Fender bassman 100 o/p transformer

[Newbietube]

Hi all I've been given a Fender bassman to repair. So far I've found one of the 470 ohm resistors from the supply to the power tubes(pin 4) to be blown apart and the remaining three to be way over tolerance (over 200 ohms in one case). Obviously my first job is to replace these, however when I checked the output transformer I found the primarys to be only about 40 ohms to the centre tap (80 ish total), when I'm sure it should be closer to about 4kohm. My initial reaction was that it is blown, but I'm confused due to the equal balance of each side relative to the centre tap. Am I doing something wrong in the way I'm measuring the primary coils? I've tried this using two different digital multimeters set to read ohms and got the same result twice. I would be very pleased (as would its owner) if its only the resistors that need replacement but I dont want to risk the amp any further damage by switching it on if the o/p transformer is at fault.
Sorry for my ramblings but any help is much appreciated.
Cheers Just

[TomMcNally]

Don't confuse DC resistanced (as measure with an ohmmeter)
with impedance ! You'll probably be back in business
after you replace the resistors and output tubes. The
tubes probably went bad and burned up the resistors.

[Gingertube]

Those 470 Ohm 2W Carbon Resistors are the Output Tube Screen resistors.
The "standard" Fender repairmans 1st job on any Fender repair/restoration is to replace them with 1K 5W Wire Wound resistors. While you are messing about with resistors mounted on teh output tube sockets, take the opportunity to also replace the 1K5 grid stop resistors with metal film resistors.

Finally measure the bias voltage between the grid and cathode pins on the socket BEFORE plugging the output tubes back in. This can be done in standby mode.

Cheers,
Ian

[jar240]

I have to agree with Gingertube...those screen resistors take a lot of heat.

Another thing to check is that the solder connections of the ground wires to the brass grounding bus/plate are still intact. You'll likely need a soldering gun to reflow these.

Also, get your self some Caig Labs DeOxit and clean out the pots and jacks.

Chris