High Voltage

[Toys4Boys]

I am reading 260V-280V on the legs of the MJE5731A transistors, double checked my connections and can't see any problems.

 

[Toys4Boys]

Just checked the 275V out from the PS and of course it is high, so I need to recheck my transformer wiring.

 

[Toys4Boys]

went back to the transformer wiring, traced my connections and double checked my readings at which point I realized that the 275V out from the PS was in the printed limit. Guess I need to go over my shunt board again.

 

[Paul Birkeland]

What are your Kreg voltages?

The +275V of the power supply board will go higher if no current is being drawn from the power supply.  The MJE5731A collectors will also be much higher than they are supposed to be if no current is being drawn through the circuit.

 

[Toys4Boys]

Should I insert the 12au7? Also please be specific as to where I should attach my probes.

 

[Paul Birkeland]

Yes, the 12AU7 needs to be installed to test the board that lives above the 12AU7.  You can slip your black meter probe into the ground post so that you don't have to hold it.  The red probe should measure DC voltage on each Kreg pad.

 

[Toys4Boys]

Kreg A 3.37 Kreg B 2

 

[Paul Birkeland]

And you are seeing 260-280V on both MJE5731A metal tabs?

 

[Toys4Boys]

Memory serves well yes, but I can double check

 

[Toys4Boys]

OB - 260, Center - 219, IB - 281
IA - 280, Center - 218, OA - 281

 

[Paul Birkeland]

What does center mean?

 

[Toys4Boys]

are there not 3 legs?

 

[Toys4Boys]

The designations that I used are what I could see on the board, they are actually Q2 - F,C,B

 

[Paul Birkeland]

Definitely do not try to probe the legs of the transistor.  It's tough to do and if you short two legs together, more damage will occur.

You have "Center" being the middle leg at 218 and 219, does this voltage also appear at the metal tab of the transistor?

 

[Toys4Boys]

Damn, I misunderstood the instructions and checked the legs of the transistors not the tab  :-[ , I'll check in the morning and let you know.

 

[Toys4Boys]

Actually, is the center leg the same as the tab? If so I guess it's good.

 

[Toys4Boys]

The tabs measure out fine, I'll chalk this up to an opportunity to double check my wiring, found a couple untrimmed leads and 1 connection that I hadn't soldered. Also for future work read then reread the instructions to make certain that I am clear.