My Amp Projects - One Man's Descent Into Thermionic Obsession

[joelster]

Lately I've been deep in the throes of a vacuum tube obsession. For months now, much to my wife's chagrin, I've been stealing out to the garage to solder whenever nobody's looking. The projects are mostly conversions of vintage technology that I've acquired over the past few years. Some from feeBay, some from Goodwill. Some were gathered several years ago and when I got them I thought I would easily convert them to guitar amps. Alas, my limited free time proved no match for the learning curve that I found myself up against. As a result these things have been sitting neglected in my garage, a collection of unfinished projects. Sort of a metaphor for my life.

Finally I just couldn't take it anymore and started digging in, ignoring my worldly responsibilities and hammering away on these thermionic monstrosities until sounds would come out. This forum has been a great resource and I have been very pleased with the various ongoing results.

Since my wife doesn't really appreciate them, and if there are no objections, I thought I'd post some pics of my progress here. If I ever get organized and motivated enough, I might post some sound clips as well.

Thank you for your indulgence,

Joelster

[joelster]

5F1 Champ:

This one represents my first successful build. My friend had a crappy Fender practice amp from the eighties. When it stopped working he gave it to me. It sat on the shelf for a couple of years until last spring when, motivated by his upcoming birthday, I decided to refit it and give it back to him. The transformer and many of the other parfts came from and old Devry 16mm projector I got off Craig's List. The speaker is an old CTS, from the early seventies. This thing sounded great. The quintessential 'crank it up to ten' amp. When I can, I will build another for my self.







Cheers,

Joelster

[joelster]

5e3:

This one represents my first attempt. I did this one last winter but when I got too frustrated debugging I set it aside. It did work well enough for my wife to come running out to the garage complaining that I was going to upset the neighbors. That, by the way, has become my standard of initial success for any of these projects. After getting a couple other builds under my belt I decided to revisit it.

It is built on an old Voice of Music VM160 amp got off feeBay a long while back. It was really hard to put together because the turret board is over the top of the tube sockets. I know the lead dress seems funky but the whole board need to flip up to access the various solder points. I also don't dig the cloth coverd wire. Feels messy. Anyway, redressed it (for the fourth time?), made some changes, added a couple of mods and friggin' screams now.






Cheers,

Joelster

[misterjohn]

I like the 12 inch record.

[hackworth1]

Nice work. Pretty darn tidy for what you're working from. What size are the filter caps in your 5E3 mockup?

[joelster]

Thanks.

I stole the idea for the LP faceplate from some weird noise box oscillator that was for sale at a shop here in town.

The filter caps in the 5e3 are 16uF. They are TADs that I got from Mojotone.

I realized after posting that the 5e3 project was actually two winters ago. My Tele was last winter's project. In fact it was through my 5e3 searches on google that I first became aware of TDPRI.

Joelster

[Telenut62]

Very very cool

[joelster]

Japanese PA (VA-50):

Here's another one. This is a Japanese tube PA from the late sixties. It was made by the Tokyo Sound Corp which is actually Guyatone.



I got it from feeBay long ago and when I got it all it would do is red plate like mad. No sound at all.

I was recently able to get the schematic out of Japan (two days after the Tsunami, in fact!).



It had been hacked up pretty bad as somebody tried to get it working before I had it. I rebuilt the power section using a tagboard and replaced some coupling caps. It still red-plated which was disappointing. After I found and removed an errant glob of solder on the PCB it came to life. Even the reverb worked! Output was pretty weak but after replacing a few more components (all of the small value caps were crazy out of whack) I've got two of the channels sounding really good. One is Fender style and one is stock as per the schematic. It's still a work in progress and I'm trying to decide how to approach the other two channels. I'll probably voice one Marshally and one Boogie like once I figure all of that out. As an experiment I will probably also set up the inputs so that you can cascade the gain stages using jumpers.

Before:


In Process:


(Learned a lesson here as the bias cap is wired backwards. POP!)





Nearly finished:


Cheers:

Joelster

(There's more. Should I keep going?)

[Robster]

Thats what we are here for, Bring em on!

[smsuryan]

that f1 is a handsome piece of work...im wondering where the on switch is, did i miss it?

[joelster]

Thanks. The volume knob is switched.

[joelster]

JTM45:

Ok... so this on was an old church PA, also from feeBay. It was a Dukane 1U460A. It was a bit of a rusty example but I never could win on the really good ones. I gutted it and put a Ceriatone JTM45 board into it. Not sure why I elected to purchase a board rahter build one. I guess I was curious about Ceriatone. I gotta say, if you wanna build something kit-style on a budget, Nick gives you pretty good bang for the buck. Using a prefab board did mess up the design a bit. The way this chassis is laid out it would have been better suited with a board that was the mirror image of this one. As a result, the tube orientation is a bit bass-ackwards. If I had it to do again I would do that or flip the control and inputs.

