Other Amps

Magnatone MP-1 Tremolo not working

1

I just convinced my wife that I could die from electrical shock unless I got the reverb on my Musicman repaired by a pro, so I'm kind of on my own for a while with the Magnatone fix.

Any easy things to check out? Light goes on and pulses to speed settings, but no trem.

Thanks!

2

Tremolo foot switch jack shorted out?

3

Tremolo foot switch jack shorted out?

– guitarcapo

Never used a foot switch with it, but that sounds brilliant! I'll take a look. Thanks

4

If the light's flashing, then it's either the photo cell, or a wire fell off. There's not a lot going on in that circuit.

5

If the light's flashing, then it's either the photo cell, or a wire fell off. There's not a lot going on in that circuit.

– Billy Zoom

Could I change that w/out draining the caps?

6

V4 is the preamp tube associated with the tremolo. It's supposed to be a 12au7 located closest in the row to the power transformer. I'd swap it out for the heck of it.

7

V4 is the preamp tube associated with the tremolo. It's supposed to be a 12au7 located closest in the row to the power transformer. I'd swap it out for the heck of it.

– guitarcapo

This is why I need you guys here! I had it over at friend's house because he wanted to check it out. "Somehow" the 12au7 was switched with the 12at7! I saw that all of the tubes were lighting up and checked off "tube issue" right there. Thanks!.....ooo it sounds nice!

8

An old amp tech told me long ago that more than half of all tube amp problems can be fixed by swapping out tubes. It definitely has been my experience as well.

The schematic for the MP1 has an interesting note. It says not to test the voltages of that 12AU7 tube by touching the pins with a probe with a meter because the voltage spike might blow the bulb. I've never seen that before. Then again, all my Magnatones use vibrato and not tremolo so no bulbs involved.

9

An old amp tech told me long ago that more than half of all tube amp problems can be fixed by swapping out tubes. It definitely has been my experience as well.

The schematic for the MP1 has an interesting note. It says not to test the voltages of that 12AU7 tube by touching the pins with a probe with a meter because the voltage spike might blow the bulb. I've never seen that before. Then again, all my Magnatones use vibrato and not tremolo so no bulbs involved.

– guitarcapo

Now my Twin is making a pulsing sound when trem is on! Ever heard of that happening?

10

The note on the schematic about the bulb is because the Estey era circuit used a neon bulb, not an incandescent bulb like in Fender type tremolo circuits. My guess is that the neon bulbs had a lower drive voltage/current than the incandescent and that the surge would exceed these levels. There is a good write up on the circuit here: http://www.magnatoneamps.co...

11

If the light flashes, then the tube, the oscillator circuit and the bulb are ok. The only thing left are the photocell, or broken wires. Don't waste time on the things that aren't broken.


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