Deluxe 6G3

[txstrat]

Today I started my new project. A 6G3 clone. (seems like I'm an addict)
I collected all parts so far. Only things I haven't ordered yet is the PT and a speaker but that doesn't really matter right now, since I expect more time for the built than tubeswell needed for his last 5E3.
The chassis is 2.5 mm aluminum and for the eyelets I use 2 mm fiberboard. Filter caps are F+T, coupling caps Mallory 150s, resistors are carbon composition except for resistors in the B+ line. That'll be 2w metal film resistors.
I'm gonna use a 125A1A OT and a Hammond "Deluxe replacement" PT with 330 volts secondary (CT) and a GZ34 tube rectifier. The faceplates are selfmade with corel draw like I described in this thread: http://www.music-electronics-forum.c...ght=faceplates
Will keep you up to date with the process of the built.

Matt

[txstrat]

Second step done.
Eventually I found the time to go on with my project (kids were asleep and the wife busy).
I drilled the holes for the jacks, pots and switches and cut the foursquare for the transformer I recently recieved.
Applied the faceplates and mounted the knobs. Next to be done on the chassis would be enlarging the holes for the tube sockets and drilling the tiny holes for the multimeter probes jacks.
Can barely wait to be starting to solder.

[tubeswell]

Those faceplates are neat txstrat

I was just looking at the 6G3 schem - interesting that they have a 1000pF (sorry that would be 100pF - thanks Gee) between the plates of the PI. By allowing higher frequency AC between the two sides of the PI, does that act like a hi-freq feedback loop, or some kind of higher freq neutralising thingy (seeing as how the signal in the two sides of the PI would be inverted w.r.t. each other)?

How are you planning to mount the chassis in the cab?

And curious to know where the extra fuse will go?

[txstrat]

Those faceplates are neat txstrat

I was just looking at the 6G3 schem - interesting that they have a 1000pF between the plates of the PI. By allowing higher frequency AC between the two sides of the PI, does that act like a hi-freq feedback loop, or some kind of higher freq neutralising thingy (seeing as how the signal in the two sides of the PI would be inverted w.r.t. each other)?

How are you planning to mount the chassis in the cab?

And curious to know where the extra fuse will go?

Thanks for the faceplates compliment. They are easy to make and quite inexpensive.

Although I tend to think it's the high frequency neutralising I would rather leave the question about the 100pF cap to the pro's in this forum.

I'm planning to drill two holes in the bottom of the chassis and use two long bolts with nuts, slightly longer than the chassis height (the chassis is about 2 inches high).
Maybe I'll put some peace of wood in between the free space of the chassis and the top of the amp to prevent the chassis from being buckled when tightening the nuts.

One fuse is for the primary winding of the PT the second is for the B+ line before the stand by switch.

[tubeswell]

The wood spacers sounds like a good idea. I guess you could even leave them fractionally deeper than the height of the chassis in order to leave a small gap between the top of the chassis front and back and the underside of the cabinet top (to avoid unpleasant vibrations).

[txstrat]

Small gap sounds good to me. Think I'll realize it that way. Thanks.

[Gee]

I was just looking at the 6G3 schem - interesting that they have a 1000pF between the plates of the PI. By allowing higher frequency AC between the two sides of the PI, does that act like a hi-freq feedback loop, or some kind of higher freq neutralising thingy (seeing as how the signal in the two sides of the PI would be inverted w.r.t. each other)?

I built a 6G3 with the 100pf cap. I removed it and and didn't notice any difference.

I also have a 5D3 and the 100pF does make a difference in that amp. It tames the otherwise harsh sounding high frequencies. SOme of the Gibson 50's amps also had a similar 100pF cap.

Many Deluxe's had that cap. I have heard that it was present to cure oscillations due to poor production lead dress. FWIW the Plexi6v6 has a 47pF instead of a 100pF.

