TUBE TYPE MODIFICATION / CONVERSIONS
AMPEG 7027 to EL34
Models: V-4, V-4B, VT22, & VT-40
Change resistors R41-42 & R47-48 (470 ohm 1 watt) to 1K 5 watt. Rebias the amp (adjust R49 to re-bias)
AMPEG 7027 to 6550
Models: V-4, V-4B, VT22, & VT-40
Change resistors R41-42 & R47-48 (470 ohm 1 watt) to 1K 5 watt. Then change R50 to 82K. Re-bias the amp (adjust R49 to re-bias)
FENDER 6L6 to EL34
1.) Remove the resistors located between pins #4 & #6 on the power tube sockets (470 ohm 1 watt) and replace with 1K 5 watt resistors.
2.) Disconnect and remove the 1.5K resistor between pins #1 & #5 on the power tube sockets.
3.) Solder one leg of a 1.5K resistor to pin#5, Remove the wire going to pin #1 and connect it to remaining leg of the 1.5K resistor.
4.) Connect a bare wire between pins #1 & #8 on the power tube sockets (pin #8 should already be connected to ground).
5.) Install the EL34’s and re-bias the amp.
MARSHAL 6550 to EL34
1.) Locate the 47K resistor above the bias pot and solder another 47K in parallel.
2.) Set the bias pot the max (around –38 volts).
3.) Locate the purple feedback wire (that is connected to the 4-ohm speaker tap) and solder it onto the 8-ohm speaker tap.
4.) Install the EL34’s and re-bias the amp.
MARSHALL EL34 to 6550
1.) Change the bias resistor to 47K (located above the bias pot).
2.) Set the bias pot to max (around –38 volts)
3.) Locate the purple feedback wire (that is connected to the 8-ohm speaker tap) and solder it onto the 4-ohm speaker tap.
4.) Install the 6550’s and re-bias the amp.
Disclaimer All information given herein is for educational purposes only. There is no warranty, implied or otherwise, as to the correctness, suitability, or merchantability of the information for any purpose.
Warning Any and all changes made to electronic equipment must be done by qualified professional service personal. Even an unplugged amplifier contains High Voltages that are easily lethal even to the experienced electronic engineer. Do not remove the cover or chassis from your amplifier without professional assistance.
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