Summer has interrupted my finally putting my awesome sounding "Breadboard Bassman" clone into a proper chassis, but it's happening! Chose to do a "Mono-block" type build, and is almost done. QUESTION: My OT has 8,4,2 ohm secondary taps, and have wired it to a rotary switch. How to wire up the NFB? Worked great on the breadboard, wired to the 4-ohm tap to a 4 ohm load (2x12). But if I'm switching cabinets/load impedances, do I need another "gang" on the rotary switch to switch the NFB as well? Or leave it on one sec winding, regardless of the winding selected for the speaker. OR, switch it independantly from the speaker rotary switch??? Like, use the 4-ohm sec for a 4-ohm speaker, but use the 2-ohm winding for the NFB...?? Thanks!
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Normally, the NFB stays hooked to the same tap. You can experiment by changing it to different taps to see what level of NFB you like. Then it usually stays there. The higher ohm tap will have higher voltage applied, so the 4 ohm seems like the logical choice, right in the middle. Obviously, the same change can be obtained by changing the NFB resistor. Depends on what you want to do.
Thanks guys, I just got the amp up and running (only one missed connection this time!), and definitely needed max NFB to tame the breakup, so wired it to the 8ohm tap (for max feedback signal). Have 6V6s in it, biased for 26mA plate at idle, and a 12AT7 preamp tube, but raised the PI grid stopper from 220K to 1M to keep the squeal down at max vol. Have ran 6L6s in it (on the breadboard), biased accordingly, and it really rocks. Circuit has an AA864 pwr section and an AB165 preamp, with only 2 gain stages. I like it!
Looks like a nice, tidy layout. If it rocks as good as it looks, you're in business. Nice to see you experimented with the NFB tap. Nothing is set in stone. What chassis size is that? IIRC, it was 13 X 7 X 2.
Chassis is a Hammond 13x7x2, barely stout enough to hold the heavy xfmrs, but easy to machine and cheap. I want to put a bottom on it and a handle on the side (which WILL need reinforcing) if I want it to be portable at all.... I put 3 banana jacks on the side to meter plate current (across 1ohm) when I swap 6L6s for the 6V6s in it now. Xmfrs are rated 40W, intentionally to be stressed when I bias the 6L6s for 50! I'm ready to change gears now and get back to a Les Paul Epiphone project - sanded a terrible paint job off it, has a set neck, killer sustain, got it for $100 in pieces. Got any favorite pickup suggestions?
Chassis is a Hammond 13x7x2, barely stout enough to hold the heavy xfmrs, but easy to machine and cheap. I want to put a bottom on it and a handle on the side (which WILL need reinforcing) if I want it to be portable at all.... I put 3 banana jacks on the side to meter plate current (across 1ohm) when I swap 6L6s for the 6V6s in it now. Xmfrs are rated 40W, intentionally to be stressed when I bias the 6L6s for 50! I'm ready to change gears now and get back to a Les Paul Epiphone project - sanded a terrible paint job off it, has a set neck, killer sustain, got it for $100 in pieces. Got any favorite pickup suggestions?
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