What is that serial range?
This was the TSB they issued. Doesn't say a serial number range
TECH BULLETIN: "Tremoverb" Update
*NOTE: This update does not apply to very early units
having a 120ohm, 10W sandblock resistor near pwr transformer.
The "Tremoverb" amplifier has two 47-ohm, 1/4-watt resistors
(one is located mext to the pair of relays and is connected
to LDR #3 - Location 26-E on diagram below. The other is
next to and connected to LDR #13 - location 14-B below).
Please replace both of these 47-ohm resistors with 220-ohm, 1/2 watt resistors.
Also, the 68-ohm resistor that is connected to LDR's 11 & 12
(location 14-C below) should be increased to 360-ohms.
Finally, please REPLACE LDR's #3 (type 5C4/2), #11 (5C9), #12 (5C9) and #13 (5C4).
*NOTE: LDR's manufactured by "VACTEC"
(has 3 lines of print on top) are more reliable
than LDR's made by "SILONIX" (has single 4-
digit number). If you encounter an amp having
several "SILONIX" LDR's, please call
Mesa/Boogie to arrange a factory repair