Conrad Johnson Owners.com

So I had the occasion to take the bottom off my recently acquired Classic Sixty SE to deal with a loose screw inside the amp, and noticed something odd while perusing the PCB. It appears the PCB has been modified by cutting a trace and adding a jumper to convert the heater circuit of the input tube (6189 or 12AU7) from 12.6V to 6.3V. I'm going to try to attach a photo of this - this is my first post so I hope it works.

The component that looks like a resistor connected to pin 9 (heater center tap) and a PCB trace is actually a zero ohm jumper. You can clearly see where the PCB trace has been cut with something like a Dremel. Pins 4 and 5 have been tied together with a jumper for parallel operation of the 6.3V heater sections.

I don't believe the previous owner would have done something like this, so I assume it was done at the factory. The amp has been back to the factory once for an output tube socket replacement, so it could have been done then, or it might have been done on the production line when new.

I'm just curious to hear your opinions on why this might have been done. I can't think of a reason for it.

Jerry

Interesting. As I presume the unit is working well it should not be a problem. It would be interesting to see another classic sixty SE to see if this is standard or truly a mod.

Indeed the amp works perfectly and sounds superb. It totally slays my previous amp, a C-J MF2100, in all aspects. If somebody else with a Classic Sixty SE wants to check this out, I believe you can probably peek at this area through the vents on the bottom panel, and not have to actually remove the bottom panel. If you do want to remove the bottom panel, just unscrew the four feet and then remove the remaining screws holding the panel on.

Jerry

Admin, can we post pic's? If so, mgttr; can you post and then someone with another Classic Sixty SE if you wouldn't mind posting pics. Using MS Snipping tool you can highlite or using paint you can show, mgttr, what is up.

I provided a photo as an attachment to my first post - are you unable to view it?

Jerry

Hola. Why don´t you ask direct to C-J service dept? Factory mods are done many times, using what they have in stock, and it is a normal practice for all brands. The serial number helps to the manufacture to track exactly the components that they use. For series use, the filament voltage is for 12. 6V and the connexion in parallel as yours is for 6.3V. (https://frank.pocnet.net/sheets/127/6/6189.pdf). The parallel connection is recommended, as your Classic 60SE is built, using that jumper.
Happy listening!

Well it took me a long time to get around to it, but I finally took Roberto's advice and contacted C-J's service department regarding this mod. I provided them a picture of it and a description, and their response was that I had an "unmodified "A" stock amplifier". From this rather brief response I would then infer that the heater circuit mod was indeed done on the production line at the factory. I had a couple other questions for them about my amp but I'll start a new thread for those.