Vox Buckingham V112 rebuild (was Vox Buckingham questions)

[seveneves]

Does anyone know if R.G. Keen released his V1121/V1151 Buckingham/Viscount supplements? I see it mentioned here, albeit from 6 years ago: http://www.geofex.com/

I have tried contacting R.G. in the recent past, unfortunately to no avail. Maybe he's enjoying retirement? I hope so.

Curious if he finished his volume on the Vox Buckingham/Viscount. I have acquired a Buckingham and it would be a great resource to have as I go through it and bring it back to life. (Yes I know about his website.)

And, if you're reading this R.G., where can one get these books like the "Safety Net" anyway? The last place I knew of, The Book Patch, is currently closed... =(

[Stevem]

I don’t know, but was nice enough to helped me out some 7 years ah
Ago on a 66 Vox that I have with changing it over to silicon outputs in regards to the bias changes needed.

I hope he is well and he responds back to you.

[Reeltarded]

Does anyone know if R.G. Keen released his V1121/V1151 Buckingham/Viscount supplements? I see it mentioned here, albeit from 6 years ago: http://www.geofex.com/

I have tried contacting R.G. in the recent past, unfortunately to no avail. Maybe he's enjoying retirement? I hope so.

Curious if he finished his volume on the Vox Buckingham/Viscount. I have acquired a Buckingham and it would be a great resource to have as I go through it and bring it back to life. (Yes I know about his website.)

And, if you're reading this R.G., where can one get these books like the "Safety Net" anyway? The last place I knew of, The Book Patch, is currently closed... =(

He will be along shortly! RG can't be contained!

[R.G.]

The Book Patch is open. Try this link for Safety Net and the others:

https://app.thebookpatch.com/BookStoreR ... dl=authors

I see that their listing in google when you search for "the book patch" says they're closed, but clicking on the link for that entry takes you to their home page. Maybe they closed down for a while and google has not updated their search blurb?????

The Buckingham/Viscount supplement is nearly complete - and has been for a while. The standing joke among my age-contemporary friends is "Now that you're retired from your day job, what are you going to do with all that free time?" We're all finding that we have to schedule in fifteen minute increments about a week ahead.

[R.G.]

Which model do you have? They come in 1121, 1123, 1151, and 1154 (at least... ).

Do you have a specific question or are you wanting to do a general update?

[seveneves]

Hi R.G.,

Glad to see you doing well.

I have a V112 en route to me. Yup, an early one: no fuzz...

Definitely want to do a general update on it. Nothing specific as of yet but now that you ask... do you have any PCBs available for the preamp?

[seveneves]

I did actually have a specific question, R.G.

Sadly, someone roached the reverb tank from this head...

In searching for a replacement, I came across this on the Vox Showroom:

http://www.voxshowroom.com/us/amp/v1121 ... _hood.html

"For those seeking to purchase a replacement pan, the modern Accutronics replacement part number is 4FB2A1C."

However, I think this is a typo because IIRC a 'C' mounting is vertical, connectors up.

The reverb pan in a "big head" Thomas Organ Vox lays horizontally, under the preamp module.

So assuming the other specs are correct (are they?), do I need a 4FB2A1B instead?

[R.G.]

I have a V112 en route to me. Yup, an early one: no fuzz...

Definitely want to do a general update on it. Nothing specific as of yet but now that you ask... do you have any PCBs available for the preamp?

I checked the source files for the V112 and V115 models, and found that all I have is a crude first pass. I did find the source Thomas data "manuals", such as they are. So something could be done, but it would take some time. The "take some time" is mostly for me to adapt the info for the V1121/51 back a model and comb my stuff for errors.

I did not do a specific PCB for the V11x series, as these were the same circuits as the V11x1 series, plus a distortion add-on baby board and a relay in the chassis. I did do a preamp board that works for the V11x1 series, and have a couple of those in my bottom desk drawer- aka "the warehouse". Thomas used the same chassis sheet metal overall for all of their Viscount/Buckingham/Guardsman/Beatle products, so they'll fit in the V112 chassis, and will work fine, given that the wires are run to the right places. There is an original distortion circuit from the V11x1 series on the board, but the V112 has no chassis opening that will let you wire in a footswitch or some such to switch it on without cutting a new hole in the chassis for the connector.

