HD Deluxe 16volt reg solution

[Mars Amp Repair]

Hello folks,
thought I would post this as a thread as opposed to just a reply to another post.

I have begun to replace those 470 resistors with 750ohm 7watt pc mount resisotors. I have about 5 of em out in the field now with no issues. See attached pic.

These zener supplies do not need to be nearly as 'stiff' as they've been designed. The 750 ohm in place of the original 470ohm dropping resistors create plenty of current to keep the zeners in hard forward bias as well as the tiny relays & couple of op-amps don't 'steal' anywhere near enough current to cause the zener's to fall out of regulation.

I'm getting them from Yorkville cause they're really for me being warranty authorized, but I'm sure Mouser or someone has them for equally cheap. Yorkville #4680.

Find pix attached. It works great & resolved the issue of heat to the pcb & interminttents.

BTW we all pretty much unanimously agree that reducing the value to 330ohms as suggested by Fender only serves to exacerbate the issue as the drop across the resistor will remain the same as it is supplying a Zener not a resistive load. The current increases to the zeners causing them to overheat as well as the resistors getting at least as hot if not hotter.
glen

[Rick Erickson]

[BTW we all pretty much unanimously agree that reducing the value to 330ohms as suggested by Fender only serves to exacerbate the issue as the drop across the resistor will remain the same as it is supplying a Zener not a resistive load]

I don't recall Fender ever suggesting to do this... It was a misconception generated by one or more techs who observed 330 Ohm resistors in the newer Fender amps and concluded that this was a solution to the overheating problem. What they didn't notice was that the incoming supply voltage had been reduced on the newer amps so the resistors were not working as hard. They also didn't do the math... (btw - I'm the one who pointed out the misconception here) The 750 Ohm resistors sound like a reasonable solution, but if your amp came stock with the 330 Ohm 5W's you probably don't need to panic. I would guess that 750 Ohms would be too much resistance in those amps.

RE

[Mars Amp Repair]

Well,
I just looked in my files for the HD Deluxe, HD Deville, & Blues Deluxe. I guess the only bulletins I see where Fender suggests changing the dropping resistors is to actually increase the 330ohm resistors to 470ohm & that is in the BLUES Deluxe as far as the bulletins I have indicate. There may be more out there I don't have.

So, perhaps it IS a misnomer that Fender ever suggested changing any resistors to 330ohm. I agree the amps that are supplied with the 330ohm resistors do not have the overheating issue.

Thanx, glen