04-10-2007, 02:32 PM
Tough one! That set has Class B output, which means the driver transformer needs to be able to handle some power. Here's what you need: Ratio 2 to 1 (primary to HALF secondary). In a similar set, the transformer measured Primary: 998 ohms, secondary 1222 ohms CT.
Note this is the OPPOSITE of the typical A52C, A63C etc (1:3CT). These simply will not work well (distortion).
In most cases I used a single ended OUTPUT TRANSFORMER back to back with a UNIVERSAL PP Output Transformer (connect voice coil to voice coil) and set the taps so that the ratio is about 2:1 primary to half secondary. I use an audio oscillator set to about 400 hz and select the tap on the universal transformer that gives me the result closest to the appropriate ratio. Unfortunately, you have to be able to hide one of the transformers, and have room for two.
The only other way is to find a universal input transformer such as the Halldorson HVAT-3 driver transformer, which has 2:1, 1.5:1, or 1:1 ratios, single or push-pull. I found one at PTOP, but it was expensive and also big.
In a real pinch you could try a PT-K2 (available from AES) which are 10K Primary to 2.5K CT Secondary. These used to be available, and were very cheap. But they are 4:1CT so gain suffers. Also, not enough inductance, and very limited frequency response (I think they don't go below about 300hz).
Dave
Note this is the OPPOSITE of the typical A52C, A63C etc (1:3CT). These simply will not work well (distortion).
In most cases I used a single ended OUTPUT TRANSFORMER back to back with a UNIVERSAL PP Output Transformer (connect voice coil to voice coil) and set the taps so that the ratio is about 2:1 primary to half secondary. I use an audio oscillator set to about 400 hz and select the tap on the universal transformer that gives me the result closest to the appropriate ratio. Unfortunately, you have to be able to hide one of the transformers, and have room for two.
The only other way is to find a universal input transformer such as the Halldorson HVAT-3 driver transformer, which has 2:1, 1.5:1, or 1:1 ratios, single or push-pull. I found one at PTOP, but it was expensive and also big.
In a real pinch you could try a PT-K2 (available from AES) which are 10K Primary to 2.5K CT Secondary. These used to be available, and were very cheap. But they are 4:1CT so gain suffers. Also, not enough inductance, and very limited frequency response (I think they don't go below about 300hz).
Dave
