uncle Daddy, Jul 22, 2021 at 9:27 AM.

  1. Uncle Daddy

    Uncle Daddy Tele-Afflicted

    Posts:
    1,803
    Joined:
    Sep 26, 2015
    Location:
    Maldon, England
    This is getting a bit much now!

    After I got on to the kit supplier, he's kindly sent me a replacement transformer (Classictone 40-18078) which should fit the Mojotone 6G2 chassis.

    Specs- 710v or 660v C/T @ 100ma

    But, I still have the Classictone 40-18112, and I've adapted the chassis to fit.

    Specs- 650v C/T @ 70ma

    Which would be the best choice for the 6G2 with a 5y3 rectifier. Looking for that fabled 315v!

    The Mojo756EXVLV (330v @ 75ma) is still out of stock.

    Thanks
     

    Attached Files:

  2. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    3,940
    Joined:
    Dec 30, 2019
    Location:
    california
    The 40-18112 would be closer. Tough to get 315V B+ out of it though. Probably a bucking transformer would be best to reduce the B+. Other methods to reduce the B+ would eat into the available 70 mA.

    The 40-18078... other methods for reducing B+ could be used and still have enough to power the amp.
     
    King Fan likes this.
  3. Uncle Daddy

    Uncle Daddy Tele-Afflicted

    Posts:
    1,803
    Joined:
    Sep 26, 2015
    Location:
    Maldon, England
    Thanks. What kind of difference would the 100mA vs. 70mA have on the performance? I guess the more powerful trannie would run cooler, but would it affect the tone much?
     
  4. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    3,940
    Joined:
    Dec 30, 2019
    Location:
    california
    Well you wouldn't want to put 6L6 tubes in either one.

    I think it would depend on how you push the amp. If you mostly play clean the 70mA is fine. It would be similar to the original amp. @King Fan and I don't have a problem with original type amps. Those low power small OT amps have a deserved reputation. They are what they are.

    The 100mA could be pushed all the time. The make it take it shock brothers would prefer the 100mA.

    In your situation, if you decide to reduce the B+ to 315V with the use of resistors or diodes, some of the power will be lost to heat. That will take up extra mA so the 100mA PT would have to be used.
     
    Uncle Daddy likes this.
  5. Uncle Daddy

    Uncle Daddy Tele-Afflicted

    Posts:
    1,803
    Joined:
    Sep 26, 2015
    Location:
    Maldon, England
    This build has a 12" driver. Would the 100mA drive the bottom end harder? I'm concerned that the basic tone control might find extra bottom end too much.
     
  6. bebopbrain

    bebopbrain TDPRI Member

    Posts:
    98
    Joined:
    Feb 5, 2021
    Location:
    New York City
    Here is a helpful guide to power supplies: hammondmfg.com/pdf/5c007.pdf

    There is one called "Full wave choke input load".

    If you use the 710 VAC transformer then you will have 710 * 0.45 = 319 VDC. You have to consider the drop in the diodes, so solid state might make sense. That would get you down to 315 VDC with extra current (154mA) on tap.

    Crazy, right? I have one choke input amp and I love it. For high gain amps, it is ideal.
     
  7. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    3,940
    Joined:
    Dec 30, 2019
    Location:
    california
    ?? Not all 12" guitar speakers have a lot of bass. The cathode bypass caps, coupling cap RC filters and changes in the tone stack can reduce bass in the circuit. Bass takes power. If you want more bass you know what you gotta do. The OT may not be big enough or designed to produce bass so there is that.
     
  8. Uncle Daddy

    Uncle Daddy Tele-Afflicted

    Posts:
    1,803
    Joined:
    Sep 26, 2015
    Location:
    Maldon, England
    I probably wasn't very clear! I have this notion that the PT with 100mA rating will lean the amp towards having more bottom end, which I wouldn't be able to dial down only having the single tone control. My big iron Princeton Reverb is often set with the bass rolled almost off to get the amp's eq right, something I couldn't do on the 6G2 without cap mods. I'm not a fan of a huge bottom end!
     
    Lowerleftcoast likes this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.