Questions concerning OT measurements

[Wes]

Hey, guys- I've got a Laney AOR 50w series 1 that a friend dropped
off with me that's not getting any signal at all. The only way I can
get any signal is by cranking the master volume waaaay up and then
it's all farty and really weak. I did this with new power tubes in and
watched their idle current (set at ~35mA) jump waaaay up into the
danger zone. I mean, I strummed a guitar; you could barely hear
it and the current went way up.

-I've checked all plate voltages on all tubes
-I've checked all cathode resistors on the preamp
-I've replaced the screen resistors
-I've got bias voltage in the negatives (again idling at ~35mA)

I've done a few other things as well. I've got not even a hiss at the speakers
and I don't even get a crackle when I put a meter lead on the plates of the
power tubes.

I disconnected all OT taps and tested them.

PRI center to one side gave me 6.5 ohms
PRI center to other side gave me 67 ohms

Don't know how important it is but the secondaries were:
Black to brown .7 ohms
Black to red .9 ohms
Black to orange 1 ohm

No taps read anything at all to the chassis/OT

Is it possible that I've got a bad OT?

I haven't checked the coupling caps from the PI to the grids, but I figured
that I'd get at least hiss or crackles when I was messing around with the
plates of the power tubes.

Any help or suggestions you may have would be greatly appreciated.

[MWJB]

The pri taps to the centre tap should be roughly, but not always exactly, equal.

6.5ohms is a sure sign of a shorted primary winding.

[Wes]

Hey, thanks for the quick response!

So 6.5 is bad huh? Whelp.....I suppose it's time for a new OT.....

How does a shorted OT cause excessive current in the tubes?

[R.G.]

So 6.5 is bad huh?

It's a monstrously important indicator. 6.5 is bad in this context where it's 10:1 different from the other side, and major different from the 100-300 ohms OT primaries usually run.

You can nail down whether it's shorted or not with this:

How does a shorted OT cause excessive current in the tubes?

It doesn't, but it makes them more sensitive to runaway.

[Wes]

Thanks, guys.

R.G., can that tester run ok off of a 9V battery?

[Wes]

Oh, and what would be the best place to acquire a ne-2 bulb?

[Jazz P Bass]

Just Google Neon NE-2 lamp.
NEON NE2 USA - NEON/NE2 USA - neon glow lamp light bulb lamp - donsbulbs - light bulbs lamps valve valves tube tubes

[Gtr_tech]

Its easier to use a neon panel indicator lamp. The current limiting resistor is built in.
http://oklahomaselltoday.com/Sapulpa...light-img-2.do

Onna them guys there....

[R.G.]

Mouser stocks them. They're also power indicators in a lot of appliances. When it's not obviously an LED, there's a good chance it's a neon, especially if the light is orange.

[Wes]

Cool, thanks for all the help guys. Much appreciated.

[J M Fahey]

The "no continuity to ground" is another important indicator.
If the ground wire is disconnected , secondary side is open, a good transformer killer.
Check it or you'll kill the new one too.