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old resistors

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3/21/1999 2:55 PM

old resistors

I noticed that in my old Super Twin the resistors have lost their nominal values, being oversized, around 10-15%. Thus the voltages are lowered down.
I need to replace a broken resistor. Should I replace at nominal value or actual value?
In particular one resistor placed just after standby switch (on the B+ line) is now 7k instead of nominal 5k. It's not broken but it much decreases B+ current into the circuit. Should I replace it?
Any suggestion will be very appreciated.

Giacomo

3/21/1999 2:59 PM
dave chun	If you like how it sounds now, you could replace it with a 7k, 1% metal film resistor to preserve the current tone. Replacing it with its original 5k value will alter the voltages, and may affect the sound (for better or for worse.) I'd try both, see which sounds better to you, and stay with that. If the amp is running fine right now, that is.

3/21/1999 11:32 PM
Dave Stork	If this is a power supply resistor, good luck in finding a 1% metal film replacement of adequate power rating!

3/22/1999 9:43 AM
MJ Harnish	Yeah, I think you'd probably have to go with a 5% 2w metal oxide resistor; they're easy to find and cheap...

3/22/1999 1:24 PM
Giacomo	I need to replace also a broken resistor placed on one 6L6GC tube socket (it's between pin 1&5). It should be 1.5k but the old ones (in other sockets) are about 1.7k. I may think it could be a good idea to replace them all since that tube should work different becoming unmatched. Right? Thank you. Giacomo

3/22/1999 7:57 PM

Giacomo:

It'd be a good idea to replace all of these "grid stoppers"- maybe get a dozen and find 6 that are fairly close in value. If you ever want to try EL34's in this amp, you might want to rewire the sockets so that pins #1 are not being used to hold the grid stoppers (you would jumper pins #1 to the cathodes, pins #8).

The 5K power supply resistor is rated at 7 watts. I'd leave it, unless you want to "blueprint" the power supply and maybe replace the two 27K/7 watt resistors, too, if they aren't up to spec. You might want to check those 220uF/265 filter caps, too, since you have mentioned hum problems with this amp. This is one BIG amp you have, rated at 180 watts R.M.S. into a 4 ohm load, so some of the "rules of thumb" for smaller amps may not apply here.

Steve Ahola

3/23/1999 11:43 AM
Giacomo	Steve: Is it really a safe mod converting a SuperTwin to EL34? That amp han no bias level adjust, only balance. EL34 bias shouldn't be different?

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