Building Mojotone Princeton Reverb Kit

[yahoo]

Hello.  I am currently building a Mojotone Princeton Reverb kit.  Just about done and would appreciate any feedback on the work I have already finished or any modifications that may make the amp better.  Specifically, would appreciate insights on the grounds I have installed; I've read that soldering ground wire to the back of the pots might not be best.  Hope to test it out next week sometime.  Thanks in advance. 

[mresistor]

I'm curious,, is there a reason for mounting the cap can so high into the chassis?  There are high voltages present on that cap can's terminals and having it mounted so high makes them more exposed, I think I'd lower it down and I mount mine flush or nearly flush with the chassis.


It looks like you have terminated the power cord ground wire to the ground for the cap can and I see there is a terminal mounted on one of the pt ground bolts that is unused. The ground wire of the power cord should have it's own separate bolt to the chassis and have some slack in it, and nothing else should be fastened to that bolt and it's best practive to not use a transformer bolt, but drill a new hole for the power cord ground bolt.  The PT center tap and filament center taps should be terminated at the same ground point as the cap can, ie the power supply central ground.


I know others will come along and give good additional guidance to you on circuit grounding. 

[mresistor]

Soldering the ground wire to the back of the pots makes it more difficult to replace a pot in the future.  It also applies heat to the case of the pot and some feel that's not a good thing to do.  Many people suspend the ground wire in the space between the board and the pots with the wire rigid enough to be suspended without any support other than the pots, but some use insulate terminals to suspend it.  But many people have soldered the wire directly to the back of the pots as you have. I did it in the past but stopped doing that a long time ago thanks to information from other forum members.

[mresistor]

The ground wire for the pots terminates at the input jacks.  I also like to tie the preamp grounds to that wire as you have done.  All the preamp grounds should terminate at or very near the input jacks.

[tubeswell]

Many people suspend the ground wire in the space between the board and the pots with the wire rigid enough to be suspended without any support other than the pots.

NB, simple method for neatly straightening and tensioning solid core single strand wire

i=5ABOW2-LE1JLbuAM

[scstill]

This is a great approach to grounding
https://el34world.com/charts/grounds.htm

[Lectroid]

I'm a new builder here, but I've just finished a PR (ish) amp a couple of months ago so I'll throw in my 2c worth.  I did replace the Fender reverb with a 1-tube reverb I got from tubenit, so it's not a 'true' PR. But it's a strong, good sounding amp with no discernible noise.  Pictures attached.

1.  Notice the main filter cap can is recessed further down into the chassis than yours, although still not flush.  I think this is a safer position too.

2.  The cord:  I used a straight-in cord like Fender.  Notice the green ground wire is grounded immediately after it enters the chassis.

3.  The power supply ground is visible at the transformer bolt, with 6.3VAC and HT voltage center taps attached to it.  The 2W resistor that drains the filter caps is also grounded there.  All of the power supply system grounds tie in to that point--transformer, cap can, bias, power tube cathodes, and the C and D filter caps on the board. 

In Image (2), what is the dark green wire going to ground that comes in from the bottom right? I can't see what it's attached to.

4.  I don't solder  to pots, I use a preamp ground, as mresistor suggested. Look at PR_PRE image, see the thick copper wire running just behind the row of pots. That wire is screwed down to the chassis, and that's the preamp ground mresistor described.  Everything in the entire preamp is grounded to that copper wire, and ultimately to the chassis. After five pretty quiet amps, I'm a believer. 
 
5.  I would certainly use two-colored wire in the heater circuit.  It's much easier to wire the power tubes' heater pins from the same  heater wire.  Once you're on into the preamp tubes, it doesn't matter.  I do find that using 5-4 colors amp-wide helps me keep track of the parts of the amp circuit.

All that said, you do good work, certainly cleaner than mine.  Is this your first amp?  What speaker are planning to use? 

Good luck with testing.