65 Twin Reverb blows fuses

[Doc Stitches]

This is an AB763 Twin Reverb, with Custom-made Merc. Mag. transformers.
It blows the fuse as soon as it is turned on.....with and without power tubes.
Both contacts on 6v pilot lamp both show continuity to ground. Is that OK ?

I am using my AB763 Super Reverb pilot wiring as a model and it
is not the same. It has no continuity to ground on either pilot light 6v contact.

I don't get it ???

Thanks
Doc

[Enzo]

Even with the standby switch off?

Check the main high voltage rectifier diodes for shorts. Measure for shorts to ground at the terminals of the standby switch.

[Tom Phillips]

If your PT has a center tapped heater winding AND you grounded the center tap to the chassis then both contacts on 6v pilot lamp would show continuity (Or at lease very low resistance such as a fraction of an Ohm) to ground. THis is normal and is the traditional way that AB763 circuits were built.

Did the amp start blowing fuses right after the MM PT was installed?
Does it blow the fuse with the standby switch in standby mode?
What about with the power tubes removed?

If ithe fuse blows under all the above conditions then disconect all the secondary PT leads and try again and report back.

[Doc Stitches]

Found that ground switch was wired wrong. Go figure ??????

Now we have a small hum from speaker.......pulled V2 and almost no hum..........

with V2 removed voltage at pin 6 is 260v.............when probe touches pin 6 there is a loud pop.......

louder that the other preamp pin 6 pins.

Doc

[MikeH]

Found that ground switch was wired wrong.

IMO, having the ground switch wired up at all is not a good idea. How exactly is and was your wired?

[J M Fahey]

What you say is a *strong* hint that one of the live power wires was connected straight to ground.
Or through an improperly rated capacitor which easily shorted.
Either of them, a deadly possibility.
Just disconnect theb ground switch from *anything* and pull and junk the capacitor.

[Doc Stitches]

Hey J M Fahey......you nailed it.
Had a power wire to ground ! " OUCH "
This was according to a schematic that was NOT Fender.
Thank you to everyone.
Doc