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

General discussion area for tube amps.

Moderators: pompeiisneaks, Colossal

User avatar
xtian
Posts: 6990
Joined: Mon Apr 19, 2010 8:15 pm
Location: NorCal
Contact:

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

Post by xtian »

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.
You do not have the required permissions to view the files attached to this post.
I build and repair tube amps. http://amps.monkeymatic.com
User avatar
xtian
Posts: 6990
Joined: Mon Apr 19, 2010 8:15 pm
Location: NorCal
Contact:

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

Post by xtian »

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?
I build and repair tube amps. http://amps.monkeymatic.com
User avatar
rdjones
Posts: 818
Joined: Tue Aug 31, 2010 2:20 am
Location: Music City, TN

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

Post by rdjones »

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
User avatar
xtian
Posts: 6990
Joined: Mon Apr 19, 2010 8:15 pm
Location: NorCal
Contact:

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

Post by xtian »

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 build and repair tube amps. http://amps.monkeymatic.com
User avatar
martin manning
Posts: 13079
Joined: Sun Jul 06, 2008 12:43 am
Location: 39°06' N 84°30' W

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

Post by martin manning »

Yes, that way it fails "cold" so to speak, where the bias voltage goes to max negative instead of floating.
User avatar
xtian
Posts: 6990
Joined: Mon Apr 19, 2010 8:15 pm
Location: NorCal
Contact:

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

Post by xtian »

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.
You do not have the required permissions to view the files attached to this post.
I build and repair tube amps. http://amps.monkeymatic.com
User avatar
rdjones
Posts: 818
Joined: Tue Aug 31, 2010 2:20 am
Location: Music City, TN

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

Post by rdjones »

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
User avatar
xtian
Posts: 6990
Joined: Mon Apr 19, 2010 8:15 pm
Location: NorCal
Contact:

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

Post by xtian »

Dimensional drawing p0rn.
You do not have the required permissions to view the files attached to this post.
I build and repair tube amps. http://amps.monkeymatic.com
Beerman
Posts: 81
Joined: Thu Mar 01, 2007 7:16 am
Location: Melbourne, Australia

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

Post by Beerman »

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.
__________________________________________
Cheers and Beers.
User avatar
xtian
Posts: 6990
Joined: Mon Apr 19, 2010 8:15 pm
Location: NorCal
Contact:

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

Post by xtian »

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!
You do not have the required permissions to view the files attached to this post.
I build and repair tube amps. http://amps.monkeymatic.com
User avatar
xtian
Posts: 6990
Joined: Mon Apr 19, 2010 8:15 pm
Location: NorCal
Contact:

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

Post by xtian »

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.
I build and repair tube amps. http://amps.monkeymatic.com
User avatar
xtian
Posts: 6990
Joined: Mon Apr 19, 2010 8:15 pm
Location: NorCal
Contact:

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

Post by xtian »

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…
You do not have the required permissions to view the files attached to this post.
I build and repair tube amps. http://amps.monkeymatic.com
User avatar
M Fowler
Posts: 14017
Joined: Wed Jan 16, 2008 2:19 am
Location: Walcott ND

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

Post by M Fowler »

Hoffman amps has the nice short test points.
Zero4
Posts: 18
Joined: Tue Dec 04, 2012 2:20 pm

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

Post by Zero4 »

Looks awesome!
User avatar
Reeltarded
Posts: 9926
Joined: Sat Feb 14, 2009 4:38 am
Location: GA USA

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

Post by Reeltarded »

Great work! Your amps always look great!

I love that bias trimmer tip. Very cool.
Post Reply