Peavey Classic 20 MH, Operating Manual

11

10

When switching from STANDBY to ON, these should then turn from red to green.
The LEDs will remain green, under normal operating conditions.
If an LED goes red then it means that the output tube is not working properly for one of the following 

reasons:
- Tube is ‘under current’: This could be due to incorrect bias, low current due to aging, open circuit due to 

structural/physical fault or missing filament heater supply.
- Tube has gone ‘over current’: In this case the resettable protection circuit will be switched in to protect 

against further damage and to allow the amplifier to carry on working with the remaining tube. This could 

be due to bias failure, over-heating of the tube or other fault condition resulting in excessive current draw.

Reset: Under certain conditions (e. g. during an adequate pause in playing), the protection circuit will 

auto-reset and allow the tube to be turned back on. If the fault remains then the LED will stay red. In these 

situations, at a convenient point, the amp should be turned off for a few minutes then back on again. If 

the fault is still there, then the amp should be checked by a qualified and competent technician for correct 

output tube bias or faulty tube(s).

STANDBY switch
Placing this switch in the“STANDBY”position will effectively shut the amp off while leaving the tube 

filaments on. Leave this switch in the“STANDBY”position for a minimum of one (1) minute after engaging 

the POWER switch (#11). This is also a useful feature, since much tube wear comes from the heating and 

cooling of the tube itself. Leaving the unit in“STANDBY”when you take a break allows the tubes to stay 

warm while you are not playing. To immediately resume normal amp operation with no warm-up delay, 

place the switch in the“ON”position. NOTE: This switch does not replace the POWER switch (#11). When you 

are ready to stop playing for an extended period of time*, it is better to turn the amp off via the POWER 

switch (#11). To prevent any undesirable noise, it is recommended to switch the amp to “STANDBY” for at 

least a few seconds before switching fully off.

* Excessive time off (more than one hour) in "STANDBY MODE" can damage OUTPUT TUBE by "poisoning 

the cathodes". 

* For an informative description of the STANDBY function, please read the Chapter 6 (Standby...For the 

Truth) of Hartley Peavey's White Papers included on this disc.  

POWER switch 
To apply power to the unit, connect the line cord and flip the switch to the ON position. The pilot light (#8) 

and the T.S.I. LEDs will illuminate, indicating power is being supplied. It’s best that the STANDBY switch 

(#10) is set to STANDBY when amp is first switched on.

The correct start up sequence is:- 
 

*Before use, both switches should be in the ‘down’ position. 

*Switch POWER to ON. Now wait at least 1 minute for the amplifier to warm up.

*Then switch the STANDBY to ON. Use amp as normal.

*Switch to STANDBY for short breaks. (Between sets, not between songs!)

*When through playing, switch to STANDBY, wait at least a few seconds, then switch POWER to  

 OFF.

Classic 20 MH

®

 Front Panel 

cont.