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Eyelet setting in progress. Stand-offs are temporarily in place to stop me putting eyelets in the holes.
You can see 220pF ceramic on the reverb send and return sockets. I presume these are intended to suppress RF noise or something. I'll probably leave them for now.
Really looking forward to seeing how this goes. Are you keeping an eye on costs involved in this? I'm building a 59 Tweed (from Stewmac) just now and might try this next.....
I guess you've seen the Rhett Shull video comparing hardwired to PCB Princetons?
Where did you get your eyelets/ fixing tool?
Zimmy
Yes I’m subscribed to Rhett Shull’s channel and I‘ve seen that vid.
The eyelets (and most of the other components) came from Modulus Amplification. The tool is from a kit for putting much bigger eyelets into banners and the like. It won’t reach to the middle of the board so I use a hammer and punch there.
Are you going to put your build up on here?
Thanks for the eyelet info
Anyway, work in progress on the main eyelet board - ground busses, filter caps/resistors, B+ links, and now working my way across the board. I've soldered some eyelets but the rest will wait till I add the flying leads.
The diagonal red wire by the filter caps is the Stokes mod, which links the otherwise unused 3rd B+ node to the plate resistor of the phase inverter.
The red stickers are to stop me inadvertently using the mounting holes as thru-holes for flying leads.
I’m fancying building an amp kit as my next project, and I also fancy a Princeton so this has totally piqued my interest!
Just the 6V filaments to wire up now.
Are you going to come from above the sockets with your heater wiring ?
@PeteC yes I am. I find this easiest to do after all the other socket wiring.
This afternoon I plugged into my Variac via a dim bulb tester (DBT) and wound up the voltage, but with no valves or HT fuse. HT and filament voltages were present, though somewhat elevated as they were off-load. Then I fitted the rectifier and confirmed I was getting rectified AC, and a bias voltage that gets less negative (i.e. hotter) as you turn the pot clockwise. Adding the HT fuse, I brought the voltage up again to form the filter caps, but had to stop short of full mains as I was already getting 500V at node A.
With the bias at its coldest I fitted the remaining valves and noted the voltage at each node. If you look at the photos you will see there is an extra voltage-dropping resistor between the HT fuse and node A. This is to get the voltages closer to the Fender specs. I am using the 240V primary on the PT but our mains voltage is typically 249V! I started with this at 100R, tried 470R, and settled on 330R. Each time I tweaked the bias for no more than 10W (70% of 14W) dissipation on each 6V6. I fitted a 1R resistor to each valve socket so that I can convert cathode voltage directly into cathode current. (At the moment they are not particularly well matched as I had to replace a noisy one with the only other one I had.)
I also discovered that I had had the reverb tank the wrong way round (putting the sensitive recovery pickup closer to the PT) so I fixed that.
This evening I plugged a guitar in and confirmed that all the controls work as expected, which they do, so I put the whole thing back together and had a play.
HOLY FREAKING COW! I never expected the rebuild to make this much difference! This is now a proper blackface amp in silverface clothing. Some of the standout differences from the already-partly-modded 68 Custom:
- The volume pot works smoothly, whereas before there was a sudden jump at about 4 on the control.
- There is more treble available.
- You can turn the bass control up all the way without it being overpowering. I might end up tweaking this for a little bit more bass, which would be useful at home practice volume.
- The reverb - omigod the reverb, massive and lush, and hum-free. Reverb at 10 was previously unusable but is now OTT ambient heaven.
- Lovely crunch when the volume is turned up high (and that is LOUD).
I do need to tweak the tremolo intensity as it currently doesn't do much until about 6 on the control. I'm going to wait on the new valves before I do this, as the bias can affect tremolo intensity.Can you tell I'm pleased?
Look out for an audio demo...