Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: newtube on October 08, 2012, 09:02:17 am
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Hello,
I have a Marshall MA100H that needs a new OP transformer, but am unable to find any technical info on it. Emailed Marshall but no help. Since it uses 4 el34 tubes, can I use an OP transformer from a JCM800?
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U.S. Music does Marshall distribution and support in the States. Try contacting them. 800-877-6863. They may or may not sell direct to consumers. If not, you'll have to get a dealer involved. Otherwise, any Marshall-style 100W replacement transformer should work and will most-likely be an upgrade. Pick the style that involves the least chassis modification.
Are you 100% sure that the output transformer is the problem?
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Thanks for the reply , Series. I think I'll just go the upgrade route. The transformer isn't bad it's just missing completely, some Einstein swiped it while the chassis was on my bench....go figure.
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What tubes?
Dont know where Doug sources his, but I have used them and the work well.
http://www.hoffmanamps.com/MyStore/perlshop.cgi?ACTION=enter&template&thispage=Transformers&ORDER_ID= (http://www.hoffmanamps.com/MyStore/perlshop.cgi?ACTION=enter&template&thispage=Transformers&ORDER_ID=)!ORDERID!
I have used Heybour as well. Little more cost, but fine product. Then there is always Mercury Magnetics for those who can hear better than me.
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Then there is always Mercury Magnetics for those who can hear better than me.
I scored a brand new EL34 Axiom Mercury OT a while back for $80. My thinking was that for the price how could I go wrong? I just hope it sounds as good or perhaps even better than Magnetic Components' or Heybours do? I've been wondering if anyone has heard the Mercury Mags OTs and can report on them?
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Then there is always Mercury Magnetics for those who can hear better than me.
I scored a brand new EL34 Axiom Mercury OT a while back for $80. My thinking was that for the price how could I go wrong? I just hope it sounds as good or perhaps even better than Magnetic Components' or Heybours do? I've been wondering if anyone has heard the Mercury Mags OTs and can report on them?
Oh yes, I have use many on repairs and upgrades for folks. I have a Fargen ole 800 and all he uses is MM. The folks at Heybour have attempted to duplicate the Drake and have done a good job. That is the same one George sells at metro. I have a couple of amps I use MM in. My latest Princeton, and a JTM45 build and a Supro Build. I like them very much, but I have never paid full price either.
Will tell you this. I had a 5 year old one go bad and they did not hesitate to send me a brand new one. If you got it for $80, it is a fine deal. I was just joking about the hearing better than me. All in all I think we spend a lot of time concerned with parts when changing speakers makes the biggest change of all. A decent build with great speakers beats a great build with poor speakers and of course the cabinet.
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Ed,
The amp in question uses four el34 power tubes, I guess that's why I thought the JCM800 trans would work for this.
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All in all I think we spend a lot of time concerned with parts when changing speakers makes the biggest change of all. A decent build with great speakers beats a great build with poor speakers and of course the cabinet.
How True Ed. I have oversized trannies in my Super Tweed Amp so that I can swap out the 6V6s for 5881s. I then switch the speaker from a Red Fang to a Heritage G12H-30 when I do this and together they transform the amp. Just played a festival last weekend doing this, and it's like having two completely different amps in one. My bandmate has a real '65 BFDR and this more than competes with it. Our singer just smiled and said how great it sounded right in the middle of the set. It pumped me up, I turned it up just a tad more, and had a great time. I don't know if in the mixing I got turned down but she was roaring pretty well right behind me. :grin:
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Ed,
The amp in question uses four el34 power tubes, I guess that's why I thought the JCM800 trans would work for this.
There are others here with much more knowledge than me, but a JCM800, 2203, 100 watt OT should be fine. It gets down to your pocketbook as well as preference. The JCM800 is a fine sounding amp IMO the OT from one will work well with EL34's.
Doug sells one for $90. Last one I got from Heybour was $145 and is great sounding as well. Both people who own them are very happy. I cannot say which one is really better if there is such a thing between because as far as I know Doug may get his from Heybour. Doug does clearly state he has a no return policy on transformers so if that is important to you he say do not buy it.
Truthfully, I have tried many OT using EL34's trying to get "that" sound. I just put some Altec Lansings in a 2 12's fender bassman cab and I have sort of gotten surprised about how much I worry about getting just the right part.
3.4k ohms is what the Mullard datasheet suggests in PP AB class. I have found I like this best as well. I tried 5.9k and 5.0k ohm and the Marshall mid was missing a little of that tone that just hits you in the chest.
Take it for what it is worth, I just an old hack anyway.
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All in all I think we spend a lot of time concerned with parts when changing speakers makes the biggest change of all. A decent build with great speakers beats a great build with poor speakers and of course the cabinet.
How True Ed. I have oversized trannies in my Super Tweed Amp so that I can swap out the 6V6s for 5881s. I then switch the speaker from a Red Fang to a Heritage G12H-30 when I do this and together they transform the amp. Just played a festival last weekend doing this, and it's like having two completely different amps in one. My bandmate has a real '65 BFDR and this more than competes with it. Our singer just smiled and said how great it sounded right in the middle of the set. It pumped me up, I turned it up just a tad more, and had a great time. I don't know if in the mixing I got turned down but she was roaring pretty well right behind me. :grin:
That is the greatest fun there is. You know you cannot trust the sound guy.
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3.4k ohms is what the Mullard datasheet suggests in PP AB class.
One thing about MM is that they don't always give you the tranny specs. So I called Patrick and 3k4 is exactly what he said that tranny is. But, he also said "you need to give the EL34s btwn 440v & 475v to get those tubes to crunch properly".
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Outstanding on the voltage! Before the trans got swiped I had the el34's at 469 volts and for a Vietnamese made amp I thought it sounded pretty good! Thanks for all the info everybody!