I learned a lot about lead dress on this one. Even though it has the largest chassis it was the hardest to sort out. I had some crazy oscillation and phase cancellation goin on.




I had to completely strip and repaint the chassis. The color is Ford Grey which appeals to my utilitarian sensibilities.




I have changed the bias to accomodate EL34s. This thing is fat and loud. I'll have to tweak the voicing a bit. The Normal channel is a bit dark and the Brilliant channel is too bright. I will prolly add a master volume and maybe a buffered effects loop. It originally had six 12ax7s so there's some room on the transformer. I might make one channel into a JCM800 style or perhaps cascade them together. For now it's giggable with my current band. Lots of clean headroom.

[Cliff Schecht]

Cool builds!

My only concern is on that Japanese PA deal, those grey signal caps that are (I think) Japanese paper in oil caps are probably no good, or at least some of them aren't. I pulled apart an old Japanese projector and saved these caps for use in a later build only to find out that they ALL leaked, badly. Mine was stored in a similar way, I think it was in an attic instead of a garage but either way, I won't ever trust or use those caps again. Even if they test good now, they seem to eventually go to crap (maybe from the heat generated inside a tube amp is enough).

[joelster]

You are exactly right. Pretty much ALL of the caps were bad. The 20mF bypass caps are the only ones that tested OK. I have swapped pretty much all of caps at this point. Two of the pre-amp channels still have them because I haven't decided how I'm going to mod those channels yet. I actually have some Japanese 22mF 20v caps that a friend gave me. I put some of those in for the bypass caps and they look identical to the originals.

[oramac7891]

Nice projects

[hackworth1]

Very nice work. Ceriatone has nice kits. My kits are also nice and much cheaper. If you haven't seen them, please check out my chassis kits 5F1, 5E3, 5F6A in the Vendor Section.

[joelster]

Thanks, Hackworth.

Those kits look great. I'm pretty much in build it from scratch mode these days but I'll pass your link on.

Cheers.

[joelster]

Here are some pics of the current project.

At Goodwill I found an old Webster Model 80 wire recorder from the forties. Without regard for it's rarity or potential museum piece status, I gutted the thing (yes, I suffered a little guilt). But inside of the thing was this:




The tube compliment was 6x5, 6v6, 6j5, and 6sj7. Ignoring the 6j5 I built a Silvertone 1331 curcuit on this thing. It sorta worked but had some issues. Rather that troubleshoot it I decided to change gears and build a 5C1 champ with a 6x5 rectifier. I also thought I'd use the extra tube socket to add an extra gain stage on the front end that could be bypassed depending on which input you use. I also figured that once I got that sorted I would also add tone controls. Kinda like this:



So it's pretty well sorted at this point. The whole thing is going to fit into a vintage Aladdin lunchbox that I picked up.







The tone control circuit I decided on is from a blonde Bassman. Partly because I happened to have a pot with the 70 ohm tap leftover from the VM160 and partly because I recently acquired a blonde Bassman. I had to add a secondary turret board to house the tone circuit. This will sit in the bottom of the lunchbox. I made it so you can bypass the tone controls and have just the coupling cap as in the original circuit. I also added a switchable bright cap.

I am having a bit of an issue with the tone control however. The insertion loss seems huge. When you engage the tone circuit the output is cut at least in half. That sound right?

I have to say that this project has gotten a bit baroque. So far it sounds really good though.

[joelster]

Here are some pics of the modified 5C1 in a more finished form.







In retrospect, the lunchbox concept is a little goofy but it was exactly the right size for the Webster amp chassis.

It's pretty much done but I'm still having trouble with loss from the tone control circuit. I've been messing with LND150 JFETs as buffers and additional gain stages but I'm just getting no love out of 'em.

Never the less, when using the extra gain stage with the tone controls bypassed this thing screams. It sounds really good with the tone controls engaged just very subdued.

[SolidbdyJazzfan]

Originally Posted by joelster

Here are some pics of the current project.

At Goodwill I found an old Webster Model 80 wire recorder from the forties. Without regard for it's rarity or potential museum piece status, I gutted the thing (yes, I suffered a little guilt).

* * *

That struck a resonant chord with me, Joelster. I have an old Harman Kardon Prelude that was my folks' since it was new. I didn't want to gut that one (it sounds great as is) but found an EL-84 version on Ebay and turned it into a Bandmaster/Bassman single-channel monstrosity (that I dearly love). The TDPRI thread is here: http://www.tdpri.com/forum/shock-bro...5-bassman.html. I felt some guilt for cutting up that gorgeous copper plated chassis.

I don't have your demonstrated skills, but I think we were bitten by the same bug. I had to have a tech (Adam at Chrome Dome Audio) get the Prelude/Bandmonster running after I got it built and wired up.

Your projects are excellent man. Keep on building! This thread is further evidence that TDPRI has one of the best amp-building subforums around.