It looks like you're new here. If you want to get involved, click one of these buttons!
Subscribe to our Patreon, and get image uploads with no ads on the site!
Base theme by DesignModo & ported to Powered by Vanilla by Chris Ireland, modified by the "theFB" team.
Comments
Good tip, that's some neat twisting
Thing is if we look at http://www.thefretboard.co.uk/discussion/151739/showing-some-love-for-the-princeton-reverb#latest there is plenty of wiring here that isn't twisted, but is run tightly in parallel instead. I can't help thinking that this would be an easier way to go (next time).
Interestingly, looking at photos of original 5E3s, there isn't much evidence of wire twisting. Maybe they were noisy buggers?
Good tip, that's some neat twisting
Thing is if we look at http://www.thefretboard.co.uk/discussion/151739/showing-some-love-for-the-princeton-reverb#latest there is plenty of wiring here that isn't twisted, but is run tightly in parallel instead. I can't help thinking that this would be an easier way to go (next time).
Interestingly, looking at photos of original 5E3s, there isn't much evidence of wire twisting. Maybe they were noisy buggers?
All very interesting, it kinda looks like it might be a real rabbit hole but I'm okay with that.
... This is a real rabbit whole isn't it? I could see myself getting REALLY into all of this if I'm not careful.
... This is a real rabbit whole isn't it? I could see myself getting REALLY into all of this if I'm not careful.
... This is a real rabbit whole isn't it? I could see myself getting REALLY into all of this if I'm not careful.
https://youtu.be/9_ceJzH3RmE
I think I worked on it for about 5 hours on Sunday. Pretty much all of it in the chassis. Quite fiddly and slow going.
Finished the power transformer connections, which meant that it was too tempting to wire up the mains lead. The mains lead in this kit is wired into the chassis, via a strain relief grommet. The earth wire is bolted down to the chassis, leaving extra slack so that if the mains lead gets pulled then earth wire is still connected if the power leads get pulled out. Which all makes you realise what a good idea IEC (kettle lead) connectors are.
So, having check for continuity between the earth pin of the plug and the chassis, I plugged it into the mains and very carefully checked for 240V where I expected it and not 240V where I didn't expect it. All OK, so I switched it on. The pilot light came on (nice) and I checked for the various outputs from power transformer. Carefully again, since there's now +/- 350V on some of those rectifier socket pins. All ok again. Heater voltages appearing at the heater pins of the valve sockets and main power appearing at rec pins. Switched off, unplugged, breathed a sigh of relief and made a cup of tea.
Squeezed the circuit board into the chassis (fiddly) to check the lengths of all the off board wires. Cut most to appropriate length and noted two that weren't long enough, so would need replacing. Pulled it out, replaced and stripped wires as appropriate.
The last thing of the day was attaching components to hardware in the chassis. The power valve sockets both have a resistor across a couple of pins. This would probably be easier to do earlier on in the process, before the sockets are fitted to the chassis. The volume and tone pots and input jacks have various jumpers, caps and resistors mounted on and and between them. This definitely needs to be done in the chassis. I elected to do the work on the jacks, but then take them out before fitting the circuit board back in.
Oh and I fitted the output transformer and output jacks. And that was that.
Right then. Monday dawned, and I thought I might reach switch on at some point before beddy-byes.
I finished off the in chassis work on the input jacks and then removed them, with the idea that it would make it easier to get the circuit board in. Here they are, I was quite pleased with them despite the limitations of my soldering.
https://www.dropbox.com/s/hqxrbkqgvburdr4/P1060496.JPG?raw=1
Next it was time for the circuit board to go in. With the pots and output jacks installed, this was a squeeze and definitely would have been really difficult with the input jacks installed. Anyway I got it in and got all the wires pointing in the right directions.
https://www.dropbox.com/s/l7n1evltjcucykl/P1060497.JPG?raw=1
Then I put the input jacks back in. Oh dear.
https://www.dropbox.com/s/le3qlcjfsj2kiul/P1060499.JPG?raw=1
The board in this kit is a turret board and is mounted on stand-offs. The way I had the jacks orientated (as per the layout drawing), they touch the top of the turrets. Oops. A look around other builds and photos of original 5E3s on the Internet generally shows them at right angles to this orientation. Ah well. The jack assemblies came out and were recreated in a way that did fit.
I carried on, soldering the wires from the 'top' of the board onto the pots and input jacks. Despite quite a lot of pre-checking I managed to come across one wire that wasn't long enough. Having already soldered plenty of joints I took the no-going-back approach and decided to extend it and heatshrink the joint.
With the top of the board wired I moved on to the bottom. The preamp tube sockets are really fiddly to solder to, with rather small and wobbly terminals, all very close to each other. I've since noticed on an original 5E3, that these terminals have been bent outwards from the centre of the socket, leaving quite a lot more space around them.
Thankfully the power tube sockets are gigantic by comparison and therefore much easier to solder to The last connection was from the standby switch to the circuit board ground bus......and then it was finished. Don't laugh too loud.
https://www.dropbox.com/s/eqjsdhof9gpel2q/P1060503.JPG?raw=1
https://www.dropbox.com/s/kbzas7oqmtqytrl/P1060504.JPG?raw=1
Having got all the soldering complete I did continuity checks on all the new joints, ticking them off on the layout drawing. Then I checked the continuity from the earth pin of the mains lead through to the chassis and the ground lugs of the input sockets. All OK.
