Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Tbone55 on September 17, 2024, 08:25:16 am
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Looking for some input on doing a cathode follower mod on a Blues Jr III. If anyone here has done it or can offer some advice I'd appreciate it. Off hand it seems like it's a good idea but I'm not experienced or knowlegeable enough to know. I've already been tinkering with my amp trying to take out some of the bottom end and this mod is easy to do and reverse if I don't like it.
For reference, I've done the full Hoffman conversion on my amp and V2 has been wired in parallel. I'll have to undo some of this in order to convert to a cathode follower. The Hoffman schematic and cathode follower schematic are included.
Thanks for the help.
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take out some of the bottom end
have you changed the values of the cathode caps on V1?
IF not;
make them both 10uf then re-evaluate
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have you changed the values of the cathode caps on V1?
IF not;
make them both 10uf then re-evaluate
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I have tried a 2.2uf and .068uf based on the frequency response curves I got using the amp books calculator. The 2.2uf cap seems to work pretty well. I had also lifted the C9 cap that bleeds off some of the highs. I'm thinking I might try putting the 22uf fat cap on V1-A cathode and putting the 2.2uf on the V2-B cathode. I think this was one of BillM's mods.
I'll try the cap changes first before doing anything else.
The other thing that seems to really make this amp sound boxy and bassy is the cabinet itself. A bigger sized cabinet really seems to benefit this amp from what I've read. I have a quarter stack cabinet that I built from Birch and all I need are a couple of speakers for it. Then I can test for myself.
I have a previous post where I asked about what mods would most benefit this amp, in particular, getting rid of some of the bottom end. That post quickly became a rabbit hole for me and brought me to places I never expected to go.
The folks that responded, especially stratomaster, were more than kind and patient with my lack of understanding, or I should say, misunderstanding, of some basic electronics circuit functions. I did, however, get exposed to different circuits of the amp and their function. My understanding of how they do it needs to improve.
Thanks for chiming in. Cheers!