Vox Buckingham V112 rebuild (was Vox Buckingham questions)

[seveneves]

It's reasonable to assume that all of the reverb transformers were identical, but -

If the reverb transformers were all the same, it will be a common part number for all the amps. All I need to do is check every amp data sheet to see if they use Thomas part number 80-5056-1, which is what the V12/V112 parts list says.

I had this same thought with a different approach: I suspect that if the reverb tanks were the same amongst the different data sheet part lists for the versions (i.e., some research tells me that the early transformer driven reverb tank was part # 23-5002-2 and the later solid-state amp driven reverb tank was part # 23-5004-2), then the reverb transformers could likely be the same amongst all of the early models and, if so, ergo: "if it's got a reverb transformer, it uses reverb pan xyz". Unfortunately, "xyz" (23-500x-2) is Thomas Organ-speak and, failing any kind of Accutronics pan markings, the specs of an original tank are about all I can rely on at this point (which you've graciously provided).

[seveneves]

as the reverbs are high impedance and do sit open side down in the cab; and they have input grounded, output open.

Another item I wanted to check with you on.

If I understand, "output open" is the same as "output insulated"? If so, I am turning up goose eggs trying to find tanks designated 4BB2B1B. A review of the specification using the Accutronics numbering system, which seems to be widely adopted regardless of the manufacture:

• 4 = type (i.e., two spring reverb)

• B = 150 ohm input impedance

• B = 2250 output impedance

• 2 = medium decay time (2.0-3.0 sec.)

• B = input grounded, output insulated

• 1 = no locking device

• B = horizontal mounting plane, open side down

Plenty of 4BB2A1B tanks available, but unfortunately the 'A' denotes both input AND output grounded... is there a way to mod this kind of tank to wire it up as an open output?

[R.G.]

If I understand, "output open" is the same as "output insulated"?

I think so. It actually means "output RCA socket's ground shell is open, and the coil "ground" is connected to ground on the input socket".
Effectively, both the input coil and output coil share a connection to signal ground at the input socket.

If so, I am turning up goose eggs trying to find tanks designated 4BB2B1B. [...]

Plenty of 4BB2A1B tanks available, but unfortunately the 'A' denotes both input AND output grounded... is there a way to mod this kind of tank to wire it up as an open output?

Yes. Fix the cable. Break the ground shield at the tank end of the cable carrying the tank output back to the recovery input in the amp. Or use a single-wire cable from the tank output to the amp reverb return input. I kind of like using a shielded cable and leaving the shield open at the tank end.

It is possible to get into the tank itself, mess with the ground shell connection on the RCA socket, and make it be an isolated-ground. Given that I always seem to be making up shielded send/return cables, it seems easier to not solder one shield termination and instead isolate the shield at one end with some heat shrink.

[R.G.]

The original Thomas service literature says the Thomas number for all the amps that use transformer reverbs is the same, as you suspected. They say it's an 80-5056-1.

[seveneves]

Thanks for confirming that R.G.

Amp arrived yesterday. I have yet to open it up (may be the weekend before I do so) but I suspect the power switch is broken: it seems to have more than 3 positions...

[R.G.]

You might enjoy reading
http://www.geofex.com/Article_Folders/T ... repair.pdf

[seveneves]

Yes, I was looking at that. Thank you.

[R.G.]

I think the repair supplement is about ready. It will go up on Book Patch in the next day or two.

[seveneves]

Wow, that was quick! Will there be one for the Royal Guardsman to follow?

[R.G.]

There could be. Which model number(s) do you need?

The techie part of the job for me was understanding the similarities and differences in the model line, and doing/revising drawings and tables. That part was fun and I ripped through it while I was engrossed in the process of writing the first few book/lets. The hard part for me is the page layout and actually formatting it into book form. I have software to help with this, of course, but after the first half dozen booklets, I got tired of the formatting and tinkering. So there are at least the start of repair supplements for every model in the lineup.
The work needed to complete one is to review the material on that model, do a detailed check of parts lists and descriptions, make any corrections, and add any new/better thoughts.

The supplement for the V12/V112 Buckingham that's in pre-press now, for instance, has corrections to some errors in the parts lists, updated schematics, an added page on swapping silicon PNP output transistors for the original germaniums and rebiasing, newly calculated and specified transistor pin voltages for the slightly different power supply arrangement of the early Buckingham, and updated PCB/component illustrations showing both top/component side views and bottom/copper side views of PCBs, and a general revision of the text with corrections and a few new thoughts.

Oh, yeah - this means the book layout shifts around. Each page gets at least a text reflow and movement of the images to stay with the text that describes it. I spent about a day doing the detailed tech thinking and the rest of the time tinkering with placing new/changed images on pages and getting the text placement to match. I'm lazy, so I generally put off the futzing around with page layouts until I have a specific request.

In the case of the Royal Guardsman, there is a V13/V113, a V1131, and a V1133. The V13/V113 has the same reverb add-on PCB and preamp PCB as the V12/V112 Buckingham, but with a few component values changed and a higher-power power supply and power amp. The V1131 has the same reverb and preamp PCBs as the V113, adds a distortion PCB and relay, and tinkers part numbers and values, with a bigger power supply and power amp. The V1133 has a complete new preamp PCB with distortion integrated into it, a new non-transformer reverb on the PCB, no relays, changed wiring, a mildly updated power amp; but it uses the same "architecture" of sections and has about 1/3 of the components new/different.

So model number matters.

[seveneves]

Don't have a need for the Royal Guardsman supplement, I was just curious given the similarities between all of these "big head" TVs that the updates would be limited to/focused around the power amps which obviously differ between each of them. Clearly, the work that goes into each supplement is not trivial. Looking forward to the one for the Buck.

[R.G.]

It's simpler going across a generation than going from generation to generation. That is, a V1131 Guardsman is more like a V1121 Buckingham and V1141 Beatle than it is like a V1133 Guardsman or a V113 Guardsman.

[seveneves]

That makes complete sense.

[R.G.]

The repair supplement for the V12/V112 Buckingham and V15/V115 Viscount (which are electronically the same inside) is now up at thebookpatch.com at this link:
https://app.thebookpatch.com/BookStore/ ... 062ec9e719
I have ordered, but not yet received a hard proof copy, although the online pdf review looks OK. You can order it now, or wait a week or so for me to receive my proof copy and review it in real life. If there's a bug, I'll send a replacement updated copy to you gratis.

I also resurrected the V1083 Berkeley III service supplement, and put that on line as well, if you're feeling frisky.

There's a fair amount of new info here compared to the earlier repair supplements, including a template to trace and make a new replacement fiberboard insulator panel for the often lost/destroyed original. This will help keep inquiring fingers off the live AC wires in the area under the on/off switch.

[seveneves]

Thanks for the update R.G.!

Edit: Just pulled the trigger on the Buckingham supplement. May take you up on the gratis updated copy if I find any "bugs" with this version.