PT verification

War Admiral · Post by **War Admiral** » Mon Apr 21, 2008 1:36 pm

O.K. I took the old mains fuse out and hooked up a light bulb(current limiter) to the mains fuse holder. I disconected the heaters and its center tap. I left the standby in the open position since the red wires are fed to there before they go to the rectifier diodes.

The light is still bright. PT fried?

War Admiral · Post by **War Admiral** » Mon Apr 21, 2008 6:11 pm

Further investigation its fried. I salvaged a 1202-164 Drake PT but its not the same colour code as the Dagnall that was in my 1987x. Heres a pic of my ''new'' PT. I want to bypass the voltage selector and just wire it up for 120 vac. I can just put the brown(120V) wire directly on the AC switch on the lug beside the blue(common) lug right and just heat shrink all of the other taps right? The AC input is still fused on the top 2 lugs of the AC switch(looking from the bottom of the chasis of course)

War Admiral · Post by **War Admiral** » Mon Apr 21, 2008 11:59 pm

Well it looks like it was the secondary of the PT. I wired up the primary of the new one and then jumped the bias supply on one of the high voltage wires from the standby on the secondary with the ct lifted and no bright light.

I measured across the 2 high voltage wires and I get 566 VAC where as before with the old tranny at the same setup I got 21 VAC and a bright light.

One last question, I bypassed the voltage selector on the primary by placing the common blue wire on the AC switch like it was before but I bypassed the selector with the 120 VAC tap (brown) straight to the other lug of the AC switch. I heat shrunk the remaining taps(100, 220, 230, 240)
I will ground the heater ct and the high voltage ct like before on the secondary. Is this O.K.? I won't be playing in Europe any time soon with this amp so.....