[txstrat]

Applied the resistors, capacitors and the PT yesterday. I decided to go for carbon film resistors rather than carbon comp.

[Fretts]

That's a beautiful looking build.
Boy, that circuit has an awesome sounding vibrato!

Thanks much for the tips on faceplate technique!

Not knowing any better, here's what I did to mimic a Gibson Discoverer chrome faceplate:
I had an original '61 that I rebuilt and brought back to life. The faceplate was rusty and beat up but had much of the original graphics, so I scanned it at high resolution and brought it into CorelDraw.
I hand-traced every curve using Bezier curves to keep the curve count as low as possible. I found a font that matched what they had used for their text and when the work was done ( LOT of work) I took it to a trophy shop. They had some shiny nickel that doesn't get used much these days and they used "sublimating" to transfer my image to the metal. That process is akin to a T-shirt transfer using heat, but they use a laser printer loaded with a very expensive $600 toner cartridge to make the paper transfer and then it is melted on to the metal using a large heated press of some kind. I was worried that the lettering would be fragile or vulnerable to cleaners like 409, but we tested it in the shop and it is at least as sturdy as the original ink, didn't melt at all, and was difficult to scratch, even with a nail file.
Since I had made crosshair marks over each hole for the pots, fuse, etc, I was able to accurately drill them in the correct positions. It was a LOT of work, but the amp looks brand new on top.

[txstrat]

That sounds great. You might introduce this kind of faceplate building to the thread I was talking about some posts before.
I did the bezier curve thing on this 6G3 faceplate as well, since I couldn't find a proper font to match the original much less to find a genuine faceplate. I took a photo, scanned it and redrew it in corel as well.

[txstrat]

Let there be rock

Finished the soldering half an hour ago. Took a second amp and pulled some tubes (5 to be more precise, 2 6V6 and 3 12AX7 ).
Put the new chassis on the second amps cabinet connected the speaker and fired the amp up.
Although I didn't have time enough for an extensive testing I might say:
Tone of glory. The tremolo effect is great. Headroom is IMHO enough for any club.
Slight drop of bitterness is a perceivable hum that is louder than I'm used to. Not that it would be THAT loud but all my other amps are more quiet.
Checked the wiring with a chopstick but nothing changed while moving any wires. I assume it's the heaters cycle hum. When checking the layout I found there is no ground wire from the speaker jack to the star ground. Don't know if that could cause the hum.
Will come back later.

[Fletcher Munson]

Congrats on the successful build! I'd suspect the grounding for the source of your hum. Fender developed effective grounding schemes through trial and error and, since your layout differs a bit from the original, you may have to do the same thing. It's a really clean looking build, but sometimes it's the little things that get ya. Have you considered putting a virtual center tap on your heaters?

Any chance you'd be willing to share your Corel drawing of the faceplate? I'm also looking to build a 6G3 and don't have an original to work from.

[tubeswell]

Hey txstrat

That didn't take you so long after all.

Post a clip perchance (when you have done with the troubleshooting maybe)?

[txstrat]

Yes, I use two 100 ohms 2w resistors as a virtual tap. I'm gonna add a wire to the star ground for the OTs ground and see if that'll change anything.
I use the same grounding scheme in all my builds. One bus wire from the far right input jack over all pots to the star ground. From the first preamp stage to the second (to the third if existent) to the PI to the star ground. Power tubes cathodes over 1 R (for bias reasons) to star ground. Bias supply to star ground. OT (black wire) to star ground. And the ground from the power socket to star ground. Heaters virtual tap of two 100 R resistors to star ground. In this case I use a transformer with a CT that goes to star ground as well (BTW the star is bolted to one of the PT bolts).
If the wire from the OT to ground won't change anything I might suspect the transformer. This is my first build with a hammond PT and the first with a CT on the secondary. AND tube rectifier.
Where should I send the corel file?

[txstrat]

TW
Right, I didn't expect being this fast myself. But I haven't started with the cabinet yet.