crate paloino 50 impedance , how to determine?

[g1]

this schematic looks to be the right one. it has the exact part number of the ot.

Then we at least know that it is 8 ohm OT.

[georage]

yeah its a 32 alright. which means the speakers are wrong. would it harm the amp to run it on 16ohms? i just tried it and the amp failed after about 20 minutes of playing. it started making really loud white noise and then made a horrible noise that sounded just like the star trek phasers noise. then i shut it off

[Helmholtz]

An impedance mismatch by a factor of 2 typically doesn't cause noticeable problems.
Though power tubes might last longer with correct speaker impedance.

Your amp seems to have an oscillation problem which needs to be adressed.
Time for troubleshooting.
But first measure R22 voltage.

[georage]

its about 11.8v helmholtz. and 62.9ohms. wouldnt that be about 47ma per tube?

[Helmholtz]

its about 11.8v helmholtz. and 62.9ohms. wouldnt that be about 47ma per tube?

Yes that means 47mA average per tube. That's very hot but not unusual with EL84s and cathode bias.

I don't think the PT thermal fuse opening is your problem but if you want to make sure, monitor the e.g. the heater voltage when the amp starts to fail.
When the thermal fuse opens all secondary voltages should drop to zero.

.

[georage]

its really nice of you to share your wisdom Helmholtz, thank you. im not sure what the e.g. is...but i have yet to actually experience the pt shutting down. that was speculation. i have experienced a failure many times at this point tho. the amp starts to produce loud white noise followed by a loud screeching noise...where i shut it off asap. sometimes it is emediate but mostly it take several minutes to happen and im hearing some signs of tube failure ..i think. i hear the tubes making a "tink" noise when they first get power. like they are stressing out. some times they make a low pitch crakle noise through the speaker...and sometimes they sound microphonic...for instance the last time i shut thebamp down, i could hear the clink of the power switxh through the speakers. so maybe its just a bad tube?? idk i dont know how to follow up with the oscillation i shared a pic of on the scope.

[georage]

i also noticed that the voltage across r22 did not change at all during the screeching noise

[Helmholtz]

. im not sure what the e.g. is....

Haha, "e.g." should say example given, because any of the PT secondary voltages would show if the thermal fuse opens.

i also noticed that the voltage across r22 did not change at all during the screeching noise

I think we can exclude the PT being the problem and focus on the oscillation.
Breaking into heavy oscillation would explain the symptoms.
The problem might be triggered by temperature or vibration.

Many possible reasons:
- bad tube
- bad tube to socket contacts
- bad connector contacts
- bad filter cap/connection
- bad ground connection
- bad solder joint or broken trace...

Do you see any oscillation without a signal?

[georage]

i havent seen any oscillations for a while now, or im not looking in the right place. i chaged a microphics preamp tube and it sounded great for about 30 minutes when it started doing something brand new.
it started dipping in volume like an extremely slow tremelo effect.

[Helmholtz]

It would help to do some output scoping and maybe other measurement while the amp is misbehaving.

See if you can provoke the problem with feeding a signal, adjusting for around 30W output and letting the amp run for half an hour or so.
Watch for changes in output signal and signs of overheating.