E.C. Vibrochamp "Clone"?

[Guitarzan]

Hi Guys,
I was unpacking more of my stuff in preparation of working on the BFTR when I ran across an old project that I'd started but never finished before we moved. I built a homebrewed chassis to fit an old Solid State Bronco cabinet. Y'know, one of those reissued little devils that you could pick up on eBay for 50 bux until I bought about 10 of 'em & then they went crazy with the pricing on 'em. I was just parting 'em out at the time & doing OK at it too until the prices suddenly jumped to about 200 bux. It was about then that our friends in Corona came up with the E.C. Vibrochamp. I decided to see if I could make one from scratch by combining the AA764 with the 5F1 and this is what I built. I never finished it, and it got packed for the move and I just saw it today again for the 1st time in at least a year. Here are a coupla pix. Tell me what you think. I made the filter cap end on piece of tag board and glued it to a 5F1 turret board. Then I used the extra space on the 5F1 board to try and copy most of the AA764 Vibrochamp board. I used what I hand on hand at the time that I wouldn't consider using in one of my actual "for sale" models. Also there's no cap can as in the AA764. Here are a couple of pix to give you an idea of where I was going with this thing and I have more if anyone's interested. I hate the thought of putting power to the thing if it's just gonna smoke a PT or OT since I could slap together a Tweed Champ clone with those trannies and put the funds toward the legs, reverb unit, and other odds and ends I still need to complete the BFTR project. So here's a peek. Don't hold back. No thin skin here. If this is a stupid idea say so. Also, how long do you actually have to apply lower than line voltage to new or even very old caps that need to be reformed? I would think that since electricity travels at light speed only a few seconds at each level of voltage on the way up, say starting at something like 70 VAC on a Variac and slowly dialing it up to whatever's coming out of the wall 115 - 125 VAC would be sufficient but I really don't know. Maybe something about the way the paper and oil and stuff react when voltage is applied makes it necessary to let it "cook" for a time at low voltage, I really don't know how that works. I have only recently acquired an actual Variac and have, 'til now, been using the old TV repairman trick of having a light bulb wired in series with a receptacle and started with a 15 watt bulb, supplying about 70 volts to the receptacle, then putting in a 25 watt, a 40 watt, 60w, 75w and finally full line voltage to the new components and have never had any issues. I've always been starting with new stuff tho except in the case of a coupla Bogen tube P.A. amps that I've brought up slowly that way. What if you had a chassis that was loaded with ancient paper caps that hadn't been powered in decades? I've seen guys mention in eBay descriptions of such stuff, that they ran the thing for hours at low voltage before bringing it up slowly. I would think that running an amp at too low voltage could be just as dangerous as just blasting it with line voltage right outta the box. So here are the pix of the ECVC “clone”, does it look like it’ll work?

[HotBluePlates]

... how long do you actually have to apply lower than line voltage to new or even very old caps that need to be reformed? ...

If the caps are not a decade or more old, I'd just turn the amp on.

You might use the lightbulb limiter, but just because you may have a wiring error that could cause damage. That said, new caps do not need "forming".

Re-forming is something that's done on very old caps, or ones that have had no power applied in a very, very long time. An electric charge across electrolytic caps forms an oxide layer on its plate which is the insulator inside the cap. That layer can disappear when no polarizing voltage has been applied in a long time.

Length of time to reform is not a set thing; you apply a current-limited voltage and observe leakage current. If the oxide is gone, there's no internal insulator and cap current can be very large. As the oxide forms, current decreases down to a trickle. There might be some leakage current with a healthy cap, but too much leakage with full-rated voltage after a short reforming period indicates the cap is beyond its useful life.

For the most part, these tricks come from the radio restoration world, where caps in an old receiver might be "unobtanium" or where replacement with new just destroys the whole aesthetic. So they've figured ways to try to rejuvenate caps (and tubes...) to keep them hanging on a little longer. That said, they're typically less attached to voodoo parts, and only care about cosmetics.

[Guitarzan]

Well now I have an actual Variac so the light bulb thingy, while sort of cute and archaic and cool in its own old school sort of way, has always been cumbersom to say the least so when I fire up a unit, old or new I'll probaly use the Variac. I appreciate the lesson on what makes a cap need reforming and what reforming actually means/does. So that's why the light bulb would always start out dim, and get brighter after a very short time since I was always working with new stuff? As always, it's a big please and thanks from the old free as a breeze, always at ease, livin in the jungle and hangin' by my knees as I swing thru the trees without a trapeze, in my BVDs, guitar picker.
-d {8^)

[Willabe]

Well now I have an actual Variac so the light bulb thingy, while sort of cute and archaic and cool in its own old school sort of way

I have a Variac but I use the "light bulb thingy" to test amps. The light bulb limits current, glows brightly if there's a problem and your meter is free to monitor what ever you want.


           Brad      

[HotBluePlates]

Well now I have an actual Variac so the light bulb thingy, while sort of cute and archaic and cool in its own old school sort of way, has always been cumbersom to say the least so when I fire up a unit, old or new I'll probaly use the Variac.

