• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Is this KT88 gone?

jcalvarez

Member
Paid Member
2021-04-16 4:57 pm
Dunfermline, UK
I may have done something stupid, I bought a Fatman iTube 182 on Gumtree. The owner reported "motorboating", and that sounded OK at low volume. The amp was recapped, I can see that all capacitors are new. I paid £80, hoping that at least the chassis and power transformer is worth that, the rest is a bonus.

I have not plugged the thing yet, just looking at the KT88 tubes, one seems to be on the way out, do you guys agree? The other tube seems to be OK.
IMG_20220126_155146.jpg
IMG_20220126_155206.jpg


Thank you!

Jose
 

pcan

Member
Paid Member
2015-12-31 4:57 pm
The tube may still work. I've worse looking ones that still measure good. The motorboating may be a consequence of the recapping. It may happen if the factory capacitors have been replaced with new ones with far higher capacitance value, or if the ground connection has been moved, maybe because they are bigger in size and don't fit on the original mounting anymore.
 

jcalvarez

Member
Paid Member
2021-04-16 4:57 pm
Dunfermline, UK
The tube may still work. I've worse looking ones that still measure good. The motorboating may be a consequence of the recapping. It may happen if the factory capacitors have been replaced with new ones with far higher capacitance value, or if the ground connection has been moved, maybe because they are bigger in size and don't fit on the original mounting anymore.
They reason the original owner did the re-cap was the motorboating. It did not fix it. I had the impression the guy spent more money than he wanted to trying to fix it, then decided that life is too short :)
I need to get some me time to plug it on and see what's going on.
 

jcalvarez

Member
Paid Member
2021-04-16 4:57 pm
Dunfermline, UK
Probably the first thing to do is try and get hold of the original schematic and compare the circuit. There is always the temptation when fixing an issue to jump straight to improvements, and maybe the previous owner excaberated an issue by moving away from the original design.
I found on the net an excellent report on repairing the same amplifier, the guy this a great job, all well documented, is going to help a lot.