Vox Berkeley II

[Leo_Gnardo]

Magical?
I don't believe in magic so any mention of it in a Musical/Tech context will bring the same respect as homeopathy/astrology/gemology or Reiki.

Now as of the sound, it was the Beatles' sound,period.
You want to sound like the Beatles? ... you get a Vox ; you don't, go get something else.

It's the germanium - there's your gemology. Good observations also on interstage transformer, the DC field within it, "lame" drive, etc. all added up to an amp with a special sound.

One of my good customers dropped off a SS Beserkely & said rip out the guts, build a tube Beserkely in it. Glad I haven't done that yet, not looking forward to a hard days night making that conversion. I'll have to flag his attention to this discussion & I hope he'll relent, let that poor little amp just "be what it is." Some fresh electrolytic caps all around, I bet it will run just fine.

[R.G.]

Thanks, JM! I could guess at some of that, but I'm by no means fluent.

I guess it's entirely subjective, but I wish someone could tell me what is magical about these amps that wasn't magical in the 70s and 80s. I remember them being door stops that we bought to take the speakers out of. I remember buying Super Beetles for $80 with the head, cabinet, and frame. Now the tube models have been desirable throughout all of these decades. But these old germanium Voxs? Really?

There are many times where I curse not being able to buy those $80 Beatles. I was busy supporting a family on not very much and had to put most of my music efforts on hold.

As to the question, it is subjective. First and foremost, magic *does* exist, but it exists only inside the human mind. The human mind is capable of enormous feats of self-convincing about almost anything.

One issue is that the Thomas Vox amps suffered from being attached to other solid state amps. Other solid state stuff of the era had bad crossover problems and harsh clipping. The Thomas stuff retained the older transformer drivers that sidestepped some of that, and the later Thomas amps had that "watchdog limiter" that didn't so much limit output as make for soft and well-controlled power amp clipping. I speculate that they were damned for their poor reliability, and then suffered guilt by association, along with piling on.

Another issue with the Guardsman and Beatle models is that Thomas insisted on designing them as a combination guitar/bass/vocalist PA unit and put those silly horns in them. The horns make them sound like jagged glass. Disconnecting the horns is a great step forward.

And they were by and large not "germanium". The only germanium devices in the Thomas Vox amps were PNP power devices in the smaller amps. The Pathfinder, Pacemaker, Cambridge, Berkeley II, Buckingham and Viscount had germanium outputs. None of the other transistors in them were germanium. The outputs replace with silicon PNPs and a little rebiasing, and this does not affect the sound much if at all.

[R.G.]

I have a Cambridge Reverb somewhere. I think it's a half power, single 12 (or 10?) version of the same amp. I'll dust it off and give it a try.

The Cambridge is a full power version of the Berkeley II; it just has one 10" speaker in a combo instead of two tens in head-and-cab. The electronics are identical.

[R.G.]

It's the germanium - there's your gemology. Good observations also on interstage transformer, the DC field within it, "lame" drive, etc. all added up to an amp with a special sound.

As you're more than likely aware, simply rubbing germanium transistors on a circuit does not make for a lot of differences in sound. Besides, the only germanium in the Thomas Vox amps was in the output transistors of the smaller-power amps.

One of my good customers dropped off a SS Beserkely & said rip out the guts, build a tube Beserkely in it. Glad I haven't done that yet, not looking forward to a hard days night making that conversion. I'll have to flag his attention to this discussion & I hope he'll relent, let that poor little amp just "be what it is." Some fresh electrolytic caps all around, I bet it will run just fine.

I think it will too. I'm pretty conflicted on this topic. I had an original tube Berkeley, and they are one of the best sounding USA amps ever. But I do love the sound of the SS Berkeleys. So much that I created a replacement PCB for the Cambridge/Berkeley to fix the ones that don't work. Yes, please try to convince him not to destroy it.

Frankly, there is not a lot of sheet metal work involved in making a new chassis that fits the Berkeley head. A little talk with a sheet metal shop could get a metal chassis that would hold the tube Berkeley and be interchangeable on the same head without destroying the only amp. I have drawings of the sheet metal if that will help.

