Vox Beatle Super Reverb V1143 Restoration Project

[nevetslab]

OK, got the 100W iron busy and removed the old cap cans. Sucked up the solder using that American Beauty with solder wick, then brass bristle brush to finish the task. Removed the shield plate from the front side of the transformer, so I had room to play with the mounting brackets. As expected, just not enough room to make it pretty, so did what I could. I tried to work from the bottom side, but that got too wierd, so had to work again from the top, Easy enough to place the rear clamp. It was the front clamp that was forced into compromise, but got it into place. Fetched my drill kit from the car, still using a vintage Bosch AC powered drill with a 1/2" Jacobs chuck on it. Drilled the holes out, after center-punching them good, deburred the holes for #8-32 mtg hardware, and installed the clamps, then the caps.





I can't say I'm overly pleased with the chassis mtg hardware hanging in that close to the V+ supply terminal. Actually, I'm not all that happy with these discrete rectifier diodes. Tempted to find a proper location for a 25 Amp Bridge Rectifier. Gotta look closer on the bottom side of the chassis for that.

[nevetslab]

I found I had a 400V 35A Bridge, so while I first looked at using a longer screw thru one of the clamp mounting holes, it unfortunately placed the Bridge wiring in the middle of where a reverb tank would slip in, so scrapped that idea. Drilled a new hole and mounted it further back. Then, unwired the xfmr secondary wires, along with the primary wires and the zip cord from the AC mains terminal. Dressed the primary leads, same with the secondary leads, them wrapped them together, re-terminated the primary leads and zip cord (AC Mains input), and broke out the secondary leads, terminating the two with 1/4" female Fast-on's. I'll end up adding bypass ceramic disc caps across the bridge terminals (0.1uF/500V Disc), though I think I'm out of them at the moment.



I then removed the large discrete rectifier diodes from the top side of the component board. Getting those unsoldered and removed was very tedious, as was salvaging the 5W resistor wires. I still need those feed-thru circuit posts to pass the buss voltages up from the caps. At least this time, current is being pulled from the capacitors, and not from the rectifiers, so you're not seeing that tidbit of charging current from the diodes. That was one of the foundation rules....always pull current from the caps, not from branch circuits that just happen to be connected to them. Shows up in the noise floor.

[nevetslab]

This morning I found my stash of 0.1uF/500V ceramic disc caps, and formed their leads to install onto the 4-terminal bridge rectifier, soldered at the base of the male fast-on terminals, out of the way of the mating connectors. Then with some copper buss wire (12AWG electricians wire), I formed a buss bar to join the two filter caps together, and added the xfmr C/T. Now, I'm in the process of trying to remove and replace the electrolytic caps on both sides of this fiberglass (phenolic?) circuit board, where all wire and components have their lead wires or connecting wires wrapped around the tall pins that pass thru to both sides. An added bonus to this method is repeated heating of the solder connections loosens the pins' friction fit into the circuit board material. I'm so thrilled. I also discovered a clever method Vox used in wiring these power amp circuit boards that are populated on both sides. To make reliable connections that won't come apart during re-soldering, they intertwine the wires/leads. Desoldering with solder wick merely heats up the connection and pin, but doesn't appear to allow anything to come undone. Unless you hold the pin with needle nose pliers below the joint at the base, and with the soldering iron tip, heat up the joint and lift the intertwined cluster of component lead and lead wire up and off. Yet, they're STILL intertwined and soldered together!! This is MADNESS!!!



I removed each of the original RCA power xstrs installed in the individual folded aluminum heat sinks and checked them on the Fluke in Diode Test mode. 1mA constant current, reading the junction voltage. On each pair, one measured around 0.485V Vbe, Vbc, while the other measured 0.51V Vbe, Vbc. Tested ok, just having this difference in junction voltage, and installed so that difference is on both upper and lower pairs in the output stage. I haven't yet ordered replacement MJ15015G's, but perhaps I should, just to have them on hand. I'm guessing if I put them on the curve tracer, they'd show similar differences. But, they've been working all these years...however often the amp was used. Just an observation and pondering while moving thru the power amp assembly to clean up and re-cap the unit.

I was about to order more of the caps like I just used, along with an MOV to place across the primary as suggested by RG in his book. As to this added difficulty in replacing components on both sides of the circuit board, that sure has slowed down progress, and extracted a few choice words in the process. I look forward to the preamp with Geat Eagerness!!

[nevetslab]

Continuing from yesterday, I now have the bottom side of the power amp wired up, replaced the electrolytic caps on both sides of that circuit board. Those are Wire Wrap square posts that are punched into the circuit board. They all looked round, but during desoldering one earlier, the true shape appeared. Makes sense, since they use them on the preamp, which on this version is all wire-wrapped harnessing.

