I have a filament/bias transformer for a Heath SB-220/221 amplifier. The part number is 54-238. It supplies 5 volts at 30 amps, the 100 volt bias voltage and the primary was configured for 120 or 240 volt operation. It is small enough to ship Priority mail flat rate. You could use this to run a pair of 3-500Z's in any home brew amp as well. $60 will get it, shipping included, in the US. I will ship it overseas if necessary for the extra shipping. You can e-mail me or call me at 616-677-3706. I will take PayPal, personal check, Money Order (USPS) or can run your credit card through my business account. Thanks for looking!