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Marshall JTM45/100 questions


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11/13/2005 1:48 PM
Ace Pepper
Marshall JTM45/100 questions
Hi,  
I've had someone ask me about building a Marshall JTM45/100 after seeing the new HW version from Marshall. I know these are based on the original 100 watt Marshalls where they used two 45w OTs. How do you connect two 45w OTs to act as one 100w OT? How does this affect impedence, both primary and secondary? How does two OTs affect tone?  
Thanx!  
Ace!8-)>
 
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11/14/2005 11:44 AM
SpeedRacer

Never looked at this, but wouldn't you just run them in parallel? That would seem to be the logical solution. The 50W OT has twice the primary imp you'd want to see (and half the current handling!), so you'd want to halve it (pointing to parallel operation). You could treat it like 2 50W output sections but then you'd always need to run 2 cabinets (or blow half of your output stage..) Ouch. I'd rather treat it as one big thing. Just parallel the primary and secondaries and go for it. I'm sure if I am guessing wrong someone will let me know. ;)  
 
Tone is dependent on so many other things that I am not even sure how you could accurately test for this. Since physical size matters in an OT, 2 trannies of equiv performance can have very different interleaves, wire sizes, etc. They almost have to sound different.. "how" they sound different is the million $ Question though. Bigger OT's as a general rule have a leg up on smaller OT's. If you use that as a base, you could argue that all else equal the amp with 2 smaller OT's could have more compression/less headroom, poorer HF response, etc. But that would be making a lot of assumptions that can't really be made, so we're back to square one. ;)
 
11/14/2005 12:10 PM
Ace Pepper

Hi,  
Could one wire the primaries individually, like 2 50w OTs w/each OT primary being fed by a pair of tubes, then tie the secondarys together/parallel? Would that make 2 8ohm secondarys come out to 4ohms?  
 
As a side note:  
SpeedRacer, do you have any of those nifty 50w Plexi OTs in stock? I've got a guy/project who needs one!(different job, actual 50w amp;) Please shoot me a note how to order.  
Thanx!  
Ace!8-)>
 
11/14/2005 1:43 PM
Ian Anderson

There has been some clones of this amp made by people over at Plexi Palace, you could do worse than ask over there.  
 
Actually, (come to think of it) there are definately guys on that board who own originals of that amp so head over there.  
 
... Ian :)
 
11/16/2005 4:27 PM
jaysg
I asked Richie Hall about these. He recalled that they're wired separately on both sides - one output to the A cab and one to the B cab, so you couldn't run with just one cabinet unless you attached a load to the other out.  
 
It seems to me that you should be able to parallel everything up. Dunno.
 
11/18/2005 11:42 AM
Ace Pepper

Hi,  
Thanx for the replies! Cool stuff. Someone @ Plexi Palace pointed me at a Silvertone schem that used 2 OTs. The outs/secondarys were each wired to it's own speaker out/load. It does seem that one should be able to paralell everything.  
Thanx again!  
Ace!8-)>
 
11/18/2005 3:09 PM
jaysg
quote:
"It does seem that one should be able to parallel everything."
I've been thinking about this a bit more. If you try, be very careful and monitor everything you can.
 

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