Thomas Vox SS Royal Guardsman - repair shop near Baltimore?

[Jot]

My Royal Guardsman head worked for about a week after I bought it via eBay a few years ago. I've been putting off finding a repair shop since then; I'd bought it mostly out of nostalgia, since that was the first amplifier I owned in the early '70s. (Used my original Royal Guardsman head with a 16-ohm Marshall 8 X 10 cabinet back then; didn't realize that it would have been a lot louder with a 4-ohm cabinet. Live and learn.)

But now I'm inspired to get the Royal Guardsman head working after playing through my recently acquired Vox Buckingham (with original 2 X 12 cabinet and TV stand) at a Gretsch Roundup here in Baltimore. Several players made a point of complimenting me on the sound of the amp, not knowing (until I told them) that they were listening to 45-year-old solid-state technology.

The Buckingham has a sticker on the back of the reverb tank with the name, phone number, 2001 repair date, etc., of the repair shop that refurbished the amp for the guy from whom I bought it. Unfortunately, the phone number has been changed to an unlisted number and I can find no record of the shop name and location in Google searches.

So---is there anyone on this list who is near Baltimore and is ready and willing to work on a solid-state Thomas Vox head? I have the Royal Guardsman schematics, which I bought from North Coast Music and which I'm using right now to cobble together a footswitch (mostly for access to the Buckingham's built-in fuzz); also, I know where to direct a repairman to find R.G. Keen's extraordinary Vox troubleshooting tips on line.

[R.G.]

The Thomas Vox "big head" amps are my nomination for best sounding solid state amps ever, at least with the original speakers.

I wish I could help with a repair shop recommendation, but I can't. These amps are just flat hard to repair, even for me and I'm a nut, and an electronically experienced nut too.

I'm in the process of repairing several of them (no, sorry, I can't take on another one; it's a long, sad story) and I'm taking pictures of the process that will eventually go on the web site. The bottom line is that they are electronically simple, but mechanically complex. It's easy to break wires while you're fixing on them.

I would be happy to do some telephone consultation for free to whomever you get to dig into it. Be prepared for him to charge you for the bench time, probably in the range of $200 or so. It's a big job. But what you get back is worth the effort, IMHO.

[JHow]

...It's easy to break wires while you're fixing on them...

Amen to that. They are cantankerous, and any movement of the board can set them off.

[Jot]

I share your enthusiasm for these Thomas Vox amps, R.G. I'll bet that, in the 1960s and early '70s, at least half of the West Coast garage and psychedelic bands gigged and recorded with them---Music Machine, Electric Prunes, Chocolate Watch Band, etc. For example, "Frantic Desolation," on the first Sopwith Camel album, has a very Thomas Vox-sounding fuzz guitar solo. Funny that there are plenty of guitar-playing fans of that music who would never consider plugging into a solid-state amp.

Still hoping that someone nearby me who's willing to take a look at the amp will reply to this thread. If not, I'll try the longest-established music store in the area---Bill's Music, in Catonsville, MD---to see whether they'd like to take a crack at the Royal Guardsman. I believe that their service manager has been working there since at least the early '70s, so he may be somewhat familiar with the Thomas Vox family of amps.

[R.G.]

I hope you have good luck with it. As I mentioned, I'll be happy to offer any advice or experience I can lend by telephone to whomever takes it on.

Forgot: which model number is it, 1131 or 1136?

[Jot]

I hope you have good luck with it. As I mentioned, I'll be happy to offer any advice or experience I can lend by telephone to whomever takes it on.

Forgot: which model number is it, 1131 or 1136?

I believe that it's the 1131, but I'll check when I get home tonight.

[drewl]

With RG's wonderful page on Thomas Vox repair, I've worked on quite alot of these over the years!
(I owe you a few drinks if I ever meet ya' RG!)
If you want to ship it to Pa, then again if you want to ship it there should be a few people out there that could get it up and screaming again.

[52 Bill]

If you ship it out, the two amp sections can be removed from the case and shipped in a smaller box. That being said, it does not come apart that easily as there are a couple of 1/4" hex head screws that can be difficult to remove.

