Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on December 04, 2018, 10:20:38 am
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Is the November amp basically a Plexi with El84's? Building a few 6V6 Plexi's with an AO-43 Hammond chassis was thinking maybe keeping one with the 9 pin sockets and using EL84's. Is this idea a bad move? Anyone have any experience how the El84's sounds in a Plexi amp?
al,
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The AO-43 is an excellent platform for a November. Here's more info on the November as well as some sound clips. The clips by Chris sound the most like my November.
http://ax84.com/index.php/oldprojects.html?project_id=november
BTW, the Plexi6V6 idea came from work on the November project.
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Thank you for that link, I did find your November build from 2007, very nice. I see your NFB switch, turning that off do you lose the presence?
al
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yes
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Figured that, just wanted to make sure, stuff starting to sink in, finally. So, I assume you put the switch in to get a little more grit or sooner distortion?
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I put the switch in 'cause early on I was caught up in some of the net hype about switching feedback, switching bias, pentode/triode switching, etc. None of that stuff lasted long for me. I actually built two November amps. The second one lives in a small Vox cab and the one you're talking about became a donor for a Matchless Lightning, which later became a donor for a Vox AC-15.
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Yes, switch this, switch that, after a while it's set and never touched again, :icon_biggrin: . With most of the adjustments in most amps I'm learning you don't need all these switches, thanks for throwing that out there. I'm striving for the neatness in your amps, they're like an art form. I did switch the NFB in my BF Vibro Champ but after subbing that tiny OT (stored it in the cab) for a slightly bigger vintage paper one, don't even use the switch at all. I'll do a Plexi el84 in one of those chassis's, fixed bias, no switches. Thanks again.
al
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Hi Guys,
I built this amp twice. First one was acc.to Sluckey/ax84 project. Second was with hot switch. My heart belongs to Hot Switch, but both are the great machines, which I can highly recommend to everyone.
On pics, there's the Hot Switch.
Regards,
Adam
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Adam
Beautiful work! Well done!
Jim
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Is the Hammond AO-43's PT, (325-0-325) voltage is too high for El84s? According to schematics for the November, B+ of 300vdc. An 18 watt TMB with EL84s runs at about 360v B+, cathode biased, so could the AO43 PT be used, fixed bias and just use dropping resistors to get around 360vdc or is that too high for the November?
al
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Hmm... I wonder what kind of tubes the AO-43 was designed for? Look at this and you tell me...
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Ok, stupid question, was reading the link above about the November, they use a 275-275 PT. Should have asked what is the ideal B+ for EL84 plexi
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It's not a stupid question. But I wanted you to see the schematic for the AO-43. That PT power supply, OT, and cathode biased EL84s were chosen by some pretty sharp engineers to work well together. Take a look at the voltages produced by that PT within that circuit. They are not very different from my November. Sure, the AO43 is running the cathode biased EL84s at about 90% to 95% max and the November will probably be biased at about 70%, so the November voltages will run a bit higher due to the lighter load. If that concerns you, then either run the tubes hotter, or use a dropping resistor, or just maybe... build it as a cathode biased amp. Life will be simpler and you may not be able to tell the difference. What you end up with is an 18 watt TMB. I suspect the November amp idea was an idea over at ax84.com to modify an 18 watt TMB to run fixed bias. I'm guessing the idea came together in November of some year. Come full circle! :icon_biggrin:
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If I build an el84 plexi, fixed bias, Hammond AO43 iron, get the B+ around 360v or whatever recommended, is this amp going to sound like an 18 watt TMB? I have a few 18 watts, cathode biased don't need another. Looking for the 6V6 tone but with the chime of el84s.
EDIT: is there any sound clips of the November el84 plexi? Found a few short clips of Nov. el84 on ax84 site, to me not the beef as with 6V6s and close to an 18 watt TMB but what I found was (4) el84s. Of course with two volumes to mix, who knows. Just wondering if any here have anything to add regarding the tone differences?
al