You can do that, and things will probably be fine.

The lightbulb limiter attacks the issue more directly:
- if you have a wiring fault or short circuit, the lightbulb will reduce the current the amp can draw and prevent anything from burning up. It also gives you an indication things are bad (bulb glows at normal brightness).

- if you use a variac, current is limited only because the line voltage to the amp is reduced. But a fault condition might not be obvious at low line voltage, and when you turn up the variac something could burn up. It's on you to monitor the amp's current draw from the line and know what a normal amp will draw at normal and each reduced voltage level.

Each tool has its uses, and they don't really do the job of the other well enough to make me want to get rid of either.

[Guitarzan]

Cool man,
That's some good info. I'll take (and use) all the tips any of you guys care to share with me. Sounds like putting the light bulb between the variac and the amp might be worthwhile.
So have got any opinion on that little ECVC-type project I posted the pix of? Have you even had a chance to see a Fender ECVC up close?  I didn't know how to try and reverse engineer that tremolo section with only one control like the Fender version has. They have speed only. No intensity control. So I guess it means that they run it wide open and the speed control actually brings the pulsations to complete stop. I was afraid if I didn't put a control on it, the function would run wild. So this is prolly one of those cases where I know just enough to be dangerous. That's why I've been afraid to finish the input section and apply power to it.
Thanks again to HotBluePlates for the great summary of the Variac v. TV Repairman Lightbulb Limiter
-d {8^)

[Guitarzan]

Well now I have an actual Variac so the light bulb thingy, while sort of cute and archaic and cool in its own old school sort of way

I have a Variac but I use the "light bulb thingy" to test amps. The light bulb limits current, glows brightly if there's a problem and your meter is free to monitor what ever you want.


           Brad      

That looks like it's going to be the concensus.
In my typical way of overdoing everything to the Nth degree, I did mount the light bulb limiter to a hunk of plywood with a good, heavy ceramic bulb socket switch, and a handy box with a high quality duplex receptacle. So I could easily mount the thing where it'll be handy once I decide which part of the basement is going to be mine and get all of my stuff set up in it. I wonder if there would be any benefit to replacing the switch with a heavy duty dimmer. Right now they way it's wired is handy box with switch > bulb socket in series with > handy box receptacle. I believe this is the customary way of doing it.

[sluckey]

I wonder if there would be any benefit to replacing the switch with a heavy duty dimmer.

No. Best to keep that noise generator far away from a guitar amp.

[eleventeen]

"Right now they way it's wired is handy box with switch > bulb socket in series with > handy box receptacle. I believe this is the customary way of doing it."

The only thing that's quirky about the variac setup you described (which is exactly the way it should be done---gem boxes & ceramic bulb socket) is that many, if not most variacs have the ability to output MORE THAN the incoming line volts because the secondary has a few more turns than the primary. Something like 135-140 volts out on a 125 volt line. So while that would be perhaps something that would be desirable for a "stress test", it would not be especially desirable on a routine basis if you decide to "crank 'er up" to the limits of that big knob. I suppose you could devise some mechanical contrivance to prevent you cranking the knob to its upper limit...but otherwise, just remember that it shouldn't be turned all way up unless you are specifically performing an overvoltage test. Stuff could blow.

[Guitarzan]

Yup. This one has that ability. I noticed that right off and it doesn't have a knob limiter of any decription other than the operatoer has to be smarter than the knob he's turning. Jane and monkey are questionable on this point but I think I can manage to keep a watchful eye on what my paws are up to...most of the time.
Good thinking about that Dimmer sluckey. I hadn't considered that..obviously. Thanks for keeping me from being reminded the hard way!

[Guitarzan]

Not one single word about the frankenboard I built? C'mon guys. Someone must have an opinion. Sharpen your arrowheards and dip 'em in poison if you want to. Guitarzan king of jungle (don't tell Jane Guitarzan said that) and poison arrows bounce right off. You may fire when ready, Gridley.

[sluckey]

Do I see gorilla glue? Got a schematic?

[Guitarzan]

Yeah, that's gorilla glue. I figured it would ooze thru the hole in the tag board and make a good  bond. Looks like it did just what I expected it to. I wasn't too worried about making it pretty since it was just a prototype. I figured if there was any market for it I'd make the fiberboards one at a time to order. I only build an amp to order anyway or I'd have even more stacked up around here than I already do. No schematic. I'm not that good. I can read one with some difficulty but to draw on from scratch is beyong my baility. I suppose that's why no one's commented. It's pretty had to tell anything from these pictures. What I think I could do, is to make a layout drawing showing what I did. It's really just a 5F1 with the section that operates the tremolo or vibrato,  pirated from a AA764 SFVC. I didn't have any of those ceramic disk caps that Fender uses to pulsate the signal but I was able to scrounge thru a box lot of Orange Drops that I copped on eBay and find 3 of those in the correct value(s). Aside from that, it is a 5F1 & AA764 combined to approximate that Tweed ECVC that our friends in southern California have been pushing