12002: 2" OT

[Strat78]

I just checked mine and it is like this:
wire hook-ups for Chris's -132
PRIMARY:
WHITE= plates (pin#3 for V6 and V7)
RED= plates (pin#3 for V4 and V5)
BROWN= Center-Tap (goes to the B+)

SECONDARY:
ORANGE= GROUND
YELLOW= 4 Ohms
GREEN= 8 Ohms
GREY= 16 Ohms

I have another one of Chris's 132's downstairs, I'll measure it and report back. This is a great thread, it will be cool to solve this problem.

[vh junkie]

I think everything is OK!

I was thrown off by the pic here:
http://forum.metroamp.com/viewtopic.php ... 92&start=2

You must have fixed it before you posted this? Which is the same as your post above
http://forum.metroamp.com/viewtopic.php ... 2&start=33

[Strat78]

I think everything is OK!

I was thrown off by the pic here:
http://forum.metroamp.com/viewtopic.php ... 92&start=2

You must have fixed it before you posted this? Which is the same as your post above
http://forum.metroamp.com/viewtopic.php ... 2&start=33

Oops, that was a different build from the one that started that thread. It had Chris's 1.5" 1998 OT Dognal clone.

[vanhalen5150]

I have white and red going to the tubes. Brown is going to the corner of the board with the choke and red voltage.

[vh junkie]

Sounds OK then.
This is what I would try:
No power tubes in.
1) Have a good fast blow HT fuse on hand.
2) Lift one end of the 8.2k/10k 2watt resistor stack (this will isolate the preamp from the mains and screens).
3) Start with the fuse out, measure the voltage at the point where the diodes meet the red wire. SB 450-500vdc
4) If OK, put the fuse in, measure the voltage at the screen resistors on the power tube sockets. SB 450-500vdc.
5) Measure the voltage at the edge of the board where the 8.2k resistor is at the end of the 8.2k/10k 2watt resistor stack.
SB 450-500vdc.

[vanhalen5150]

Leave preamps in? Shouldn't matter anyways right?

Standby switched off?

[ValveStorm]

Yes on the pres

Can't measure HI-V unless it is switched on... not sure if that means standby is off or on... but both switches down...

[vanhalen5150]

Lifted the 10k 2w resistor.

Diode at red wire is 500vdc.
8.2k 2w resistor at edge of board is 500vdc.
Screen resistors read 500vdc.

[vanhalen5150]

Had the standby to "on" .

I also got new slow blow fuses.

[ValveStorm]

Now, double check all the voltages on the power tube sockets... let's be sure the plate voltage is making its way through the OT onto the correct pins on the power tube sockets.

[vanhalen5150]

V4-V7 all read approx. 500vdc on pins 3,4,6. Heaters read 3vac.

Pin 5 is -45 bias.

Since I lifted that 8.2k resistor I can't drain the caps from v1 pin1 so do I just drain them from the points I checked correct?

[ValveStorm]

If you lifted the 10k end of the 8.2k/10k stack, you can drain it there... otherwise from the screens... you can put the 8.2k/10k stack back and lift one end of each of the downstream 10ks... this will give HI-V to only the PI(v3) preamp tube... you could do this with the preamp tubes out, but you should use a variac to keep the HIV below 350v so you do not stress the preamp coupling caps. You can proceed re-adding the 10Ks towards v1... the two under the preamp filter cap are backwards from the logical flow. Ensure that the heater ans HIV voltage are present at the tube sockets as you go.

[vanhalen5150]

So what your saying is test the voltage up to the 10ks from where you lift them.

[vanhalen5150]

Added 8.2k resistor back variac down to 350. Pulled preamp tubes. Voltage at v1,v2,v3 pin 1 is 338vdc.

[ValveStorm]

Pins 1 and 6 on each preamp tube should be the same... do you have heater voltage at each socket... not sure where you go from here could add the preamp tubes one at a time looking for an issue as you raise the voltage. The tubes will absorb some of the voltage so that will be lower keep it below 350 on the unused sockets. See when the voltage doesn't make sense or the heater voltage gets weird. Might have a bad preamp tube...