Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: squierstrat on August 17, 2023, 08:07:12 am

Title: Grounding advice for AB763-ish point-to-point layout
Post by: squierstrat on August 17, 2023, 08:07:12 am

I'm the guy with a Precision S35 PA that y'all recommended I play & enjoy as is, which I have been doing.

However, I have the itch to do another build and find it hard to resist this enclosure and its transformers. I started laying out Rob Robinette's AB763 Blackvibe with 7868s as a point-to-point amp in this chassis.

I've been trying to keep the aesthetic of the original PA by re-using the power, potentiometer, and input jack placements. I find myself with a preamp ground point on the front of the amp which I need to run to the input jacks and V1 area in the back of the amp, and it looks very different to a single neat ground bus. Will this cause problems if I continue and lay out the preamp components near V1 with a ground bus to the input jacks and run that wire from the front? Or do I need to rethink it? There's room to squish the pots together on the front, in which case I could move input jacks and even V1 to the front right corner...

Thanks for the help.

RobRob's Blackvibe Layout https://robrobinette.com/RR763_BLACKVIBE.htm
Sluckey's AB Lite Layout https://el34world.com/charts/Schematics/files/Sluckey/AB763_Lite_II.pdf

Title: Re: Grounding advice for AB763-ish point-to-point layout
Post by: Dave on August 17, 2023, 01:40:08 pm

I don't think anybody will be able to answer that with any certainty. Grounds can be finicky. It may, and for all anybody knows, probably will work fine. The problem is that if it doesn't work fine, you may wind up ripping it all apart and redoing it, so it maybe better to do it another way to start with.


Dave

Title: Re: Grounding advice for AB763-ish point-to-point layout
Post by: pdf64 on August 17, 2023, 02:55:36 pm

It’s not clear to me what’s going on at the rectifier.
Schematic?
Mains Transformer wire colour coding?
Whatever, it looks to be a hot switching standby, which Rob’s layout doesn’t have.
What’s the rationale behind that change?

Title: Re: Grounding advice for AB763-ish point-to-point layout
Post by: PRR on August 17, 2023, 08:25:47 pm

Quote from: pdf64 on August 17, 2023, 02:55:36 pm

It’s not clear to me what’s going on at the rectifier.

The original was a Silicon bridge. He seems to have added a tube rectifier, and then a 5VAC heater transformer. I can't figure from the drawing. Here's Grommes' plan, which IMHO was not bad:

https://i.imgur.com/7yd5gx1.jpeg