Tweet
I've been reading RG Keen's suggestion to add fuses to protect my 5F6A to make it an "immortal amp", and would appreciate suggestions on selecting fuse values. I'm going to add fuses to the tube heater supply and rectifier tube supply. Those values are easy to choose. The tube heater current total is 2.7A, so I'll use a 3A slowblow fuse. The rectifier heater is 3A, so I'll use a 4A fuse. My PT is rated at 200mA - 720 volts, and I'd like to put fuses on the HT feeding the rectifier, and also put a fuse on the B+ between the rectifier and standby switch. What values of fuses are required to withstand the current surge of normal capacitor charging inrush. I have a 50 mfd main filter cap (two 100 mfd caps in series) before the choke.
-
-
'like to put fuses on the HT feeding the rectifier, and also put a fuse on the B+ between the rectifier and standby switch'
A 500mA slo blo in series with the ground return of the B+ winding centre tap, in conjunction with silicon diodes in series with the B+ winding feeds to the rectifier, should cover almost all failure modes.
Additionally, a current inrush suppressor (NTC thermistor) in series with the primary, allows the use of a quick blow line fuse, which should greatly reduce the time that the transormer has to cope with fault currents, when they occur.
Many new amps have these, see TH1 on the fender re-issue
http://www.fender.com/support/amp_sc..._Schematic.pdf
In the UK on 240V, I use ones rated at 3 amps, 25ohms at room temperature, for 30-50 watt amps, I'd up the current and lower the resistance spec for use in USA at 120V.My band:- http://www.youtube.com/user/RedwingBand -
Thanks, I appreciate the good advice!Comment
Comment