The rest of the commissioning was pretty brief. Put the rectifier in and switch on. Note that the rectifier heater is working. Wait for smoke or fuse blows. All ok, so set the standby switch to on. This should apply the 350V supply to the circuit board. Wait for smoke etc. All seemed ok so turn off. Then very carefully check for volt across the filter capacitors. About 240V and discharging slowly through the volt meter. That'll do. Then plug in the preamp tubes and switch on. Wait for smoke and note that their heaters are on. All ok. Finally plug in the power tubes and a speaker and switch on..........
The good news - It hasn't killed me and it does amplify my guitar nicely. Yay!
The bad news - it hums. Quite a lot. Boo!
Next step - troubleshooting (probably followed by trying to sort my half-arsed wire twisting).........
Its looking very much like Modulus have had a change of power transformer supplier and the layout that I’ve been working from doesn’t match the transformer that came in my kit. The PT on the drawing has a green/yellow wire, which I assume is a ground reference. My PT doesn’t have this wire. I had an updated drawing from them this morning and I’ve just noticed that it indicates 2x100r sitting on one of the power tube sockets. Those resistors weren’t supplied in the kit, so I’ve just emailed Michael at Modulus to ask if he’ll send me them down. Hopefully that’ll make a big difference.
FWIW the hum is there all the time, including volumes at minimum. Turning the controls changes the tone of the hum, but doesn’t make much difference to the level. I’ll get a chance to do some diagnosis over the next few days and I’ll do an update when I have some news.
on the positive side the amplified guitar tone is pretty sweet so I don’t think there is an issue with any of the valves. Plus I’m continuing to learn a lot
http://www.valvewizard.co.uk/heater.html
, which points out that it’s possible to do the same virtual heater circuit centre tap with a couple of quarter watt 220Rs. I had some of those in the parts bin so I soldered them in. The updated Modulus drawing has them soldered in on one of the 6V6 bases, between the heater pins and the cathode pin. I tried this and it has worked a treat. The amp still hums a bit but not enough to be annoying.
In terms of sounds I’m pleased with what it does. The cleans are nice. It has to be taken quite loud to get much overdrive out of it though. I pretty much have to turn the volumes up to 11 or so to get much drive, which makes it bloody loud. I’ve tried it through a Vintage 30 and also through the Jensen CH12/70 that’s in my Cornell Romany. Both are fairly high sensitivity. I think I’m going to be going old school and getting it a Jensen P12R. I have no need for it to be particularly loud. I might consider a resistive power scaling mod too.
Incidentally, I checked it’s voltages and they are all a bit on the high side. For instance the volts delivered to the 6V6 anodes is around 406V. It’s a similar story across the board. I’ve got a Sovtek 5Y3 installed and looking around the web, the rumour is that that they tend to deliver somewhat higher volts than a typical 5Y3.
I've checked what the transformer is putting out, which is +/- 343V with no load, and +/-330V with everything running normally. Pretty much in line with the manufacturers specs. I have a manufacturer drawing for the transformer and its rated for 240V on the primary side, with no options for other voltages. They state the secondary voltage as +/- 330V at 138mA load.
So I think everything is ok on the tranny side and I still think its an overperforming rectifier. Apparently the Sovtek 5Y3 is an 'improved' design, with an indirectly heated cathode (presumably the original 5Y3 had the cathode and filament all-in-one), with the result being that it produces more volts than it should (ie doesn't behave like a 5Y3 should).
The higher voltages aren't too much of a worry at the moment. One thing I've learnt from this is that even with the amp running at nominal levels the quiescent anode power dissipation on the 6V6s would be way above the 12W 'safe' limit that is stated for these valves. This amp design is well-known for this. With the voltages on my amp, the power dissipation looks like it is about 20W! So I'm a bit concerned about red-plating, but haven't see any signs of it yet. Apparently 6V6s are known for being able to take quite a bit of abuse........
So next steps:
1. I've ordered the bits to do a resistive quarter-power reduction mod as per the Rob Robinette site.
2. Try a different 5Y3.
3. Get off my backside and start on a cabinet.
4. Fork out for a speaker.
The 5E3 has been a bit dormant for, ooh, almost 2 years. You know, life, money.........
I'd only tried it with a Celestion Vintage 30, which had been quite a loud experience, and not particularly nice. So a few weeks ago I was lucky to source a Jensen P12Q from @surfguy13 of this parish. Thanks again to Guy, who was an absolute pleasure to deal with.
I must admit to being a complete ignoramous when it comes to speakers. I was quite amazed at the differences between the V30 and the P12Q. OK the V30 is (I believe) quite high sensitivity, which I guess explains the massive magnet and the weight of the thing, but the P12 weighs nothing, and under the rear dust cover there appears to be, well not much. Just a brackety thing.
Anyway I tried the Jensen with the amp, and it all made sense. Sounded sweet and it was easy to make out the squish without deafening myself. Nice
So next, a cabinet. Money is a bit tight, so its got to be a DIY job. I already had a speaker cabinet that I built about 10 years ago, made from 18mm birch ply, with the dimensions of an Orange PPC112. I decided to recycle this into something more 5E3 sized.
Here's the donor cabinet.......
https://www.dropbox.com/s/86trc8sas4u8fw2/P1060626.jpg?raw=1