Modifying 5F2A circuit for EZ80 and EL84

[stephenhartley]

Hi - this is my first post for a while - so far I've built a 5E3 and a 5E5 based amp and they're both running beautifully.

I'm building a 5W class A amp using the Fender Princeton 5F2A as a blueprint but with an EZ80 rectifier and an EL84 power valve. (I'm in the UK).

The PT gives out 190-0-190 and there's just one 6.3v-0 heater tap at 2A.

Question 1: Can I run the lamp (6.3V) and all the tube heaters off the 6.3v tap (pre-amp tube is 12AX7)

Question 2: Do I need to alter any of the resistors or caps?

Thanks in advance

Stephen Hartley

[mozz]

Heaters should be fine. Voltage should be ok, maybe a little low so you may not get the entire 5 watts output. You will have to change the el84 cathode resistor to get to the bias you want.

[stephenhartley]

Heaters should be fine. Voltage should be ok, maybe a little low so you may not get the entire 5 watts output. You will have to change the el84 cathode resistor to get to the bias you want.

Thanks very much. Should I be going up or down with the cathode resistor?

Best wishes

Stephen

[Dave H]

Should I be going up or down with the cathode resistor?

Down, the AC4 uses 150 ohms.

[stephenhartley]

Thanks - I'll give it a go

Cheers

Stephen

[stephenhartley]

I've read that if the EZ80 blows, it will send HT through the heater circuit and blows the tubes and transformer - is it reasonable to put a 2 or 3 amp fuse into the heater circuit for protection?