More importantly, you never said what was wrong with the amp. If it worked when you first got it, it may be something simple that came loose during shipment. Are you handy?

[Jot]

Turns out the head works after all, after reassembly (took it apart years ago, looking for easy fixes) and some coaxing (the problem was squealing and motorboating, but plugging and unplugging the guitar cord a number of times seemed to make those problems gradually disappear). 52 Bill, thanks for asking what was wrong. If you hadn't asked, I would have taken the head to a repair shop instead of checking it out first.

As it is, assuming the squealing and motorboating don't recur, the one remaining problem is that the top boost doesn't work. I suspect switch contact corrosion, since it seems likely that the squealing and motorboating were caused by corrosion on shorting input jacks. Corrosion is probably a good guess; the circuit boards are covered with decades-old filth, so the switches and pots are probably pretty dirty too. They crackled and worked intermittently until I switched and rotated them all several times. If cleaning the top boost switch contacts doesn't help, I'll be back for advice, since top boost is a great feature of these heads.

R.G. asked the model number. The Royal Guardsman is a V1133, serial number 1203448. The Buckingham is a V1123, serial number 123768. If it's actually possible to ascertain the year of manufacture from the serial number, I'd be interested to know when these were built.

I have one more Vox head with problems: a British mid-'60s AC-50 with erratic tone controls. I'll haul that one out of the closet and check it out so that I can specify the symptoms in a new thread.

[52 Bill]

I think that you need to get a can of Deoxit and spray the pots, switches, jacks and the chassis interconnects of the head.

I've had to clean those rocker switches multiple times to get them working again, but they usually do come back with a little coaxing.

Sounds like the same treatment for the pots on the AC-50.

[cthulhu]

I'm curious about which heads you're repairing. I have a '67 Vox Defiant head and the distortion channel isn't nearly as loud as the normal channel. I'm wanting that Hey Bulldog fuzz and it doesn't quite do it. I've thought of rebuilding the distortion circuit card but I haven't replaced all the electrolytics in the amp yet either (since plugged into the normal circuit the amp sounds fine).

When I first got it, only one of the output transistors was working, and the reverb doesn't work (still). Finding a replacement mono cartridge with the same package characteristics is a futile task. Any hope for it? Thoughts on getting the distortion circuit sounding more stock?

Thanks,

The Thomas Vox "big head" amps are my nomination for best sounding solid state amps ever, at least with the original speakers.

I wish I could help with a repair shop recommendation, but I can't. These amps are just flat hard to repair, even for me and I'm a nut, and an electronically experienced nut too.

I'm in the process of repairing several of them (no, sorry, I can't take on another one; it's a long, sad story) and I'm taking pictures of the process that will eventually go on the web site. The bottom line is that they are electronically simple, but mechanically complex. It's easy to break wires while you're fixing on them.

I would be happy to do some telephone consultation for free to whomever you get to dig into it. Be prepared for him to charge you for the bench time, probably in the range of $200 or so. It's a big job. But what you get back is worth the effort, IMHO.

[R.G.]

I'm curious about which heads you're repairing.

It's a USA Vox, manufactured by Thomas Organ.

I have a '67 Vox Defiant head and the distortion channel isn't nearly as loud as the normal channel. I'm wanting that Hey Bulldog fuzz and it doesn't quite do it. I've thought of rebuilding the distortion circuit card but I haven't replaced all the electrolytics in the amp yet either (since plugged into the normal circuit the amp sounds fine).

I harp on replacing electrolytics because I've brought a number of Thomas Vox amps back to life by doing that. Electrolytics decay inside over time. I'm glad to see the original poster could get it to work with less invasive techniques (and the Caig Labs Deoxit stuff is absolutely correct!) but this just means that an electro cap inside the head hasn't completely failed. Yet. My Thomas Vox Beatle head squealed uncontrollably no matter what I did until I replaced the filter cap in the reverb driver circuit after days of debugging, and repairing wires I broke while debugging. That one cap replaced made it sweet as silk.

For two months. Then another cap let go in the normal preamp. Then one in the limiter. At that point I took note that it was only a little more misery to replace all the caps than it was to open it up again. Never looked back. It is still working 12 years later.

