My junk box build (5E3, mostly)

General discussion area for tube amps.

Moderators: pompeiisneaks, Colossal

Post Reply
va3dxv
Posts: 26
Joined: Sat Jan 06, 2018 6:37 am
Location: Ottawa, Canada

My junk box build (5E3, mostly)

Post by va3dxv »

This is what I started with. I neglected to take a picture of mine before I started, so I stole this picture off the interwebs (only one I could find!).

Image

It's an Eastman-Kodak amplifier out of a 16mm film projector. It uses a single 12AY7 driving a 12SL7 and two 35L6's in push pull. It was missing tubes and connector cables, and was full of bad caps, so I decided to gut it and build something else in the chassis.

Things I re-purposed from the original: Chassis and related parts, tube sockets, pots, terminal strips, a 100 ohm rheostat to use for adjustable bias and a bunch of cloth wire cause that's where the vintage tonez are, right? :mrgreen:

Image

I left the original schematic on the bottom cover to confuse the hell out of whoever finds this when I'm gone.

Image

Above is the original circuit before I wrecked it. I kept the output transformer and the little filter choke for other projects.

Image

Chassis and board stripped down, and a Hammond output transformer installed. Power supply started. Unfortunately I didn't have any axial capacitors handy, but I'll probably order some later and redo the HV section. You can see the green/yellow heater supply left as it was in the original amp. I decided to leave it as it was (because I'm lazy like that).

The power transformer I used is from a small Heathkit shortwave receiver. It has no 5 volt winding, but the 6v winding is pretty beefy at 6 amps, since the receiver used a 6v rectifier.

I have a 6AX6 I could have used, but since I was building a circuit with a cathode follower phase inverter, I really wanted the extra octal socket for that tube, since the first half of the PI tube is the second pre-amp stage. I like octal tubes (and happen to have a rather vast supply of 6SN7's somehow).

All that to say, I used 1407 diodes to rectify. Ended up with pretty low B+ in this amp at about 290v.

Here it is with wiring mostly done. I added a second 9 pin socket (hiding under the big cap on the left) since I plan on adding tremolo or reverb next.

Image

Preamp: 12AU7 - Just using one triode. I'm gonna play around with 12AT/AY/AU/AX combos and see what I like.

I used a standard Fender Volume/Tone stack (.0005 and .005 caps on the tone) between this stage and the next. Basically up to this point it's inspired by a Fender Princeton 6G2.

Phase Inverter: 6SN7 - The first triode is the 2nd preamp and the other is a cathode follower. Except for the fact it's a 6SN7, it's Fender Deluxe from here on. Of course I can swap this out for a 6SL7 any time and that would drive the output stage harder. I added an adjustable negative feedback loop (50k pot through a 10k resistor).

Output: 6V6GT push pull, dissipating about 18 watts total.

As you may have noticed, the heater wires are now replaced... lesson learned, don't be lazy. Rewiring those after I wired everything else, and found out how bad the hum was, was a real pain in the ass.

Image

Looks sweet and sounds sweeter. All the tubes lined up in a row is why I liked the chassis. Everything works great, there wasn't much troubleshooting needed after the hum issue... We won't talk about a small brainfart where I forgot to give the 6SN7 a DC reference and couldn't figure out why it wouldn't make sound. :mrgreen:

(btw the blue is from something else, not anything I did to this... but it might be cool to change the yellow LED for a blue one).

Still a slight hum, but it's hard to tell if it's 120hz or 60hz. Doesn't really annoy me until I crank it. Hoping it's just a leaky cap, and when I replace them all with new axials, it will fix it.

Now I just need a cool looking cabinet to put it in...

Image

That might just work.

Image

Not quite, but an hour or so with a chisel and...

Image

I plan on refinishing the wood (but not too much, I want to keep some patina) and adding a handle... I wanted to put the original radio glass back in it, but I'm afraid the tubes won't get enough air. I might make a metal screen for the front instead... or something. I dunno. I want a nice looking cabinet without losing the patina. I'll figure something out.

