Vox Berkeley Super Reverb

[Brad1]

Vox Berkeley Super Reverb tube amp...one tube missing. I'm guessing it's the rectifier 6CA4/EZ81 coming from the power supply?

Schematics? Is this basically a Cambridge in head form, called a Berkeley...same schematics?

I need to figure out where the reverb leads go, change a couple caps, install a grounded cord. Bypass "Line Reverse" switch after installing grounded cord?

Resolder someone else's sloppy job. Test the old Telefunkens and find two
EL84's that aren't different brands and (obviously) different ages.

How many of these things are floating around? Most Berkeleys I've seen were SS. Anyway...shouldn't take too much to get this thing going.

Thanks,

Brad

[52 Bill]

Originally Posted by Brad1

Schematics? Is this basically a Cambridge in head form, called a Berkeley...same schematics?

Yes, the same amp with 2-10's in a piggy back design.

Originally Posted by Brad1

How many of these things are floating around? Most Berkeleys I've seen were SS.

Like the tube Cambridge Reverb, they only made these for a short time before switching to all solid state.

[Brad1]

Once again...Bill comes to the rescue!

Thanks Bill. Most of these questions are for verification of what I THINK is right, but not 100% sure. I've printed out the Cambridge schematics, and it is obvious it's right.

Also, I like to throw things out there in case someone sees that I'm about to do something foolish, and get hints and warnings that I may have overlooked.

Thanks,

Brad1

[Brad1]

Looks like this thing needs a 40/30/10 multi-cap can. Anyone know where to find these...or something that would work? I've looked a few places. Oh...and I'll need some kind of mounting hardware for it.

Thanks,

Brad1

[Fretts]

http://tubesandmore.com
They have the old Mallory machinery and are making new can caps.

[R.G.]

Originally Posted by Brad1

Looks like this thing needs a 40/30/10 multi-cap can. Anyone know where to find these...or something that would work? I've looked a few places. Oh...and I'll need some kind of mounting hardware for it.

Leave the old can in place for looks. Mount new (and much smaller) axial electros inside the chassis.

[Brad1]

Originally Posted by R.G.

Leave the old can in place for looks. Mount new (and much smaller) axial electros inside the chassis.

I was hoping to avoid that. Not much room left in there, but I guess it will free up a bit right behind the old cap base.

And, they'd have to be pretty small to get three in there.

Checked with Antique Electronics...this is the closest they have 80, 40, 30, 20 (not use the 80, use the 20 for the 10?)


CAPACITOR, ELECTROLYTIC, 80/40/30/20 µF @ 525 VDC

C-EC80-40-30-20

Made in the USA, to Mallory's original specs, on Mallory original machinery. 80 µF, 40 µf, 30 µF and 20 µF section, all rated at 525 VDC.
1-3/8" diameter x 3 1/2" tall
-10% to 50% tolerance
Made in the USA by CE Manufacturing

The problem is that the original is only about 1" diameter, and not a lot of room between the side chassis and the transformer to mount it.

May have to think about 3 other caps inside chassis, and try to get a bit creative in there.

Thanks,

Brad1

[Fretts]

I have the same challenge, I have a Cambridge Reverb Combo. My plan is to use this one:
CAPACITOR, ELECTROLYTIC, 40/20/20 µF @ 500 VDC

C-EC40-20-20

Made in the USA, to the same specs as the Original Mallory, on Mallory's original machinery.

* 3 sections - 40/20/20 µF @ 500 VDC
* -10%, +50% tolerance
* 85° temperature rating
* 1-3/8" diameter x 2" tall

and piggy back an outside 10 onto one of the sections to get a 30, and use the remaining 20 for the final "10". I don't expect that having a little extra filtering on the 150V leg is going to hurt anything.
The 1-3/8 diameter will not cause any interference problems, I hope... that's 3/16 more on either side, plus this unit is shorter than my original.

If this proves to be impossible, and I can't stuff individuals inside the chassis (I think I probably could) then I will gut the original one, melt out the tar and stuff it with skinny individual caps and rebuild the thing. That is DEFINITELY a last resort.

[52 Bill]

Did anyone check to see if Ted Weber can make the smaller diameter multi-cap? I know that he was making the larger ones to order, maybe he has the smaller size as well.

