BassmanPaul

@ValleyArtsSo how you doing with this project?

But, but, but it's a transistor amp with just one lonely 12AX7 twin triode!!!

It's great to hear about companies who stand behind their products.

@msb You've got more stuff than even I have and that's saying something!!

You're from Chester a city I have a soft spot for. At one time my family lived in Helsby in fact they are all still there after they all passed away. I went to Helsby Grammar School for Boys and bought my first bass in 1962 when I was sixteen. Thank you for an unintended walk though memory lane. Stay well.

@ValleyArts did you get the Bright box repaired?

For me it's the Acme B2 2x10 three way cabinet. I use a pair stacked on their ends for a vertical 4x10. Stacked this way improves dispersion out into the room and brings the sound up by my ears for easy monitoring. On stage the set just takes the same amount of room as one cabinet. The plum is how well they handle the low B of my six stringed instruments. A pure delight!

If you feel that you need four tens may I humbly suggest that you consider a pair of 2x10s stacked on their ends for a vertical 4x10. This brings the top cabinet closer to ear level and two cabinets take up the same stage area as one. They also disperse better out into the room. All in all a win win situation.

To explain a bit more: a 5U4, or a GZ34 for that matter, can power a typical 50W amp. The Mesa amp being 100W needs more current from its power supply. Thus two rectifier tubes to supply that. If you try to run the amp on one rectifier you risk blowing the tube which could possibly take out a high voltage secondary winding on the power transformer. It's something that you just don't want!

But not cheap!

I'll bow to your superior knowledge. Many thanks for helping out.

It looks as though the pre-amp is powered between the positive rail via a regulator and ground. that's a little odd in my mind. The negative rail just seems to drive a couple of lamps. Hmmm!

Connector pin assignment Pin 1 - Ground Pin 2 - Full Positive rail Pin 3 - Audio Signal Pin 4 - Full Negative rail Pin 5 - Not used Pin 6 - Not used

Thank you @bartelby for going to the trouble of supplying the schematic. @prowla if you are wishing to use this pre-amp standalone you'll have to provide a power supply and audio cabling to feed a suitable power amp. Good luck with that!

I'd be looking at it from below!

I have to admit that I'm glad that I don't have to lift those amps though the Class D, which is not in anyway 'Digital', is going to be much lighter. That being said, I hope you derive much pleasure from using them.

I agree that it's for connecting a Trace power amp board. I tried to read the schematic I found on the web and could see the wiring for the socket but the site was flaky so the diagram didn't stay long enough on my screen to be certain. I'm betting that this unit came from a deceased head as it has no connectivity on the back panel.

I'd go to Glasgow to try it out but I can't swim!

It's not a lamp it's an electron tube/valve. No it's not safe to use. GZ34/5AR4 tubes are readily available and are simple to install. Pull the broken one out and push in the replacement tube in it's place rotating the tube as needed to let the key into the socket base. it's that simple. Edit: Apparently the two rectifier tubes are 5U4G. I beg your pardon. Same applies though.

Oh BABY!! LOL

Yes they can be a bit bright but that can be readily tamed by the tone controls. When I got my B15NF it was red plating the output tubes, leaky capacitors were the problem. Having replaced the amps filter caps and the tubes I had several events of flash over of the GZ34/5AR4 rectifier tube. Adding a silicon rectifier, UF5408, to each plate to increase the PIV solved that permanently. On the whole the amp is a pleasure to use and a delight to hear. Incidentally I play six stringed basses.

A thought that struck me was that if the heater winding fed into a rectifier/capacitor to run the heaters at DC Did the designer multiply the current draw by 1.4 to allow safe operation of that supply. That would equate to 630mA . That's much closer to the 800mA limit of the 12V winding.

Just remember that it's not a complete kit. You'll have to find a suitably sized metal chassis that you'll have to have punched holes for tube sockets, controls and other through chassis mounted components. A face plate and control knobs are needed too. All in all not a suitable project for a neophyte to tube amp construction.

Didn't Fal make the Actifry Air Fryer?

If a 100W tube amp is all you can find you could pull the outside pair of output tube and run the amp at 50W.