I routed the ground wires that both terminate in the 9-pin connector housing to mate with the Preamp connector, and the other ground wires that I had clipped off of the original cap cans ground liug. wired those on both sides of the xfmr C/T, added the chassis ground wire, which is now fastened to the adjacent chassis mounting screw, with that chassis ground wire exiting with the plug harness to connect to the preamp. I just ordered male fast-on terminals to stud-mount blades. That was a nightmare to attempt to order with Mouser's selection tree. Couldn't be done. Had to go on line, spell out the terminal, came back with numerous correct renditions of the terminal, one from Mouser, even, and followed that path to add it to my existing parts order so I could buy the stupid thing! The best I could do when I went to Keystone Electronics was a rivet-mounted fast-on blade. Can't specify the mounting stud size. Even TE-Connectivity's data sheet had crossed out all hole options but one (#6-32 size thru-hole), so I guess I'll have to enlarge them per use, but at least I will have them again. Sigh.......



I checked in with Jimbo, CenterStaging, LLC's general manager and long-time friend of Mike and Tom, and yesterday morning, he drove over to their facility where a trade show shipper was packing the pallet of the amps that I had just done, delivering the Gibson L5 combo and the Magnatone M10 combo. All nicely packed up for the trip to Chicago. I asked about the reverb tank, as this amp didn't have one when I removed the rear panel to take it apart and finally begin this restoration work. I got the ok to track down a suitable tank. So, I need to know what to order. I have an idea of what, though there's no doubt a couple models out there that are form-fit function replacements to the original tank. Anyone have that info?

I just looked at the cabinet to see if the two metal clips that hold the back end of the tank into place were present. They are. Based on the height off the floor of the chassis, they'd be expecting the tank to have the fitted shock-mount feet present. I'll no doubt have to tweak the metal brackets to fit. All of the revised wiring now fits out of the way of a new tank, so now on to the top side clean-up. I've already replaced the electrolytic caps...just now have harness work to do in that clean-up. Every time I place a parts order, I'm always fearful I'll have left something off the order that I won't know about until the next phase of the project is on the bench. Which always forces another delay plus more shipping fees.

[Bill Moore]

The tool is a "panel nut socket", us mechanics were requires to have several to work on the different dash switches back in the day, I think I have half a dozen, some are for antenna nuts!
I sure don't envy you with this project, I've been putting off pulling the board and replacing the caps in my old GA-40! (I know there will be lots of broken wires when I do!)

[nevetslab]

The tool is a "panel nut socket", us mechanics were requires to have several to work on the different dash switches back in the day, I think I have half a dozen, some are for antenna nuts!
I sure don't envy you with this project, I've been putting off pulling the board and replacing the caps in my old GA-40! (I know there will be lots of broken wires when I do!)

Ah hah! So that's the tool used on the dome-shaped phone jack mtg nuts on the Vox amp! Never seen one before. Looking at the nut with my calipers at hand, the width of the relief (for the tool's teeth) looks to be 2mm, and the span between the grooves in the nut look to be 13.7mm. Does that sound right?

At the moment, I haven't started on the preamp, and not yet sure if I'm going to need to remove any of the jacks. I have a Snap-on socket that fits the Vox switches, that have the slotted dress nuts, but it won't fit these jacks. Panel Nut Socket. Good to know....thanks!

[nevetslab]

I spent some time looking to see what I could find on the this V1143 Reverb Tank. Saw one statement from Reverb.com that the original tank in these amps was made by Accutronics. Looking at the specs to call out what's needed, I'm guessing?

4FB2 or maybe 4FB3 for the first four characters (Long tank, two springs, 1.475k input Z, 2.25k output Z, either medium or long decay. The connector configuration....not sure....Grounded input, insulated output, maybe the opposite, maybe both in/out grounded. Doubt if both were insulated. Locking mechanism was used on the original tank, from what g1 stated. Open side faces down, so that would be #B in the code. Does anyone know or recall what the original Accutronics p/n was on these amps?

[52 Bill]

There were a few different tanks used. The only difference was the input impedance all of the tanks were input and output grounded.
If you look at the two wires that connect the tank, the input side is not shielded, just like Mesa's.

I think that R.G. covers the two types of tanks that they used in the book.

[nevetslab]

There were a few different tanks used. The only difference was the input impedance all of the tanks were input and output grounded.
If you look at the two wires that connect the tank, the input side is not shielded, just like Mesa's.

I think that R.G. covers the two types of tanks that they used in the book.

I figured the V1143 reverb tank would be a higher input impedance, not having the transformer drive feeding the tank. Whether 600 ohm or 1.5k input Z, probably either would be usable. I haven't yet lifted the Preamp PCB up. I looked at the chassis while pondering the connector issue on the tank, but one of the cables disappears under the PCB, so didn't know....but thanks for that bit of info. I was certain RG would have provided the tank information in either the two books, but looked thru them carefully, and didn't find any details on the two tanks. I also checked his website, and didn't find any info in the links there either. Then, waded thru all of the threads on the Vox Beatle V1143, but didn't find it there either.

