JTM 100 PT help

[lifer]

i was playing my 45/100 and using my UA. a couple minutes in...the whole thing shuts down. i mean stone cold dead!
(UA fuse ok) the amp is dead.....

both amp fuses are ok. used my meter to check continuity. plug,voltage swtch, all check ok. i guess the next step is to check the PT primary. how do i do that?

[axeman]

Does the amp turn on?

[lifer]

nope! she's dead!

i have continuity from the power cord prongs...up to the PT. i simply dont know how to check each winding ......i'm sure its simple but i never had to do it b-4

[lifer]

oh hey- axeman btw....... you sell tubes dont you? or am i thinkin of someone else?

[axeman]

Yah, How can I help you. If you or other member's need there power and preamp tubes tested, I will do it for free longest you send them with return postage.

[Roe]

the ua is a 30ohm load. if you use the 16ohms out this means running the tubes at 8k primary impedance, something which is way high. dont even think about 4 ohms

[lifer]

cool! thanks axeman

[lifer]

the ua is a 30ohm load. if you use the 16ohms out this means running the tubes at 8k primary impedance, something which is way high. dont even think about 4 ohms

ok, back up a sec! so then was i using the UA incorrectly? i was told to keep the amp set for 16ohm---regardless of the cab/spkr. impedence cuz the UA 'matches' it up somehow.......?

i also run the amp using the UA's 100v supply.

[demonufo]

That is correct. 16 ohm setting is the closest match you can get to the 30ohm loading of the UA.

[Roe]

the ua is a 30ohm load. if you use the 16ohms out this means running the tubes at 8k primary impedance, something which is way high. dont even think about 4 ohms

ok, back up a sec! so then was i using the UA incorrectly? ...

no, you are running a too high Z, something which stresses the screens. not the safest attenuator for this amp

[Flames1950]

You can argue attenuators all day, but that's not the point here.

Is this a clone or an original amp? Is the indicator light a 6V or 120V lamp? If it's a 120V lamp and it doesn't light up, then there's no 120V inside the amp going to either the transformer or the lamp.

[lifer]

flames- yes it is a clone-- georges PT & OT. i'm using a 6v lamp -directly to the PT.

i've been carefully looking inside of course but nothing looks out of line. nothing burnt, damaged, etc.

[Flames1950]

I'd start by rechecking for 120VAC at the two primary transformer leads then. If the fuses and switches are good, and there's 120VAC going into the transformer, and no high voltage B+ and/or 6.3VAC for the heaters coming out, then your PT is likely gone. You'd have to start disconnecting the transformer from the amp to check anything after that.
I'd still be surprised if the power tranny went before the tubes or output tranny with the UA though.......

Have you wiggled the voltage selector switch around (assuming you built it with one) to ensure good contact inside the switch?

[lifer]

yeah-- i'll recheck again.... but i had continuity from the wall and thru the voltage selector and up to both sides of the power switch. im so bummed--- that PT is probably gonna be a fortune if i have to go to MM. maybe heyboer will wind one up for me.

anyway, i guess i should disconnect the PT leads. how do i check continuity of the windings?

[lifer]

wow..... i'm kinda doubting my volt selector now. it's the old JMP style-w/ the removable pin. i disconnected it from the circuit and decided to check it. held both leads on and wiggled the pin. it did interrupt the signal (beeper on my meter) a couple times. i guess thats a real likely culprit, too. gunna keep checkin around though.