Melos MA-222 Tube Preamp info needed

WOPL Sniffer

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#42
If there is a maker name and part number on the transformers you might find it’s designed specs…
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..).
 

WOPL Sniffer

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#43
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???
 

WOPL Sniffer

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#48
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.
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).
 

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#49
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..).
Well there goes the green Perry...
 

WOPL Sniffer

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#50
Well there goes the green Perry...
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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WOPL Sniffer

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#51
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
 
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