Brand New THD Power Transformer for BiValve-30 or Flexi-50 Amplifier

THD Replacement Power Transformer for BiValve-30 and Flexi-50 Amplifiers, Brand New, Direct From Our Factory, 14-Day Money-Back Guarantee. 

This is a replacement power transformer for THD Electronics' BiValve-30 and Flexi-50 amplifiers. (Yes, they both use the same power transformer.) It is brand new, straight from the factory. Our power transformers are all wound in the USA. They are vacuum impregnated to eliminate the possibility of corona damage. 

They are a perfect drop-in replacement for the THD BiValve-30 and Flexi-50 model guitar amplifiers. 

The transformer has two primaries, each 120V end-to-end, with a 100V tap. This allows the transformer primaries to be wired in combinations of partial or complete series and parallel for used at wall voltages of 100, 120, 140, 200, 220 or 240 VAC.  

It has a secondary for 6.3-volt filaments, which does not have a center-tap, as it was designed to be used with a full-wave bridge rectifier for DC tube filaments. In this configuration, the negative of the DC supply is grounded, and the two power tubes are run on the AC before rectification. It can take any two octal power tubes up to 6550A ratings, and up to five 12AX7-family preamp tubes (if 6550s are used in the power stage, more if you are using 6L6 tubes). It wants to see a maximum of 4.75 Amps on the filament supply. 

The B+ winding is also designed for a full-wave bridge rectifier, and has a tap for voltage reduction. The actual voltages you will get depend upon how much current you are drawing, but with a pair of 6550A power tubes, run class-A single-ended parallel (like in a BiValve-30), with individual cathode resistors of 400 ohms, the full winding will give a plate voltage around 460 VDC, and the tap will bring it down to around 320 VDC. At either setting, it will happily deliver 550mA all day long. We recommend a 1A Slo-Blo fuse on this winding. 

PLEASE NOTE: There is no bias winding. In the push-pull class-AB Flexi-50 model, we run a separate bias transformer, which steps down the high-voltage winding of this transformer to create the bias voltage. This way, when you switch to the lower voltage tap, the bias voltage changes, as well, but the same proportion. If you need one of these bias step-down transformers as well, please contact us. 

The transformer is HUGE and VERY heavy at 11 lbs., 10 oz. The core measures 4.5” on the long side, 3.75” on the short side, and the stack is 2.5” tall. 

The money-back guarantee applies only when installing this transformer in a THD BiValve-30 or Flexi-50 amplifier. Any other use is at your own risk, and not covered by our guarantee.