tardishead
Well-known member
I have an old PA amplifier 2 EL34 output which drives a 600 ohm line. I want to use it as a variable Motor Drive Amplifier for an Ampex 350.
After recapping power supply and replacing a few out of spec components I hooked it up to a capstan motor and it did not work. On looking at the scope I have a badly distorted sine wave so obviously I have a bit more work to do on the amp.
The EL34s are operating correctly and drawing the right amount of current - plate and screen volts etc.
There are some preamp and phase splitter stages provided by 2 12AX7s.
I dont have a schematic.
I presume I have to treat this amp like any other high power tube amp and power it up with a load accross the output transformer secondaries. Do I need a 600ohm 50/100 watt resistor?? How would you guys recommend I test the amplifier without hooking it up to the motor? I can buy 50watt100watt 4,8,and 16 ohm DUMMY LOADS but not 600 ohm. HELP
After recapping power supply and replacing a few out of spec components I hooked it up to a capstan motor and it did not work. On looking at the scope I have a badly distorted sine wave so obviously I have a bit more work to do on the amp.
The EL34s are operating correctly and drawing the right amount of current - plate and screen volts etc.
There are some preamp and phase splitter stages provided by 2 12AX7s.
I dont have a schematic.
I presume I have to treat this amp like any other high power tube amp and power it up with a load accross the output transformer secondaries. Do I need a 600ohm 50/100 watt resistor?? How would you guys recommend I test the amplifier without hooking it up to the motor? I can buy 50watt100watt 4,8,and 16 ohm DUMMY LOADS but not 600 ohm. HELP
