112 RD 65 dating and tubes?

jckid649

Was wondering. I just bought what is said to be a 1977 Music Man 112 RD 65 watt. My friend and I were discussing why some of these amps used 6CA7 power tubes such as the 1978-79 version while the 1980-84's call for 6L6GC tubes. I cannot find a schematic to a 1977 so it leaves me wondering if the store I bought it from has the correct year. The store had recently changed the tubes when they purchased it from the original owner and the originals were 6L6s. He replaced them with the same. But my friend said the readings for B+ and c- seemed crazy. It reads 744v at the plate with a c- of 21. Is this right for these amps with 6L6 tubes and why do some use 6CA7s? I really wonder how much different the 2 sound.

The vitals are as follows:

Chassis Number: 2165 RD
Serial Number: DN05136

Full Name
Lars Verholt
Music Man Equipment
HD-130 head, 210X cab, 210RH cab, RD-50 110 combo, Sixty-Five 112 combo, RP65-112

Member for

10 years 7 months

lmv Thu, 01/21/2021 - 19:12

Hello,

The first two versions of the RD amp used 6CA7/EL34. The very first, GD-1 came out in 1978 so may have some components marked as 1977 manufacture dates. Look at the PCB inside the amp, it will help you determine the vintage. The GD-1 would have silver badges and a mechanical relay to switch between the two channels. GD-2 has solid state switching and would also have black on silver badges. The voltages you note are somewhat high but not out of spec. The actual plate voltage is 50 or so volts lower than that as the cathode is the reference point.

If you post some pictures of the pcb and the speakers from the back, we could help you pinpoint the age further.

Cheers,
Lars Verholt