Bringing A 1965 JMI Vox AC30/6 Up To My Standards - Part 2

Webpage: www.bradsguitargarage.com.au
Facebook: bradsguitargarage
Instagram: / bradsguitargarage
Equipment:
Soldering:
Pace MBT station w/SX100 & PS-90 handpieces
Hakko 474 w/815 handpiece
Hakko 936 w/907 handpiece
Hakko FX-888D w/FX-8801 handpiece
Quick 861DW hot air station
BOFA fume extraction unit
Loctite Multicore solder (C511 / 362)
Test Equipment:
Fluke 11, 175, 177 & 179 handheld DMM's
Tektronix 2236 analog oscilloscope
Rigol DS-1054z digital oscilloscope
BK Precision 4017A sweep / function generator
BWD 160a function generator
HP 6236B triple output DC power supply
Kyoritsu 3132A insulation / continuity tester
Video equipment:
Overhead cam: Panasonic HC-V785 w/Audio Technica AT9946CM mic
Handheld cam: Panasonic DC-G85 w/Olympus M.Zuiko Pro 12-40mm f/2.8
On location cam: Panasonic DC-GH5s w/Panasonic-Leica 9mm f/1.7 & 12-60mm f/2.8
Capture card(s): Magewell HDMI USB, ATEN UC3020-AT, ATEN UC3021
Headset Mic: Audio Technica BP892xcW-TH
Lapel Mic: Rode Go
Editing: Adobe Premiere Elements
Hand Tools:
Wiha, Felo, Stanley screwdrivers
CK & Engineer cutters / pliers
RS Pro wire strippers
Sidchrome & Gear Wrench spanners, sockets & shifters
Veritas planes & chisels
Materials / Consumables:
JJ's / TAD electron valves
Elixir / Ernie Ball / D'Addario / Rotosound strings
Electrolube & DeoxIT cleaners, lubricants & chemicals.

[@_alexsams]

Very clean work Brad.

[@74cannelle]

Beautiful work Brad 👏

[@danielsaturnino5715]

Really nice work mate.

[@YeatzeeGuitar]

Wow, insanely clean work

[@ReinoutVrijhoef]

7:30 so that’s the way the jacket crumbles!

[@davidjennings9253]

I think you will find that the residue on the chassis is eminating from the transformers which can either show as drips of wax underneath the coils or as a wax mist from when they are running hot. This can gradually build up over the years and then dry out and become hard. I have seen this on several AC30s and it can also be what has created a film through the valve sockets. Strangely one amp I worked on had large ammounts of wax which had run out of the mains transformer but it still tested and worked fine. As you have also found, over the many years in service the wiring insulation can also deteriorate by losing plasticiser which probably mixes with the wax mist and hey presto, quite a mess. That top boost looks to be original but maybe added as an after market Vox kit. Great videos!!!

[@terrydemol5354]

So they were using some kind of wax for transformer varnish... eek! I remember rewinds of AC30 PT's and OPT's coming in (to transformer shop) but memory is foggy on the varnish. Also from memory the OP was fairly decent quality with a few interleaved windings and what looked like decent lamination steel but never personally measured them.

[@joelmahan]

JMI vox subcontracted with other companies to supply demand at their peak. The top boost add on is a perfect example of how much variation their was in layout/construction 😎

[@twelve_point_buck]

What a delightfully straightforward and cooperative restoration! haha, beautiful attention to detail as always :)

[@johnwilliamson467]

The resistance of the heater to cathode is greats above or below 40 volts best place . Lowest is about 2 volt negative worst place that when the heater is grounded and the cathode bias is about 1to 3 volts. This does vary by maker and type of tube however a workable rule of thumb. RCA internal book on making tube is my source. Search the internet and you can see the number of test on this .

[@Dr.Sheldor]

You go so far above and beyond. I’m in amazement at folks like you who actually understand what they’re doing and then take the time to do it right. Well done - you’re a role model for others. I just wish others would take note and not just do a dodgy job to get it out the door and get paid.

[@DL-oy2qn]

Every day's a schoolday on here.

[@tedmich]

Its like surgery on an octogenarian; extra care is required. Great work as always Brad!

[@fiddlix]

I knew I was going to have a good start on today. Thank you Brad. Looking forward to part three.

[@TheMorganOrgan]

Lovely work as usual.

[@dennisflock3958]

Good morning from Chicago

[@Splattle101]

Looking forward to hearing this amp.

[@sjgreaves]

Do you have links to more on the heater elevation stuff - you mentioned it in the video. I have a cathode biased 15w single ended amp that has the heaters currently referenced to ground and it is pretty quiet (given it is single ended) but I'm thinking of moving that refernce to the cathode but a bit of theory would be useful.

[@BradsGuitarGarage]

www.valvewizard.co.uk/heater.html