The "Bordello Red" GSG build and questions

2nd harmonics for the masses

The "Bordello Red" GSG build and questions

Postby AlexLTDLX » Sun Feb 09, 2014 10:03 am

Hello All,

I've never owned an SE amp of any kind, and after much research, I find myself here - the GSG looks like a great starting point. My friend recently called up wanting to put together a modded Dynaco like the one I've got - a KT88 monster that can rock the house; it was based on of the mod kits and ended up getting way out of hand. It sounds fantastic. But...

The new tripath amps come pretty close to glass quads these days. They might lack some of the magic and detail of a big tube amp, but, at the risk of being labelled a heretic, one must admit, they're about 80% of the way there; and if you're listening loud, the difference isn't that big. The unobtainable sound that is still the sole domain of glass is the S.E.T.; the low power's not an issue because near field is where it's at for critical listening. So I told Matt (the guy who called) that's the way he should go; after all he already had a bigger tripath. So then he gets back to me and says, "I've ordered us two GSG boards."

That's great - but what's with this "us" stuff, Cochise? And so it begins.

I initially went through the same process most people here have: What's the highest regarded triode? I thought it was the 300b. What, you say 2a3's are more detailed? Huh, who knew? And a 6a3 is a 2a3 with a 6 volt filament? And a 6B4G is an octal of a 6a3? Ok, then.

So I looked at all the schematics of S.E.T.s I could find. At one point I told Matt to quit ordering parts. Ultimately, the GSG looked like a very pure, clean circuit that's been thoroughly evaluated by folks like you; looks like Matt made the right choice.

Here are my beginning questions:

1. I have an original dynaco 060s power transformer; can that be used in a GSG or is the B+ too high?
2. Is there any value (other than tube availability) of modding to a 2a3 right off the bat?
3. Has anyone added a passive volume control? What mods to the circuit did you do? Did you use a standard 100k pot? How much did it affect the sound quality?

Sorry for the long post and thanks in advance!
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Re: The "Bordello Red" GSG build and questions

Postby AlexLTDLX » Sun Feb 09, 2014 10:32 am

<forgot to add>

4. Is there any way to get rid of the hum on JAN 6b4g tubes (the 6av5 triode strapped ones)? Shannon had mentioned something about the cathode connection and filament in another post not working with the GSG hum scheme...
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Re: The "Bordello Red" GSG build and questions

Postby TomMcNally » Sun Feb 09, 2014 10:15 pm

Hi Alex -

I've build over a dozen get*set*go amps ... mostly 6B4G, a few 300B, 6AV5GA, a convertible 300B/6A3 ... no 2A3,
as it requires a lot of changes with not much merit.

One of the beauties of the get*set*go design is the DC filament circuit ... no hum, no hum-pots, no little filament
transformers under the chassis.

To answer your questions ... the PA 060 is too big, go with the PA-774
stick with 6B4G's or 300Bs ... 2A3's are too much work for too little benefit, unless you have a big stash of them
a volume control is easy, no mods, just a hole in the chassis and a couple of wires. no sonic detriment
those fake Sylvania 6B4G's are no good. If you want a cheap tube, use the 6AV5GA with the simple mods you
can search on here. they are basically "free" ... I've built a few get*set*go's with them ... nice results

pictures at http://tmamps.com
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Re: The "Bordello Red" GSG build and questions

Postby AlexLTDLX » Mon Feb 10, 2014 9:18 am

Thanks, Tom. I spent quite a bit of time looking at your (many) amps! Do you think it's possible to squeeze a GSG into an 8 x 10 x 2.5 chassis? I'm trying to put this thing on my desk. (using James 6112 or 6113 opt's and edcor power trans)
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Re: The "Bordello Red" GSG build and questions

Postby TomMcNally » Mon Feb 10, 2014 1:11 pm

The 8 x 10 chassis might be a be good. The James 6112/6113 aren't very big. I mounted the last couple of sets
very close to the back corners with no problem. You can put the choke on the back panel at an angle, so no
problem there.

Good luck with the amp - show us some pics!

... tom
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Re: The "Bordello Red" GSG build and questions

Postby AlexLTDLX » Tue Feb 11, 2014 10:24 am

Thanks! I definitely will share some pics. Matt and I are both building 6b4g amps, but with slightly different variations - iron, brand of tubes, attenuators vs pots, etc. I even ordered up a pair of 6av5 to try. We'll be doing a comparison between the two.

For pics, well let's start here. My current glass amp:
Image

That's a heavily modified Dynaco running KT88's. The thing below it is a hybrid/modified Squeezebox/ZeroDac pre with rolled OP amps - it's my music source. Here's a more stylized shot:

Image

BTW, I'll be calling this thing "The Bordello Red" because I had this idea to powder coat the polished aluminum chassis with a couple of clear powders - black chrome around the edges and candy red over all of it. I tested it out on a piece of scrap aluminum:

Image

We'll see how it turns out...
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Re: The "Bordello Red" GSG build and questions

Postby AlexLTDLX » Mon Apr 14, 2014 10:06 am

Wow... funny how time gets away from you. Well, we've actually *almost* have all our parts together (a pair of 22mf caps are in the mail... don't ask). The Edcor transformers took a while to come in. We've got three different types of NOS output tubes - two RCA 6B4G's with "connected plates," two RCA 6B4G's with separate plates and two RCA 6AV5GA (in case we wanna try something a little different). The other tubes are also NOS - three RCAs and one Dumont. Matt's going to be building a more "typical" GSG on a wood-sided Hammond chassis with Edcor power and opt x-formers, I've gone with a smaller 8x10 Bud box, James H6112HS opts and an Edcor power transformer; I'm also using Mundorf coupling caps because I had them (I didn't like how they sounded in the Dynaco).

