This section describes the amplifier housekeeping, using GM3SEK's Tetrode boards:
In my Plisch TH327 amplifier, the screen voltage was original been taken from the HV, and is being regulated with OA type regulating tubes. As described by Ian, this is not the ideal way in creating the G2 voltage. We decided not to use the original G2 power supply, but to add a 560 VAC transformer to make the G2 voltage. The G2 voltage is then being stabilized by a Mosfet device, and being controlled by the logic.
This board does everything needed, it will monitor the G1 and G2 current, and will trip the amplifier in case of problems.
In further optimizing the amplifier, I decided to build a separate rack for housekeeping, to control the TH327 and giving it the correct voltages and protection. Use special care for the grounding of the chassis of a separate housekeeping rack, make sure you have a perfect ground between the housekeeping and the amplifier deck !
Following is the datasheet of the TH327, look at the last page for my setup with 550 VDC on the screen.
I need around -85 DC on the G1 gitter to go for around 150 ma Idle, to bring the tube in AB1. A few modifications to the board where needed, described below.
Working conditions: UA 4000 VDC, UG2 550 VDC, UG1 -85VDC for IA idle 150 mA, -140VDC for cut-off including grounding of G2 in RX. UF 5,8 VAC @ 34 A
Below is a picture housekeeping chassis.
Modifications to the original board: (See tetrode board manual for details)
Transformer voltages : G1 170 VAC G2 580 VAC
Adjustment range : G1 -82 to -91 VDC G2 450 to 560 VDC
Installed 4K7 R107 and connected G1switch
Changed Zener diode to 1N5375 ( 82V )
Installed the wirelinks on K2/3 for G1 switching
Changed R10 to 220K
In place of LK3 : 150 K
Changed R13 to 20 K 5 watt
Changed R14 to 2K2 50 watt
Changed R12 to 3K9 50 watt
Using 50 K 50 W for RS
Changed VDR's to V480LA80BP
Changed C101 and C102 to 100 uF 450 V
Changed R101 and R102 to 100 K 5 watt