Tube Lab #28 Prototype E80cc Preamp Circuit & Grounding 

The chassis has resistance. What we do by creating separate star ground points is put a litle resistance (the distance across the chassis) between those 2 points. The largest amount of noise (main source, heaters, decoupling capacitors, etc.) should be close to the main ground side as possible. Then, the secondary grounds (audio) should be "chassied" on the opposite side, so they are slightly "higher" in potential to ground respect to the main/safety ground-chassis connection (we are talking about the resistance of the metal of the chassis, probably in order of milliohms) When there are multiple stages and high gain, the first gain stages should be the "furthest away" (more resistance) in the ground path, then the middle stages, and at the end (with less resistance, near the main chassis ground connection from the outlet socket), the exit stage. The ideal is to have distributed ground connections (a bus wire/bar for example), so you don´t put signal (audio) grounds inside a return ground path from a noisy section

I've just used a pair of Hytron Det20s in a prototype amp I've built. Be careful as the topcaps were the reverse of the datasheet. I'm very lucky not to have blown them when I plugged them up.

With Switch mode power supply, how d oyou deal with the very high frequency switching noise, which is inherent to switch mode power supplies. The brick used to power up a laptop, even in brand names, spews all sorts of radiation into the air and onto the power lines. You can here it very clearly on the Broadcast and Shortwave bands. What was your thinking in deciding switchmode PSU over a linear PSU?

Hey Jim, thankyou for your wonderful videos sir! Random question. I have a hybrid headphone tube amp (sabaj ph3) that takes 6j9 e180f 6688 tubes. They are run in a starved plate setup, simply as a buffer, in series with a pair of op amp chips. I was wondering what the difference between the 6j1 and the 6j9 was as I'm looking at getting an exduoo mf-602 aswell (6j1). Forgive my ignorance but can one be used in place of the other if the pin outs are the same in the case of my amp? They are both b9f fittings. I wondered this as mine aren't creating gain as such... merely following.. or would I have to change resistances and pin positions etc? Please tell me if I'm being an idiot. Cheers xx

Jim, as a fellow R8 owner i'm interested. If you added sound clips to your channel, I think you would gain a lot more purchases. It is hard to buy and build an amp on mere suggestion. I believe some would even pay to ship a pre built amp, with a CC deposit to demo at home before commitment.

I thought MWT was Marconi Wireless and Telephones.

Very nice design, but how can you make such an ugly casing and screw up a cool design like this, Oh you English. Greetings from Poland.