Some questions for F5 build


2018-11-12 10:12 am
hi - could i ask a few questions regarding my F5 build?

1) on the variable resistors P1-P3, can some be reversed so that all three are facing the same way?

2) on the universal PSU, i bought some TO-3P diodes. In the guide, it says that it's recommended that i should buy an insulator to connect to the heatsink but these are made of plastic so why are they conductive?

3) there is a 3300pf cap. Can spec should this be? is it the X1/Y1 type or any high voltage metal cap is fine?

thank you very much

Dennis Hui

Paid Member
2002-08-27 7:19 pm
Toronto, Canada
1) The pots can be reversed. You can leave out P3 if you don't have tools for measuring distortion.
If you intend to install it, you should start with it at midpoint. The only thing
about P1 and P2 is to make sure they are set to minimum value prior to first power up.
Forget about directions, and just adjust P1 and P2 so that the measured resistances
across R5 and R6 are close to zero.

2) No additional insulator is needed if your diodes have insulated cases.

3) That cap goes across L and N on the AC lines so it needs to be safety-rated; you can't just use a high voltage film cap.
Last edited:


Paid Member
2010-10-22 6:43 pm
Denver, Colorado
Thank you Dennis. :yes:

An additional point on 2) - you actually don't need insulators on the diodes/individual heatsinks at all (even with metal bodied devices) because the heatsinks are all isolated and are not in contact with anything. But, it is a good idea to use insulators in that example as the heatsinks would become live with the secondarys attached... But in your case, with plastic case diodes, there is no need as Dennis says.