5E3 / Blackface amp

[printer2]

Thinking of trying this. Four pole switch to go from a 5E3 preamp to a BF sound. The pots are dual pots, so you have Vol 1, Tone, Vol 2, then switched, Vol, Treble, Bass. Reverb pot has a push-pull switch on it, have not worked out the circuit yet so just put a couple of jacks in for now. The power amp section switches between cathode bias-no negative feedback to fixed-negative feedback operation. Put a 1k resistor inline with the bias voltage so when the switch shorts you do not get a short on the cap. I am not sure if it will effect the operation of the bias, I am guessing not. Not sure on the output tubes yet, thinking of some 12BK5's for under 10W.

[loudthud]

The only thing I find strange is that the Blackface Mode requires that you use the Normal 5E3 input. I would think you would want to use the Bright input so you could go from Blackface to 5E3 without having to change where the guitar is plugged in, just flip the mode switch.

[printer2]

Yeah, I guess I can switch it. I had a Harvard option on the bright channel before but eliminated it when I simplified things and just kept the BF where it was. Glad you caught that.

[printer2]

Updated for bright input and BF in the same jack.

[tubeswell]

Maybe you ought to prototype it before you build a fancy chassis'n'all - just in case you're not happy with all the switchery. (Just thinking about the potential for noise when you have all those switch poles in the signal path (lead dress and coupling etc))

[printer2]

Me, fancy chassis? I got some flack for using galvanized steel instead of using stainless.

Don't see noise as being more of an issue than any other amp. I usually keep my leads short, built another one a while back using dual pots and the same BF - Tweed circuit and had no problems. It was only a single channel amp though and I would like to see what all this 5E3 thing is all about. The added reverb and fixed bias is new to me but I think I can manage it. Heck, I left out the switched PI on this one.

[tubeswell]

Ah well. My bad. Sorry 'bout that

[printer2]

No problem, the last one was a learning experience, thought the same things when I was making that one. Was quite pleased when it turned out not being a fancy oscillator. Lent it to a buddy though and it is taking a while getting back. So I need to build another amp.

[tubeswell]

So I need to build another amp.

Story of my life

[printer2]

And we are all the better for it.

[Enzo]

I too concern over noise. I am woried about all those unterminated switch points begging to carry charges. Makes pops in the speaker when switched. Not referring to lead dress or picking up anything. For example up top, the entry to your tone stack. There is no DC path to ground there. Those caps ar free to hold little charges, which when switched in result in pops. Same lower left, that tube grid is not terminated. Every time the switch is thrown, that grid gets free for a moment. In each of those cases, I think good practice wants a high value resistor to ground. 1meg or something ought not to mess with the sound, but would keep all the caps in place, charge-wise.

Likewise the switchfield between the plate of lower left tube and grid of center tube. That plate cap is left unterminated so the end of it can charge up. And the grid is not terminated. With all those intervening circuit paths switching in and out, there is potential for lots of noise. Not saying it WILL be noisy, but it very often is in this sort of situation.


In similar fashion, your FX loop jacks float. If either end of whatever external device you connect happens to have a capacitor, that can cause a pop every time you switch over to that side.

SOmething to think about anyway.

[printer2]

I was not too concerned about pops, in the same realm of plugging a guitar into a jack with the volume up. Yeah I'm bad. Consider the resistor on the tone stack input and the tube grid done. Same with the grid resistor on the second tube and the reverb loop. Thanks.

[überfuzz]

Just a thought: most amps sit in the same setup for years. Then maybe a sniff more bass. Why not test build it find out what sounds best and build that. Without all the junk.

[printer2]

Just a thought: most amps sit in the same setup for years. Then maybe a sniff more bass. Why not test build it find out what sounds best and build that. Without all the junk.

Built this already.



Tweed on one position, Blackface on another, a few odds and ends thrown in to see what they will do. Wish I still had it right now, lent it out to a guy I work with. I enjoyed both flavours of the amp and switched between them depending what I was doing. I do want a BF with reverb and have never tried a 5E3 yet so decided to do them both, otherwise I would have to build one of each anyway. Besides, I have read a few people that wished they could have both in one amp so I decided to see what needs to be done to do it. Just wait until I do my 5E3/Bassman/Blackface cross with a couple of different PI's thrown in not to mention the pentode preamp tube thrown in.

[überfuzz]

Just wait until I do my 5E3/Bassman/Blackface cross with a couple of different PI's thrown in not to mention the pentode preamp tube thrown in.

Ampzilla?