dropping resistor?

[K-MAN]

I'm rebuilding the power supply in my SCA35 and I'm having a hard time finding the 5W 50ohm dropping resistor at the local electronic stores. They seem to have values close to it so I'm wondering how close to resistor value has to be for things to work properly? If I understand right this resistor determines the B+ voltage?

[TomMcNally]

50 ohms should be a pretty common value - doesn't Radio Shack have them ? 47 ohms is fine, a higher wattage like 10 watts is fine. You could also put two 100 watters in parallel to get 50 ohms. It's not all that critical. What values do they have ?

[EWBrown]

If you have room inside, use a C354 choke or Hammonf 156R (1.5H, 200 mA, DCR = 56 ohms). This helps kill any residual hummmmmmmmm levels. Anthing that approximates 50 ohms, and can handle around 160 mA is good enough.


My usual SCA-35 mod was to remove the preamp board, and install in its place a home-made cap board, based on Shannon's ST35 PSU, and throw in the choke, and replace the vintage silicon rectifiers with uF4007s or MUR 4100s, and insert a CL-90 ICL in the AC primary side. Made it sound a LOT better, and eliminates that nasty power-on slam. :o

That original preamp, those pesky PECS and the tone stack & filter "rat's nest" were complete and total sonic mayhem (and I'm being too nice here).

I usually replaced the driver boards with aftermarket ST-35 types, so I didn't need pricey NOS (or lousy Sovtek) 7199s.

J/J ECC832s are a LOT better than Sov 7199s (which aren't really 7199s, they're just a generic SCO pentoad and 6C4 clone triode stuffed into the same jug). Yellow_Light_Colorz_PDT_09

/ed B in NH / NC