Lt Bob amp build - an alliance of superpowers

[Greg_L]

Now shit is getting really real.

Time to put this thing together








[BBvideo=560,315]https://www.youtube.com/watch?v=Y6_uc1xDosM[/BBvideo]

[JD01]

I understand very little of this... but I'm impressed.
Looking forward to the first sound test.
Looking forward to the first gig report.

You taking a quick trip to Florida with that, Greg?

[Greg_L]

I understand very little of this... but I'm impressed.
Looking forward to the first sound test.
Looking forward to the first gig report.

You taking a quick trip to Florida with that, Greg?

Lol no it will ride on a truck that says UPS or FedEx.

[Greg_L]

Awwwwww shit..... [mention]Lt. Bob[/mention]


Looky what we done did....








This here is a done built amp!!!

[BBvideo=560,315]https://www.youtube.com/watch?v=Hs2JJ8C85HA[/BBvideo]


Next up.....electricity.

[Lt. Bob]

Now shit is getting really real.

Time to put this thing together

what is that multi-colored snack?

[Lt. Bob]

Awwwwww shit..... Lt. Bob


Looky what we done did....


This here is a done built amp!!!

[BBvideo=560,315]https://www.youtube.com/watch?v=Hs2JJ8C85HA[/BBvideo]


Next up.....electricity.

KA-BOOM!!!!!!











lOOKS GREAT MAN ...... absolutely beautiful work!

[Greg_L]

what is that multi-colored snack?

That is a Buc-ees Fruity Pebbles rice krispie treat!

[Greg_L]

KA-BOOM!!!!!!











lOOKS GREAT MAN ...... absolutely beautiful work!

Lol no kaboom!

I'm building this thing at the same table that my wife is working from home from. She's on one side, I'm on the other. I told her it was time for electricity and her reply was "bzzzzzzt".

No faith in teh Gerg!

[Lt. Bob]

No faith in teh Gerg!

LOL ..... well never forget, teh boob had faith in teh Gerg!

[WhiskeyJack]

[WhiskeyJack]

This thread has gotten as have most of them in the last two weeks have gotten away fro mme entirely. I am taking some time off next week to really go thru it all and watch the videos.

regardless, that thing looks like a work of beauty. Bang up job [mention]Greg_L[/mention] and [mention]Lt. Bob[/mention]

[Greg_L]

Fresh outta Buc-ees!

[Lt. Bob]

I understand very little of this... but I'm impressed.
Looking forward to the first sound test.
Looking forward to the first gig report.

You taking a quick trip to Florida with that, Greg?

Lol no it will ride on a truck that says UPS or FedEx.

Be sure to pack one of those Buc-ees Fruity Pebbles rice krispie treats!

[Greg_L]

Be sure to pack one of those Buc-ees Fruity Pebbles rice krispie treats!

Ha ok!

[Lt. Bob]

EEEEEEEEEEEeeeeeeeeeeeeeeeee!



I saw pictures of it!




It's AWESOME!!!!!!!

[Greg_L]

EEEEEEEEEEEeeeeeeeeeeeeeeeee!



I saw pictures of it!




It's AWESOME!!!!!!!

Yeah well I've heard it.

[rayc]

The videos are excellent. I've been watching as soon as they've appeared. Incredibly detailed and tidy work in that amp.
The I/O Feedback loop switch makes perfect sense...particularly with the redundancy of the old polarity, or whatever it was, switch in the circuit.
Excellent stuff. I look forward to more.

[Greg_L]

The videos are excellent. I've been watching as soon as they've appeared. Incredibly detailed and tidy work in that amp.
The I/O Feedback loop switch makes perfect sense...particularly with the redundancy of the old polarity, or whatever it was, switch in the circuit.
Excellent stuff. I look forward to more.

Yeah we had two unnecessary features on the back so we made them into something useful.

AB763_neg feedback and bias mod.jpg

The red box contains the original auxiliary AC socket and ground switch. We don't use or need that crap anymore in the modern world.

The auxiliary AC socket got repurposed into a bias test point. I've been adding 1 ohm resistors to ground from the cathodes of the power tubes on my amps. Those are the blue blobs I drew in coming off the power tubes on the schematic. This makes bias testing super simple. Reading millivolts is way easier than reading milliamps, so Ohm's Law and those one ohm resistors handle the task. Just probe at each resistor and read the bias as millivolts. That's easy to do, but you still have to get inside the amp to do it. To get around that I just ran wires (the blue lines) from those resistors to the dormant AC socket. Now [mention]Lt. Bob[/mention] can check and set his bias, if he ever changes tubes, and not even have to remove the chassis. Multimeter probes fit right into the AC socket and he can read the bias as millivolts. Remember when we were kids and we were warned to never stick anything into a wall outlet? Well now he can on this one. I'll provide him with his plate voltage which should never change, so he can go from there. With 6V6 tubes and his approx 439 VDC plate voltage, the readings should always hover around 18-22mv at the AC bias socket for safe bias. And with the external bias pot adjustment under the chassis the amp never has to leave it's cabinet.

The ground switch (green circle) got turned into a negative feedback on/off. All I did with it was move it...physically and electrically...into the path of the negative feedback loop (green line and blob). The amp is designed for signal coming off the speaker jack and fed back into the phase inverter. This loop kind of cleans up amp wildness. Some amps have this feature, some don't. Amps that have a lot of negative feedback usually have a tighter punch and low end and good headroom (Fenders and old Marshalls). Amps without negative feedback are wild and hairy and very harmonic (Vox and Mesa). By repurposing the dumb unnecessary ground switch we can now turn the negative feedback on and off. It just breaks the circuit. Stock or none.



BUT....we have a new...slight issue with fitment. The chassis is made by one company, the head cab is made by another. The chassis fits in the head cab just fine, but the rear panel covers the AC socket we actually need to plug this thing in! So what I'm gonna do, actually already started doing, is I'm just gonna flip-flop the AC socket we actually need with the what is now a bias test AC socket. I just gotta unhook some shit and make them trade places. It was either that or cut the rear panel, and I'd rather not do that even though I have Boob's blessing. We'll fix it electrically.

With the flip-flop of part locations though, the AC plug in problem will be fixed, but the panel might now get in the way of the bias test points. I'll have to put it back together and check that. If so, I'll leave the socket there, hooked up to nothing, and install actual bias probe test sockets.

[WhiskeyJack]

This thread is pure witchcraft. But i like it. Its an entirrly different language. Freakin fascinating.

[Greg_L]

This thread is pure witchcraft. But i like it. Its an entirrly different language. Freakin fascinating.

Yeah I'm just learning as I go and I get a little better grip on it each time I go into an amp.

Then I read stuff from guys that truly understand these things and I'm like.....

If expert is a 10/10, I'm like maybe a 2 at best.

But I will say that my past experiences have made this thing fly together and it powered up perfectly first try. I blew up capacitors on my own amp. Didn't do that on this one. I haven't documented the start-up yet, but it'll come soon. Not a single hiccup yet. Not electrically anyway.