[J M Fahey]

Not many VOX amps this part of the World, if any at all, way back then closed Customs doors plus high USA price plus being so strongly associated with The Beatles (that was the main advantage *and* handicap at the same time, what eventually killed them until the resurgence with Queen many years later), but I distinctly remember the chunky punchy sound of early Acoustic amps, the transformer driven ones, same as we are seeing here (but all Silicon, we skipped the Germanium era).

Main point I remember was that , being the poor/no PA era all were customarily overdriven (tube amps too), not because a special sound was searched but in a desperate move to be heard through the muddy ball of sound, in large horrible acoustics venues.

And when overdriven they were fat and punchy, into a good cabinet of course, which here was a 4x12" loaded with LEEA speakers, Altec Lansing clones built under licence.
As I said before, the above FAPESA amplifier was the SS MI amp standard, period.

In fact, when I started selling my first 200W amps, many (even shop owners) challenged me that "there is not such a thing as a 200W amp" and "open that chassis , we *know* you have a driver transformer there, you are selling what all others do" ... they were amazed when they saw no driver there.

The point is that the FAPESA gives you *almost* 100W , very good ones at that, and not a drop more, because of the lack of drive current: the transformer is 1:1 and idle current is 12V/50 ohms= 240mA peak best case, probably only 200mA peak into the 2N3055 base.
100W/8 ohms takes 5A peak so transistor Hfe @ 5A should be 5/0.2=25 ... almost impossible, so overdriven amps were current limited and in a way behaved similar to what, say, a Twin Reverb output did: a reasonable damping factor while clean, turning into poor damping (good) when overdriven, so distortion had both body and bite.
Add to that low NFB and the amps are closer to tube behaviour than what looks on first sight.

Even adding parallel transistors dis not help much, since available base current stayed the same.

I could successfully fight and eventually beat them, because my TIP31/32 drivers could supply as much as 3A peak and my guitar amps easily provided more than 200W RMS into 2 ohms cabinets, while the Bass ones provided twice as much int 2 x 4 x 12" stacks.

Musicians played with them , unamplified, (cheesy PA was good only for voice and drums) in Luna Park, our Buenos Aires Madison Square Garden clone.

Now the Thomas VOX amps had a 3:1 or 6:1 (RG ?) ratio so base current was much higher and they were spec'd as 120W into 2 ohms loads with +/-31V rails; it's curious that the UK ones were completely different : totem pole series outputs, hairy +/- 70V rails, 100W into 16 ohms.

"Somebody" (I'm looking at you, RG ) should build both power amps, USA and UK, and try them side by side ... obviously each into the proper cabinet.
You might add a FAPESA to the test , I wouldn't mind

FWIW our M.I.A. friend Steve Conner built a hybrid amp, an EL84 output stage driving a transformer driving a couple power transistors ... MP3 clips were very good.

[R.G.]

Not many VOX amps this part of the World, if any at all, way back then closed Customs doors plus high USA price plus being so strongly associated with The Beatles (that was the main advantage *and* handicap at the same time, what eventually killed them until the resurgence with Queen many years later), but I distinctly remember the chunky punchy sound of early Acoustic amps, the transformer driven ones, same as we are seeing here (but all Silicon, we skipped the Germanium era).

Main point I remember was that , being the poor/no PA era all were customarily overdriven (tube amps too), not because a special sound was searched but in a desperate move to be heard through the muddy ball of sound, in large horrible acoustics venues.

And when overdriven they were fat and punchy, into a good cabinet of course, which here was a 4x12" loaded with LEEA speakers, Altec Lansing clones built under licence.
As I said before, the above FAPESA amplifier was the SS MI amp standard, period.

Interesting. It's a whole different technical branch.

I had to search literally for years to find any tech info on driver transformers at all.

The point is that the FAPESA gives you *almost* 100W , very good ones at that, and not a drop more, because of the lack of drive current: the transformer is 1:1 and idle current is 12V/50 ohms= 240mA peak best case, probably only 200mA peak into the 2N3055 base.
100W/8 ohms takes 5A peak so transistor Hfe @ 5A should be 5/0.2=25 ... almost impossible, so overdriven amps were current limited and in a way behaved similar to what, say, a Twin Reverb output did: a reasonable damping factor while clean, turning into poor damping (good) when overdriven, so distortion had both body and bite.
Add to that low NFB and the amps are closer to tube behaviour than what looks on first sight.

