TX wiring I.D Help

colin.hepburn · Post by **colin.hepburn** » Fri Oct 26, 2007 8:49 pm

Hi All
OK require some help with a TX stripped out from a Marshall 100Watt lead Amp TX made by drake transformers model DET 4145D assumed spec 350volts @295mA
Can’t find a wiring diagram for it but found one for the replacement model MTP 100
Wiring colours and continuity check out with the MPT 100 apart from two wires green wire on prim side no reading and no green wire on heater centre tap on the sec side I'm not sure which colour is for the 240v mains as the TX was connected via a voltage selector
I have checked
Intended use for EL34 Or 2A3 SE Amp
DMM on 200 ohm range
Mains
Orange comm. /violet 240v@ 05.4 ohms
Blue 220v@ 04.48
Red 120v@ 01.7
Green no reading
Secondary HT
Gray plus yellow CT 07.2 ohms
Blue plus CT 06.9
Gray /Blue 13.5 ohms
Heater Black/Black 00.6 ohms
Bias Green/White 38.1 ohms
Hope someone can help work it out
Thanks

Post by **Nick** » Fri Oct 26, 2007 10:38 pm

I would get a 6v tx, and feed the 6v into what you think is the 0-240 tap.

Then measure the AC voltage on all the other windings to make sure it all apears sane.

colin.hepburn · Post by **colin.hepburn** » Fri Oct 26, 2007 11:04 pm

Hi Nick
Ok then if I connect up low voltage TX to this and try all the primaries in turn checking the secondary for the highest voltage should be the 240 primary
I think I only have one of those wall supply for 6v can I use this

Post by **Nick** » Sat Oct 27, 2007 9:33 am

Possibly, it depends on exactly what you mean.

What is it you don't know? it wasn't clear from your first post.

Do you know which are the primay and secondary wires?

Post by **Nick** » Sat Oct 27, 2007 9:35 am

Ok, I just read it again. Put the meter on the secondary HT. Then the pair of primary wires that produce the lowest secondary voltage will be the 240 pair.

colin.hepburn · Post by **colin.hepburn** » Sat Oct 27, 2007 3:36 pm

Hi Nick
Sorry for the confusion in my first post as to the 6volt wall supply forgetting that it’s a 6v DC supply so the only other TX I have is a 240 volt 22-0-22volt assuming this
Will be ok if I connect one side of the 22-0 and checking the secondary on the Marshall TX for lowest voltage reading

Post by **Nick** » Sat Oct 27, 2007 5:13 pm

Yes, connect the 22v on the primary such the the HV secondary gives the lowest voltage.

colin.hepburn · Post by **colin.hepburn** » Sat Oct 27, 2007 7:38 pm

1. Ok Test done with 22v TX lowest Volts 16.5v so orange/violet is 240v Mains
Voltage test done with 240v mains connected
Secondary 184V X2 368Volts
Heater 6.5volts
Bias 103volts
Can you work out the TX VA and mA ratings from the above; thanks the TX is from a JMC mkII Marshall 100watt lead running three ECC83/four EL34s the copy TX is @ 290 mA

PS. I also have the Choke T100, 1471-263 but don’t know what the Henrys are it is ether 3H or 5H is there away of testing this

colin.hepburn · Post by **colin.hepburn** » Sun Oct 28, 2007 4:22 pm

I have found out on a guitar BB that the choke I have is a Drakes 3H, 100ma, 100ohms would adding in this choke be of any benefit to a psu that already has a 30H giving
a CLCRCLCRC adding the 3H before the last cap just not sure if you can add a small choke after a larger one
Also can anyone say what the VA rating of the TX is on the above post?
Thanks

Post by **Nick** » Sun Oct 28, 2007 6:05 pm

I don't think there is enough information to guess the rating of the secondary turms. I dont know if you could make any assumptions if you could see what load pulled the oltage down 5%, I assume the bias supply is a very low power winding though.

colin.hepburn · Post by **colin.hepburn** » Sun Oct 28, 2007 6:28 pm

i have found the original schematic for it but no other info
it is a hefty TX as a comparison i have a 270-0-270 TX which is 200VA @200mA so the Marshall one must be bigger but by how much i don't now

colin.hepburn · Post by **colin.hepburn** » Wed Oct 31, 2007 2:45 am

Hi All
OK may require a .little help here
Trying to workout the VA rating of this Marshall amp TX OK so I have 186-0-186 @290ma so to get the VA its
186*0.29/53.94*186/0.6=167VA? Am I close? or should i go to the corner of the room

Again I may have got it wrong I got this info from a how to convert VA-Watts.
http://www.powerstream.com/VA-Watts.htm

Post by **Nick** » Wed Oct 31, 2007 7:56 am

I would have expected a much larger power factor than 60%, Paul may know.

For a simple guess, I would just use VA, so thats (I guess) about 100va for the secondary. But you also need to add the other windings in the same way.

Out of interest, if you know what current the secondarys deliver, why do you need its VA rating?

colin.hepburn · Post by **colin.hepburn** » Wed Oct 31, 2007 8:27 am

Hi Nick
I guess its from sold state stuff I have built where its recommend that you use a higher VA rating than the circuit requires up to a limit so was under the impression that the bigger the better I have seen some txs that lets say have 150/250 mA but not man enough to run a some valve amp so I figured I would require something like 200VA to run a valve amp so as not to over heat the TX

Post by **Nick** » Wed Oct 31, 2007 1:15 pm

Well a bigget TX will always be under stressed, but it will also be over voltage, so it works both ways.

I guess its more of an issue with SS stuff as the low voltage high current will lead to huge charging peeds in the power supply.

audio-talk

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