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 Post subject: Yikes that's brite
PostPosted: Thu Nov 27, 2014 12:32 am 
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Joined: Fri Jul 10, 2009 12:49 am
Posts: 16
Location: Fountain Hills AZ
Yikes that's brite....That's what my buddy said when we test fired my lightning build.
(He should know, he has been repairing amps and designing music electronics since the 70's.)
"yeah it's supposed to be that way to cut through the mix"
Hah, when was the last time you did a gig? he said with a grin.
"Point taken" as I finished my beer.

ANYWAY, after literally days of parts substitution, scratching my head and Internet trolling until I couldn't see straight, and then going back to most of the values on my original build...I found a very simple solution that works well and doesn't screw up the gain structure or change the voicing of the amp. Just a little off the top Please.
A 200pf cap (after R9 220k) to ground. This forms a low pass filter cornered at approximately 3.6k Hz
Bingo....happy dance!
If you have an IOS device, there is a very useful app called Circuit Playground by Ada Fruit Industries.
It has a calculator for high and low pass filters and a bunch of other useful electronics stuff.
I plugged in the 220K value into the low pass calculator and went up and down in Pico farads until I got what I wanted frequency wise.

Another discovery on this rebuild...for those of you who don't want to BarBQ those nice old
NOS EL 84's, you might try a Sovtek 5Y3GT regulator, yeah, the one that ran your champ too hot..LOL
It's in between a 5AR4 and a real 5Y3GT voltage drop wise, has enough ma's to do the job no problem. With the West labs power tranny I'm seeing 320V between the plates and cathodes, I run my screens about 10V lower and bias the pair with a 150ohm cathode resistor. I run my finals close to rated specs and keep the PD under control. They great, last a long time and I don't worry about a failure taking something else with it.

I hope this info helps bring other Lightning builds off the shelf and back into circulation...
Cheers,
Steve


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 Post subject: Re: Yikes that's brite
PostPosted: Sun Dec 14, 2014 1:40 pm 
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Joined: Wed Aug 26, 2009 11:27 pm
Posts: 273
Location: Ontario
Glade you got what you where looking for.
Just out of curiosity what speaker where you running during your test ?

And now i have checked the schematic for this amp what's the cut control supposed to do ?


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 Post subject: Re: Yikes that's brite
PostPosted: Mon Feb 23, 2015 1:13 pm 
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Joined: Fri Jul 10, 2009 12:49 am
Posts: 16
Location: Fountain Hills AZ
speakers: WGS alnico 12 and Canibus Rex 12

cut control is a hi frequency cut wired backwards (Vox style), this helps to reduce the really hi end parts of the signal.


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