Testing output transformer

[fossilshark]

Hi all, I have a crate blue voodoo 60w el34 on the bench today. I noticed the impedance selector was sent to 16ohms and I was told this was playing through an 8 ohm cabinet when it suddenly stopped making noise. Unit does power on and fuse is not blown.

I want to test this output transformer to see if it is still good, how would I go about doing this?

I also haven't noticed anything burnt on the board but I have not had time to test voltages, anything else I should test?

[tubeswell]

Unit does power on and fuse is not blown.

I want to test this output transformer to see if it is still good, how would I go about doing this?

Could be OT and/or output tube or speaker failure.

To test OT, disconnect all primary and secondary leads from amp circuit, and run 6VAC* to the secondary and measure for highish VAC on each side of the primary. Looking for the ballpark Pr:Sec voltage ratio (which will be the square root of the impedance ratio). You also want to see equal VAC on both sides of the primary

Be careful not to touch the leads with your bare hands. (Use insulated gator/test clips). You also don’t want the leads shorting to each other or to any other circuit or ground/earth.
(Edit: *Or whatever lowish AC voltage you have handy.)

[kagliostro]

Give a look here

Note that this way you can find shorted turns within the same windings, not necessarily between primary and secondary

Franco