Scott,

You are correct. The intention by SY was to connect the positive regulator to one side of the heater and the negative regulator to the other side of the heater. The HMN heater schematic shows a connection to common, but that connection doesn't exist. The total across the voltage across the heaters on the ECC88 should be 6.3 VDC as you noted. Even with that set-up, the regulators are working at a voltage difference from common. Since common is lifted well above ground, noise is reduced from a balanced set-up where common is at ground. At least that's how I understand it.

You are correct about the heater regulator power supply voltage being key in the temperature issue. It would take a good size heatsink for +/- 13 V. Even with a lower voltage transformer, I was happier using a heatsink on the regulators.

Jac

Thanks Jac;

That makes sense. There would be no reason to run them via the heater common if you were trying to eliminate noise. My heater common is elevated at about 20 volts relative to the B+ supply ground.

I also found that his EO power supply schematic has a small error. The LM337 regulator has pins 2 and 3 swapped. He shows it with the same pinout as the LM 317, but that has pin 3 as input and pin 2 as output. The 337 has pin 2 as input and pin 3 as output. Of course I laid out my board the wrong way..sigh..

I ordered a 2 amp 5 volt CT transformer to replace the 9 volt CT one I have. That should give me about +/-7 volts DC with a bridge rectifier, and only 3.5 volts of overhead, so about a watt of dissipation.

Scott

@mrdave -- pm me -- if you have a paypal account it furnishes a shipping label automatically, but if i have to go to the post office the amount they charge depends on who's pms-ing on the given day...

Two mrdave's and two Jack's. Let the fun begin.

Jac

Hi jackinnj,
I took a look to your board an found the resistors to adjust the current.
The 2,7k (20mA), is it prallel to the 120Ohm Resistor?

thank you for your work