VT40 Restore - Is my OT Bad?

[Micajah]

Rebuilding an early (71?) top mount VT40. I've attached a scematic. Replaced all the filter caps and a few drifted resistors. Brought up the voltage on my variac slowly and went to start measuring voltages and one of the resistors I replaced - V40 (it was burnt and not measuring anything) started getting hot so I turned it off. I checked all the Diodes and they seem to be good. After looking at the circuit I was wondering if the OT was shorted. It's a direct connect to the dropping resistor string of which VT40 (2 watt) is the last. The other 2-3K resistors are 5 watt.
Before I spend some good money on a replacement OT- I wanted to get some other opinions.
Using RG Keen's OT testing procedure with the OT still in the amp and Caps discharged. http://www.geofex.com/ampdbug/outtrans.htm
Primary side

"Noting which leads connect to the B+ line, measure the resistance from the B+ lead to each plate of the output tube(s). Plate windings are almost always in the tens to a few hundred ohms of resistance. A reading much over 1K is pretty sure sign that the winding is burned open."

Red to Blue - 151.1 Ohms - OK
Red to Brown 141.3 Ohms -OK

"measure the resistance of every lead to the chassis. This reading should be very high, hundreds of K or preferably megohms."

(here's where I think it's got a problem)
Red to Ground 28.32K
Blue to ground 28.48K
Brown to ground 28.47

From Primary to secondary

"Finally, test for the resistance from primary to secondary. A low value, under a few K indicates an internal short"

Red to Green secondary 28.41K
Red to Black Secondary 28.46K

I'm going to disconnect the Red B+ and the Blue and Brown Plate wires from the circuit and run these measurements again before I start spending but wanted to see what others thought.
   

[Micajah]

Ok so It's not the OT - After disconnecting the OT promary leads from the circuit and rechecking, It has same resistance as before on the primary side on Red to Blue Red to Brown.
And there is no reading on the Red/Blue or Brown to ground as well as the Primary leads to Secondary leads. So I think it's OK
Next step is pulling the diodes and checking them out of circuit specifically D7 - D10.
Stay tuned up.

[Hangman]

I dont find transformers shorted to ground as often as I find them open or shorted them the same winding, ie you might measure 160ohms on one half of the primary and 33 on the other half. That being said, it does happen. Which resistor did you have burn up? V40 isn't a resistor reference designator. What is the value and reference designation?

[Micajah]

I dont find transformers shorted to ground as often as I find them open or shorted them the same winding, ie you might measure 160ohms on one half of the primary and 33 on the other half. That being said, it does happen. Which resistor did you have burn up? V40 isn't a resistor reference designator. What is the value and reference designation?

Sorry - typo - it was R40 and it is in the string of resistors coming off the 40/40/40 filter cap - the other two resistors are R41 & R42 and are 5watt 3K's

[Hangman]

If R40
Is burned and you just replaced it, then we can assume there is a great deal of current going through R40. The OT would have nothing to do with that.

It is more likely there is a short on the other side. Did you replace the 40x40x40 cap?

I'd recommend looking over your work and making sure that the wiring is done right. It's very easy to wire some up backwards. You can uses your multi meter to help you.
I can guide you if you want.

[Micajah]

Been working on a number of old Ampegs - Rockets, Gemini's B15n's. I've also replaced the 40/40/40 cap can exactly as it should be wired. Thanks for your offer. I know the problem was there before I took possession of the amp - vis a vis the crispy R40 resistor. I'm replacing the questionable diodes and also do some other checks.

[Hangman]

I meant no offense, I had misunderstood your original post and thought that you had already replaced this crispy resistor, and then it blew up again.
if you're checking diodes, it doesn't sound like you know the problem. there are only a handful of diodes in that amp and none of them would cause R40 to fry.
Do you have a variac? why not slowly bring the power up and see if the amp pulls too much current, or if R40 drops too much voltage?
what have you checked?

[Micajah]

No offense taken - just wanted to let you know that I've worked on a lot of AMPEGS - but this is my first foray into the VT amps.
Found a spot on the board where there was arcing between the feedback at R48 and the common line going to R22, R19, R6, R5, R7. Cleaned it up and I think that was the problem. I also realized that the previous owner had substituted a 12AX7 for V3 which is specked as a 12DW7. They probably read Aspen Pittmans tube amp book where he says that the 12AX7 can be used in place of the 12DW7 in the VT40, but I'm not so sure considering the unique characteristics of the 12DW7.
Brought up the Amp on a variac with a dim bulb tester - before the arc cleanup I would get a bit of glow on the bulb, now It stays dark - checked voltages seem to be good. Waiting on a new 12DW7 and then I'll be able to test it completely.