There are a few common problems with all the Thomas bigger head-and-cab amps.
> The electro caps are well past their bury-me-now date; they will all need replaced.
> That's a pain, because detaching and bending the board up to get at the bottom PCB solder joints often breaks off one or more of the solid (yikes!!) hookup wires at the PCB joint. It's easy to get into chain failures, where fixing one thing breaks a wire, fixing that wire breaks another, ... This is one reason amp techs often flatly refuse to work on them.
Sadly, you're going to have to bend up the PCB at least once to get at the axial electro power fiter caps in the "basement" under the PCB. Best advice is to get all of your parts ahead of time and figure on bending it up as close to only once as you possibly can. Do your repairs/testing in one go, with the board up, and only when it's in great shape bend it back down into place. Verify correct operation on the preamp head by itself before hooking up to the power amp chassis.
Here's a quick photo of how I did them:

> The input NPN transistors, and NPNs in the tremolo and reverb are often noisy, making a wall of hiss. Fortunately, the common-as-dirt 2N5088 is a suitable replacement for all of the small signal plastic NPNs in the head.
> The Buckingham uses PNP germanium power transistors. If you're lucky, the ones you get will be OK. If not, don't even try to find exactly replacements. I found half a dozen usable ones by searching exhaustively - over 20 years ago. They're all effectively gone. Luckily, you can replace them with silicon PNP and re-bias the output stage by changing resistors.

Most of this can be found in separated articles on geofex.com. Search "geofex vox" to turn up the leads.

Unfortunately, I'm not a reverb tank expert. I think you got it right, as the reverbs are high impedance and do sit open side down in the cab; and they have input grounded, output open.

[R.G.]

Forgot to add: in the picture I linked, the AC mains switch is on the very left side. That stuff is al hot to the AC mains, and deadly as a pet rattlesnake. Touch that section while the line cord is connected, and you could well die. Note that it's hot even when the power switch it turned off. The life you save could be your own.

I have a layout of the nomex cardboard shield thing somewhere in the archives. These are critical to safety in the finished amps, but have often been torn out as they're a pain and deteriorate. Auto store gasket material can be used to make a replacement if it does not contain metal fibers as some materials do.

[seveneves]

I did not do a specific PCB for the V11x series, as these were the same circuits as the V11x1 series, plus a distortion add-on baby board and a relay in the chassis. I did do a preamp board that works for the V11x1 series, and have a couple of those in my bottom desk drawer- aka "the warehouse". Thomas used the same chassis sheet metal overall for all of their Viscount/Buckingham/Guardsman/Beatle products, so they'll fit in the V112 chassis, and will work fine, given that the wires are run to the right places. There is an original distortion circuit from the V11x1 series on the board, but the V112 has no chassis opening that will let you wire in a footswitch or some such to switch it on without cutting a new hole in the chassis for the connector.

I did a quick study of the schematics between the V112 and the V1121. It seems that the activation of the fuzz is merely by grounding out the K401 relay? If so, what I was thinking (instead of drilling another hole in the chassis) is to do a similar thing happening with the reverb and tremolo switching function: use a TRS 1/4" in place of the MRB RCA and then I can switch the MRB *AND* the fuzz... do you see a problem with that? Then I could utilize your PCB and get the fuzz functionality.

Speaking of which: are you planning to make these PCBs available for purchase? I couldn't find any means of acquiring them, either through geofex.com or other, despite documentation being available.

> The input NPN transistors, and NPNs in the tremolo and reverb are often noisy, making a wall of hiss. Fortunately, the common-as-dirt 2N5088 is a suitable replacement for all of the small signal plastic NPNs in the head.
> The Buckingham uses PNP germanium power transistors. If you're lucky, the ones you get will be OK. If not, don't even try to find exactly replacements. I found half a dozen usable ones by searching exhaustively - over 20 years ago. They're all effectively gone. Luckily, you can replace them with silicon PNP and re-bias the output stage by changing resistors.

A few more questions on transistors now that you have me thinking about it...

• I read on geofex that you've also mentioned the 2SC1815 as an ideal replacement. Would the slight increase of noise be discernable over the 2N5088, especially if I were to replace them more-or-less wholesale (i.e., does the noise add up?)?

• Do I need to purchase more of these small signal transistors than what's actually needed in an effort to sort for specific characteristics besides gain?

• Can 2N5088 be used to replace Q201 and Q202?

• Do you recommend replacing the peak limiter output (Q211)? If so, with what?

Whew!

[seveneves]

I had some edits to my last post but mistakenly hit "quote" instead of edit. Sorry 'bout that. I guess there's no functionality to remove/delete posts here.

[R.G.]

