Question about Fender Twin...

[CJ]

No. I saw the Coney Island contest on the news last night, and I knew you liked the place, so it was a friendly joke.

You could also use a db measurement from a mic setup, but I think that would be overkill. It's hard to tell the digfference nbetween 50 watts and 100 watts, so no matter what your power measurements say, it does not really tell you how loud the darn thing is.

 

[NewYorkDave]

I think our East Coast/West Coast brawl broke the message board. I kept getting "service unavailable." :shock:

 

[CJ]

OK, I found Darr's book, well most of it, as a pdf. The schematics are not there.
There is a little on power measurement in the output/speakers chapter.
He uses a dummy load, so I guess that I am the dummy.

He mentions using a scope for checking power at an undistorted waveform, which is a good idea. Maybe at 1 khz

Anyway, it's a cool book so print it out if you don't have it. A little dated, but that can be a good thing.

Will edit hotdog joke out.
This is all Joel's fault, so don't sweat it.
Let's concentrate on beating him up. :green:

cj

http://www.diyguitarist.com/Misc/J_Darr.htm

BTW, I think it was 49 Nathan's in 10 minutes by the same guy who won last year. Did you see the hot dog special on PBS last week?

 

[NewYorkDave]

I'm glad to see someone scanned the Darr book and put it online. I remember years ago when we guitar-amp techies would distribute Xeroxed copies amongst ourselves. I still have mine somewhere.

I can't bear to watch the hot dog eating contest. "Competitive eating" of any sort makes me retch. Food should be savored, not "slobbered!" :thumb:

 

[Mbira]

Hey thank you both for the links to the info. I have printed it up and now time for some reading...

I especially like that amp repair book-good stuff!

Joel

 

[BYacey]

It is important to measure power output just before clipping to get a true reading of maximum power. A clipped signal will produce more power, albeit not usable (under normal circumstances). A light bulb is not useful other than determining if there is signal output because the resistance is not linear with the voltage across it. The filament resistance changes drastically between cold filament and hot.

I usually take a peak voltage reading on the scope at 1kHz, multiply the reading by .707, and square it, divided by the load resistance. I wound my own resistors with 16gu. nichrome wire on a ceramic form, the type they use in pottery kilns for holding up the shelves. I spread the turns out far enough to cut down the inductance somewhat. If you are going to be doing any serious load testing, this is a good thing to have. I have put as much as 3000 W across these (for short periods of time) - they light up almost white hot, but they haven't burnt yet. Oh yeah, keep them away from anything flammable when testing.