two amps with one powertransormer, is it possible?

[rexindigo]

hi there,
i was wondering if it is possible to put two amps in one cabinet with one powertran for both circuits and two outputtransformers powering two seperate speakers. in the moment i try to combine my self made 18watt minimalist and my selfmade Princeton 5F2-A clone.
the idea is to have the 18watt for the more clean an crunch sounds and the Princeton for the overdriven sound.
thank you in avance for your ideas.

[Enzo]

Of course it is. It is then called a "stereo."

[rexindigo]

cool, i always thought that stereo was two identical amps, but you are wright, its pretty much a stereo amp only with two different poweramps.

my idea was instead of having two preamp channels for different sounds, to have two totally independent amplifiers with different stages of Power amp saturation, switchable or controlled by a "blend-pedal" and in one Cabinet, and powered by one Power supply so i do not have the troubles with hum cycles etc.

[Don Symes]

have two totally independent amplifiers with different stages of Power amp saturation, switchable or controlled by a "blend-pedal" and in one Cabinet,

Just as long as each power amp always has a load connected - and running two power amps into one load is a BIG no-no - you're good.

[Enzo]

He did mention two separate speakers.

I was thinking, there is a SIlvertone twin with a power amp for each speaker. And I can think of a Gibson amp or two that did that.

[rexindigo]

Thank You, now that sounds encouraging, does anyone have a schematic for such an Silvertone or gibson "Stereo" amp?

How would you split the "mono" Input Signal to the two Power amp sections?
Any Suggestions?

[hasserl]

I rescued a stereo tube amp out of an old console unit sitting curbside one fine afternoon; one power trans, two output transformers, two pairs of cathode biased EL84's, two 9 pin sockets. I'm planning to turn it into a stereo 18 watt lite, or possibly add another socket for som other options, i'm sure the power tranny can handle another preamp filament. I'll run it into a 2 x 12 stereo cabinet, or maybe make it 4 x 10" (I'm thinking a V front would be cool) with each OT feeding a pair of 10's in a cross pattern; and put an "Off" switch on one pair of output tubes so I can switch it between 18 and 36 watts. One of these days when I get a few other projects completed.

[pdf64]

Gibson GA88
http://www.harpamps.com/gibson/pg_0268.jpg
Hope that helps. Good Luck - Peter

[rexindigo]

thanx vor the schem, i ll need some time to adjust it to my idea

[Enzo]

There is nothing special about it. It is just two amplifiers that share a common power supply.

The power transformer must be hefty enough for both. But the transformer doesn't know there are two amps, it only knows how much power is being used. In other words if 10 tubes are drawing heater current, the power transformer doesn't know if that is two amps with 5 tubes each or one amp with 10 tubes.

If you use a rectifier tube, then the 5v winding for it only has to power the heater in that tube, it doesn't know where the power goes.

And then the B+ - the high voltage. All it must do is power both amps, but again, it doesn't know the difference between one 40 watt amp and two 20 watt amps.

And for that matter, as long as they get enough power to operate properly, the two amplifiers will never know that they share the power supply with another, any more than you know in your house whether the house across the street has the water heater running, even though you share the same electrical supply.

[drewl]

I have an old Realistic stereo power amp that I use for recording monitoring that would be perfect for this application. 2 EL84's per channel w/vol and bass/treble for each channel.
I thought about building something like you were saying, but I'm far too lazy.
you could probably get something similiar cheap if you could find one.

[Shea]

Thank You, now that sounds encouraging, does anyone have a schematic for such an Silvertone or gibson "Stereo" amp?

How would you split the "mono" Input Signal to the two Power amp sections?
Any Suggestions?

The first thing I'd try is to have one input jack that connects through a grid stopper to the grid of a 12AX7 gain stage, the plate of which will be direct coupled to a cathode follower like the 2nd gain stage of a tweed bassman or 4-input Marshall. I'd connect the output from that cathode follower to the volume pots of both amps, which would be maybe 250k or 500k pots. So, you'd have one input gain stage for both amps, and the lower output impedance of the cathode follower would be good for driving a long lead from one chassis over to the other chassis without picking up a bunch of noise.

Another option would be to put some kind of solid-state buffer circuit on a little PCB that it would share with the input jack. Then you could run lead from the buffer to each of the input gain stages.

But if you want to select one amp or the other, or both, with a footswitch, then you need to figure out where the switching is going to take place.

Shea

[rexindigo]

Thank You Shea, that is very helpful, i will try to make a schematic according to Your Ideas, but it will take some time.
on the other hand i am still thinking about two totally separated Amps with independent inputs sharing one Power supply.
Actually i have this stage setup today: Guitar into stereo chorus, left goes to a Transformer that seperates the ground for Hum Cycle elimination and then into my 18 Watt clone. Right goes into a Morley wah/volume pedal wich i use as Volume only and then into the 5f3a Clone wich is wide open.
With the Volume pedal i can now add Overdriven amp to my sound whenever i want. No that works, but its a lot of cabeling and now that i can build amps (actually i'm getting a feeling for how its gonna be to be able to build amps;-)
i thought i can combine the amp part of my setup in one housing and safe some Cabel and Hum Cicle Problems.
i have a test amp i can start to mess around with: its a P1 ive build with a EF86 instead of the 12ax7 in the preampstage, i have a very small poweramp, a parallel 12au7 to Fender Reverb driver poweramp wich makes about 1 watt this two i will try to combine....
Ill keep You informed about the process.

[justinbelshe]

Years ago I was in a band with a dude that had a Gretsch stereo amp. I don't remember the model, but it had one power tranny and two output trannies, two pairs of 6L6s. It was my job to keep everybody's gear in working order, and that thing gave me nightmares! It was a fairly complex amp, yet it had no circuit board, everything was true point to point with a few terminal strips here and there (it looked like a plate of spaghetti inside). When the amp was working it sounded great, the owner described it best when he said it sounded "like a Super Reverb that was about to catch fire."