vibro-champ when and how did circuit change

[fiestabender]

how much changed from black face to silver face. and how long once it became silverfaced did the circuit change. is one more or less desirable.

[muchxs]

Pretty much the same amp through the entire production run.

Early versions get the desirable black face panel.

Late versions get the yucky plastic wire and the low buck brown caps. You'll probably want to replace the electrolytics either way.

[mike shaw]

IIRC, I don't recall that there were any circuit changes at all. I know that the voltages strated to rise a bit but don't remember if that was because of a PT change or the voltages coming out of the wall went up. Really, the only thing to watch is that the 6V6 doesn't redplate. Some people swap out the stock 470(?) cathode bias resistor for a 1k resistor to calm the tube down a bit. I think the cathode bias cap. is slightly changed as well. I did mine a long time ago and the details are a bit foggy! I know there's a lot of info on the 'net about this - a very common issue. The speaker had likely changed through the years but a Weber speaker can get the old sound back.

Yeah, muchxs brings up some good points. The caps did change as on all Fender's.

[Groovey Records]

The PT chane was very early during the first year.

The same Circuit through 75 with a few component changes.

other the that it is cosmetic and cabinet and baffle construction.

The 1971 and earlier have finger joined pine cabs, and wood baffles after that particle board and staples started to be used more and more.

here are some pictures of a 67 BF

http://s227.photobucket.com/albums/d...%20VibroChamp/

[fiestabender]

so a 72 will have a similar sound as a 66 more or less?

[backline]

Originally Posted by fiestabender

so a 72 will have a similar sound as a 66 more or less?

As others have said, it is almost the same amp. Groovey pointed out some cab changes I was not aware of. So like the guys said, check you bias, it is probably wrong do to the PT "upgrade". The standard change was to a 1k 2 watt resistor in the bias circuit.
Good Luck

[Groovey Records]

Yes put some NOS tubes and a Weber 8a125 it will be smoking if it has the original Oxford

[mike shaw]

The Signature series speakers are also a good bet depending on what you like. I had an old 8A125 style Weber (one of the original ones before Ted went to the letter / number model scheme) and it sounded great for clean stuff but didn't really get 'raunchy' enough for me. I swapped in an old Mojo taken from my Victoria and they sounded more like what I wanted to hear. The Weber signature is now in the Vicky and sounds great. Depends on what you want to hear!


One more thing to consider .... I replaced the RCA speaker jack with a 1/4" jack. This will allow you to easilly plug into another cabinet if you like. This mod is easilly reversable as both jacks mount in the same size hole

[backline]

+1 to the 1/4" speaker jack. As Mr. Shaw said, there is no drilling required.

[Groovey Records]

curious. how do i remove the chassis from the vibrochamp which i did get to look at the input jack. I appreciate your assistance and support on this amazing forum

First do not touch any of the caps inside the amp. even unplugged they can still hold a lethal charge.


The ac cord has a support guide on the side of the cab, remove that screw and the cord guide.

Disconnect the speaker contacts from the speaker, they may be soldered or clipped use a little heat from the clean tinned tip of a solder gun if soldered or gently spread crimped clip with needle nose pliers.

Remove all the tubes gently but firmly do not wiggle from side to side too much. pull straight down. be careful not to break the plastic guide pin in the center of the 6V6 and the Rectifier tubes

remove the four corner bolts from the top of the cab, under the chassis there are four nuts and sprocket washers. A nut driver is helpful to stop the nuts from spinning but if your careful a pinky finger will do.

After this is done the chasis should slide out with a little wiggle.

support the chassis while you work on it so the OT PT and VT are not damaged on the under side of the chassis

Reinstall in reverse order.

While you have it apart you may want to remove the handle brackets and clean the tolex with a little warm soapy water on a sponge.

That's about it

Good Luck

I'm going to post this on line so others may benifit

[mike shaw]

Yep, the above is good advice. Might want to add that you can also disconnect the RCA speaker plug from the chassis instead of unsoldering leads from the speaker - a little easier. Also, if your speaker leads are the clip on knid, mark each one so you know where it connects. Won't make any difference if you use the amp alone, but if you use two amps together it could be out of phase.
Also, leave the power switch on and disconnect the power cord from the from the wall. That will drain off some juice from the filter caps.

[Groovey Records]

Oops in my mind I was swapping speakers too:aok

[fiestabender]

so i took it apart. did not get shocked. the connections were all intact. everything was seemingly normal but no sound out of the first input. what next. how could it not work. was making a good connection.