Melos MA-222 Tube Preamp info needed

J!m said:
If there is a maker name and part number on the transformers you might find it’s designed specs…
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Glad I didn't spend much time making my own schematic.... I tested the left toroid........ it was dead, and the primary was drawing a shitload of current with no output to the secondaries. Then I tested the right toroid, it was also dead. I pulled them both and the underside of both was MELTED and many of the components and solder was fried. SOOOOOO, I remembered I had one of those big toroid transformers and I think I will try it to see if it will fit. It fit in the chassis and while I was looking at the documentation, I saw it has 160VAC on one pair of secondary windings. It is 160V-ct-160V and I do believe I can use that for the High voltage input to the preamp (after rectification and filtering etc..).
 
Has anybody ever used one of the tube preamp power supplies they sell on the net? I saw a couple and they put out the voltage I need. One of them is adjustable from 100VDC to 350VDC with appropriate AC in and it also has a 6-12vdc output for the filament. I don't want to spend BIG bucks on a power supply but I do want good clean stable power though. No tube power supply though. I priced out tubes for the pre and you can loose your lunch when seeing the price of the 6 tubes I need to change so no tubes for the power supply. I could buy a bare board and buy the good parts for it over the winter. Anybody???
 
J!m said:
If this is for you, I say go for it.

If it’s for a customer, and they buy-in, I say go for it.

If it’s just a fix-n-flip, maybe not.
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Naw, it's just a project, maybe a garage system. I have a 700 II waiting in the wings and who wouldn"t want a blaster in the garage?? That way when I'm on the riding mower, I can still head-bang..... :)

I won't get rid of my Acurus RL-11 preamp. so the tube pre is for fun (free fun).
 
WOPL Sniffer said:
Glad I didn't spend much time making my own schematic.... I tested the left toroid........ it was dead, and the primary was drawing a shitload of current with no output to the secondaries. Then I tested the right toroid, it was also dead. I pulled them both and the underside of both was MELTED and many of the components and solder was fried. SOOOOOO, I remembered I had one of those big toroid transformers and I think I will try it to see if it will fit. It fit in the chassis and while I was looking at the documentation, I saw it has 160VAC on one pair of secondary windings. It is 160V-ct-160V and I do believe I can use that for the High voltage input to the preamp (after rectification and filtering etc..).
Click to expand...
Well there goes the green Perry...
 
Gepetto said:
Well there goes the green Perry...
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No sweat Joe, I found a Power Supply board for B+ (250VDC) and the 6.3VDC heater voltage and they are green. I'll be building the boards soon. The power supply is adjustable and should work for the 2 voltages I need for the preamp for left AND right. The big old toroid I have is overkill but will work if I don't replace it with a smaller version. THEY, are green.
 
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Got some work done on the Melos. I replaced all 26 of the gold plated RCA's, replaced a bunch of caps and transistors, installed the cables for the power supply to preamp which I reworked and installed a left and a right power supply boards. The wiring is pretty much temporary and will redo it after I get it up and running and debugged. The one ps board was running a bit warm so I built the second board to help take the load and now have it left channel, right channel kinda like the original ps. I got a couple plated through holes which need some attention (on preamp board). They have TO-220 transistors stuffed into where the board was made for TO-92's so I will probably drill and reset the pth's as I see a couple are questionable.

The first pic is how the interconnects between the power supply and the pre units should look. Each cable has 4 pins (6.3VDC + and Gnd and High Voltage + and Gnd). They are interchangeable so any bonehead can hook or unhook them.


Melos PS Pre interconA.jpeg
 
This pic is the prelim setup of the power supply. After debugging the preamp box, I'll clean up the wiring and do some noise testing. No AC leaves the ps so we'll see how quiet the pre is. The power supply boards are set at 6.3vdc, and 200vdc for the High Voltage.


Melos PS Pre intercon.jpeg
 
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