BahHumbug's 5E3 project

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  • BahHumbugBahHumbug Frets: 349

    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?

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  • BahHumbugBahHumbug Frets: 349

    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?

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  • springheadspringhead Frets: 1583
    edited May 2019
    It's all down to space and layout. That princeton chassis is a bit bigger than a 5E3. Also the heater wires although parallel are stood about an inch above the valve bases, i.e. away from sensitive noise inducing spots like grid pins.

    Like a lot of the early Fender amps the 5E3's I've seen inside of have one half of the heater winding connected to chassis.  So a single wire from the transformer and each valve base had a braiding strap to chassis from one half of the heaters. Saved Leo a few pennies per amp and I guess the hum level was acceptable. 
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  • sharpjimbosharpjimbo Frets: 36
    Lot of great info in this thread already, thanks guys. @BahHumbug there's an absolutely wealth of info on https://robrobinette.com/, thanks for sharing!

    All very interesting, it kinda looks like it might be a real rabbit hole but I'm okay with that.  
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  • sharpjimbosharpjimbo Frets: 36
    Really interesting thread so far, @BahHumbug thanks for posting this link (https://robrobinette.com/), there's an absolute wealth of information on there!

    ... This is a real rabbit whole isn't it? I could see myself getting REALLY into all of this if I'm not careful.
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  • sharpjimbosharpjimbo Frets: 36
    edited May 2019
    Really interesting thread so far, @BahHumbug thanks for posting this link (https://robrobinette.com/), there's an absolute wealth of information on there!

    ... This is a real rabbit whole isn't it? I could see myself getting REALLY into all of this if I'm not careful.

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  • sharpjimbosharpjimbo Frets: 36
    Really interesting thread so far, @BahHumbug thanks for posting this link (https://robrobinette.com/), there's an absolute wealth of information on there!

    ... This is a real rabbit whole isn't it? I could see myself getting REALLY into all of this if I'm not careful.
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  • thermionicthermionic Frets: 9499
    I think this is an appropriate point to remind you of my heater wire preparation.

    https://youtu.be/9_ceJzH3RmE
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  • BahHumbugBahHumbug Frets: 349

    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.

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  • BahHumbugBahHumbug Frets: 349

    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).........


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  • springheadspringhead Frets: 1583
    edited May 2019
    I had the same turret board/jacks proximity issue as you!  I may re-do mine on an eyelet board at some point.

    I'd check all your voltages first against usual known 5E3 values.  Could be one 6V6 not pulling current or any number of things.  I'd then be checking continuity from chassis to all components that should be grounded.  On the leg of the component, not the wire or turret.  Also other usual problem chasing - does it do it with volumes down, what if you remove V1, V2 etc. Plug a guitar lead in, can you measure continuity from the sleeve at the guitar end down to the chassis (i.e. jacks grounded?). 

    Good luck!  Let us know how you get on.

    Edit: Can't see either a heater centre tap or the usual 2 x 100 ohm ground reference in your photo's.  Is your heater supply floating?
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  • BahHumbugBahHumbug Frets: 349
    Thanks for your input @springhead.  Yes my heater supply is floating at the moment, but I get the impression from your question that it shouldn’t be.  
    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 :)
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  • springheadspringhead Frets: 1583
    Yes the heater fake centre tap with the 100R resistors should help. Sit them on either the left hand 6V6 base or the lamp holder and take the junction down to chassis at your power supply ground point. Mine still has a little bit of hum, not a problem at gig level but I might redo it at point and try and reduce it.  


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  • BahHumbugBahHumbug Frets: 349
    Well, while waiting for some half watt 100R resistors to arrive I read through this article...

    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.
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  • springheadspringhead Frets: 1583
    edited May 2019
    Glad you sorted the hum.  The amount of drive doesn’t sound right. These amps are usually only clean upto about 4. Your volts are a little high. Could be the rectifier or maybe your 6V6’s aren't pulling enough current. What are you measuring on their cathode resistor and what value is it. 


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  • BahHumbugBahHumbug Frets: 349
    The cathode resistor is 250R.  There is 24V on each of the 6V6 cathodes.
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  • springheadspringhead Frets: 1583
    Well that's roughly right for cathode voltage, slightly high perhaps.  I get around 21V with 365V on the 6V6 anodes, that's using a NOS Philips 5Y3.  Haven't tried any others.  Not accidentally running it on a 230V winding are you?  You could pull the 5Y3 and measure the PT secondary from centre tap to each leg and check with Modulous if your no load voltage is correct for whatever transformer they supply.
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  • BahHumbugBahHumbug Frets: 349

    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.


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  • springheadspringhead Frets: 1583
    I think a more conventional 5Y3 is a good idea. They are usually very lossy so hopefully that'll get your volts down.  If it all measures ok with that in, and you hit around 360-380 on the 6V6 anodes and you're still not getting plenty of break up by 4 or 5 on the volume then you have a signal path rather than DC problem to find.

    I built a rheostat (rather than the usual domestic L-Pad based) attenuator and that works quite well with my 5E3. Rob Robinette's fixed pad will be somewhat similer I guess.   But I also built a variable power circuit into it.  Voltage reduction for the whole amp, same basic VVR circuit that's all over the internet that Lazy J also uses in his amps.  Works really well in a 5E3 to back the volume down whilst preserving the tone and distortion.  I've done one gig with mine and had the power wound down a bit.  Sounded fab!


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  • BahHumbugBahHumbug Frets: 349
    Sooooo............

    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

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