Hello Ian!
Hope all is well with you.
The final few back ordered parts for my build have arrived at UPS and I'm picking them up tomorrow.
I'm having a bit of a problem with my HT board.
My power transformer is a centre tapped dual secondary with 120v on each side.
I am reading 240vac output from the transformer using the two outer coil leads with the centre tap unused.
How should I connect this to the board power input marked at 240v on the schematic?
Connect the two outer leads that read 240ac to the pads marked 'AC' on the HT350 power supply board.
I'm wondering what voltage dc I should be seeing at the HT output points?.
I'm also having trouble getting the 75vdc output point to work.
With no load on the output, the dc voltage across the pads labelled 'HT' will be in the region of 340 volts. Under these conditions, the dc voltage between the pad marked '75V' and the 0V pad of the HT will be around 85 volts.
Be careful when testing the power supply with no load because the smoothing capacitors take a long time to discharge - many minutes.
I've placed the components according to the schematic provided but just to double check, could you re-post the resistor values for R1 through 4?
Thanks!
The values of R1 ,R2 and R3 depend on the amount of HT current you intend to draw. This document:
http://www.ianbell.ukfsn.org/EzTubeMixer/docs/power/HTdesign.pdfshows you how to work out the values for these three resistors depending on how many EZ tube modules you need to power.
R4, and R5 generate the 75V from the HT. R4 is normally 220K and R5 is 75K.
Because the smoothing capacitors take so long to discharge when unloaded, you can change R4 to 100K and R5 to 33K to speed this up. However, this increases the dissipation in R4 which needs to be changed to a 2 watt type.
Hope that helps.
Cheers
Ian