But back at your Defiant.

When I first got it, only one of the output transistors was working, and the reverb doesn't work (still). Finding a replacement mono cartridge with the same package characteristics is a futile task. Any hope for it? Thoughts on getting the distortion circuit sounding more stock?

I've just dug through a Defiant and the service literature therefor in detail in the last year. The Defiant is remarkably easier to work on than the Thomas Vox heads. You can actually take them apart with some semblance of grace. Be @#$%@$ sure you are careful with the hardware, as it's all British hardware, fine thread stuff, and easily available USA hardware does not fit the threads.

You're right about the piezo cartridges in the reverb being a lost cause. I never found any. I rewired a Supreme to use a stock magnetic reverb delay line years ago. Not fun. Use a reverb pedal.

Getting the distortion circuit to sound right is not tough. After a year of so of effort, I have the correct - and readable - schematic for that preamp. The service lit from Vox is illegible in every copy I've ever found. I traced the values from the one Defiant head I was privileged to have loaned to me (Thankyouthankyouthankyou, you know who you are!) and some pictures of other boards all over the world.

I would suggest - yep, replace all the electros as a starting point. That may be all it needs.

One caution. The distortion is on the same board as one of the preamps. You have to take the preamp board out to get to the distortion. The PCB is on screwed-in metal standoffs which have nuts on the component sides of the PCB. Two of the standoffs have their flat screw heads under the appearance trim plate. If the nuts come off, fine. If they stick and the standoff and screw spin in place, you'll have to take all the controls and all the switches off the control panel to remove the appearance plate to get at the heads of the PCB standoff screws.

The British fine thread hardware and those standoffs were the only cursing I did at the mechanical layout.

[cthulhu]

Thanks RG!
Couple more things. On mine I had to replace the inductor, and I've had the PCBs out. I'm familiar with the HAIR thin connector wires. I've had no issues with the connecting hardware.

When I got mine it had issues in the power amp. One of the biasing adjustable resistors was set to keep the trannie always off. I had to replace the sliding resistor and bias correctly. Also, there are 820 ohm resistors that are 1 watt but when you check the math are pulling more than 2 watts. On mine they were burned. I replaced them with 3 watt versions.

On replacing electrolytics, do you mean ALL of them, even the ones that are normally not electrolytics in amps but were used because higher value non electrolytics weren't easy to get??

pix; I can provide some pix of my amp guts if you'd like for your reference. With the schems I had and looking at the PCB I was able to get the values from the circuit.

I don't have the original cab, I'm using a closed back Bluesbreaker extension cabinet, 16 ohms with one weber silver bell and one blue dog, both 30 watt speakers and 12".

It's a USA Vox, manufactured by Thomas Organ.


I harp on replacing electrolytics because I've brought a number of Thomas Vox amps back to life by doing that. Electrolytics decay inside over time. I'm glad to see the original poster could get it to work with less invasive techniques (and the Caig Labs Deoxit stuff is absolutely correct!) but this just means that an electro cap inside the head hasn't completely failed. Yet. My Thomas Vox Beatle head squealed uncontrollably no matter what I did until I replaced the filter cap in the reverb driver circuit after days of debugging, and repairing wires I broke while debugging. That one cap replaced made it sweet as silk.

For two months. Then another cap let go in the normal preamp. Then one in the limiter. At that point I took note that it was only a little more misery to replace all the caps than it was to open it up again. Never looked back. It is still working 12 years later.

But back at your Defiant.


I've just dug through a Defiant and the service literature therefor in detail in the last year. The Defiant is remarkably easier to work on than the Thomas Vox heads. You can actually take them apart with some semblance of grace. Be @#$%@$ sure you are careful with the hardware, as it's all British hardware, fine thread stuff, and easily available USA hardware does not fit the threads.

You're right about the piezo cartridges in the reverb being a lost cause. I never found any. I rewired a Supreme to use a stock magnetic reverb delay line years ago. Not fun. Use a reverb pedal.

Getting the distortion circuit to sound right is not tough. After a year of so of effort, I have the correct - and readable - schematic for that preamp. The service lit from Vox is illegible in every copy I've ever found. I traced the values from the one Defiant head I was privileged to have loaned to me (Thankyouthankyouthankyou, you know who you are!) and some pictures of other boards all over the world.