Yep. Starved base current is a component. The 2N3055 and variants were the workhorse power transistors of the era. And they were distinctly marginal at total power supplies over 60V.

Even adding parallel transistors dis not help much, since available base current stayed the same.

Interesting point: beta fall off. The 2N3055 and its contemporaries had decent beta up to perhaps 3A, but current gain fell off rapidly after that. This drop in current gain caused a compression by the transistors not only being base current limited, but also gain limited on top of that. It's a transistor effect that not may people consciously sort into the power amplifier design. On the other hand, beta fall off meant that paralleling might succeed better that one would think, as splitting up the output current well below what you needed to do for power or second-breakdown considerations meant the devices were operating at much lower currents, and hence in the higher gain parts of their characteristic. Adding many parallel transistors may well have helped, but it's quite an expensive way to solve the problem.

Modern power transistors do much better. The Toshiba power sets have gain that hardly falls at all out at higher currents, as do some of the newer ON Semi devices.

Now the Thomas VOX amps had a 3:1 or 6:1 (RG ?) ratio so base current was much higher and they were spec'd as 120W into 2 ohms loads with +/-31V rails;

The Beatle and Guardsman were about 4.5:1, based on reverse engineering. I only recently received a "victim" to actually unwind and find the true story of their ratio and turns. But they did have a stepdown.

If I were winding one of the driver transformers you posted, I would be very tempted to wind it quad-filar (four wires all in parallel) and be able to series or parallel two of the windings on the primary to test out the step up/down operation. Running the primary driver at higher voltage and lower current is easier on the driver.

I notice that the picture shows a 2N3055 as a driver device (did I get that right?). That makes sense if you need to drive a 1:1 output. Thomas used +27V for the driver voltage supply, and biased the Beatle driver at about 250ma. It was stepped up by over 4:1 by the ratio, so the Beatle output devices could run on about 500ma each, substantially more base current.

it's curious that the UK ones were completely different : totem pole series outputs, hairy +/- 70V rails, 100W into 16 ohms.

Well, the Supreme model did. The Brits always liked 16 ohm speakers, and that needs more volts. The Conqueror and Defiant used the same preamp section as the Supreme, but they had lower voltages on the output and did not use the totem pole stack on the output that the Supreme did. The Supreme/Conqueror/Defiant series were remarkably similar to the Buckingham/Guardsman/Beatle series in many ways in the preamp section as well.

"Somebody" (I'm looking at you, RG ) should build both power amps, USA and UK, and try them side by side ... obviously each into the proper cabinet.
You might add a FAPESA to the test , I wouldn't mind

I'd love to - but it will have to go into the list somewhere below finishing the "Vox Owner's Safety Net" book I'm writing. The book and accompanying per-model technical repair guides, and the replacement preamp PCBs that are now going out are intended to help keep US/Thomas Vox amps out of the dumpster. This is much more than the Thomas Vox service literature's schematic and parts list. I hope I can save some of them.

[J M Fahey]

Ok, fine.

I fact I must actually have one or two Argentine amps driven by "FAPESA 100W" in the junk pile ... the problem is finding them.

If I do, and the drivers are fine, I'll repair and test them ... with MJ150xx transistors of course.

I repaired at least one of them, in a hurry (think Saturday afternoon 2 hours before the show) with a couple fake-but-not-that-bad Red script "Toshiba Japan" (yea, sure) 2N3055 supplied by the customer.

By some kind of miracle, they held that night , but died a few days later, the customer wouldn't wait and bought one of my regular 100W heads (fine with me) leaving the carcass.

So I have basically what's needed for the test, save the beefier transistors which I'll get when I go downtown.

EDIT: yes, the driver was another 2N3055 ... cheaper and easier to find than some funny TO66 metallic.

[R.G.]

