Hammond stout built from hammond AO-43 additional gain stage?

[Blackhawkamplifiers]

Hello all, I have built a stout from a hammond AO-43. I love the cleans but would like to get the gain into JCM 800 territory without using a boost. I have an additional unused tube socket in the chassis and would like to add another gain stage (or two seeing as its a dual triode) has anyone done this and if so have you created a layout yet? Thank you!

[eleventeen]

I've done such a thing. It was in a SF Princeton reverb I modded long ago. I did not have the knowledge to perform any form of calculations, I just kind of cobbled together an additional triode gain stage. It turned out "great" in the sense that I was looking to create a Mesa Boogie kind of pre and post gain sort of topology. I probably had it just before the PI. It actually worked fairly well, but I was using whatever junkbox parts I had and the post gain pot could only go to about 2.5 before the the thing was monster loud and borderline out of control. But it sounded positively evil and got really cool feedback that was controllable by turning towards/away from the amp. It was quite fun in a borderline out-of-control, overgained way. It started to get pretty noisy after a while, which could have been the junky old tubes I was using and it went into storage for some years, and when I took it out I had no idea what I had done so I ripped it all out and went back to stock.


Anyway, I don't think this is the biggest of big deals if you are willing to experiment some. With a simulator or with paper calcs, you should be able to figure out a super simple 5x-10x 12AX7 gain stage and throw it in series with your signal. Feed with a 250K or 500K pot coming from the prior stage through a cap to block plate DC from the prior stage. Use a typical 1500 ohm/25 u cap under the cathode, 100K plate resistor and then another cap to where you cut the output wire. I mean you are talking about half a dozen parts and you certainly aren't inventing anything. I wouldn't worry about layout, I'd just point-to-point build it until you get it close to how you'd like it. Probably the whole circuit could be built on a 5 or 6 place terminal strip. You really cannot develop a "neat" layout until you establish how many parts the thing will use. I actually think it is better to just hack it in there until you get it where you want it. Then you can think about whether you want to be able to switch it in and out, whether you want an indicator LED, whether you need to change the feedback R and various other items.