What size chassis do you use?

2nd harmonics for the masses

What size chassis do you use?

Postby hembrook » Sat Nov 03, 2007 1:20 pm

I am planning a G*S*G around 6A5Gs so I am wondering what size chassis I need. I am not sure about the transformers yet, but I am leaning towards Trafomatic toroids in pots.

What size are y'all building?

Robert
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Postby TomMcNally » Sat Nov 03, 2007 1:55 pm

Hi Robert -

The original get*set*go amps that Shannon and I built used a
top plate from Front Panel Express with everything top mounted.
The panels are 13 x 9 with about 2" clearance underneath.
If you plan on using a Hammond or other pre-made chassis,
give yourself a little extra room.

Keep in mind that the gsg design requires two 6.3 volt
windings ... you can't do it with one big one.

Remember that all of the diytube boards have the unique
ability to be used as a template for drilling and punching
your chassis. You can put it in place before you solder
to it, mark a couple of mounting holes, bolt it down, mark
the rest, then do your metalwork with a perfect fit.

If you haven't seen the pix I took, check out my site

http://tmamps.com/gsg
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Thanks for the dimensions, and Yes, I have seen your site

Postby hembrook » Sat Nov 03, 2007 2:17 pm

You do good work on your cases. I am a guitar builder, so woodworking and a bit of metalworking are no biggie for me, I just want to know what I need before I jump in.

Good advice about the 6.3V supplies. Why 2 separate? One for the power/preamp tubes and one for the rectifier? I guess I need to dig more into the schematics.

Thanks!
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Postby TomMcNally » Sat Nov 03, 2007 2:26 pm

The bias for the 6B4G's is dependent on the two windings,
take a look at the schematic and you'll see. They are also
run on DC, which helps minimize the typical DHT hum.
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Postby hembrook » Sat Nov 03, 2007 4:42 pm

I got the DC part, but I am still unclear on the bias part. Would i need this for 6A5Gs?
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Postby TomMcNally » Sat Nov 03, 2007 5:16 pm

Shannon can give you a better answer than I can - but it looks
very similar - so I think it will work.

Here is a comparison on the tubes ....

http://www.6a5g.com/SylvaniaNOS6A5G/6A5G%20to%20sell%20info%20and%20links.html
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That's funny.. . That's the dude I got the tubes from

Postby hembrook » Sun Nov 04, 2007 4:07 am

Too cool.

Anyway, I think it has to do with the fact that the cathode is attached to the heater internally, so if both the cathodes were on the same transformer, theoretically the left and right channels would be hooked together. I am not sure hw much difference it would make if the cathode is truly just a source of electrons. I would worry more if the plates or grids were cross linked.

Still, I specced a 220V tranny like a Dynacloen from Trafo. I'll see what they say.
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Postby Shannon Parks » Sun Nov 04, 2007 6:25 am

It is more about biasing than anything regarding channel separation. With cathode biasing putting a DC bias on the filament line, the two channels would be fighting over controlling the DC on that circuit.
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Aha. I see. You have to bias the cathode...

Postby hembrook » Sun Nov 04, 2007 8:53 am

...to keep within the tube limits, right? So if you bias each tube where it is happy, then life is good. Separate power supplies make that much easier. Is that on track?

I love learning... Thanks!
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