super 60 combo amp

[Doc Stitches]

R 168 on the schematic shows a 10w 30K Ohm resistor...... ( cracked from overheating and discolored the board )

Can I safely use a 10w 25K Ohm resistor or 10w 27K Ohm ?

The amp has been making popping noises sometimes so

I am replacing the 4 main filter caps, as well as cleaning all pots.

....power tube pins need cleaning,

solder joints look good.

Thanks
Doc

[Jazz P Bass]

Can you please post the schematic?
And kindly provide "where" (ie: which circuit) R168 is.

[g1]

schematic here: http://www.webphix.com/schematic%20h...er_60_rack.pdf (schematic is for rack and combo's). R168 is from supply node C (417V) to ground.
Those boards are a pain to work on, tough to flip over. When they came out, factory said it was ok to desolder bad component, push it out of the board, shake it out of the chassis, and mount the new part on the foil side. This was for things like plate and screen resistors though, not sure if there is room to mount a big power resistor topside. But if you are changing caps you will be flipping the board anyway so this is not an issue.
A 25k or 27k will run even hotter there, voltages at point C and D (and everything they feed) will be slightly reduced. Going bigger than 30K will increase the voltage at C and D which is not good (modern line voltage means all voltages are already probably higher than stock values). For all the work if that resistor (or the board) doesn't like the extra heat, I would try to get a 30K. On the other hand, how many years did it take for the stock 30K to burn out? Half that life span may be acceptable to some, might even outlive those new filter caps

[Enzo]

Here: http://www.webphix.com/schematic%20h...er_60_rack.pdf

Lower right, B+ supply. A glorified bleeder, except it also sets the B+ voltage at that node. (Phase inverter)

The more you lower the resistance the more you lower voltage there. 25k would be like 15% low. ALso, the 30k dissipates about 6 watts, while a 25k more like 7 watts, so I'd be happier with a 15 watt resistor then.

WHy go off value when Mouser stocks a couple of them for $2.58 each?


40F30KE Ohmite Wirewound Resistors - Through Hole

CW01030K00JB12 Vishay/Dale Wirewound Resistors - Through Hole


Certainly replace this burnt part, but pops and crackles are 99% of the time a sign that power tubes are failing.

[Doc Stitches]

I will use a 15w 30K and check the power tubes.

Thanks to all.

Doc