What went wrong? AA864 / AB165 on toggle switch

[pompeiisneaks]

I think due to the fact that there's a 500pF cap after it, there won't be any, it blocks dc so there's no path through the switch for it.

No?

~Phil

[fevzay]

Would this be the appropriate wiring for a DPDT switch?

[pompeiisneaks]

Yes that looks correct to me. BUT the jumper on the top means that when the switch is 'down' you'll get the top, just remember that part

~Phil

[fevzay]

Ha! That part I know.

[pompeiisneaks]

It's just bitten me several times lol

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[sluckey]

It's just bitten me several times lol

Speaking of that... Be careful with that switch. It's pretty hot!

Is your point of this crossbreed just to see how the AB165 preamp circuit compares to the AA864? There's not a lot of gain in that extra stage. If you really want a hot gain stage with some growl, there are other more suitable circuits or you can modify that circuit for some hot sounds.

[fevzay]

It's just bitten me several times lol

Speaking of that... Be careful with that switch. It's pretty hot!

Is your point of this crossbreed just to see how the AB165 preamp circuit compares to the AA864? There's not a lot of gain in that extra stage. If you really want a hot gain stage with some growl, there are other more suitable circuits or you can modify that circuit for some hot sounds.

Thanks again for your help. Does the DPDT switch wiring look correct above?

Yes, this amp is just a testing ground. I consider it a bit of a personal playground to learn on. I have the original chassis boxed up, and when I'm done messing around with it I figure I'll know how I want to restore it. As you can see, I used a lot of non-blackface style things when wiring this one up (pvc wire, stand offs, etc.).

I agree regarding the circuits. After goofing around with the AB165 for a while, I'm sure I'll want to try a cathode follower style tone stack. When I go that route, I'll probably keep the Normal channel as an AA864 to free up V2 and V1 in order to build out a Bass channel. Will probably go for some Marshall style values at first. I believe the 4k OT matches up fairly well although I know 6L6's just aren't going to sound exactly like a Marshall no matter how its wired. I may even go another route and wire up a Vox top boost style sound. I had a Top Hat Super Deluxe mkII a few years ago (cathode biased 6L6's with no negative feedback), and it can do a decent Vox style at some settings.

Long story short...I have three SF Bassman amps (67,67,71). I have almost no money into them after a few unique gear deals. One 67 is nearly perfectly stock with the old blue caps. When my chops are better, I'll restore that one and sell it off (to fund my own amp builds). I have another 67 that has already been hacked and needs troubleshooting. Will do more of an overhaul on this one as the Bass channel looks really goofed up. The 71 was nearly free, so I felt comfortable tearing into that one (still with a Mojotone chassis to goof around on). It's been fun! Learning as much as possible. I've already got an itch to get my own chassis to do some scratch builds. These three amps will likely all be sold off at some point to fund that.

[sluckey]

Does the DPDT switch wiring look correct above?

Yes. The switch may 'pop' when operated.

[fevzay]

Thanks! I'll put the amp in Standby mode when toggling.

Would you still place a .047uf cap between the V3-Pin 6/Plate resistor junction and the DPDT switch, or is it unnecessary now that the switch is DPDT instead of SPST? Your schematic has the symbol for it, but no value so I wanted to check.

[fevzay]

One last bump about the .047uf cap if you're out there Sluckey. : )

[sluckey]

I'd use it.

[fevzay]

10-4. Thank you.