[Brad1]

None listed on his site, Bill. But, I filled out the form to see what happens. 1" diameter x 3" length for existing one. A bit larger would probably fit, though not much. The chassis has a perfect triangular cutout that I may need to also deal with.

There's just not much room to put three individual caps inside the chassis.

Thanks,

Brad1

PS...Fretts, I'll post what Weber comes up with in case you want an idea. Will be AT LEAST $40...so....

[52 Bill]

Originally Posted by Brad1

...1" diameter x 3" length for existing one. A bit larger would probably fit, though not much. The chassis has a perfect triangular cutout that I may need to also deal with.

I guess you could re-build the cap yourself, or find someone that will do it for you. I read something on line somehwere, where antique radio guys would take the cap can apart and fill it with modern miniature electrolytics. New caps in the old case.

Just a thought.

[R.G.]

I guess you could re-build the cap yourself, or find someone that will do it for you. I read something on line somehwere, where antique radio guys would take the cap can apart and fill it with modern miniature electrolytics. New caps in the old case.

If this proves to be impossible, and I can't stuff individuals inside the chassis (I think I probably could) then I will gut the original one, melt out the tar and stuff it with skinny individual caps and rebuild the thing. That is DEFINITELY a last resort.

I have done this. It's not as big a pain as it sounds like. Drill a few holes in the phenolic end cap, use diagonal cutters to cut the rest of the cap out in pieces, then pull out the fillings. I didn't find any tar in the ones I opened, YMMV.

[Brad1]

It LIVES!!! A few minor problems, but sounds good so far.

Reverb only makes more noise as turned up...no 'verb. Check cables and connections and associated components.

Weird thing. Disconnected all the "Line Reverse" components. Now, 'Standby" doesn't work. It just turns on whether it's in "Standby" or "On", and the green light, only, works. Of course, I don't know if it worked before, so I don't know if that caused anything. Guess I'll have to get the old meter out and start tracing connections.

Little RCA speaker out jack is flaky, but works well with the 1/4" front panel "Aux Speaker" jack.

I'll mess with all this before I go further with caps, for now. Actually...not that noisy. Plugged a Les Paul in, cranked it up...and it was pretty loud and smooth through an EVM12L speaker.

Brad1

[Brad1]

Can't get my head around this. When someone removed the "convenience plug" wires, it seems they did some other rewiring.

I removed the Line Reverse wiring and cap, and installed a grounded cord. Black wire to fuse and to the primary winding, white wire to switch common. The Cambridge schematics show the "On" and "Standby" switch lugs jumped, and then going to the other end of primary winding. No problem...it's wired that way. And, now, in Standby, the Standby lamp lights, and in "On" the On lamp lights. (Originally, whoever did this had the white going to On position). But, it does not go into standby. It is on, either way.

On the secondary winding, it shows the switch common to ground, which it is. It shows the switch down (standby) position connected to in between the lamps, and it is. It shows the switch up position (On) going directly to the center of the secondary winding....and that's my problem. It's actually going to the grounded contact of the On lamp.(All schematics I have found is missing the very bottom symbol of that light...but I'm assuming it's ground?)

The circuit end (center contact) of the standby lamp goes to pin 5 of the 6AC4 tube...not pin 4 as shown.

Which wire is the center tap of that secondary winding where the On switch connects? Should I move that lamp wire to pin 4?

The amp works, but it's On in both positions. I need it to go to Standby. Something is funky, and it's obvious someone has changed things. I SUSPECT that's probably why the rectifier tube was missing in the first place...because they knew it was futzed up.

Please help?

Thanks,

Brad1

[52 Bill]

Originally Posted by Brad1

On the secondary winding, it shows the switch common to ground, which it is. It shows the switch down (standby) position connected to in between the lamps, and it is. It shows the switch up position (On) going directly to the center of the secondary winding....and that's my problem. It's actually going to the grounded contact of the On lamp.(All schematics I have found is missing the very bottom symbol of that light...but I'm assuming it's ground?)

The second end of the "on" lamp does go to ground. The two lamps are wired in series, and each lamp has a different current draw. The theory is that when the two lamps are wired in series, the "on" lamp will light up brighter than the "standby" light. When the switch is set to standby, the "on" lamp is out of circuit, so the "standby" lamp lights up. Each of the two lamps is a different number. I will have to look them up, but I do have the info somewhere.

