Thanks for the earlier advice. I have been able to determine that the high voltage transformer does indeed have a short on one of the high voltage windings. It has a Dietz 84C-1, 29-2500250 transformer number printed on it. Since I do not have a schematic and so do not know the rated voltages I am trying to determine what kind of replacement transformer to buy. The 12AX7 tube heaters are wired to 6.3 V DC so I know that voltage rating, but the high voltage can be anywhere from 180 to 250 V DC.

Any ideas?

Thanks,

Steve

Hi Stephen, I'm sorry to hear the transformer is actually bad. It might be worth emailing some people on those guitar web sites, someone there might know the amplifier and be able to tell you the voltage. Although the 12AX7's can run on a high voltage, it's possible they might work on a low voltage in this application. I'm guessing they're part of the "tube distortion effects" system. One clue is to look at the voltage rating on the electrolytic filter capacitors, The B+ should be less than the rating and probably not a lot more. I would suspect it's a fairly small transformer if it's only running three 12AX7's and would expect a silicon bridge rectifier but your ststement "one of the high voltage windings is shorted" indicates more than one. Is it a center tapped winding with a pair of diodes? Sorry I can't be more specific, hope you get it sorted out. Don Black.

: Thanks for the earlier advice. I have been able to determine that the high voltage transformer does indeed have a short on one of the high voltage windings. It has a Dietz 84C-1, 29-2500250 transformer number printed on it. Since I do not have a schematic and so do not know the rated voltages I am trying to determine what kind of replacement transformer to buy. The 12AX7 tube heaters are wired to 6.3 V DC so I know that voltage rating, but the high voltage can be anywhere from 180 to 250 V DC.

: Any ideas?

: Thanks,

: Steve

Yes, the high voltage secondary winding on the transformer is center tapped. The center tap is grounded and each of the other leads goes directly to a silicon power rectifier then through a 820 ohm resistor to the power filtering capacitors (rated at 450 V DC). Since the 12AX7's plate is rated up to a maximum of 300 V DC then I still can't discern the proper voltage rating by looking at the circuit.

You're right about the original designer of this guitar amplifier picking the point on the tube curve for the distortion effects. It could be any one of serveral voltages.

I am checking out the guitar amplifier pages - WOW so many......

Thanks,

Steve