Dukane 1u460 PA to Bassman conversion

[sydthegnome]

Hello,
I've made/modded a few tube amps over the years, but I'm pretty awful at designing circuits.

I have a DuKane 1u460 PA. Here's a schematic:
http://marcrochottedesign.com/images/dukane-1u460.jpg

So right now I want to start out by rewiring it to convert one of the mic inputs to a 1/4 jack instead of the old screw-in mic jack. I also want to make the tone stack more fitting for guitar. I will be putting a 3 prong power cord in first, and will replace caps as needed.

How would you wire a 1/4 in place of the mic jack? Any suggestions that would make the circuit more guitar friendly? was sort of confused why pin 2+3 of v4 were connected by c19, and wondered if i should wire the jack into the resistor right before pin3 on the first 12ax7. At first I was going to gut the whole thing and use it for parts but when I put tubes in and played through the aux channel it sounded great as-is, though the aux channel is pretty low volume.

Thanks!

[Leo_Gnardo]

Nice project Syd, and before you start soldering pay attention to that good sound you got thru the aux channel. Your Dukane is a mile away from a Bassman; I'd let it "be what it is" before wrecking out the EQ & output drive & preamps etc.

Do you have the mic transformers or are jumpers in place as marked by dotted lines on the schematic. If jumpers yes, transformers no, I'd make up an adapter cable to get your guitar (and other test signals) into mic inputs, quarter inch jack one end, and XLR at the other. In the XLR shell, pin 3 carries your guitar signal, pins 1 & 2 both ground/shield.

Interesting you have cascaded triodes at each mic input - for guitar that's a lotta gain, and you could develop some interesting overdrive tones right there. (cascade = one triode straight into the other, gains multiply, should be rather ripping!)

Let's get some guitar signal thru those inputs & stock EQ, who knows you might love it right there, would save a lot of faffing towards a "bassman" sorta copy. Looks like a "James" EQ in there, not a bad thing at all.

Another attractive feature is your filaments are floating on DC, should help keep hum down.

One thing I don't see, it would be handy to have a master volume control, say at the grid of the output drive tube.

[loudthud]

was sort of confused why pin 2+3 of v4 were connected by c19,

There are four V4s (V4a, V4b, V4c, and V4d) and no C19 I can find anywhere. Did you mean C15? They're just for noise suppression.

Does your amp have the input transformers plugged into the S3 octal sockets? The transformers are for low impedance microphone inputs, remove for guitar use. For a high impedance guitar input, just hook the input to pin 6 of S3(s) or pin 3 of S1 if there is a jumper between pins 5 and 6 of S3.

[sydthegnome]

I meant c15, and I figured that's what it was there for I just thought I'd check since it's the first time i've seen a circuit like that. There aren't any trasformers, but there are the jumpers, and the bassman thing in the title was my mistake, I meant to change it but posted the thread before I noticed it still said that. It's a great amp as is but the EQ is super bass heavy, at least it was through the aux. I'll try out what you guys suggested and be back here if I run into any issues.

thanks a lot, thought it was a good idea to ask the experts before I messed something up.

[sydthegnome]

Just tried wiring it up like you suggested, and it sounds great! Gonna have to wait til its day time to try it out more and see how it breaks up because it gets really loud. reeaallly loud. There's a decent amount of hum, which I assume means I need to replace capacitors, though it works a lot better than I expected. Which caps would you start off replacing? c6 and c7?

[Leo_Gnardo]

Just tried wiring it up like you suggested, and it sounds great! Gonna have to wait til its day time to try it out more and see how it breaks up because it gets really loud. reeaallly loud. There's a decent amount of hum, which I assume means I need to replace capacitors, though it works a lot better than I expected. Which caps would you start off replacing? c6 and c7?

So far so good! All your old electrolytic caps are suspect in a unit this old. What a PIA . . . but you can replace some with individual caps. I'm NOT a fan of the CE multisection caps, super expensive and not very reliable. I'd look into some of the dual-section 50+50/500V and 32+32/450V from F+T, JJ, Ruby. Only 2 sections = you'll be replacing the remaining sections with singles. The caps I mentioned need mounting brackets, extra hassle but worth it so you can install reliable parts.

First thing I noticed in the signal chain was the huge 0.25 uF cap connecting the first triode's plate to second triode's grid. Holey smokes! You could swap in 0.01 uF and still have plenty of bandwidth. Try it on one channel, see if that doesn't take some boom off the signal.

[sydthegnome]

First thing I noticed in the signal chain was the huge 0.25 uF cap connecting the first triode's plate to second triode's grid. Holey smokes! You could swap in 0.01 uF and still have plenty of bandwidth. Try it on one channel, see if that doesn't take some boom off the signal.

Are you talking about c11 by v3a?

[sydthegnome]

Also, I'm thinking about trying out turning one of the 12ax7's from one ofthe the unused channels into a tremolo. Something like this: http://www.thevintagesound.com/ffg/s...g9-b_schem.gif

Does that look like it work? I've never experimented with trem circuits

[olddawg]

There are many more experienced than me on this board, but I think you had the right idea to begin with. Especially if you want to "add" a tremolo circuit and such things. You have a lot of tubes to work with. You will probably have to replace a bunch of caps. You might as well gut it and make a new, fresh tag or turret board. It's much easier than modding point to point in a relic. Look at a Fender Deluxe Reverb schematic. Consider using a solid state rectifier to increase the B+. You will then have reverb and tremolo. Maybe change the outputs to 6v6s.

[sydthegnome]

Well one thing I've really come to like about this amp is the unique tone it gives me, it's super warm and very responsive, and I like the tone stack a lot more than your standard 3 knob mid scooping treble mid bass setup.

not to mention I don't have a lot of free time or extra money to completely redo it. i got the amp for 30 bucks and actually really like it, i'd just like to utilize some of the extra tubes (maybe an overdrive boost on one and tremolo on the other) but I dont need more than one channel, unless I would make two channels that sound very different tonally. Being that there are 3 channels already (well 4/5 if you count the low gain aux inputs) I figured that a tube tremolo would be a nice addition and that I could re purpose the aux jacks for a foot-switch connection.

I already have an amp with 6v6's and i've been trying to get an amp with 6L6's for a while now. I do like the idea of adding reverb, though I don't have a tank to work with currently. First tube amp I played/recapped/changed tubes in was my friends fender quad-reverb, and I loved the reverb in that, but the tone was always a bit off for my style not to mention that the amp was way too d@#n loud for most situations. Right now I have a epiphone valve senior which has just about the worst reverb i've ever heard, but i've done a few mods to make it more tolerable. before that i built a 36 watt variant of the marshall 18 watt from parts from an old organ, point to point, with 4 el84's, so I've tried a few options and this dukane amp is near perfect for my style tone wise.

anyways i'll stop ranting haha.

[TimmyP1955]

Resurrecting an old thread: Anyone have a current link to a schematic? There's one in the amp, but I've not been able to get a good scan of it.