Twenty-watt, simplified, customized 6g3 build "SBS"

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xtian
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Twenty-watt, simplified, customized 6g3 build "SBS"

Post by xtian » Tue Dec 04, 2012 6:04 am

Building this for a client, a simplified version of a 6g3 Brownface Deluxe with SS rectification, adjustable fixed bias, adjustable NFB, and stiffer filtering.

This is all guesswork, and the layout is all new, so all comments on my third draft are welcome and then some.
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xtian
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Re: Twenty-watt, simplified, customized 6g3 build "SBS"

Post by xtian » Tue Dec 04, 2012 6:05 am

I may be screwing myself by using a single multisection cap for the entire filtering. No way to separate the grounds. What do you think?
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Re: Twenty-watt, simplified, customized 6g3 build "SBS"

Post by rdjones » Tue Dec 04, 2012 6:21 am

xtian wrote:I may be screwing myself by using a single multisection cap for the entire filtering. No way to separate the grounds. What do you think?
Watch the cap polarity, the 2 cathode bypasses are reversed.
I like to have a safety resistor (50-100K) between the bias pot wiper and the supply end terminal.

rd

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Re: Twenty-watt, simplified, customized 6g3 build "SBS"

Post by xtian » Tue Dec 04, 2012 6:45 am

rdjones wrote:
xtian wrote:I may be screwing myself by using a single multisection cap for the entire filtering. No way to separate the grounds. What do you think?
Watch the cap polarity, the 2 cathode bypasses are reversed.
I like to have a safety resistor (50-100K) between the bias pot wiper and the supply end terminal.

rd
Thanks. Caps reversed.

So, if the bias pot wiper lifts, you've suggesting a voltage from a resistor that connects the wiper to the neg end of the capacitor?
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Re: Twenty-watt, simplified, customized 6g3 build "SBS"

Post by martin manning » Tue Dec 04, 2012 1:37 pm

Yes, that way it fails "cold" so to speak, where the bias voltage goes to max negative instead of floating.

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Re: Twenty-watt, simplified, customized 6g3 build "SBS"

Post by xtian » Thu Dec 06, 2012 3:41 am

Board be built.

I got a sheet of black, 3mm G10 from mcmaster. Decided to buff out the top surface, leaving a really sexy, primer-black, like a radar-invisible race car.

Then I made it extra sexy by glooping gold paint on the board while trying to mark the jumper keys. Duh.

Have just pinned down the components with solder to hold them in place, and will fill and crown after all wiring is in place. Have discovered that the solder in the holes of these large bore turrets will liquify and sink when attaching wires.
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Re: Twenty-watt, simplified, customized 6g3 build "SBS"

Post by rdjones » Thu Dec 06, 2012 4:57 pm

xtian wrote:
rdjones wrote:
xtian wrote:I may be screwing myself by using a single multisection cap for the entire filtering. No way to separate the grounds. What do you think?
Watch the cap polarity, the 2 cathode bypasses are reversed.
I like to have a safety resistor (50-100K) between the bias pot wiper and the supply end terminal.

rd
Thanks. Caps reversed.

So, if the bias pot wiper lifts, you've suggesting a voltage from a resistor that connects the wiper to the neg end of the capacitor?
I started doing this when I found a pot that had failed where the resistive element separated from the terminal at the supply end.
The wiper still had solid contact with element strip and therefore good continuity to ground.

The high(ish) resistor between center wiper terminal and the supply-end terminal protects against pretty much any form of pot failure.
As Martin says it fails "cold" but usually can still be played through a gig at reduced output or tone.

rd

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Re: Twenty-watt, simplified, customized 6g3 build "SBS"

Post by xtian » Thu Dec 06, 2012 9:58 pm

Dimensional drawing p0rn.
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Re: Twenty-watt, simplified, customized 6g3 build "SBS"

Post by Beerman » Fri Dec 07, 2012 1:39 am

The DR trannies were mentioned in the previous thread - are you sticking with those?

Following this with some interest. Keen to see your further progress.
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Re: Twenty-watt, simplified, customized 6g3 build "SBS"

Post by xtian » Fri Dec 07, 2012 4:36 am

I'm using Fender and Hammond trannies and choke from CEDist:

http://www.cedist.com/products/P-CF22707
http://www.cedist.com/products/P-TF41316
http://www.cedist.com/products/P-T1760H

Chassis drilled! Time: about three hours, including printing guide (remember to mirror for outside of chassis!), taping, double-checking components, drilling, cutting, filing, and cleaning up (best three dollars spent: deburring tool!).

Three hours means I'd never choose to do this for a client wanting a standard build, man, I'd buy a $90, pre-drilled chassis. I'd only do this much work (and this doesn't include the hours of planning this week!!) for a custom build or for myself.

Amount of blood loss: surprisingly little!
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Re: Twenty-watt, simplified, customized 6g3 build "SBS"

Post by xtian » Fri Dec 07, 2012 4:58 am

Just an observation: don't be a bum. Take an extra moment and drill the index holes for the pots, instead of breaking off those tabs. My last build, the Fiddy BKB, which I put on consignment; I broke the pins off those pots. And what happened? The meat heads --um, "customers"-- turned the knobs so hard, the pots rotated in the chassis until some leads grounded to the chassis. Duh.
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xtian
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Re: Twenty-watt, simplified, customized 6g3 build "SBS"

Post by xtian » Fri Dec 07, 2012 6:24 am

Next observation: Don't put the components so damn close to the edges of the chassis! Makes it tough to tighten the nuts, man.

Also, someone let me know where I can get test points with a lower profile. People are going to be asking me what those are for…
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Re: Twenty-watt, simplified, customized 6g3 build "SBS"

Post by M Fowler » Fri Dec 07, 2012 6:54 am

Hoffman amps has the nice short test points.

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Re: Twenty-watt, simplified, customized 6g3 build "SBS"

Post by Zero4 » Fri Dec 07, 2012 6:59 am

Looks awesome!

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Re: Twenty-watt, simplified, customized 6g3 build "SBS"

Post by Reeltarded » Fri Dec 07, 2012 9:58 am

Great work! Your amps always look great!

I love that bias trimmer tip. Very cool.

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