5F2-A Circuit
Hello Skip,
As a novice about to try and make an amp I would have thought it best not to mess about with a design classic. That said I just wanted to ask if there are any simple/minor tweaks to a Fender 5F2-A circuit that would be appropriate for harmonica amplification.
Thanks
Joel
Thanks very much Skip.
Joel
Hello Skip.
So, I've got a completed 5f2a circuit and chassis hooked up to a speaker in a cardboard box. It seems to work though I can't really test the sound with my makeshift cabinet. I though it would be sensible to test the voltages even though finding a definitive answer on the correct values seems to be difficult. My concern is that I've followed instructions for calculating the plate dissipation of the 6v6 GT tube and keep getting a figure of around 18 watts. Should I desolder the 325 output transformer leads and use the 275 volt ones instead? I've tried searching online for some answers but that is not proving fruitful...
Thanks
Joel
Output transformer centre tap = 419.5 V
6V6 plate = 408 V
Cathode = 22 V
OT centre tap to plate resistance 328.4 Ohms
Cathode bypass resistor 464 Ohms
Hello Joel- Thanks for writing. Yes, you should use the lower voltage (275V) taps on the power transformer. Remember, all the work has been done before you when you it comes to a Fender circuit. You don't need to worry about plate dissipation and other complicated stuff- just go by the DC voltages.
Mojotone.com sells beautiful reproductions of the Fender schematics and "layouts". Forget the internet, start there!
Thanks very much Skip, that Mojotone schematic is just what I was looking for. Everything looks fine now with the 275v transformer taps.
https://www.instagram.com/p/COXVvUKpq-s/?igshid=143qh6498cav0
https://www.instagram.com/p/COXVmcap1P4/?igshid=h9fom8yvhuyb
Here are a couple of photos of the cabinet I've made for my amp prior to "tweeding".
Looks excellent Joel, well done
Hello Joel- Thanks for writing. The 5F6-A is a fine choice and won't really need any tweaking for harp. You might try a lower-gain preamp tube (12AY7) or a higher-value roll-off cap in the tone circuit. Instead of the stock value of .005, try a .01.