Dukane Power Amp> Guitar Amp?

[ArnC.]

I have this old tube amp: DUKANE 1A435B POWER AMPLIFIER 50W , I was wondering what would be a good preamp that I could build that would compliment this amp. It's intended use would be for guitar. I noticed it has auxillary ouput connections for 6.3 volts and also B+. I will assume this is so I can connect a tube preamp to the existing power from the transformer.

The service literature says: "auxillary power 225 volts DC @7.5ma; 6.3 voltsAC@1.4amps, B+ and filament power for audio preamplifier..."
So, yes all set up for a preamplifier. Anyone know of a good tube preamp for guitar? I know there are many out there. Just can't decide what would sound the best. I like clean, also a little overdrive or extra gain. I would love to have this for bluesy and rock sounds. I have many pedals to use with this amp for other sounds. It doesn't matter if the preamp has a lot of wiring or not, looking for the sound not the complication of it.

I really just want to make a good complimetary preamp, possibly tube or possibly sollid state. I already have an amp case with 12" speaker that I took this out of, which already has a space for 19" rack(for preamp). I made a tube MIC preamp a lonnng while ago that did not have enough volume. So then I made the carlsboro preamp and I could only get one channel to work. But, that was a long while ago.
First thing is I have to recap the amp, real noisy, I also may replace the resistors as the resistance has jumped up considerably on all of the resistors.

I am wondering if the ROG amp simulation circuits would have enough output as a preamp to push the tube amp or would I have to add something else to get a bigger signal to the power amp?

So, a tube preamp is not out of the question, but I am also interested in using ROG type circuits if possible. I play blues, rock, country, country rock, pop and folk.

Thanks for any and all input!
Any suggestions would be appreciated.

Thanks!
Arn C.

[sportster4eva]

That could indeed be useable! What kind of power tubes are in it? Some of those old PA heads had the schematic stuck inside on the bottom cover. A pic of the schem would be cool to have.. Over on Thundertweak there are a couple of dukane schems. By the looks of them you may be able to create a Fender twin out of that baby. The one I was scoping out had 4-6l6gc outputs and a long tailed pair PI, and dual 5u4 rectos. That's half way there!

[Enzo]

Schematic Heaven has several DuKane drawings, not yours, but they may be similar, one is a conversion even.

[spearguner]

Your on the right track with a tube PA amp or a organ amp as they have less pigyback circuitry involved. The best case senario would be a stand alone power amp out of an organ, Hammond has one model like this. All you need to do is hook up a modern tube preamp with an effects loop, channal switching and tone controlls. Just add a 1/4" input jack to the tube power amp to plug the preamp into and have the best of both worlds as modern multi-prosesser guitar effects can be added in to the parallel effects loop with wet dry mix capibilities. In the tube PA case you have to rework the tone control circuitry as the frequency is different for human voice than it is for the guitar. The tone control seems to be ineffective when a PA is used for guitar work. I suggest you check out the book " Inside Tube Amps" by Dan Torres. It will give you a good basis to work from and even shows how to hot rod a tube amp with another 12AX7 tube. There is a handy chart for Biasing tube amps with different power tubes in relation to Plate voltage. Hope this helps!

[bob p]

One note of caution about working with old gear like this -- some of the old 1950s amps you'll find are downright DANGEROUS by today's electrical safety standards. You'll find lots of amps out there that have transformerless power supplies, for example. Amps like those should be avoided like the plague because of their significant electrocution risk.

I was recently inside of an old Allied Radio HiFi amp with the intent of turning it into a guitar amp. I recoiled in horror when I found that the amp had a transformer, but that some of the back panel speaker hookups didn't go through the transformer -- they had connections on the speaker terminals that connected directly to the "cold" wire from the 120 VAC outlet! To make the amp safe, I had to gut it and start over from scratch.

If you're going to tinker with some of the old gear that's out there, please be careful. Always be certain that you are working with an amp where the user is isolated from the AC mains by a transformer. Some of those amps that are out there could kill you. Get help if you're not absolutely certain about any potential safety problems.

[spearguner]

AC/DC Amp

Hi Bob, I found that a lot of old cheap tube amp circuits were designed to be what is termed AC/DC type circuitry. To save money on parts some designers would do away with the power transformer and use 3 tubes that would drop the whole 110 line volts down between them. I can't remember the tube numbers but two of them had the numbers 50...etc, 35...etc. with the third it wound up dropping the whole 110 volts. The other noteable difference was the heaters were wired in series, if one tube went out all of them went out. I see these all the time on ebay for high prices and in my opinion they don't sound as good as a sick solid state type amp. If you don't see a power transformer and there are only three odd ball tubes look out you have an AC/DC circuit! Best Regards! Gary