The preamp needs 18 volts. Can you supply external 18 volts to the preamp and see if the hum disappears?
The 0 volts ground wire connection to the preamp may cause this problem if there are two grounds made. Power amp or power supply or speaker grounded to chassis along with input sockets. 

I have this amp, i just want to have schematic to try mods

What is the problem you are trying to solve?                                                                                                       

Quote from: dmeek on July 07, 2025, 10:48:25 PMHere is the preamp schematic. The Tone switch is a gyrator notch filter. I can't see the value of the silver capacitor on the tone board but if
I assume it is 1000PF the frequencies are: 1 - Flat, 2 - 230Hz, 3 - 1kHz, 4 - 3.4kHz. If you can read the value, let me know.
I couldn't draw the reverb section because the foil side is hidden by the footswitch jack. If you can move it and post a photo I can do it.
If you want to lift the power board and post a photo of the foil side I can do that too.

You cannot view this attachment.

Thanks Dmeek, incredible job, as usual.

What I find *weird* is that the exact same amp (differences are just "modernization" but design/ideas are the same) was made "on both sides of "the Curtain/Wall"" because Regent maker was an East German/DDR State run Factory.
So much so that components used are "Soviet Block" type.
Transistors are Tesla, made in Czekoslovakia, guess other components too.

Not sure where did "the Reds" get Reverb tanks, for example.

Also curious about what speakers were fit in those amps.

My point is that *maybe* East Germans copied a British amp (although an earlier discrete transistor version), the opposite sounds unlikely.
But the Londoner uses American transistors (RCA) and ICs (Texas Instruments) but Britiish Cliff jacks and capacitors.
No brand visible but those large Blue ones look same (or very similar) to those used by Marshall.

Mysteries of International trade.

Hi,
I'm looking for a schematic of an Elka AC 12110r.
It's an old Italian brand.
If someone knows these amps its a good beginning !

Thanks

Hello,

I bought a used RG1003, that is VERY clean and works great, with the exception of changing channels using the footswitch. Hitting the channel buttons on the amplifier works fine. I received the amp a few days ago, and it seemed to work fine. Then out of nowhere this issue started happening. I can always change to channel 3. But I have issues getting it back to channels 1/2. I opened up the footswitch and everything seems fine in there. I played with the wires a little bit to see if it would change anything and the only thing that changed anything is.......it typically works fine when I hold the footswitch upside down. When this issue happens, I also typically lose a lot of power output while playing, but ONLY in the bridge pickup. If I switch to the neck pickup, I get power back. This does not fix the footswitch issue, but they seem to go hand in hand.

This issue in general is not always present, but it's happening all the time. I can play for a bit without it, then it just happens.

What I've tried:

-Cleaning contact by spraying the footswitch input and plugging it into the footswitch jack on the amp.
-Tried using another 2 switch footswitch I have that goes to a Peavey classic 20MH (this works... but it ends up having the same issue, which leads me to believe it's the amp).
-Swapped some cables around, and tried different guitars.


Any ideas?

Not exactly off-the-shelf, but my two main cabs use hi-fi speakers.

One is a 1x10 using a woofer off some generic cab, that the gym right in front of my house threw away many years ago, and I grabbed and got it fixed at a local speaker repair place:


The other is a 2x6 using speakers off an AIWA microsystem they threw away at work:


I also have a shoebox with a full-range 5-inch "ETM" branded "5EFR" model speaker, 25w 4R, that I bought to experiment with. Brazilian brand, seems to have vanished a couple years ago, but there's still speakers out there available to buy, and they're decently built.

You could probably replicate that tool in a 3D software and get it printed in some of the many services out there in metal, and have a decent tool for ages.

or even turn/mill it out of a solid metal cillinder.

More pics of the build.

Drilled some holes, routed and soldered some wires, now I'm wainting on another order of 1M Log pots (weirdly weren't available before today) and knobs, coming tomorrow.

The extra jacks are for using the P.A. with my headphone amps (Vox AP2-AC, Joyo JA-03B, Xvive GA-3). They plug on the top P10 jack, Phones out goes into the 3.5mm jack next to it, guitar cable goes on the jack on the back of the cab.

When these are unplugged, they connect back to the internal preamp.

Another thing I wanna do is add a power jack, and also have the original speaker contacts be a utility power out for pedals and such. Curently, it's the power input.

Lastly, I wanna see if this "passive compressor" on the last pic could help with the P.A. input overload. I'll put it on the protoboard and see how it does.

Thanks for the info.
Checked a few sites.
Seems like a bicycle tool, made of zinc or aluminium alloy.
Does not feel strong.
Regards.