Modulus Amps Princetown Kit Build

spev11

Well, i've tested all the voltages, all seem to be within parameters (although I only have Mojotone and StewMacs guide for them) no smoke or flames. I've followed the startup as per both of them and although the tubes are glowing, voltages are right I have no sound. I did get a loud crack from the cab when I turned it off so i'll run though continuity again and double check the speaker jacks. Ive got two jacks but as I'm going to use it as a head I should remove one for simplicity I think.
 Will re-investigate tomorrow as its getting late.

Wazmeister

What a brilliant thread !

Full respect mate. Id love to build a Princeton.

spev11

mmmm houston we have a problem......
 So it powered up which was fine, no smoke, no sound either. Didnt have time to do much today (apart from hit junkies with pedal spanners but thats a different story altogether. I did check all the resistors, continuity again just in case and I checked the input jacks wiring. All seem fine (apart from the junkie). I've been looking back at the voltages that I checked (from the Mojotone/Stewmac instructions) and one or two seem a little low, the voltage into pin 3 of V1 should be 1.3v but I have .66v so roughly half.
 I have a day off tomorrow so I'll sit down with the schematic and some other diagrams (to point me in the right direction) and check every voltage to every where.
 I did notice that checking the voltage on the pre-amp sockets , when putting the prob onto the grid resistor pin 5 of either V5 or V6 that I generated a little noise. I'm also questioning whether V4 did actually glow at all (I know the rec.V5,V6 and the other pre amp valves did but I'm starting to think V4 didnt and that is split between trem and phase inverter). All good fun and a good learning experience. More info tomorrow, maybe even some sound (sadly the amp is better than my playing even now)

gdculley

Loving this thread! This is the point where I'd be waking at 4am with an "idea", and nipping down to do some early morning soldering (which invariably didn't fix it!), then back to bed hoping the wife hadn't noticed! You sound far more relaxed about it so good on you! I'm sure it'll be up and running very soon...

spev11

Haha, I know that 4am idea, if I try to sneak out the dog (my shadow at all times) would follow me, she's old and not as graceful and would certainly wake the wife up. I've become much more "zen" about these things as i've got older, I'm still frothing to get at it and find out what the problem is but I'm tempering that urge with the realization that I fell asleep on the sofa after having my tea so I'm probably too tired to make sense of it all 

Sharky77

Also loving this thread - looks really great so far and will be tuning in tomorrow to hopefully find out what the problem was 

MartinB

Have you got any background noise when it's powered up? They're never absolutely silent when working, especially with the stock grounding scheme. So listening to whether you can hear the tremolo working on the background hiss, whether the volume, bass and treble affect it, and whether you can hear anything if you tap on the reverb pan with the reverb turned up could help narrow down what part of the circuit is going wrong.

spev11

So far, the testing has shown that all the voltages are low, as an example V1 should 160v to pin 1 I have 89v, Pin 3 should be 1.3v I have .6v, pin 6 160v I have 87v , pin 8 1.3v I have .6v . So I'm losing half my voltage somewhere, time to get the googles out and have a deeper investigation.
  

spev11

i've removed all the valves and starting the testing from the beginning. Theres a little crackle and pop from the cab , not got the reverb pan connected yet. Theres a couple of leads I need to follow to check connections which could very well be the initial cause, will report back soon

spev11

I think I've made an error with the underboard wiring, that'll teach me to get cocky do the superneat, put all the wires under the board thing. So i'm going to take the board out and check it all. It's all a learning experience. Me and the solder sucker are gonna have a busy day tomorrow

hollywoodrox

springhead said:

thermionic said:

spev11 said:

I will add this, despite enjoying myself thoroughly so far the bloody twisted heater wiring did try my patience somewhat, I'm sure there is a proper way to do it but I haven't found it so it was just get it done 

This is how:

https://youtu.be/9_ceJzH3RmE?si=dhI1PS_ES7aPNh80

I’ve always used a hand drill with the other ends of the wires in a vice. I then let the drill hang on the wires for a while (hour or so) for them to settle. Otherwise they can start untwisting when you release them from the chuck and vice. 

Using a drill gives you an even twist rather than one wire wrapped around the other which is important for hum cancellation, as well as looking neat.  

We did this in a place I worked when younger 

spev11

Could'nt wait until tomorrow so I did some more testing and comparing to various schematics and yes It was me, I missed out on one connecting lead and switched two around. I've moved the long connecting wires from the capcan to the various points along the board to above rather than under (it looked neater but much harder to check).
Voltages tested and much closer to schematic now (within 5-10%, Fender schematic say 20% which seems a lot). Only problem is a duff tube, tested by dropping each one out in turn until the weird crackling stopped, then moved the suspect tube to the end and back to crackling. 
 Don't have a tube here , got one in my Vaporizer which is at the shop so I'll continue tomorrow. Hopefully that will allow me to finish voltage testing on the power tubes and then I can crack on with the cabinet build.

TTony

spev11 said:

Could'nt wait until tomorrow so I did some more testing and comparing to various schematics and yes It was me, I missed out on one connecting lead and switched two around.

Congrats on finding the culprit!

spev11

Tube replaced, WE HAVE SOUND, sorry got excited. Reverb is very noisy at the moment, need to do some reflowing of a couple of joints but I'm very happy so far. Once the joints are re-done/tidied up I'll see how the cabinet plans shape up

gdculley

Excellent! Glad it's running, good work!

Dave_Mc

Awesome news!

spev11

So it works , I’ve built a headshell for it but the bloody reverb is mega noisy, I’ll most likely use my external pedal reverb but it’d be nice to get it clean. I’ve reflowed the rough joints , checked all the wires. Anything else I should be looking for?
I’ll post pics of the head shell when I get in

spev11

in no particular order, one head cabinet shell thing. I built a finger joint jig this morning. Pine came from a b-stock (2 warped) shelf kit from Wickes. The fingers are bit rough but i'm happy enough for a first go. Some wax stain the wife had in the cupboard and a bit of clear oil for the front panel. 
 I'll likely build another cab, maybe a combo. Its not finished yet as I need to sort this reverb noise out and i'm waiting for the stain to dry  (its only been assembled for the pics)
Overall I'm pleased with the progress so far.

Oh and any tips on finding why the reverb is so noise please let me know.
I'm currently looking at the ground wire running across all the pots, some build plans have a continuos wire, some have the trem circuit on its own (but still grounded to the chassis via the pot), a couple wire the reverb ou/in a bit different. Some have said without a pedal/switch connected that can cause it. Anyway I shall keep investigating until I find the culprit (its likely me)

spev11

And its fully working at last, thank you to all that commented, sent me luck , those that helped, @RiftAmps and @ICBM on my other thread about the reverb. i'll post more pics once I finalise a name for it and maybe if I either build a better headshell or a combo box for it.
Again, ta

robinbowes

spev11 said:

And its fully working at last, thank you to all that commented, sent me luck , those that helped, @RiftAmps and @ICBM on my other thread about the reverb. i'll post more pics once I finalise a name for it and maybe if I either build a better headshell or a combo box for it.
Again, ta

Well done!

I'm curious - what was the reverb noise caused by?

R.