Vibro Champ Tremolo question!

[blueznet]

Fixing to fire up a AA764 Blackface Vibro Champ. First time for me to build one of these.
I will use my Current Limiter as I always do. These amps have no Standby switch. Once I flip the slide power switch on the front there is no going back.

Should I hit the amp with a full 120VAC, or less AC using my Variac at first?
I take it that the build will have AC and DC voltages pretty close to the original Layout.

I do not have a single button foot switch to test the Tremolo. I have a bunch of 2 button Fender foot switches. I don't know if I could use these as a temp switch.

On the sketch below, I am thinking all I have to do is Ground the Blue wire to chassis and it will be engaged all the time. Am I correct on this? If so, I could grab a RCA input jack and insert a wire inside the tip, then solder it from tip to the RCA's ground side. No pedal needed correct? I would just use the front knobs to turn intensity and speed off or on.

BTW, a standby switch can be installed between pin 8 on the rectifier and the first filter cap stage on the Can?

Thanks!

[rafe]

My silver face vibrochamp tremolo is on without the footswitch ...the footswitch turns it off....I believe yours should be the same? If not you could just short out an RCA plug for testing

[sluckey]

On the sketch below, I am thinking all I have to do is Ground the Blue wire to chassis and it will be engaged all the time. Am I correct on this?

No. Your blue wire will turn the trem off.

BTW, a standby switch can be installed between pin 8 on the rectifier and the first filter cap stage on the Can?

yes

[HotBluePlates]

You might be figuring this out...

The smaller amps (VibroChamp, Princeton, Princeton Reverb) with trem have a small circuit difference in the oscillator which keep the trem on unless a footswitch is used to turn the trem off. The bigger amps have the other oscillator circuit which keeps the trem off unless the footswitch is used to turn it on.

[blueznet]

You might be figuring this out...

The smaller amps (VibroChamp, Princeton, Princeton Reverb) with trem have a small circuit difference in the oscillator which keep the trem on unless a footswitch is used to turn the trem off. The bigger amps have the other oscillator circuit which keeps the trem off unless the footswitch is used to turn it on.

Hi HBP.. So, not using a footswitch at all, this will not harm the amp?
Should I hit the amp with a full 120VAC, or less AC using my Variac at first?
I take it that the build will have AC and DC voltages pretty close to the original Layout?

[HotBluePlates]

So, not using a footswitch at all, this will not harm the amp?

No harm at all. I have owned 4-5 original Fender VibroChamps at various times, and only had a footswitch for one of them. While the capability was made available, I think it was seen as unlikely to be used since this is a student amp instead of a stage amp. The player is likely to be within arm's reach (which may not apply now if used for recording).

Should I hit the amp with a full 120VAC, or less AC using my Variac at first?

You had mentioned using a lightbulb limiter, so there should be no harm in applying full line voltage.

I never had a variac until very recently (thanks Stingray!!). You can limit fault current by applying less-than-line voltage, or you can apply full line voltage and limit current with the lightbulb limiter.

I take it that the build will have AC and DC voltages pretty close to the original Layout?

Yes, but possibly higher, in a way typical with all modern copies of classic amps expecting 110vac lines. That is dependent on your specific transformers and line voltages.

[blueznet]

I take it that the build will have AC and DC voltages pretty close to the original Layout?

Yes, but possibly higher, in a way typical with all modern copies of classic amps expecting 110vac lines. That is dependent on your specific transformers and line voltages.

Thanks HBP. Fired the VC up with current limiter, and the Variac set to 120VAC. Light bulb was barely luminated... looked good to me. Clean and pretty loud.. tremolo worked just like you said. I just used a 2 button Fender foot switch, and plugged the RCA input that is used for the reverb side. Worked well for testing the tremolo off/on function.

Voltages are much higher. HV taps to pin 4, 6, read 345VAC each. Layout calls for only 315VAC. B+ from pin 8 at rectifier tube shows 380VDC. Layout calls for 355VDC. Pin 3 at 6V6GT is 372VDC. Seems all the higher voltages are about 30 Volts higher than it calls for. Didnt see any red plating at 372VDC on the plate. Hope thats not to high. I guess it is cause the wall volts is 120VAC. Correct?

Thanks,
Darrell-

[HotBluePlates]

Voltages are much higher. HV taps to pin 4, 6, read 345VAC each. Layout calls for only 315VAC. B+ from pin 8 at rectifier tube shows 380VDC. Layout calls for 355VDC. Pin 3 at 6V6GT is 372VDC. Seems all the higher voltages are about 30 Volts higher than it calls for. Didnt see any red plating at 372VDC on the plate. Hope thats not to high. I guess it is cause the wall volts is 120VAC. Correct?

It seems like it. This was a Mercury Magnetics transformer, right? It's kinda sucky that they give you the authentic part, but don't adjust it for a 120v primary (or maybe that is an option with some of their products).

It seems to be due to wall voltage. The voltage ratio for the original PT is 110:315 (x2). 315v / 110v * 120v = ~344v, which is same as what you're reading. Wall voltage is about 10-11% high, and so you're seeing about the same result in all your amp voltages.

Of course, the same thing happens with any vintage amp plugged into 120vac.