Another old friend... Now a HRD > Bassman project!

[F15hface]

Yeah is this something we follow along at home or what?
‘Here’s one I made earlier…’

[JSett]

Yeah is this something we follow along at home or what?
‘Here’s one I made earlier…’

[Dr Tony Balls]

Alright here's the layout:



Its amazing how much better I can make a layout when I dont take shortcuts. Notes:

1) I tried to color code the power supply nodes to make things a little easier to read.
2) The black ground and the grey ground should be separated. Ground the grey somewhere near the input jacks or right side of the board. Ground the black on the right. Grounds from the speaker jack and power tube cathodes can go wherever is convenient and/or close.
3) This doesnt include the primary side of the PT, but that you wont need to reconfigure.
4) This doesnt include filament wiring, but I think you know ow to do that.
5) R30 and R31 are the artificial center tap resistors for the filaments. You can configure those wherever its convenient.
6) You're on your own figuring out how to get those big caps in there, but i'll consult as needed.

Big Layout
Big Schematic

[JSett]

Oh wow, that's absolutely perfect! I'm actually glad for the parts to be noted as per the schematic rather than values as this will force me to cross-reference between the two and, hopefully, improve my schematic reading skills (if that's not intentional then it should have been )

Parts are all ordered so I'll make a start when it's all here.

This amp is actually being lent out as backline for a small festival next weekend so it's best I leave it as-is anyway until that's over.

ALL HAIL BALLS!

[Dr Tony Balls]

Are you replacing the speaker jacks or leaving them be? I just realized that on mine I left them as is, since they were just fine. Only difference from a layout perspective would be running a wire to replace the green/yellow wire on the layout.

[JSett]

Are you replacing the speaker jacks or leaving them be? I just realized that on mine I left them as is, since they were just fine. Only difference from a layout perspective would be running a wire to replace the green/yellow wire on the layout.

I hadn't decided to be honest. I was going to change the input jacks with traditional switchcraft ones as I'm not a huge fan of plastic jacks. The speaker ones I'll probably leave as-is seeing as they basically see zero traffic. Where would you replace the GRN/YEL wire if you were to swap them out?

The input jacks I'll just wire up like a traditional Fender amp...unless there's some weird issue with doing that I'm unaware of?

[Dr Tony Balls]

Are you replacing the speaker jacks or leaving them be? I just realized that on mine I left them as is, since they were just fine. Only difference from a layout perspective would be running a wire to replace the green/yellow wire on the layout.

I hadn't decided to be honest. I was going to change the input jacks with traditional switchcraft ones as I'm not a huge fan of plastic jacks. The speaker ones I'll probably leave as-is seeing as they basically see zero traffic. Where would you replace the GRN/YEL wire if you were to swap them out?

The input jacks I'll just wire up like a traditional Fender amp...unless there's some weird issue with doing that I'm unaware of?

For the speaker jacks reference mine, which are basically stock. The one on the left is the main (internal) speaker jack and the one on the right is the external speaker jack. The green wire from the OT is the 8Ω tap and the green/yellow is the 4Ω tap. These jacks are wired such that with the normal speaker you're using the 8Ω tap, but with an 8Ω extension speaker you're using the 4Ω tap. To get *proper* AB165 Bassman negative feedback the 4Ω tap needs to be connected to R21. So just run a wire from the green/yellow connection on the external jack to R21. It can be seen on mine as the purple wire, but I was using the 8Ω tap.



And no issue with using metal jacks and wiring like a Fender. In that case the jack sleeve is already grounded, so you can just run your grey preamp ground wire to that spot.

[JSett]

Ahh, okay, that makes sense. I was going to use an 8ohm speaker though as those are what I have already laying around and what the majority of options are out there in the world. Maybe I should hook them up in parallel instead so its 8 for one speaker, 4 for 2 speakers?

(Sorry if you saw the old message I wiped and re-typed, changing my mind )

[JSett]

Wait. I've just realized. It's already set up like that.

Is your schematic/layout for a 4ohm output or 8ohm? I'll be leaving an 8ohm speaker in the cabinet.

[Dr Tony Balls]

Wait. I've just realized. It's already set up like that.

Is your schematic/layout for a 4ohm output or 8ohm? I'll be leaving an 8ohm speaker in the cabinet.

I left my schem/layout setup for the 8Ω speaker but the negative feedback connection to R21 should *technically* be to the 4Ω tap for an AB165 Bassman, regardless of what speaker is used.

[JSett]

Wait. I've just realized. It's already set up like that.

Is your schematic/layout for a 4ohm output or 8ohm? I'll be leaving an 8ohm speaker in the cabinet.

I left my schem/layout setup for the 8Ω speaker but the negative feedback connection to R21 should *technically* be to the 4Ω tap for an AB165 Bassman, regardless of what speaker is used.

Ahh, okay. I'll just do it as per your schematic/layout and go from there. Thanks Tony

[JSett]

PARTS!

Not all of them, by any stretch, but a big chunk. Mouser are always particularly fast which is nice

[Dr Tony Balls]

FYI I asked on AmpGarage re: panel engravers in the UK and two people sugested checking with Mike @ Modulus Amplification. One said he's done that simply by sending him a sketch with dimensions, but a graphical file (.ai, .eps, .pdf) seems even simpler.

[JSett]

FYI I asked on AmpGarage re: panel engravers in the UK and two people sugested checking with Mike @ Modulus Amplification. One said he's done that simply by sending him a sketch with dimensions, but a graphical file (.ai, .eps, .pdf) seems even simpler.

Ahh, okay. I've used Mike before and he's a good dude. I'll give him a shout when it's time then. Thanks!