There are to220 devices today that do the driver job well. I specify a 2SC2073 for a replacement driver in the Thomas Vox rebuilds. So far it's worked ever time. It's rated at 150V, 20W, 1A dc. It's SOA includes 20V/1A at DC, and the hfe rises from 0- current to 350ma before starting to fall off. And it's cheap - about US$0.50-0.80 in ones.

[Jot]

One of my good customers dropped off a SS Beserkely & said rip out the guts, build a tube Beserkely in it. Glad I haven't done that yet, not looking forward to a hard days night making that conversion. I'll have to flag his attention to this discussion & I hope he'll relent, let that poor little amp just "be what it is." Some fresh electrolytic caps all around, I bet it will run just fine.

Your customer should try cranking the Brilliant channel on the Berkeley---maybe with a boost pedal, just for fun---and playing the intro to Sunshine Of Your Love. Roll off the tone on the guitar, and you're in Clapton/Marshall brown sound territory. These SS California Voxes will pass anyone's blindfold test--even Olddawg's, I would bet---in a comparison with a tube amp, I suspect, except that they're far more versatile than the equivalent tube amps.

[loudthud]

I dug out that old Cambridge. It has a 4 Ohm 10 inch speaker so it is the same power as the Berkeley II. When I played through it the speaker sounded like it wasn't all there so I plugged into a Marshall 4x12. Not much different so I think it's time for a cap job. Even at low levels, it does have a nice sweet tone. The insides of this thing are a nightmare. The PCB does have the same number as the PDF file, but there are some differences, a couple of components in no-mans land on the left side of the PCB. And lots of components on terminal strips not shown in the pdf. This amp is a V1032 and it has an E tuner. I'm gonna have to take pictures just so I can get it all back together and in working condition. I'll have to go shopping for axial leaded caps and try to find non-electro film caps to replace the NP electros.

[lowell]

I'm recapping this Berkely II as we speak. Using polarized electros for the NP ones. Don't see any issue looking at the schematic as long as orientation is correct. If you disagree please do enlighten.

[R.G.]

The insides of this thing are a nightmare. The PCB does have the same number as the PDF file, but there are some differences, a couple of components in no-mans land on the left side of the PCB. And lots of components on terminal strips not shown in the pdf.

Yep. Thomas Organ didn't do really neat assembly. I suspect the component changes and additions are related to the model change. The 1032 added the E-Tuner, and they pasted some more parts in on the same old PCB.

I'm gonna have to take pictures just so I can get it all back together and in working condition.

I did a PCB that replaces it all. New parts, new board, same schematic.

I'll have to go shopping for axial leaded caps and try to find non-electro film caps to replace the NP electros.

1. Don't go for axials unless you have a thing with originality. The leads on radials can be easily bent to fit. Also, it is **possible** if you are good with a soldering iron to clip out the axial from the top side and solder the replacement cap's leads to the old stubs on the component side. Takes some skill, but possible. Axials are much more expensive, too.
2. Use film caps to replace the 1uF and 2uF NP electros. They'll never rot away and die again later.

I'm recapping this Berkely II as we speak. Using polarized electros for the NP ones. Don't see any issue looking at the schematic as long as orientation is correct.

Polarized caps actually need a polarizing voltage. If the voltage across them isn't a significant fraction of their rating, they tend to have more like shelf life than working life. NPs have oxide on two facing surfaces are are more resistant. NPs should be used for low-DC and true AC situations if you can't replace with film.


Here's the replacement board being tucked into the Berkeley II, which is electronically identical to the Cambridge.

I was on a mission to clean up the rats' nest of wiring.

[J M Fahey]

I did a PCB that replaces it all. New parts, new board, same schematic.

Here's the replacement board being tucked into the Berkeley II, which is electronically identical to the Cambridge.
[ATTACH=CONFIG]35806[/ATTACH]
I was on a mission to clean up the rats' nest of wiring.

WOW !!!!!!!!!!!!!!!!!!!!!!!!!!!!

Congratulations !!!!!

[lowell]

Wow. +1! Are they for sale?

[R.G.]

I had to buy several when I did the prototype. Yeah, I can sell you one. Email or PM me and I'll send the documentation so you can see what you're getting into.

I put the docos on geofex, but the host for geofex is having some kind of problems so geofex is temporarily off line.