2 carlsbro 100 tops, with different problems

[per111]

Hi.
Could need a little help. I`ve got 2 100 tops with different problems (and only a dmm, no scope)
1. one top is playing fine, untill pushed, especially with much bass, then osicilliating (motorboating) untill I turn it down...all electrolytic have been changed, so has the 3 0.1 decoupling caps. any suggestion where to look next?
2. second top is playing 10 % of the potential, same caps have been changes, and no change...
In both amps all resistors have been measured fine, and all tubes have been changed several times, without any change
I would be gratefull for any help.
I excuse for any misspelling, I`m a dane

[Jazz P Bass]

How about a few voltage readings.
The preamp tube readings of the plate & cathode will tell how well it is conducting.
The output tubes: Bias voltage & plate voltage readings may help.

[per111]

Hi. here are some readings:
ecc 83both halfs)
plate: 150 v
cathode 1,1 v
EL 34 plate: 540v biascurrent 37 ma (maybe a little hot?)
thanks for your reply.
Per

[Steve Conner]

Check the output transformer on the second unit. Could have some shorted turns. Maybe try swapping it with the other unit.

On the first unit, try increasing the 20uf capacitors to 47uf as an experiment.