Melos MA-222 Tube Preamp info needed

[WOPL Sniffer]

Looks pretty basic Perry.

Now if I can figure out the voltages which are fed to the pre-amp box. Plus not knowing the output of the transformers makes it difficult. I suppose I could hook the transformer(s) up to 120vac and see what the pairs of windings are putting out. Without a load on the system it may not give me the info I need.

I know that we can use 6.3AC/or DC for the filament/heater

B+ can be +130VDC for the 6GK5 Phono tube
B+ can be +250VDC for the 6922 Triode tube

I think I saw a PS that is adjustable from 100VDC to 300VDC and 6.3 outputs so it might be doable.

HUH?????

 

[WOPL Sniffer]

I guess I should just pull the PS board and make my own skizmo.....

I have a couple (2 on each side) unmarked Zener Diodes that I'll have to figure out what the hell they are. They are in the regulator circuit and marked

Motorola SZP 401 82 8240 which MAY be a part Melos had custom marked (???). They are in the TL783 regulator circuit (for short protection) and can they be deleted??? OR???

 

[Gepetto]

I guess I should just pull the PS board and make my own skizmo.....

I have a couple (2 on each side) unmarked Zener Diodes that I'll have to figure out what the hell they are. They are in the regulator circuit and marked

Motorola SZP 401 82 8240 which MAY be a part Melos had custom marked (???). They are in the TL783 regulator circuit (for short protection) and can they be deleted??? OR???

No way custom made Perry

 

[WOPL Sniffer]

No way custom made Perry

Not custom made, maybe custom marked??? I found zero info on a part number like that and this is from the 90's so it aint that old.

 

[Gepetto]

Not custom made, maybe custom marked??? I found zero info on a part number like that and this is from the 90's so it aint that old.

More likely they picked up some surplus from Fry's electronics and used them by the looks of that assembly.

 

[WOPL Sniffer]

More likely they picked up some surplus from Fry's electronics and used them by the looks of that assembly.

I wouldn't doubt that. Any way to ID them if I have the one side of the PS up and running or by seeing how they had it in the circuit with the resistor?

 

[Gepetto]

I wouldn't doubt that. Any way to ID them if I have the one side of the PS up and running or by seeing how they had it in the circuit with the resistor?

Apply voltage through that series resistor and see where they zener out...

 

[Gepetto]

I assume that is the zener you are referring to...

 

[WOPL Sniffer]

Apply voltage through that series resistor and see where they zener out...

I can do that.

 

[WOPL Sniffer]

Apply voltage through that series resistor and see where they zener out...

View attachment 79383

Yep, that will work. I'll use my little 12VDC Power Supply on it. If I need more power, I'll crack out the big guy. I want to try making 2 separate boards.

 

[WOPL Sniffer]

I assume that is the zener you are referring to...

Yeah, there are 4 of them.

 

[WOPL Sniffer]

Thanks Joe, nice to get fresh eyes on it.

 

[Gepetto]

Thanks Joe, nice to get fresh eyes on it.

I can see a lot of the traces through the board in your photo.

 

[WOPL Sniffer]

I can see a lot of the traces through the board in your photo.

Yup, my BIG 1 piece board is to charred to see through.

 

[J!m]

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

 

[WOPL Sniffer]

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

They are coated and wrapped, painted with something.

 

[WOPL Sniffer]

I just about finished with the reverse eng of the board.

 

[J!m]

Okay, this is just the power supply. I was having trouble locating the tube sockets…

 

[Gepetto]

They are coated and wrapped, painted with something.


View attachment 79398

But they are green so that is a plus...

 

[WOPL Sniffer]

I'm going through 800 pages of Motorola diodes

It says:
SZP
401
82
8240

It appears to be a zener but I aint finding shit