OT, kinda: Thomas Vox amplifiers

[R.G.]

I've been off messing with my first love for a while - Thomas Organ Vox amplifiers. This affair started in about 1966. I only recently got to where I could replicate the insides of these things.

I've designed boards to replace the entire working guts of the preamps. The audio circuits are the same, but I fixed the obvious problems with the power supply, and redesigned the cabling and wiring to the controls so they can be repaired in the future.

Three PCBs cover the Thomas Vox models V1121, V1151, V1131, V1141, V1122, V1152, V1132, V1143, V1123, V1154, V1133, V1143, V1011, V1021, V1031, V1081,  V1012, V1022, V1032, V1082, which are all the common models of the Beatle, Royal Guardsman, Buckingham, Viscount, Cambridge Reverb, Pacemaker, Pathfinder and Berkeley II. I believe that the V14/V114, V12/V112, and V15/V115 are also covered, but there are not as many of these around, so that's a "maybe" until proven.  The Berkeley III is sufficiently different that it has to get its own PCB. Some day. 

Got a few pictures of a Berkeley II installation in shape to see. This one was built by a guy I've met only through the net who had a busted Berkeley. He was kind enough to send pictures. Here's a good overview:


The original power filter cap was left in place for looks (upper right corner of the chassis) but disconnected. The terminal strip for the rectifiers was used as a tie point for the wires leading to the new board's AC input to the the on-board rectifier and filter caps (right side of the PCB).

I was impressed with the craftsmanship the owner put into building the PCB and getting it wired in.  Nice he did work there.

I don't have pictures yet, but there was also a conversion of a Buckingham V1121 done with one of the other PCBs. It required not only replacement of the preamp PCB, but also conversion of germanium output transistors to silicon and rebiasing, and rebuild of the flakey power switch assembly. The (very accomplished!) tech that did the conversion tells me the owner thinks it sound just like it used to, but without a lot of the hiss.

[Gus]

R.G.

I am surprised a company has not started to sell vintage solid state amps.

[Fp-www.Tonepad.com]

That looks like it's built to last way longer than things today.

[R.G.]

Yeah, the original design was pretty sturdy. I have some commentary on geofex about how to make amps more reliable, specifically with PCB main circuits.

You put the pots and switches on flying wires so that manipulating the controls doesn't flex the PCB or the solder joints holding them.

The MBAs have (accurately!) decided that people will buy a modestly cheaper amp obtained by making it less long-term reliable. This is only a problem compared to the amps from the 50s and 60s that are still running 50 years later.

I designed the PCB to correct a major flaw of the Thomas Vox amps - their original PCBs were wired to the controls with solid-core copper wires, and lots of them. The Cambridge/Berkeley here isn't all that bad, but the Beatle/Royal Guardsman/Buckingham had a real bundle of these wires to the controls. Each wire was mechanically stripped, and usually nicked by the stripping tool right at he end of the insulation, so they had stress concentrations right at the nicks, and often broke right there. They *especially* broke right there if you flexed the PCB up from the chassis to work on it, so every time you bend the PCB up to work on it, you run a big chance of breaking another wire. It makes them uneconomical to fix, as many techs will not touch them because of the wire breakage issues and the fact that once a repair crosses a few hundred dollars, most musicians can't afford it.

Anyway, this is a labor of love. I hate to see these amps go into a dumpster. So the owners can now replace the entire guts with new parts but the old circuits, and a new, and fixable!, wire harness. I'm hoping some of them make it to 100.

[bool]

...
You put the pots and switches on flying wires so that manipulating the controls doesn't flex the PCB or the solder joints holding them.
...

Oh yeah. And I/O sockets.

[Transmogrifox]

The MBAs have (accurately!) decided that people will buy a modestly cheaper amp obtained by making it less long-term reliable.

If old amps didn't wear out maybe they would have to get a lot more creative to sell new amps.  Making good stuff may long-term dry up your market.   Think of all the new amps that aren't being sold because of all the old well-built amps still in active use.

Sadly I got news of a Fender Bassman that got pitched in the dumpster by my old high school because it didn't work.  Likely the only things wrong with it were dirty pots and old tubes.  I wish I could have been there to do some dumpster diving when they did that.

[Fp-www.Tonepad.com]

The point missed is that the sound quality is also sacrificed some.

[StarGeezers]

  RG, back in the late 60's , we had two (2) super beatles...  loved the look,  sound and power  ( and the wheels/stand)  , but one or the other was ALWAYS in the repair shop ... something  always breaking, or blowing horns ...   bit of a PIA really , and expensive ,  so sadly we had to get rid of them  ...   
  Best of Luck on your board re-design ...  That's very Cool !!!   

[bool]

...  I wish I could have been there to do some dumpster diving when they did that.
...

Dumpster diving done with style is a good thing. It builds character.

[garcho]

You put the pots and switches on flying wires so that manipulating the controls doesn't flex the PCB or the solder joints holding them.

I wish all amps were like that!

[R.G.]

The point missed is that the sound quality is also sacrificed some.

In modern construction, you mean??

  RG, back in the late 60's , we had two (2) super beatles...  loved the look,  sound and power  ( and the wheels/stand)  , but one or the other was ALWAYS in the repair shop ... something  always breaking, or blowing horns ...   bit of a PIA really , and expensive ,  so sadly we had to get rid of them  ...   
  Best of Luck on your board re-design ...  That's very Cool !!!   

Yeah, that's when I got the bug, too. Thomas Organ made some very good looking amps, but they had little clue about making them road-worthy. I figure that very few of the survivors will ever get hauled around on the road, so at least I can make them repairable. 

So far, so good with the test boards.

You put the pots and switches on flying wires so that manipulating the controls doesn't flex the PCB or the solder joints holding them.

I wish all amps were like that!

Yeah, but its not going to happen with any new-manufactured stuff. Too much labor content. The MBAs are right about what to do for the mass market - make them cheap. The number of people who will pay 2, 3, or 8 times as much for an amp is much smaller, and those people are being gobbled up by the boutique amplifier makers' cottage industry.

[Fp-www.Tonepad.com]

Yes, I meant in modern construction. Seems they're more flimsy mechanically but also don't sound as good, even when in perfect shape.
Not that EVERY vintage point wired amp is great sounding either. Or that modern amps can't sound better than old ones, but most of them just don't.
Nostalgic, maybe.

[R.G.]

Honest, guys, I didn't set this up.

I got a request to quote geofex in a magazine article long enough ago that I'd forgotten about it. This showed up in my email this afternoon:

http://issuu.com/eeweb/docs/08-2014-modern_printed_circuits_2_p/5?e=7607911/12319739

[snap]

This in new: http://www.wah-wah.co.uk/mmb.html



Castledine done it?

[R.G.]

Yes, Stuart's Magical Mystery Box is a sub-set of the MK1/2/3 amplifier preamp circuits, one of the preamp channels in a stomp box format.

The PCBs I'm describing are the entire set of the preamp circuits; all the preamp channels, all the effects, set up to replace all of the old circuits inside the amps. They're intended to be amplifiers, not stomp boxes.

I have field reports now on three of them. The Thomas Vox V11n1 series, the "suitcase amp" series including the Cambridge and Berkeley II, and the UK UL700 series preamps seem to work well. I haven't done prototype PCBs of the MK1/2/3 preamps yet. Still recovering from buying prototype boards for the other three.    

[LightSoundGeometry]

my little chinese made VOX amp sounded great this morning ..with my rangemaster hooked to it lol !!

I was going to get rid of the Vox and go with a blackstar .I may hang onto the vox now