Express power supply board, question...

[riscado]

I have a question regarding the resistors used in this power supply, I can't seem to find metal oxide resistors of the 9.1k or 18.2k values where I live, I'm inclined to use wirewound 10K+8.2k in series for the 18.2k and 8.2K+1k in series for the 9.1k, any thoughts on this?

Also I'm haven't been able to get the 25w 1k resistor, would a 17W workout?

thanks

[novosibir]

No prob, you may do so!

Larry

[FYL]

any thoughts on this?

The actual values aren't critical. You may use slightly different value R's, 2w or preferably 3w-rated.

Also I'm haven't been able to get the 25w 1k resistor, would a 17W workout?

It will. the original 25w is vastly oversized : a 3 or 5w model is more than adequate!

[mlp-mx6]

For the current through it, yes it is oversized. However, it is entirely possible that there is some inductance from that resistor that helps shape the tone. According to "legend," EVERYTHING on the Wreck was chosen carefully and specifically.

[Allynmey]

Riscado, Those resistor combos are fine. You could probably use 10K throughout. The larger watt 1K resistors will run cooler. That resistor does heat up once you start spanking. The 25W stays cool but, the 10W heats up quite a bit if I remember correctly.

Allynmey

[riscado]

thanks allyn

by the way I also noticed the express uses two 100k 3w resistors, I can't find those unless I use 1W because I haven't found wiredwounds as high as 100k...

[novosibir]

1W types are on the border!

They'd withstand, because each of the 100K is dissipating only 0.4W @ a voltage of 400VDC across both in series - but due to their small body size/surface they'd become fairly hot and the steady radiation due to the heat will be sucking dust and dirt to it over the time.

Larry

[JammyDodger]

Re: 100K 3 W Resistors.

I've wondered why he used Carbon Comps here (Francesca). I found a couple of 2 Watters in my stash that I'm using for my build.

I have to think that Ken used what he would have around in some cases.

Cheers, Mike

[FYL]

However, it is entirely possible that there is some inductance from that resistor that helps shape the tone.

It physically can't. Wirewounds such as the ones used on Wrecks show very little inductance and have totally negligible effect in a power supply RC network.

According to "legend," EVERYTHING on the Wreck was chosen carefully and specifically.

Yeah, this is the legend. Ken F. did an outstanding job with the Wreck architecture, which is basically medium/high gain with balanced disto from stage to stage and overall an amp always on the verge of instability.

He used whatever components were available to him, fine tuning/voicing each and every amp to his liking.
He knew his stuff.

That's why he was one of the true greats, not because he sprinkled his perf boards with vintage mojo powder or used polyester caps potted in the Outer Hebrides by blind zen monks.

[sliberty]

Mouser has the 9.1K and 100K 3 watters in Metal Film.

http://www.mouser.com/catalog/631/547.pdf

[riscado]

I understand mouser has pretty much anything necessary, however I'm in europe and it would be overkill to order 5 or 7 resistors from the states.

However thanks for pointing it out.