I did a quick study of the schematics between the V112 and the V1121. It seems that the activation of the fuzz is merely by grounding out the K401 relay? If so, what I was thinking (instead of drilling another hole in the chassis) is to do a similar thing happening with the reverb and tremolo switching function: use a TRS 1/4" in place of the MRB RCA and then I can switch the MRB *AND* the fuzz... do you see a problem with that? Then I could utilize your PCB and get the fuzz functionality.

I believe that will work fine.

Speaking of which: are you planning to make these PCBs available for purchase? I couldn't find any means of acquiring them, either through geofex.com or other, despite documentation being available.

They were available (and still are...). I just quit advertising them. You can get one.

A few more questions on transistors now that you have me thinking about it...

• I read on geofex that you've also mentioned the 2SC1815 as an ideal replacement. Would the slight increase of noise be discernable over the 2N5088, especially if I were to replace them more-or-less wholesale (i.e., does the noise add up?)?

• Do I need to purchase more of these small signal transistors than what's actually needed in an effort to sort for specific characteristics besides gain?

• Can 2N5088 be used to replace Q201 and Q202?

• Do you recommend replacing the peak limiter output (Q211)?

Re: 2SC1815 vs 2N5088: For this purpose, the only difference is the pinout. The 1815 has a collector-center pinout, which is what the originals were. The 2N5088 is center-base, so you would have to bend pins to fit the original holes in the Thomas PCB. I laid out the preamp boards for 2N5088s. The slight differences in noise are immaterial in this application. Another issue is availability. The 1815 is no longer being manufactured, but leftover stocks are OK, I think. The 5088 is still being manufactured. The noise does not add up to any real extent. In any amplifier, the noise of the input stage far dominates the noise of the whole rest of the amp because its noise is amplified by all the later stages. For me, I would replace them all with 2N5088, not least because I have a couple of hundred.
Re: buy many to sort: You will almost certainly not need to sort them. The Thomas Vox amps are highly forgiving of gain variations as long as it's enough, and 5088s (and 1815s) are. I have not ever needed to select them. The exception is in the limiter circuit and the transformer driver, which isn't a TO-92 anyway. So get the right number plus a few spares and you're probably Golden.
Re: Q201 and Q202: Q201, sure. I've used a 5088 for that position. 2N3904 works there, too. Q202 is not suitable for a TO-92, as it needs to handle too much voltage and current. I would pick one of the many and several TO-126 or TO-220 medium power devices. I started to type "KSC2073", which I recommended for the Guardsman and Beatle for years, but I see that Mouser no longer stocks it. I'll have to go filter through online selection guides to come up with a good alternate. I dimly remember the BD139 and TIP31C working, but that needs checking.
Re: replacing the peak limiter output Q211: The limiter circuit is a little touchy in some of these amps. I'd say replace all the electros, the input transistors, and the two recovery transistors in the reverb receive and the tremolo, then see if you're up and running OK. Leave the limiter alone until it's proven not to work right; excepting that its electro caps need replaced in the all-electros sweep. Thomas did (at least) three versions of the limiter, with different transistors, resistors and hence gain apportionment from the first to second transistor. Put off dealing with the touchiness until you need to.

[seveneves]

Q202 is not suitable for a TO-92, as it needs to handle too much voltage and current. I would pick one of the many and several TO-126 or TO-220 medium power devices. I started to type "KSC2073", which I recommended for the Guardsman and Beatle for years, but I see that Mouser no longer stocks it. I'll have to go filter through online selection guides to come up with a good alternate. I dimly remember the BD139 and TIP31C working, but that needs checking.

Yes, the straight KSC2073 is obsolete but I'm hoping the TU and H2TU suffixed versions will work?

[R.G.]

Dang! missed those variants. Yep, they'll work fine.

[seveneves]

Unfortunately, I'm not a reverb tank expert. I think you got it right, as the reverbs are high impedance and do sit open side down in the cab; and they have input grounded, output open.

(I'm asking more questions than I initially anticipated. Guess I should have created a new thread? Oh well...)

I'm getting confused on the reverb pan specs as I've been thinking about it. Because this particular amp is a V112, it has a transformer driving the reverb. I know in classic Fender reverb amps, the tank is also driven similarly. But, in the case of the Fender, those tanks are 8-ohm, low input impedance. I know the V11x3 forego the reverb transformer and I suspect this is where the high input impedance tank is used.

Wanted to validate with you as you have much more knowledge on these Thomas Organ Voxes. Am I purchasing a replacement tank with a 150 ohm or 1475 ohm input impedance for my V112?