Originally Posted by Brad1

It shows the switch up position (On) going directly to the center of the secondary winding....and that's my problem. It's actually going to the grounded contact of the On lamp.

My guess is that someone tried to rewire the switch to make the lights works better. If the switch doesn't un-ground the HV secondary center tap, the amp will not go into standby.

Originally Posted by Brad1

The circuit end (center contact) of the standby lamp goes to pin 5 of the 6AC4 tube...not pin 4 as shown.

Shouldn't matter, pins 4 and 5 are AC filament connections.

Originally Posted by Brad1

Which wire is the center tap of that secondary winding where the On switch connects?

Normal color codes would make the HV secondary windings red and red, with the center tap red w/stripe (yellow maybe?). This wire was probably grounded when the switch wiring was modified.

[Brad1]

Weirdness. Thanks, Bill. OK, the red/yellow-stripe wire was grounded. (I suspected that was it...but wasn't sure).The "On" switch wire was connected to the "Ground" end of the "On" lamp.

I disconnected both, and connected them together. That un-grounded the "On" lamp, and it wouldn't light, so I connected a jumper to ground. Now, they both light when they are supposed to, and "On" is on, and "Standby" is in standby...tubes lit. Makes more sense while looking at it, now.

Only one problem. A heck of a lot more hum is coming out of this thing now, while on, and pops pretty healthy when switching. And, this is the only difference from before. Why more noise than before? Signal runs through...it's just way more noisy.

Thanks (again),

Brad

[Brad1]

OK...got back to this amp. Besides the hum, voltages run consistently about 30V higher at all schematic measuring points. (I have the Variac adjusted to 120VAC.) I definitely have the switch wired exactly like the schematic minus the "convenience outlet" and polarity switch.

With volume at "0", it passes signal like it is set to about 1 or 2, then smoothly increases all the way up. It increases hiss, along with a bit more hum.

Reverb increases hum slightly as turned up. Schematics call for a 12AU7 tube, but it came with a 12AX7, and swapping out for a 12AU7 didn't lessen the noise, but did lessen the reverb amount a bit.

I'm thinking a load of caps needs replaced...but why is it passing signal with volume minimum? Any quick, obvious ideas? I'm thinking a ground somewhere, but I jumpered all grounding points and no difference.

Thanks,

Brad1

[Brad1]

Are we sure this is a Vox Cambridge in head form? Instead of a 1M volume pot, this has a 250K pot. Instead of 120K input 1 and 2 resistors, it has 68K.

It all traces out the same, but values don't match.

Why some volume when turned down? I'm going crazy...

Brad1

[Brad1]

Main hum and volume problem fixed. Ground problem was culprit. Ending topic here, and asking next question in Repairs.

Brad1

[Brad1]

Removed polarity switch, and rewired On/Off/Standby switch according to Cambridge schematic. That all works fine. Rewired input jacks with shielded cable. (It had shielded cables, but ground screen was connected to nothing. That helped a tad with noise).

Amp is fairly noise free, and everything works good except reverb. It had a 12AX7 tube for the reverb driver, but I tried a 12AU7 (as schem shows) and a 12AT7. Both latter tubes lowered the noise a bit, but also lowered reverb effect. It gets more hum as reverb is turned up. I tried changing reverb cables. Will standard signal RCA patch cords work? Could this be a bad reverb unit?

A very slight amount of volume comes through when volume turned down. The schem shows 1MG input jack 1, and 120K jacks 2 and 3 resistors. This has 68K on 2 and 3.

Voltages still slightly high according to schematics, about 30V high. I am running a variac at 120v. The 270V reads almost 300, the 240V reads 270, and the 150V reads 180.

I changed a couple of caps that looked like they got hot. One was C13 (between pins 3 of the output tubes). The other was C1, off the input tube.

I swapped the tubes around to see if anything changed. Nothing does.

Any ideas why higher voltage, reverb noise as reverb turned up, and/or faint volume when volume turned down?

Thanks,

Brad1

[Brad1]

Well, this got moved back here. I started it in "Repairs" after I received no recent response here, so I guess I'll just have to forget about it for a while.

Thanks,

Brad1

[Brad1]

OK...here I am.

Anyway, with both cables unplugged from reverb, turning up reverb yields more "white noise".

Can a Fender tank (Blues Jr., Deluxe Reverb) safely be temporarily attached to test?

Bear with me...I'm still learning things.

Thanks,

Brad1