"stripping down" a 5E3/5C3 build

[f13ndus]

Figured this'd be the best place to post this. I've been wanting to build an amp for a while and getting some parts together, just came into some spare cash so I figure now is the time to dive in! Please excuse my rambling in this post...

I love the tone of the 5E3 circuits I've played, but I want to build my version (a head) a bit simpler. I'm pretty sure I just want 1 input, 1 volume, 1 tone, and that's it. I'm also toying with using octal preamp tubes, kind of a hybrid 5C3-5E3 design.

First of all, does anyone have an opinion of octal vs. noval preamp tubes in these amps? I'm leaning towards octal, because it's my understanding I could build some adapters (kind of like Yellowjackets) to allow me to use noval tubes in the octal sockets, so I could have "the best of both worlds" as it were... Anglela's Super SE amp has the option of using either, but they do it with parallel-wired octal-noval sockets, so adapters would be the same idea as I see it.

Now, looking at the schematic of the 5C3 (same would apply to 5E3, I think), if I just want 1 input, I end up with 1 triode in V1 unused. Should I try to do anything with it (any suggestions?), or just let it be? I don't want a terribly complex amp, but maybe a switchable extra gain stage would be fun to have...

As for that tone control - I'm actually still not sure I even want a tone knob (my favorite amp is a Gibson Gibsonette with only a volume control) - Has anyone here had experience with a toneless 5E3? if I did want to remove the tone knob as well, am I correct in assuming I can just delete it from the circuit? Would a "tone bypass" switch be a better option?

And also - if I do go with the 1 volume, 1 tone setup - are there any downsides to using a concentric pot setup vs. two separate pots?

I appreciate any opinions/answers from you guys!

[Rocketrob]

For the extra triode you could wire it in parallel with the first triode and put it on a switch to take it in or out of the circuit. Parallel mode sounds fatter and has more gain. A single pot tone control like a tweed princeton would work well also.
Rob

[f13ndus]

Well, I got bored last night and started editing the 5E3 schematic I had. Dropped it to one input, Tried to wire the two triodes of V1 in parallel and add the 5F2 tone and volume controls, but I'm sure I've gotten some wiring wrong/missed something important/picked wrong component values. If anyone wants to look this over and let me know what I should change or what I've got right, I'd appreciate it... tube amp theory is still over my head, but not as far over as it used to be!

All the changes I made were before the 12AX7 part of the circuit... I did redraw the power input to show a 3-prong connector, though. Once I get the schematic sorted out "in theory" I'll move on to putting together a turret board layout...

If I wanted to make the parallel wiring of V1 switchable like Rocketrob mentioned, where would I put a switch/what would I be switching?

[cminor9]

Interesting thread. I found a place in town with boxes and boxes of NOS tubes for dirt cheap. Of course, I probably missed the blackplate RCA 6L6s by a decade or two, but some NOS oddball tubes were there. If I had a use for some octal preamp tubes, I'd be in hog heaven. I have been wondering the same things with the octal vs noval preamp tubes. I have also been wondering why 12a*7 became the tube of choice. There are a bunch more dual triodes out there, why did they lose the battle?

I am also considering something similar for a future 5F4 build, dropping the extra channel in favor of using the extra triode for I don't know what (yet.)

I have a 5E3 I built and I absolutely LOVE it. Here's the thing: I never use the tone knob or the first channel. I only use the bright channel. The tone knob stays dimed at all times and I just use the guitar's volume pot. Also, the channels are interactive, but I usually leave the unused volume control in the same place, at about 2 oclock. I could easily replace two of those pots with resistors. I think you're onto something here... I think the trouble *you'll* have is that you won't know what values to use for those resistors unless you first try the circuit with pots.

[tubeswell]

Well, I got bored last night and started editing the 5E3 schematic I had. Dropped it to one input, Tried to wire the two triodes of V1 in parallel and add the 5F2 tone and volume controls, but I'm sure I've gotten some wiring wrong/missed something important/picked wrong component values. If anyone wants to look this over and let me know what I should change or what I've got right, I'd appreciate it...

You need a grid load resistor (1M to ground) at the first stage of V1. This is bypassed by the tip ground-switch inside the socket, and the whole thing comes before the 68k grid stopper. Why don't you have a 'hi' and 'lo' input at the start (like a 5F2A) - just a bit of added flexibility in tonal options.

The way you have drawn the plate resistor for V1 as a shared resistor to both plates, you need a 200k resistor there if you are to achieve the equivalent characteristics of a 100k resistor on a single triode (because the triodes are in parallel, and you are forming the plate load for two triodes). With a single 100k plate resistor feeding both parallel stages, you will get a steeper load line and more compression (like running a 47k plate resistor on each side). Another way to set up this stage as a parallel stage this is to have a separate 100k plate resistor for each triode (but keep the shared cathode resistor) - i.e. closer to the 5E3 schematic

Depending on your taste you could also try a smaller value coupling cap after V1 (e.g.; 22nF instead of .1uF)

If I wanted to make the parallel wiring of V1 switchable like Rocketrob mentioned, where would I put a switch/what would I be switching?

The way you have drawn it, you could switch out one of the plate supply lines between the single plate resistor and the 2nd plate in a way that leaves the other plate supply connected. However it might be better to have a separate plate resistor for each plate as I mentioned above.

[f13ndus]

Thanks for the tips! You're right, I'll probably go ahead and redraw it with high and low inputs. I was just trying to keep the control panel as "clean" looking as possible. I suppose I could also use one input, with a switchable high/low option... but then that kind of negates the "clean" factor as well.

As for the plate resistor(s), I'll just go ahead and add the other 100k. If I add a "fat switch" to take the second triode in or out of the circuit, is connecting/disconnecting the plate supply the best way to do that? Would switching the input to the grid work? I'd want it to be something that could be used while gigging, IE finish a song and switch it, or better yet something footswitchable... assuming I even make it a switchable option.

I guess I'll make a few changes tonight when I get home, and then start sketching out a board layout... should be fun...

[balcorn80]

Well, I just built a 5e3 head, and I, too, wanted octal tubes. So I used 6sl7 tubes, and just adjusted the pin locations. I tried running one volume, and one input, but ended p adding the second input. It's weird how the unused volume control affects the way hte amp sounds...
I also changed my output tube cathode resistor from a 250 ohm/5 watt to a 390 ohm 5 watt. The octal tubes seem to dirty up faster, and by changing this resistor, I pulled the output tubes out of the deep class a way they were running a little bit for a little cleaner sound, with less compression and squash to it. Some people think the compression and squash is part of the charm of a deluxe, and thats fine. I think it sounded good before I changed that resistor. But i think it sounds better and more versatile for myself with the new resistor in place...