50 watter blowing mains fuse

Guitar Adjuster · Post by **Guitar Adjuster** » Mon Feb 26, 2007 9:10 pm

Just finished it and it's blowing the mains when switched on with or without tubes. The PT is a Mercury Axiom P455JT-G2 and I was not sure if I wired it correctly.

chubs · Post by **chubs** » Mon Feb 26, 2007 10:14 pm

If it's blowing the main fuses without tubes you have a short somewhere.
Is this in standby? Is so might be the HV taps that have a short somewhere.

I would:
1- make sure you drain the caps.
2- retrace the whole circuit with the layout next to you.
Use a highlighter and highlite every part oyu check.

Odds are you will find it. If not, go away for a half-hour and come back.
Are you using Slow-Blo fuses? I have had that problem with non-slow-blo.

Guitar Adjuster · Post by **Guitar Adjuster** » Mon Feb 26, 2007 10:28 pm

Using 2 watt slo blo fuses. While in standby, I think it's the PT wiring for some reason. Cannot find anything on the pre-amp board that would make it blow fuses.

chubs · Post by **chubs** » Mon Feb 26, 2007 10:36 pm

You can disconnect all secondaries and test the PT... then reconnect one set at a time... and see when it start blowing fuses again....

Guitar Adjuster · Post by **Guitar Adjuster** » Tue Feb 27, 2007 8:56 am

Nobody else????

Guitar Adjuster · Post by **Guitar Adjuster** » Tue Feb 27, 2007 8:55 pm

Thanks to Steve (SDM) I found out the problem. I was using a SPST standby switch and when I turned on the power it was shorting out the high voltage taps (two twisted blue wires) so in order to correct the problem I have 2 choices, 1. Dump the SPST toggle (carling) switch and go with a regular plexi style switch or 2. Wire the standy similar to a JTM 45 were the high voltage off the PT goes directly to the diodes and the blue wire coming off the cap can goes to the switch on one side and directly to the diode on the other with a jumper from the diode to the bias circuit. So, if anyone else is planning on building a 50 watt plexi take note!!!!!

chubs · Post by **chubs** » Tue Feb 27, 2007 11:11 pm

Take note not to short out the high voltage tap? OK! I'll take note of that.

I think....

neikeel · Post by **neikeel** » Wed Feb 28, 2007 6:41 am

Guitar Adjuster wrote:Thanks to Steve (SDM) I found out the problem. I was using a SPST standby switch and when I turned on the power it was shorting out the high voltage taps (two twisted blue wires) so in order to correct the problem I have 2 choices, 1. Dump the SPST toggle (carling) switch and go with a regular plexi style switch or 2. Wire the standy similar to a JTM 45 were the high voltage off the PT goes directly to the diodes and the blue wire coming off the cap can goes to the switch on one side and directly to the diode on the other with a jumper from the diode to the bias circuit. So, if anyone else is planning on building a 50 watt plexi take note!!!!!

It's easy for me to be wise after the event

but I thought that wiring looked a bit funky, I could not tell which set of blue twisted wires were going where! I used the DPST switches for my 50 watt new build to avoid this problem.
Well done.
It's a horrible feeling when things dont work and you end up pulling all your handiwork apart to fix it - ususally in a rush, often late at night!

You will, of course, have to build another one now...............

Guitar Adjuster · Post by **Guitar Adjuster** » Wed Feb 28, 2007 8:27 am

[quote="neikeel" You will, of course, have to build another one now...............[/quote]

I am going to pitch this one and start over

neikeel · Post by **neikeel** » Wed Feb 28, 2007 10:31 am

Didn't mean junk it

Just nextime you will be more familiar.

I fancy a metro 68 100 watter but other fish to fry

Guitar Adjuster · Post by **Guitar Adjuster** » Wed Feb 28, 2007 3:12 pm

neikeel wrote:Didn't mean junk it

Just nextime you will be more familiar.

I fancy a metro 68 100 watter but other fish to fry

Yes valuable lesson learned!!!! I won't forget

rockstah · Post by **rockstah** » Wed Feb 28, 2007 4:54 pm

hey Allen - did you ruin the pt or something or get it resolved?

Guitar Adjuster · Post by **Guitar Adjuster** » Wed Feb 28, 2007 6:33 pm

rockstah wrote:hey Allen - did you ruin the pt or something or get it resolved?

PT is OK, it was just blowing fuses cause they way I wired the standby switch it was shorting out the HV taps, no harm done.

rockstah · Post by **rockstah** » Wed Feb 28, 2007 7:09 pm

gotchya.

Guitar Adjuster · Post by **Guitar Adjuster** » Fri Mar 02, 2007 10:28 pm

Ok, got the new "plexi" style main and standby switches installed, it biased up to 35ma with a B+ of 440, take off standby and hit the strings and a loud crackling sound? It you play the strings lightly no crackling but once you hit the strings it makes that horrible crackling sound. Power down, check all wiring, re-solder and touch up almost everything on the board including ground and the same thing happens????? Any ideas, photo's at the beginning of the post. I also switched out tubes including pre's and same thing.

Allen