Output transformer knowledge sought...

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by mojowrkn, Jan 5, 2006.


  1. mojowrkn

    mojowrkn Member

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    I posted this over at the Webervst Transformer board but not sure it gets near the traffic as here...

    OK, bear with me...

    I recently replaced all the electrolytics on my '65 GA15-RVT Explorer. It seemed to be working fine for a while, then cut out on me (after making a hissing sound), and I smelt (smelled?) a burning smell. I powered her down.

    Later, I thought I would investigate more and tried it again (ill-advised I know). It did the same. Worked for a while then cut out.

    After poking around I noticed that there was melted epoxy (small amount) dripping out of the OT. I know it's recent because I had also replaced the speaker and it dripped on the new speaker frame.

    These amps, I have learned, have a notoriously small output transformer and I think the after effects of the new caps (all original specs) have pushed the OT too far, or it was already damaged from a bad filter cap. (one was leaking/bulging). I suspect the heating up of the OT is melting the old epoxy after it runs a while.

    I guess my questions are (1) any troubleshooting advice? and (2) what recomendations for a replacement OT?

    I have a couple of places I have located to get a used Pro Jr, or Blues JR OT (cheap), and I have also considered a Hammond, or Weber (middle of the road price). And, am also curious about one of the newer OT's designed for the 18 watt crowd. Can anyone recomend one of these, and if so what are the pluses and minuses of each?

    Thanks a lot guys. I am pretty green at the repair side of all of this, but I am also the type that will study for a long time before taking action. Thats why I am looking for input. Thanks!
     
  2. Wakarusa

    Wakarusa Member

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    OT as glue gun is usually a pretty bad sign :)

    I'd be wary of some other failure in the amplifier... i.e. was it the bad filter cap event that sent the OT under (or old age, or kismet), or is something else broken that will smoke your brand new OT when installed. A visit to the local tech for a thorough checkup may, in the long run, save you trouble and $$
     
  3. Shea

    Shea Member

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    Heyboer's 18-watt OT is great. You might have to get one through GDS amps.

    I liked the Hammond 1608 in 18-watt style amps, but it's probably a lot bigger than what you had in there, and it's a very clean and transparent transformer at 15 watts compared to your other choices. That's fine if the amp's tubes give you all the warmth and crunch you want, but a lot of people prefer a transformer that will add a little bit of its own distortion and tonal coloration.

    How well does that amp break up? I've never tried one with an interstage transformer.

    Shea
     
  4. twangbanger

    twangbanger Supporting Member

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    I'd agree with Wakerusa something else might have at least contributed to the smoking of the ot. That being said I would recommend the heyboer 18 watt trans. Graydon over at GDS is a good person to do business with, You might want to ask this question over at the 18 watt.com sight.
    Rob
     
  5. mojowrkn

    mojowrkn Member

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    Thanks guys,

    I appreciate the replys. I think I will try the Pro Jr first and see what happens. Before I started "fixing" this thing it sounded pretty anemic and thin, except when you dimed it, and then it sounded great and had this really cool sag/compression. Now it has more balls and low end across the volume, but has less break up and compression. Or so it seemed the little I tried it. Anyways, my thinking is that the smaller OT of the Jr might help keep it in the same ball park.

    I'll let you know how it goes.
     

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