Here's where I'm at with the Bordello Red:

Image
Image

Of course, nothing's been powder coated yet, and the top still needs to be cut. It looks like everything will fit nicely, but I'd love to have another half inch front to back.
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Re: The "Bordello Red" GSG build and questions

Postby AlexLTDLX » Tue Apr 15, 2014 5:23 pm

Things are moving along... today I finished up the holes in the chassis and mocked things up:

Image

You can see one of the power transformer bells is deformed... apparently it was made that way. I called Edcor and they said they'd ship out a replacement. Which is good, because the bells will be receiving the "Bordello Red" powder coat scheme too.

Here's the chassis, ready for powder:

Image

I didn't want to go to a mirror polish for two reasons: a little texture will give the powder something to stick too, and based on the test above, where the scrap wasn't polished at all, it still came out with tons of depth. This will (hopefully) look pretty good.
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Re: The "Bordello Red" GSG build and questions

Postby AlexLTDLX » Fri Apr 18, 2014 3:58 pm

This was a nightmare. I screwed up the first layer of black chrome, but couldn't tell until the partial cure. Stripping this powder is close to impossible. Twenty minutes to screw it up, three days to strip it (in my spare time, anyway). I finally got a pretty good finish on it. It's a little more textured than I'd like, and there's one area where the black chrome is too thick, but that can be covered up. Overall, it turned out pretty good, and if the last three days is any indication, it will be impossible to damage the finish :)

Image

I did the volume knob in heavy black chrome. In sunlight it looks really deep and shiny. I'll probably be happier with it after I forget the nightmare it took to get here...

EDIT - Tips (for me, as much as anyone else) - to get the "fade" effect with transparent powders, first coat your base color completely, then blow it off in the middle of the panels; trying to get the fade just by spraying in select areas causes you to vary the distance of the gun too much, causing problems.
Last edited by AlexLTDLX on Fri Apr 18, 2014 5:09 pm, edited 1 time in total.
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Re: The "Bordello Red" GSG build and questions

Postby Geek » Fri Apr 18, 2014 4:57 pm

I like it (y)

It reminds me of a type French polish that shows the lower layers :))
(there's a name for it, I forget)
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Re: The "Bordello Red" GSG build and questions

Postby AlexLTDLX » Fri Apr 18, 2014 6:22 pm

Thanks - so I guess I got at least close to the mark - I was picturing a French Victorian-era bordello. With the heavy red velvet and general "warmth" of lusty, bosomy women. Or something like that. Since I had a little time, I was dying to see how everything fits on this small chassis - it's only 8x10. I definitely wouldn't go any smaller. You can see the "spot" of too much black chrome powder in this shot - it's on the bottom left of the front panel:

Image

I was going to make a dark-stained wooden scrollwork over the front, but it looks so nice that I might just stick a little metal badge there.

Here's the seedy underbelly of the bordello:

Image

I'm probably just going to wire it up in situ; getting some of those things screwed in there wasn't terribly pleasant.

Poll: What should I do with the end bells on the power transformer? Flat black powder or more of the "bordello" treatment?
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Re: The "Bordello Red" GSG build and questions

Postby Geek » Fri Apr 18, 2014 10:57 pm

If you're going to do more and want better consistensy, I'd suggest do the red powdercoat and then a black laquer after with an airbrush ;)
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Re: The "Bordello Red" GSG build and questions

Postby zman01 » Sat Apr 19, 2014 3:53 am

Good stuff Alex! :)
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Re: The "Bordello Red" GSG build and questions

Postby AlexLTDLX » Sat Apr 19, 2014 8:05 pm

Thanks guys. So I wired it up tonight (in a bit of a rush, in all honesty; work is piling up). I powered it up without tubes and checked out the voltages. Everything seemed fine, so I powered down, plugged in the tubes and decided to go for broke - I decided to play it risky without taking any other measurements. Right out the the box, it's dead quiet at idle, and makes beautiful music.

Here it is, playing some Harry Connick:

Image

I decided to go with flat black on the power transformer bells. Since the replacement bell hadn't arrived from Edcor, I took a shot bag, metal working hammer and come cheap sockets and re-shaped the deformed section. Turned out pretty good.

First impressions - it's currently powering giant, highly refined 3 way 12" speakers. It sounds nice. It's a little "closed" and the soundstage is a little lacking. This is relative to the dynaco above, that I spent literally several years dialing in. The GSG has a lower noise floor than the dynaco. I wonder how much of the of the issues are the Mundorfs. I pulled them out of the Dynaco because they sounded dull. The Bordello doesn't sound dull; just a little "closed." Detail is on par with the Dynaco.

Keep in mind - this is literally "right out of the gate." It does some stuff better than the Dynaco already. As I type this, listening to it, it's already opening up. Even my 9 year old hears the change. I'll do some real testing and playing as soon as time allows. Great job, Shannon!
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Re: The "Bordello Red" GSG build and questions

Postby AlexLTDLX » Sat Apr 19, 2014 8:12 pm

I typed that last post 15 minutes after powering up. I just got that S.E.T. smile on my face. Getting much, much better fast...

Interesting that the vast improvement coincided with most of the fluorescing gases burning off. You can see them in the above photo. The blue glow in the right tube is now completely gone (you can see it towards the top). In the left tube it's barely visible.

Also, with these OPTs, this thing has more bottom end than the Dynaco. And for those who've heard the dynaco, that's saying something.
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