Good morning Stuart, I removed the secondary windings from the circuit board as you explained and yes it blew the fuse again. Now I know its the power transformer. I had a hammond 290cx power transformer in it. There are some more companies out there and would like to ask if it really makes a difference in the power tranny? Weber makes one and so does Mercury and I believe Classic Tones. I do know that a output tranny can make a difference in tone but what about the power tranny. Thank you for your time...........
Realy nice video and thanks for the reply. Some info you can use in a new video? is a Bias methode like: Wattage 6l6GC = 30watt, devided by the measured plate voltage (400V ?) = limited plate current of the tube/valve. To fixed bias in push pull mode, you could use: Hot bias is to adjust to 70 % of the calculated limited current. Cold is about 50% of calculated current. Medium is 60%. Going lower then 50% often gives crossover distortion. Some tech use a scoop to fine tune that.
Hello Stuart, I just installed my new Weber power transformer, the other tranny had shorted out. The Weber tranny did not fit, that is the bell was too large, so I removed the bell end that has the wires coming out and the tranny was able to fit in the chassis. I think it will run cooler without the bell and the amp now powers on. I started to check the bias and found out I had to decrease the resistor in order to get a higher range on the bias pot. Thank you for your videos........
Excellent video Stuart....it looks identical to my silverface Pro-Reverb I am working on. Same amount of old white mallory caps also...5 in total except the one on the far left is 50 volts at 5uf...I'm having difficulty sourcing that. Any suggestions? ( UK suppliers) Your recommended supplier at the end of the video sells valves only
I wouldn't call 45mA 'cold'. I like to bias tubes on the coller side of the oiptimum just to extend tube life and stop everything running so darned hot all the time. You'd never hear the difference between 45mA and 54mA. 'Cold' would be about 25mA!
Hello Stuart., I found that I have to change my bias resistor to a smaller value. Once I put back my chassis I blew a fuse. I inspected the circuit board and found a piece of metal that came dislodged from above which fender uses as a heat shield and found it in the heater section where the pilot bulb is. This caused the short. I removed and put a fuse in and it blew again. Do you think the power tranny is ruined? thanks
Hi Jim. Oh no, what a nightmare! The inly reak way to check is to disconnect the heater winding from the board and try again. Actually, I'd disconnect ALL secondary windings and try. If that blows a fuse it's probably the mains Tx. Good luck.
I can;t remember now. Sometimes I do this because the originl is hard to remove and replace. Sometimes I do it to show that it is a modification and also to help the next person easily locate the bias resistor change.