Either way, this is my first "complete" guitar amp I've ever built, and I'm pretty happy with how it sounds. I've never played a vintage Fender amp, so I have nothing to compare it to, but I'm in love and I can't wait to build more (I have lots more stuff to rebuild). Totally open to constructive feedback! Thanks for reading :)
ChopSauce
Posts: 1038
Joined: Wed Mar 15, 2017 12:08 pm
Location: So Paris, France

Re: My junk box build (5E3, mostly)

Post by ChopSauce »

Well, er... I won't say I'm totally convinced by the layout...

(a reluctance towards PTP from mine)

... but I definitely enjoy this kind of build 8)
User avatar
norburybrook
Posts: 3290
Joined: Mon Jan 06, 2014 12:47 am
Location: London
Contact:

Re: My junk box build (5E3, mostly)

Post by norburybrook »

love this :D


One day I'd love to do a true point to point in a funky old reclaimed chassis like this.

Marcus
va3dxv
Posts: 26
Joined: Sat Jan 06, 2018 6:37 am
Location: Ottawa, Canada

Re: My junk box build (5E3, mostly)

Post by va3dxv »

I scraped the numbers off the glass and put it back in... I'm going to cut some slots in the wood on top for cooling but it actually doesn't seem too bad, the back is open and the speaker cloth lets air through.

Image

re: PTP... Why are people so against it? It was going to be hard to jam a turret board in this chassis... but I might try it that way for my next build if I can find a cheap source for boards/turrets.
User avatar
pompeiisneaks
Site Admin
Posts: 4222
Joined: Sat Jan 14, 2017 4:36 pm
Location: Washington State, USA
Contact:

Re: My junk box build (5E3, mostly)

Post by pompeiisneaks »

I think the reason people are against ptp are twofold:

1. it's a lot harder to do repairs on PTP vs turret/eyelet/tagboard
2. It's a bit more complicated to build them that way as well, harder to see problems/troubleshoot, vs a board with things more linearly laid out in front of you.

~Phil
tUber Nerd!
User avatar
M Fowler
Posts: 14017
Joined: Wed Jan 16, 2008 2:19 am
Location: Walcott ND

Re: My junk box build (5E3, mostly)

Post by M Fowler »

I love PTP as long as it is in the smallest possible chassis to keep those leads short.

Bigger 17x6x2.5 Marshall chassis are much better suited for a board build.

Using tag strips instead of a board is not PTP and makes no sense to me unless your cleaning out your parts bin.

Have fun guys, Mark
ChopSauce
Posts: 1038
Joined: Wed Mar 15, 2017 12:08 pm
Location: So Paris, France

Re: My junk box build (5E3, mostly)

Post by ChopSauce »

I feel like you should avoid cutting slots in the top - unless it is absolutely necessary. I find it is really cool like it is, and more interesting to keep most of the original appearance.

About any P2P reluctance, also: it's just that I am not confident enough I would stay cool enough while doing that - for my own :wink:
User avatar
pompeiisneaks
Site Admin
Posts: 4222
Joined: Sat Jan 14, 2017 4:36 pm
Location: Washington State, USA
Contact:

Re: My junk box build (5E3, mostly)

Post by pompeiisneaks »

ChopSauce wrote: Wed Feb 28, 2018 1:08 pm I feel like you should avoid cutting slots in the top - unless it is absolutely necessary. I find it is really cool like it is, and more interesting to keep most of the original appearance.

About any P2P reluctance, also: it's just that I am not confident enough I would stay cool enough while doing that - for my own :wink:
Yeah absolutely true on the top slots, many radios and such never put slots in the top, they had a few holes in a backer board to let some heat out, but really, the temps inside the cabinet were above the chassis and went 'upwards' not down toward the components so it's not usually a big deal unless you're cranking a 4x pp with huge glass or more :D

~Phil
tUber Nerd!
Post Reply