Bad Tube ??

[martin manning]

Hello Martin. Thank you for taking me to task...

Not scolding of course, it's all in the interest of learning. On the first point it looks like you were talking about measuring the DC resistance of the secondaries, so the 4-ohm should read less than the 8. Still hard to get a good reading at these low resistances with a typical meter. On the second point, I didn't look at the picture, so I probably took your words out of context. Cheers!

[playonit]

Alright..... I am going to fore-go the second check..I did write all the steps down for future reference.

I attached a pic of my output jacks.. you mentioned they looked like they are wired in parallel?? I run through a 2/12 8ohm cab.. I haven't noticed any issues running this way?

Now.. this brings me back to my initial problem.. no sound from my normal input jacks.. I am waiting for my new 5881's I just ordered. So far I have checked for loose/broken wires , continuity and resistors and caps.. what do you recommend as my next steps to chase this issue down?? While I wait for the new tubes .. I think I will run through and check all my voltages to see if they are still in line with the specs...

Phil.. I can't thank you enough for the time you're taking to help me out..

Greg

[Phil_S]

Hello Martin. Thank you for taking me to task...

Not scolding of course, it's all in the interest of learning. On the first point it looks like you were talking about measuring the DC resistance of the secondaries, so the 4-ohm should read less than the 8. Still hard to get a good reading at these low resistances with a typical meter. On the second point, I didn't look at the picture, so I probably took your words out of context. Cheers!

Martin, you have kept me honest here more than once. I always appreciate it.
Best regards,
Phil

[Phil_S]

Playonit/Greg: Those output jacks are wired as I thought. When you use only one jack, it doesn't matter which one and you set the selector to the tap that matches the load and the other jack has no effect.

Because they are wired parallel, when you use both jacks, the total (sum) of the loads divided by 2 is what your OT will see, so set the selector accordingly. IOW, if you run a pair of 16 ohm cabs, they are 8 ohms together in that arrangement and you select the 8 ohm tap.

Ordinarily, people either use a single jack with a selector switch or, in this case, 3 jacks, one for each tap. No buss on the tip, just one OT wire to each jack, and a common buss on the sleeve the way you have it.

There is nothing wrong with the way you wired it as long as you understand the implications, remember to do the math, and set the selector.

Back you your problem, I suggest a pop test. What's a pop test? I'm glad you asked. First, put everything back together, and put the tubes in the sockets. Now, power up the amp and probe for DC voltage. For DC, red probe on the target, and black probe on the chassis. Use a clip with the black probe. OK, for safety, one hand in your pocket. Power up and then probe all the active pins at each tube (plate, grid, cathode). See which ones make a pop. scratch, or other noise. See which ones don't. This should help to isolate the problem and then you can refine the search. Start at the power tubes and work backwards. Well, you really do need power tubes or you can't hear any popping noises at the speaker, can you?

[martin manning]

Ordinarily, people either use a single jack with a selector switch...

FWIW, two speaker jacks wired in parallel with an impedance selector switch is pretty common- Marshall and Hiwatt heads, e.g., Dumbles too.