Fenter Twin Replacement Transformers

[newAmpBuilder]

I need some technical help with a mod. I want to replace my fender twin 100 watt output transformer with a 40-50 watt OT - like in a bassman or something like that. Would I have to change my Power Transformer or would it still work with a lower wattage OT?

[bepone]

no need to replace power transformer

[maxkracht]

No need to change the PT. What are you hoping to achieve with the lower wattage OT? If you just want to run two fewer power tubes you can do that without changing the transformer, but you would probably want to run half the current speaker load if you did that.

[martin manning]

I want to replace my fender twin 100 watt output transformer with a 40-50 watt OT … Would I have to change my Power Transformer or would it still work with a lower wattage OT?

I would check the heater voltage to see if it is still ok with the reduced current draw of two power tubes. The upper limit is usually assumed to be +10%, or 6.9 VAC. I don't know if this is an old or new Twin, so modern voltages might play a role.

If you are looking to reduce output power, and you have 2x 8R speakers in the cab, then pulling two tubes and disconnecting one speaker to rematch the output impedance would be a no-cost option.

[Stevem]

In all likelihood the reduction in heater load of 1.8 amps will take the Heater voltage above 6.9 volts, but you can just leave all 4 output tubes in the amp, but only have two of them wired up to the B+ on pins 3 and 4 .

[newAmpBuilder]

In all likelihood the reduction in heater load of 1.8 amps will take the Heater voltage above 6.9 volts, but you can just leave all 4 output tubes in the amp, but only have two of them wired up to the B+ on pins 3 and 4 .

Would there be a way to reduce the heater load if the extra tubes are removed and the other two sockets weren't wired?

[martin manning]

Why don't you pull two of the output tubes and measure the heater voltage?

[newAmpBuilder]

Why don't you pull two of the output tubes and measure the heater voltage?

Thanks Martin I will do that.

[WhopperPlate]

If you don’t need that 100w twin iron I will take it off your hands!