Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Ed_Chambley on October 03, 2011, 08:58:15 am

Title: JTM 45 Board Layout
Post by: Ed_Chambley on October 03, 2011, 08:58:15 am

I have a kit from Mojo and I was reviewing Metro Build instructions.  I noticed there is a difference in the board layout. There is a 16uF e-cap on the metro board and seems to connect to pin 8 of V2, whereas pin 8 on the Mojo kit connects to series of resistors and caps.  Anyone know what the difference is?

Title: Re: JTM 45 Board Layout
Post by: sluckey on October 03, 2011, 09:42:24 am

Quote from: Ed_Chambley on October 03, 2011, 08:58:15 am

I have a kit from Mojo and I was reviewing Metro Build instructions.  I noticed there is a difference in the board layout. There is a 16uF e-cap on the metro board and seems to connect to pin 8 of V2, whereas pin 8 on the Mojo kit connects to series of resistors and caps.  Anyone know what the difference is?

That 16uF cap on the Metro board connects to V2-6, not V2-8. And that agrees with the schematic. V2-8 connects to the resistors and cap for the tone stack. I don't have the Mojo layout/schematic, but I bet both are electrically equal even if the layouts vary slightly.

Having a Mojo kit and reviewing the Metro instructions 'may' cause confusion. I would stick with the Mojo instructions.

Title: Re: JTM 45 Board Layout
Post by: Ed_Chambley on October 03, 2011, 11:39:20 am

I appreciate the sticking with the Mojo layout.  I have built a few JTM-45's from Metro, but they no longer offer kits.  I as just being curious as to why this cap was placed on the board.  I am "generally" following the Mojo layout.  I am adding a VVR and moving one of the 32 caps to the top of the chassis where it will wire under the board.  This shortens the wire considerably and with couple of underboard connections all you are left with 2 wires to connect and a ground.   I have done this before and it reduces hum a bit, plus it cleans up the power section considerably.  You are correct in the pin 6, it does connect there and also connects to the 32/32@500 which is now under the board.  I guess it is a different way of doing the same thing.  I am wondering if having a separate cap has any benefit.

Title: Re: JTM 45 Board Layout
Post by: sluckey on October 03, 2011, 11:53:51 am

Quote

I am wondering if having a separate cap has any benefit.

One benefit is that it allows you to put the cap near the circuit it feeds.