1960’s TUBE Vox Pacemaker project

[Drew9783]

Hey everyone! I recently bought a mid 60’s tube Vox Pacemaker, and have done a decent overhaul to it so I thought I’d share. I played one of these at a music store years ago and loved it, but hadn’t seen a tube one under 1K since then. I got this one for an absolute steal because it was barely passing signal and had some cosmetic flaws (tolex, grille cloth, etc). I know these USA made Thomas Organ Vox amps don’t quite hold a candle to JMI’s but I wanted to take on the challenge of bringing some life into this little guy.

Once I recapped the power supply, bias supply and cathode bypass caps I got a decent signal from the amp, and replaced the Celestion G10L it came with for an Alnico Gold 10 which really opened up the top end and gave some much needed volume and punch. From there I tweaked, adding screen grid and grid stopper resistors to the EL84’s and phase inverter, and bringing the preamp/phase inverter voltage up. The original schematic and my readings showed about 60-70v on the plates of the preamp tube, which from what I can tell was quite on the low side. I brought voltages up to about 180 for the preamp and 220 for the PI which really helped! Power tubes are biased with a 100 ohm 5w resistor running 308V on the plates. Starting to get to AC15 territory!

This is the amp as is when I got it, will upload some after pics and a sound sample later today.



Attached is the original schematic I found online, which had a few errors. I attached my schematic with changes highlighted in red.

Anyone have any thoughts on these or similar amps? This was a fun project, and I’m open to suggestions on getting a little more out of this. Ideally I’d love for this thing to sing like an AC15, and I’ve thought of changing the tone stack to a cathode follower/Vox top boost style but I’m not sure if that’s needed.

[mortatone]

Cool project!

I don't have any experience with Vox stuff except for building a few AC15 clones with little to no modifications but it sounds like you've got this one by the horns and anything else would just be a matter of experimentation and taste.

I recently picked up a Thomas built Vox V807 Echo Reverb (oil can style delay) that doesn't work properly but also isn't completely dead. I'll get to it eventually.

For Thomas Organ Vox stuff, there's a whole facebook group dedicated to it. If you wanted to know exactly what type of feet were used on a specific amp from a specific year, they'd probably be able to give you the person's phone number or gravesite location that supplied them

[Devin]

That's dope; definitely curious about clips of that thing

[Drew9783]

A little late on this, but here are some "after" photos, redid the grill cloth, piping, and replaced the speaker




And a little sound test

[ajaxlepinski]

Great job! It looks so much better!!!

I dig the full volume tone!!!

[Drew9783]

Great job! It looks so much better!!!

I dig the full volume tone!!!

Thanks! I dig it, it’s definitely loud enough to gig with. Now if I could get my hands on a tube cambridge reverb I’d really be set!

[Devin]

Damn dude it sounds fuckin awesome

[Drew9783]

Damn dude it sounds fuckin awesome

Thanks! I’m super happy with the results.

I’ve got JJ’s in the preamp and power section right now, But I just bought a set of NOS Tungsram EL84’s that I can’t wait to put in. I hear these are great tubes for Vox style amps. I also just bought some NOS GE, Amperex and EI 12AX7’s and am going to do some tube rolling.

Anyone have 12AX7 preferences in amps like this? I’m curious to see differences (if any) in the v1 position.