1970s Ampeg V4 Low Distorted Output

[g1]

Is it possible to test with 2- power tubes? If so, which 2? Also, until I get 470r 10w resistor, would it be advisinle to test with 470r 5w resistors I have extra to find bad tube? Maybe 2-connected together? Thanks.

Yes you can test with 2 power tubes at a time. Use either the inner pair of sockets, or the outer pair of sockets. Put a single 5W 470R in R55 position for test. Tap gently on the tubes with the handle of a screwdriver or something similar. Rubber type preferred. Watch for flashing lights at power tubes. Hit standby immediately if you see any.
Check that R55 is still ok after each test.

[ca7922303]

Yes you can test with 2 power tubes at a time. Use either the inner pair of sockets, or the outer pair of sockets. Put a single 5W 470R in R55 position for test. Tap gently on the tubes with the handle of a screwdriver or something similar. Rubber type preferred. Watch for flashing lights at power tubes. Hit standby immediately if you see any.
Check that R55 is still ok after each test.

So with a 470r 5w@R55 and power tubes in V6/V7 tapping both tubes, don't notice anything out of the way except R55 blown. So new 470r 5w@R55 and next 2 power tubes in V5/V8 and tapping on tubes, nothing out of the way there but R55 does not blow and I voltage @ pin 3/4/5 on power tubes and 585vdc on both ends of R55. Also able to get correct output. I really appreciate the help again and only 34 posts. I will try first two power tubes one at a time to weed out the bad tube. Thanks again

[ca7922303]

Yes you can test with 2 power tubes at a time. Use either the inner pair of sockets, or the outer pair of sockets. Put a single 5W 470R in R55 position for test. Tap gently on the tubes with the handle of a screwdriver or something similar. Rubber type preferred. Watch for flashing lights at power tubes. Hit standby immediately if you see any.
Check that R55 is still ok after each test.

Strange thing on the way to finding the bad tube, thought I had found it, went ahead and put it in to test and it didn't blow R55. Installed all four(4) power tubes and R55 is 570/570v and have normal output. This is with a 470r 5w resistor still installed@R55. While testing yesterday, noticed a nut wedged in between two(2) terminals on one of the 500v cap cans. Had to pulled it out. Both terminals have burn marks where the nut was touching both of them. Is it possible that could have blown R55 instead of a power tube. Removed nut, installed all four(4) power tubes and have normal output?

[g1]

It's possible, if the cap was one that goes to the lower voltage end of R55. But also possible is that a bad tube has an intermittent fault, that only shows up once in awhile.

[ca7922303]

It's possible, if the cap was one that goes to the lower voltage end of R55. But also possible is that a bad tube has an intermittent fault, that only shows up once in awhile.

Installed the 470r 10w resistor @ R55 and experiencing low distorted output but all voltages are there. Removed it and reinstalled 470R 5w resistor and have normal full output. Any explanation of that? This amp has 3-new can caps and 2-new(1-40uf, 1-100uf spague atom caps) and some related resistors to the cap work and the R55 resistor. The rest looks original.

[g1]

Measure resistance of both resistors. If they both measure the same 470R, the only way the 10W could cause a problem was if it is touching something it shouldn't, due to it's larger size.

[ca7922303]

Measure resistance of both resistors. If they both measure the same 470R, the only way the 10W could cause a problem was if it is touching something it shouldn't, due to it's larger size.

Both measure 470r. I'll put the 10w back in and make sure there clearance. Thanks

[ca7922303]

Measure resistance of both resistors. If they both measure the same 470R, the only way the 10W could cause a problem was if it is touching something it shouldn't, due to it's larger size.

Took 4-7027s and to a tube tester in Nashville, looks like maybe late 50s early 60s design as far as I can tell and tech plugged them into 6L6 socket(no 7027 listed) and two(2) of them tested 100 % good and other two held at 100 and then slowly dropped off to red. Tech says it means a short in two,(2). What do you make of that. Amp sounds strong with all four(4) power tubes installed and hear no issues. Will these tubes blow R55 likely under heavy, long playing? Thanks.

[g1]

I'm not sure what kind of tube tester he is using so can't say. On my tester if the meter falls off into the red that means the tube is weak/worn. Shorts are checked for with a separate test. But his tester could be very different. He should know what readings on his tester mean.
It's also possible that the loose nut you found was the cause of the problem.
Why not run some music through it and let it run for awhile. Into a load resistor or a cab on it's face in the closet you can run higher volumes without it being as annoying. Or use a low frequency tone like 40hz or something.

[ca7922303]

I'm not sure what kind of tube tester he is using so can't say. On my tester if the meter falls off into the red that means the tube is weak/worn. Shorts are checked for with a separate test. But his tester could be very different. He should know what readings on his tester mean.
It's also possible that the loose nut you found was the cause of the problem.
Why not run some music through it and let it run for awhile. Into a load resistor or a cab on it's face in the closet you can run higher volumes without it being as annoying. Or use a low frequency tone like 40hz or something.

Its one of those self serve floor testers that you used to see here in stores everywhere. Guy thought when 2 of them fell off into the red that it meant both had shorts but I wanting to get a 2nd opinion. Cause amp sounds as good as it does. Will test it like you suggested. Thanks.