No Cathode Current / No Sound

[MWJB]

I'm not Enzo, but...

With nothing plugged into the speaker jack, the jack will be shorted to ground via the switched terminal on the speaker jack socket, you need to have something plugged into the speaker jack. But even so, DCR will still be very low, you might not be able to measure it. Its probably not relevant anyway, as if there is a short, it will be in the primary winding.

[jmaf]

I'm not Enzo, but...

Heheh, was directed at all of course, I just typed as I thought.

Your own reply got me thinking of the possibility of a shorted jack as well. Without an input signal the secondary will just sit there shorted, though his tubes would run pretty hot due to the very low reflected impedance.

[pdf64]

'secondary of the output transformer ... reads zero ohms, so I would assume that it is shorted'
No you can't assume that. You are probably measuring the resistance of a few turns of heavy gauge wire, using a regular DMM the measurement is meaningless and has no relevance to the problem.
Best to do the tests that Enzo advised above.

[Gibsonman63]

You guys got me kickstarted again. I was looking right at it and and even checked the jack to make sure it came un-shorted when the cord was plugged in, so obviously it will read zero ohms on the leads from the transformer when the speaker cable is not plugged in. With the cable, plugged in, I was able to read a small amount of resistance measureing at the end of the cable, but my meter is unstable reading resistance that low. From what I can tell, it is a little less than an ohm.

I have a session tonight at the local ice-house, so further trouble-shooting will have to wait until tomorrow evening. I will run through all of the suggestions and report back.

[Enzo]

You cannot measure a problem in the secondary of the output transformer with a hand meter. ANyway, as MWJB points out, shorts are going to be on the primary side anyway. If you just can;t trust it, disconnect the secondary wires from the jacks, and connect them directly to the speaker with clip wires.

The very essence of troubleshooting is to isolate the problem. I laid out a systematic approach above to do that.

[jmaf]

Eager to hear from Gibsonman now. Though I haven't been of much help I'd really like to see this case closed and find out who was the culprit.

[Enzo]

He appears to be a morning poster, we'll see.

[Gibsonman63]

Sorry guys, no troubleshooting last night. I was busy throwing down some tasty licks at the local ice-house. This is a great forum. You guys are unbelievably supportive!

[Gibsonman63]

Success

Enzo's systematic aproach prevails. One of my silverface to blackface conversions was to remove the tone-sucking caps from the power tubes and pin 8 of the power tubes was no longer grounded. I grounded pin 8 on both power tubes and she fires up loud and proud.

Once I get the tremelo circuit working and get the chassis installed, I'll post some pics.

Thanks again to everyone for your help.

[jmaf]

Enzo's systematic aproach prevails. One of my silverface to blackface conversions was to remove the tone-sucking caps from the power tubes and pin 8 of the power tubes was no longer grounded. I grounded pin 8 on both power tubes and she fires up loud and proud.

Once I get the tremelo circuit working and get the chassis installed, I'll post some pics.

Thanks again to everyone for your help.

There you go! Glad to hear. Indeed it was one of the simpler cases that were mentioned. Sorry for scaring you with the thought of a bad OT.

Congrats and send us pics of this baby on stage!

[Gibsonman63]

Finished Product

... well almost. One speaker has a rub. Other than that, I am good to go. Thanks to all who helped.

A little history. I bought this amp about 25 years ago for USD$250. The music store owner gave me a deal because I was in his shop every Saturday when he opened, this amp was in really rough cosmetic shape. The grill and baffle looked like someone had fallen into the amp and the tolex was in very bad shape. I used this amp as my main gigging amp for almost ten years before I started buying Marshalls. I ended up having to pull the tolex off because the corners had come unglued from hauling it around. I really regret not taking the before pictures, but here is how she looks now.

Now I have a new problem. I can't take this amp anywhere until I get a road case for it!