Fender Bassman 100 OT loose test

[BonesMachine]

I'm a novice testing an output transformer pulled out of a 70's Fender Bassman 100 head that has seen some high voltage (arcing, clicking). I'm also testing a brand new Hammond 1750W replacement OT for the bassman to compare results. I guess the bassman OT looks good? The only difference between OTs is higher resistance from primary red to brown/blue on the bassman OT. Any thoughts on the health of the bassman OT based on below results?

Bassman:
resistance: primary red to blue: 53 ohm
resistance: primary red to brown: 48 ohm
resistance: blue to brown: 100 ohm
continuity: either secondary to primary red: none
continuity: all wires to OT case: none
resistance: secondary to secondary .2 ohm

Hammond 1750W replacement:
resistance: primary red to blue: 13 ohm
resistance: primary red to brown: 12 ohm
resistance: blue to brown: 26 ohm
continuity: either secondary to primary red: none
continuity: all wires to OT case: none
resistance: secondary to secondary .2 ohm

[xtian]

Both "appear" to be healthy, based on your DCR readings. Doesn't mean it's in perfect shape. You also need to test it energized and under load to know for shore.

[neskor]

try this method

[martin manning]

That test will find a shorted turn that would be near impossible to detect by resistance measurement, but it might not detect insulation punctures that do not cause problems unless full working voltage is applied. Comparing the new and old in a listening test is the last word.

[cdemike]

That test will find a shorted turn that would be near impossible to detect by resistance measurement, but it might not detect insulation punctures that do not cause problems unless full working voltage is applied. Comparing the new and old in a listening test is the last word.

Martin helped me find this same problem that popped up a recent build of mine. How are your fuses holding up? Have you opened the old transformer?

[BonesMachine]

i'll have to try the NE2 neon bulb test just need to get the bulb. i haven't opened up the old transformer i need a better flat head screwdriver the screws are pretty tight. so i'm looking at both the old transformer and new hammond replacement and the hammond is about half the size with different mounting holes. does this make sense?

[BonesMachine]

any reason the OT has to be mounted traditionally to the amp chassis? The bottom and mounting holes of the old OT look painted. for the hammond replacement i was thinking maybe i could mount a piece of wood to the chassis holes and then mount the hammond OT (with different mounting holes) to the wood. any reason i shouldnt do this? thanks

[martin manning]

It's a lay-down mount isn't it? Seems like the replacement OT should be similar in size to the original, and basically the same as a Fender Twin OT.

[bepone]

ot on bassman 50-100w is normal vertical mount.

[bepone]

here they are, left one is 50w right one 100w

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