If 27K primary impedance would be “ok” then I’m definitely curious to see how using #4 as the common wiring (ground for both 4 & 8 ohm) would affect the behavior.
Yeah, that thread may have been me. Sorry for all the noise. This OT is making more sense ... but only a little. I usually turn the amp off entirely before flicking the switch (and plugging or unplugging one speaker).There was a thread about this recently. I believe the consensus was go for it, no big deal. Make sure you have wires 2 and 8 going to the top terminals of the switch. NFB from wire 2. Wire 4 can go to the bottom middle terminal in junction with the black wire--or you can leave the bottom terminals empty and just send wire 4 directly to the jack sleeves. With all this testing going on, remember to not switch impedance while anything is being amplified.
Yeah, I was wondering about that. I guess it's no biggie. I need to get better at not making the ends of the wires be a tiny bit melted. But I'll give it a go and see how it sounds.Oh and you will have to swap the OT primary leads because the phase of the NFB is now inverted with the swap of wires 2 and 4.
I’m curious, with the 12BH7 power tube, would I need to use a different cathode resistor to make it take full advantage of it’s power capabilities? When I put it in before just to test it, it didn’t sound any louder than the 12AU7. Or would that be more of the case of needing to use a different output transformer?
Yeah, just trying to understand & learn how it all works.
Plate-to-Cathode voltage: 302.3 V
Cathode Resistance: 816 Ohm
Actually, I think those ^^^ are the 12AU7. With the 12BH7 the values are…
Plate-to-Cathode voltage: 296 V
Cathode Resistance: 816 Ohm (obviously same)
Good to know there's that option. That's kind of what I was thinking (dropping the cathode resistor value). I think for now I will just play with it ... meaning ... play my guitar with it. If I need to get louder, I've now got the way-to-loud 18w TMB. I'm sure I will still experiment with mods here and there though and this might be a great candidate.Looked at the load lines for the 12BH7. Similar input headroom as the 12AU7. Probably the only thing you need to do is drop the cathode resistor value to 550-ohms or thereabouts to bring up the bias current. Twice the power doesn't mean twice as loud, and the 12BH7 doesn't even have twice the power as the 12AU7. Still, you should hear a difference.
Maybe bump up the grid leaks to 100K on the power tubes as well.