• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Problems w/biasing a lC50

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Jump to Latest
G

gtrtech

Member
Joined 2005
A customer brought in a Laney LC50 combo, It's not the Ser. 2 but it should be close enough for me to use the schematics from one. The problem I’m having is trying to bias it. After installing 1 ohm res. to the cathode and setting the volume to where the wave on the o’scope is just under the breaking point. On one side I get a reading of 0.70 and I get a reading from the plate at 390v which after multiplying them I get 27.3 which is way to hot. I’ve reversed the tubes, tried different tubes and still the same. The customer has 2 JJ EC 803s preamp tubes in it and I’ve heard because of the long plate structure you shouldn’t use these in a combo, am I heading in the right direction or should I look else ware. BTW curious at what freq. & amplitude does everyone use when checking the wave w/ a O’scope and what are the best setting for the scope in dual mode for the setting
Thanks
Tony
:confused:
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Top Bottom