Gibson GA16T/GA-18T

Bloozestringer

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I’ve been gathering parts and have most everything on hand except the iron and chassis (which is on the way). I wanted a small head version of this amp so I’m going with a Hoffman Stout chassis. Iron is a Musical Power Supply PT275.2 (550vct/100ma) and OT20PP. I plan on putting a 1/8” aluminum plate over the Stout’s precut transfer hole. I’m thinking of changing the trem intensity pot from a 500kc to a 1MA switched so I can turn it on and off without the footswitch. I’ve added a master volume. changed the tremolo caps to make it wider/slower, and added screen resistors to the 6V6’s, but the rest is pretty close to the original schematic. Anyway, here’s what I’m thinking. Anyone want to take a look and tell me what I may have wrong or could improve (especially grounding)?

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echuta13

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The 47uf power cap seems out of place, any reason for that value?

Maybe replace the cathode resistor/cap combo on the trem circuit with a 1.5v red led? It will make for a deeper tremolo with a light that pulses in sync with the swells/rate.

I would add a grid resistor to pin 2 of your PI triode. 470K-1M should help minimize blocking distortion (common on concertina PI's)
 

Bloozestringer

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The 47uf power cap seems out of place, any reason for that value?

Maybe replace the cathode resistor/cap combo on the trem circuit with a 1.5v red led? It will make for a deeper tremolo with a light that pulses in sync with the swells/rate.

I would add a grid resistor to pin 2 of your PI triode. 470K-1M should help minimize blocking distortion (common on concertina PI's)
Thanks. Yeah, I forgot to remove the 47uF cap actually. That was from a previous version. Thanks for the eagle eyes and suggestions.

I’ve replaced the schematic with the 47uF removed.
 
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Bloozestringer

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So My main concern is the grounding. I’m using non-insulated jacks, fwiw. Should I take the can cap and tie its ground to the end of the long bus bar, or leave it straight to chassis on its own connection? Should I rely on the input jack connection to the chassis or run a small dedicated connection to the chassis close by as well? As far as the OPT ground, tie it to the output jack or back at the preamp bus?

Thanks in advance for any help.
 

Bloozestringer

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I've decided I really don't think I want to use the Stout chassis. It's small, but I don't like all the signal wiring going right over the tubes. So I reworked it to fit in a JTM45 chassis using the appropriate sized board. I redid some of the grounds and trem wiring too. Any help I could get on layout I'd appreciate.
 

BigDaddy23

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Check where your shielded cable leaves your input grid stopper resistors - it looks to be connected to your ground bus.

Everything else looks good with the ground returns close to their relative filter capacitors.

Personally, I would not rely on the input jacks as the chassis ground. I would be inclined to put in a dedicated lug in the floor of the chassis between your input jacks and the board and connect your bus bar and also the jack grounds to it. Similar to your power cord safety ground. This way, if your jacks ever end up loose or with a dodgy connection, the circuit will still maintain a good ground to the chassis.
 

Bloozestringer

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Check where your shielded cable leaves your input grid stopper resistors - it looks to be connected to your ground bus.

Everything else looks good with the ground returns close to their relative filter capacitors.

Personally, I would not rely on the input jacks as the chassis ground. I would be inclined to put in a dedicated lug in the floor of the chassis between your input jacks and the board and connect your bus bar and also the jack grounds to it. Similar to your power cord safety ground. This way, if your jacks ever end up loose or with a dodgy connection, the circuit will still maintain a good ground to the chassis.
Yeah. The shield connects to the bus. I did a lousy job showing the separation of the shield and wire.

That’s a good suggestion on grounding the jacks to the chassis. I'll move the ground wire from the Lo jack (going to the gain pot) and add a ground wire from the Hi jack to a chassis lug. The chassis is all I have left to order, so hopefully I can get started on this by the first of next month. Layout is a little different because this one is in inkscape instead of DIYLC.

jack grounding.png
 
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