Help measure output transformer..

  • Hi guys!
    Thanks for the help perviously.. I've soldered the my MadAmp A15 MKII Deluxe complete today, and all measurments so far has been good - except the Primary side of output transformer.

    The secondary side (4, 8, 16)ohm is OK, i just measure the pins against the 0 at the transformer, and its all ok.
    BUT.. I cant seem to find out how to measure the primary side.. ?
    Which pins to measure, and against what? The manual says that the primary side should be 500ohm.
    I tried measure pin 6/7 against 0-ohm and it gives me resistance-bumb.. It runs up and down from 0 to 8-9Mohm and then settle at around 65kohm.

    Help please! This is the last thing left before I can plug the tubes and try the amplifier.

  • Thank you for replay. Here are some pictures:

    [Blockierte Grafik: http://img593.imageshack.us/img593/281/trafomadamp2.jpg]

    [Blockierte Grafik: http://img32.imageshack.us/img32/3717/trafomadamp.jpg]


    At lug 6/7 I managed to break the thin wire from transformer, then I soldered it back to the lugs.. It sits very well, but maybe there is still no contact? It seems like its hard to get contact with this thin wire, it was hard to solder it.

    I think its this one:
    http://www.musikding.de/product_info.p…-Push-Pull.html

  • Hi,
    the wire is coated with lacquer, so soldering is easier when you remove it before (e.g. scratching it cautiously with a knife). When you measure the resistance of the primary windings, you have to measure between pin 6/7 and pin 12 or 13 (the other blue wires). What is the resistance you measure?
    Regards,
    Martin

  • Zitat von MAD;324158

    Hi,
    the wire is coated with lacquer, so soldering is easier when you remove it before (e.g. scratching it cautiously with a knife). When you measure the resistance of the primary windings, you have to measure between pin 6/7 and pin 12 or 13 (the other blue wires). What is the resistance you measure?
    Regards,
    Martin

    Pin 6/7 against 0ohm: up and down, but it settle at around 60-70k ohm.
    Pin 12 or 13 against 0 ohm: No connection.. :confused:

  • Ah, i misunderstood!
    I tried it now, and both results give me no connection.

    I will try to resolder the broken lug, remove some of the cout with a knife or something and then measure again :)

  • Sorry for bumping old topic.
    I just want to update you guys:
    - I bought a new output transformer from Klaus and it solved my problem.
    All measurments are ok now.

    So far i had two problems:
    - Somehow the rectifier was broken, so I put a diode-rectifier instead:
    ^Problem solved

    - Bad measurements of the output trafo, i buy new trafo
    ^Problem solved


    So now the rectifier voltage is 309V, its supposed to be 355. And Supply voltage is also a little low.
    BUT. I tried the amp yesterday, adjusted bias and played it
    It works!! And it sounds REALLY great. I have a Marshall JVM at home, but the Madamp suit me better for home use.

    Thank you again for help and designing great amps. The A15MKII sounds much much better than i thought it will be!! Good job :)

  • Hi,

    I'll resume this old topic.


    Assembling my A15Mk2, I've just finished the primary and secondary connections on the output transformer. But when I measure the primary side I don't get 500 Ohm, as said in the manual, but only about 263 Ohm measuring between 6/7 and 13 pin, between 6/7 and 12 pin I don't get any measure. I checked all the wires and soldering and it's ok. Secondary sides measure are ok. Could it be a bad transformer ?

  • Hi,

    according to Klaus it was a bad transformer and he sent me another one. But I noticed that the pre-assembled wire which arrives to pin 10 is disconnected. It was the same on the other one. Could someone please tell me if it has to be soldered to pin 10, behind at the bottom or I just have to leave it as it is? Soldering that wire is very difficult because it's very thin copper and I don't want to make damages. I attach a picture to let you see it

  • Hi Bernd,

    thank you for your answer. Yes it's the ATRA0427. I managed to solder that wire to pin 10, intuitively as the opposite to pin 9, they are internally connected to primary side as I can see in the schematic. In fact I didn't have any connection between pin 6/7 and 12, only between pin 6/7 and 13. Now that I soldered that wire I have continuity in all primary side: about 263 Ohm between pins 6/7 and 12 or 13 and about 523 Ohm between pins 12 and 13, I think it's ok right? I didn't mean to connect pin 9 and 10 together.

    On the old OT I had the same problem, I soldered that wire to pin 10 ma nothing changed so I contacted Klaus, maybe internally something was wrong. I assure you I didn't touch those pre-assembled wire on both the OTs, they are extremely delicate and disconnect easily, even with the lacquer treatment.

    Anyway, thank you again for your interest

    Best regards

    Carmine

  • Hi,

    for your understanding: Pin 10 is a tap for a grid-2-Connection in UL (ultra linear) mode normally used only in hifi amps.
    That means the primary winding has a tap at a certain location so the lug has two wires - one comes out, the other returns to the winding.
    If one of these wires is not connected to the lug, the primary winding is interrupted and therefore useless.

    About the "engineering level" of the ATRA0427 I've already wrote enough...

    Regards
    Bernd

    Jaichweiß (Andy Pipkin)

  • Ok Bernd thank you for the explanation. Now I would like to know if the resistance measures I told you are correct considering the "engineering level" of this OT.

    Please let me know.

    Thank you

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