I would suggest - yep, replace all the electros as a starting point. That may be all it needs.

One caution. The distortion is on the same board as one of the preamps. You have to take the preamp board out to get to the distortion. The PCB is on screwed-in metal standoffs which have nuts on the component sides of the PCB. Two of the standoffs have their flat screw heads under the appearance trim plate. If the nuts come off, fine. If they stick and the standoff and screw spin in place, you'll have to take all the controls and all the switches off the control panel to remove the appearance plate to get at the heads of the PCB standoff screws.

The British fine thread hardware and those standoffs were the only cursing I did at the mechanical layout.

[R.G.]

Thanks RG!
Couple more things. On mine I had to replace the inductor, and I've had the PCBs out. I'm familiar with the HAIR thin connector wires. I've had no issues with the connecting hardware.

Yep. The Defiant is much, much easier to work on than the Thomas Vox stuff.

When I got mine it had issues in the power amp. One of the biasing adjustable resistors was set to keep the trannie always off. I had to replace the sliding resistor and bias correctly. Also, there are 820 ohm resistors that are 1 watt but when you check the math are pulling more than 2 watts. On mine they were burned. I replaced them with 3 watt versions.

Good catch.

On replacing electrolytics, do you mean ALL of them, even the ones that are normally not electrolytics in amps but were used because higher value non electrolytics weren't easy to get??

I mean all electrolytics. Every single one. Electrolytic caps have a built-in wearout mechanism. The insulator in aluminum electrolytics is aluminum oxide, literally grown on the outside of the aluminum conducting foils by an electrolytic process, hence the name. It's relatively stable, but over time does dissolve back into aluminum and oxygen in the semifluid electrolyte. Eventually, all electrolytic caps get leaky and go bad. The only question is when. Cap makers only guarantee a shelf life of about five years. Electros last longer if you turn them on periodically, as the voltage on them helps re-form the insulator in the thin spots. But it's a race against time.

So my advice for amps which are over forty years old is to set them all to "new" at one time. That way when one goes and you fix it, you don't have to fix another one next month. I'm a big proponent of things oughta work when I turn them on. Other people value not replacing old components more than having the amp work reliably. It's a different viewpoint. I view amps which are "too vintage" to replace about-to-fail parts as pieces of sculpture. Nice, perhaps, but too rich for my pocketbook. If it doesn't work reliably, it had better be pretty because some day all you can do is look at it.

Enough ranting. Yes, I advise replacing them all. The ones which were used for filter/timing components where big enough non-electros were not available, replace if you can with modern film caps. You can now get 63V 1uF and 2.2uF film caps for under US$1 each. These do a great job of what the original designers wanted to do but could not. IF it's smaller than 2uF, put in film. If it's bigger, put in a new electro.

pix; I can provide some pix of my amp guts if you'd like for your reference. With the schems I had and looking at the PCB I was able to get the values from the circuit.

I'd very much appreciate you doing some checking, and providing pix. I've actually done a reverse-engineering effort and have encapsulated the entire brilliant channel, with distortion and added tremo from the normal channel onto a single PCB. It's been shelved for quite a while as other things ate up my time, but I'm in the process of dusting it off.

I don't have the original cab, I'm using a closed back Bluesbreaker extension cabinet, 16 ohms with one weber silver bell and one blue dog, both 30 watt speakers and 12".

If you're a wood worker, I also have collected the dimensions of the Defiant cabinet, with the aim of making myself one. Just a thought.

I'll PM about the pix.

[cthulhu]

I also forgot to mention that the trem still works like a dream and sounds like The Beatles' "Flying".

If you're a wood worker, I also have collected the dimensions of the Defiant cabinet, with the aim of making myself one. Just a thought.

I'll PM about the pix.

I answered your PM, but about the cab, what would you do about the horn? Is that a decent part of the tone equation?

I had dreamed of marrying the Defiant/Conquerer distortion preamp channel to the 7120 power amp section (or something similar) because I think the all guitar amps sound better without the ss ice pick top end from ss power amp.