So, now home, I'll wade thru some YouTube videos of taking the V1143 (or other versions) apart to see if I can find it there. There was a lot of photos of Vox Beatles on-line, and waded thru all of that. Found a number of the internal images I had taken now posted there among them, but never found any showing the tank removed with it's number visible. So, onward on the hunt. Thanks for your input on that.

[nevetslab]

I didn't find anything on the disassembly videos. But, looking thru the MOD series tank, I think the closest fit is a 4FB3A1B, which is 2-spring 1.475k input Z, 2.25k Output Z, grounded input/outputs, Long Decay (couldn't find a medium decay with these features), Long tank 16.25" long, open side face down. No lockdown feature, which would be handy to have. The threaded fastener is present on the bottom of the cabinet, so perhaps I can cobble a locking mechanism to push the floating tank up and lock it for transit. Usually where the breakage happens....in transit. I do get tired having to repair broken xfmr wires in the tanks, as well as having to replace them. P-RMOD-4FB3A1B. Around $25 + shpg.

Anyone have details on the Vox lock-down mechanism? I know g1 has seen them, having taken one apart that had it.

[drewl]

The tool is a "panel nut socket", us mechanics were requires to have several to work on the different dash switches back in the day, I think I have half a dozen, some are for antenna nuts!
I sure don't envy you with this project, I've been putting off pulling the board and replacing the caps in my old GA-40! (I know there will be lots of broken wires when I do!)

We actually have a bunch of these in different sizes and patterns as they are "keys" to equipment cabinets in cell sites.

Snap ring pliers do the job just fine.

[g1]

Anyone have details on the Vox lock-down mechanism? I know g1 has seen them, having taken one apart that had it.

As mentioned in the other thread, there is no locking mechanism. They just run the thumbscrew right up into the inner pan.
There is a second threaded hole that functions solely as a 'holder' for the screw when the reverb is in use.
Crude but effective.

I couldn't figure out what the headshell's extra threaded hole that was missing a screw was for. At some point my brain's 'dim bulb' turned on and I understood the locking 'system'.

[nevetslab]

When I drive in tomorrow, I'll stop by the other shop and pick up one of the dead 17" Accutronics tanks to have here for when I decide to locate the lock-down fastener hole, though the new tank may arrive before I get to that task. I saved the P/N for the McMaster-Carr threaded knob/shaft that I'll cut to size. Also found they carry fish paper (vulcanized insulation paper) in a wide range of thicknesses and sizes, so I'll order some of that while I'm at it. Should have done all this last night when I ordered rubber cabinet feet, so I didn't blow another shipping charge. Hate that.

I got thru the clean-up of the top side of the power amp chassis, and also de-soldered the bias pot (after taking DCR measurement of it's setting, in circuit, just so I had that as starting point). Then, took it apart. It's mounted with twist-tabs on the pot, rather than threaded bushing. CTS pot. So, as expected, the silver plated wiper contact ring was heavily oxidized, and all needed cleaning and lubricating. Used metal cleaning goop to restore the bright silver surface, cleaned that off, then applied red grease to the mechanics of the rotor, to the resistance track and wiper contacts, then reassembled it, closing the cover tabs. Then, remounted it to the driver xstr's heat sink panel, twisting the tabs to lock it in place.





Now, I'll set this assembly aside, and move the preamp chassis to the bench to start the task I've been avoiding. The link g1 provided in a recent thread on this project shows the insides of the preamp with the circuit board lifted up, exposing the battery of filter caps that are on the V1143 schematic, but only saw the hint of them from the view above the circuit board. Most of what I have for the replacement filter caps are radial lead, so I'll have to look at this to see how those will work out. May have to order axial lead parts....we'll see.

http://www.voxshowroom.com/us/amp/v1...eamp_hood.html

Didn't Vox engineer Brad Plunkett work for UREI in the mid-70's? Seems like I had met him there at their factory when I was working on a project.

[52 Bill]

As mentioned in the other thread, there is no locking mechanism. They just run the thumbscrew right up into the inner pan.
There is a second threaded hole that functions solely as a 'holder' for the screw when the reverb is in use.
Crude but effective.

I couldn't figure out what the headshell's extra threaded hole that was missing a screw was for. At some point my brain's 'dim bulb' turned on and I understood the locking 'system'.

There are two holes on the bottom of the head cabinet. One is for the original shipping reverb lock bolt that secured the tank during shipment from the factory, which was to be removed by the dealer during inspection/setup. The second one located in the center of the bottom panel is for the thumbscrew that held the metal bracket that secured the head to the roller speaker stand. There are probably photos of the stand clamp out there on line.

[g1]

There are two holes on the bottom of the head cabinet. One is for the original shipping reverb lock bolt that secured the tank during shipment from the factory, which was to be removed by the dealer during inspection/setup. The second one located in the center of the bottom panel is for the thumbscrew that held the metal bracket that secured the head to the roller speaker stand. There are probably photos of the stand clamp out there on line.

Well that makes sense, I never had the speaker cab with the head.
I'll have to look for pics. Odd that the screw was left in this unit. And it fit so nice in that 'spare' hole.