New Project -> Hammond AO-63 to Modded 5F6 Bassman

[Colossal]

I really like that new layout, nice and clean. Cool choke input supply too; you don't see those every day. I noticed you chose the Frondelli style master volume versus the Type III Fischer/Larry style master. Have you tried it before?

[turbofeedus]

I really like that new layout, nice and clean. Cool choke input supply too; you don't see those every day. I noticed you chose the Frondelli style master volume versus the Type III Fischer/Larry style master. Have you tried it before?

I haven't no, it's one of Robrob's recommended mods, and I figured why not? Would you do something different?

[Colossal]

I really like that new layout, nice and clean. Cool choke input supply too; you don't see those every day. I noticed you chose the Frondelli style master volume versus the Type III Fischer/Larry style master. Have you tried it before?

I haven't no, it's one of Robrob's recommended mods, and I figured why not? Would you do something different?

No, I wouldn't change it, I was just curious. Definitely check it out. If you don't like it, it is very easy to just swap the leads to the Type III PPIMV type master configuration. With the Frondelli, it's good to have the large coupling cap so you retain the low end as the master is turned down. The Frondelli might be a good fit for your design because 0.1uF is part of the Bassman power amp.

[martin manning]

Check your tone stack. It's missing the mid cap, mid pot should be 25k, and the slope resistor should be 100k. The presence pot should be 5k, and there is no NFB shown. I'd start with a 56k FB resistor, and tweak from there.

There's no reason you can't go with 1Ω for the power tube current sense resistors.

[turbofeedus]

No, I wouldn't change it, I was just curious. Definitely check it out. If you don't like it, it is very easy to just swap the leads to the Type III PPIMV type master configuration. With the Frondelli, it's good to have the large coupling cap so you retain the low end as the master is turned down. The Frondelli might be a good fit for your design because 0.1uF is part of the Bassman power amp.

Cool will give it a go.

Check your tone stack. It's missing the mid cap, mid pot should be 25k, and the slope resistor should be 100k. The presence pot should be 5k, and there is no NFB shown. I'd start with a 56k FB resistor, and tweak from there.

There's no reason you can't go with 1Ω for the power tube current sense resistors.

Thanks, I updated it. I actually misread the mod I was going for, I believe the current rendition of the tone stack is correct. Increasing the mid to 250k should let me dial out the tone stack almost completely, and in fact the pot I found is switched, so it actually will lift the tone stack at the very end of the wiper travel.
The schematic shows 56k slope resistor, but it sounds like Fender quickly changed it to 100k?
Also I could have sworn somewhere I read Fender changed the presence to 25k, which made it more usable. Worst case I can swap it, no biggie.
The NFB is on a push-pull switch on the bass pot. Lots of tone shaping in this build!

[martin manning]

Thanks, I updated it. I actually misread the mod I was going for, I believe the current rendition of the tone stack is correct. Increasing the mid to 250k should let me dial out the tone stack almost completely, and in fact the pot I found is switched, so it actually will lift the tone stack at the very end of the wiper travel.

You could add a lift at the bottom of the mid pot, but the way it is it will flatten the whole response.

The schematic shows 56k slope resistor, but it sounds like Fender quickly changed it to 100k?

Correct. Note the bass cap is 100n, not 22n.

Also I could have sworn somewhere I read Fender changed the presence to 25k, which made it more usable. Worst case I can swap it, no biggie.

They did, but you have a mixture of the old and new circuits there.

[turbofeedus]

You could add a lift at the bottom of the mid pot, but the way it is it will flatten the whole response.

Oh I see where I was getting messed up. All the fender TMB pics show the mid cap to the wiper of a 25K pot for mid, but the tone stack calculator shows the mid pot as a variable resistor. I think I want the latter, where the "mid" pot is just be a variable resistor on the tail, which would give more volume and mids by defeating the tone stack. Looks right just messing with the tone stack calculator. Will call it something other than middle, maybe like "voice" or "guts". I updated the schematic.

Correct. Note the bass cap is 100n, not 22n.

Gotcha, updated.

They did, but you have a mixture of the old and new circuits there.

Alright, I'll keep the 25k, see what happens.
Thanks!

[sluckey]

Here's the reissue presence circuit...

[turbofeedus]

Here's the reissue presence circuit...

Oh I see, so that would solve the swooshing too.
Hmm, so it's either 5k with the original circuit, or 25k with the reissue circuit?

[Colossal]

The classic circuit (5k/0.1uF) has a much better range across the knob. The revised circuit sacrifices a portion of that range for no scratchy DC on the pot. I much prefer the Classic or Dumble presence circuits.

Just my $0.02 on that.

[turbofeedus]

The classic circuit (5k/0.1uF) has a much better range across the knob. The revised circuit sacrifices a portion of that range for no scratchy DC on the pot. I much prefer the Classic or Dumble presence circuits.

Just my $0.02 on that.

Ah I see, I suppose I should use 5k instead then. I don't care about the scratchiness.

EDIT: little update, sockets mounted and filament wiring done. Also stuffed a cheeky little fuse holder on the side wall for the HT.

ao63-3.JPG

[Colossal]

That's looking real good.

[sluckey]

You did a great job cleaning up those terminal strips.

[turbofeedus]

You did a great job cleaning up those terminal strips.

Absolutely not, I bought new ones . I hate desoldering and cleaning terminal strips.

[sluckey]

They do look new. I'm surprised you found new ones that fit the original holes. Cleaning terminal strips and tube sockets is a very tedious job. I've done it before but always have to get in a certain frame of mind!