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Breaking in a Re-Tubed Sensitive Old Head

Siegler

New member
Joined
Jul 21, 2001
Messages
956
This is an amp I have been asking about here, an old JTM45 that's just serviced, re-tubed and running on 110volts off a variac -- it blew a filter cap the first day I had it when I unknowingly gave it 125v.

That day, I plugged into the upper left input with the lower left input bridged to the upper right and very gradually increased the amount I was driving it 'till, in the last 30 minutes before it blew, I got to bright volume 7.5 normal at 3, guitar volume at 10 (the guitar has '60s humbuckers).

Since getting it serviced, the most I've played it was yesterday where I had it on for four hours straight, bright channel at 5, guitar volume at 4.5 and playing half the time. Today, I'd like to put it on 7.5 with the guitar rolled off to 4.5 and play four hours again. Then, after the neighbors split, turn the guitar up to 10 for a couple hours.

Any thoughts about breaking in a head that makes you nervous?
 

NewOldCokeDave

Active member
Joined
Jul 16, 2001
Messages
4,945
No I think you're fine.. The only thing that really needs to be "broken" in would possibly be the caps, but they should be well formed by now, so I wouldn't worry about it.. But with any old piece of equipment, I'd just be a little extra careful, as 1) it's old 2) it's VERY expensive to replace if it burst into flames and 3) you'd probably not want to run a JTM 45 fully dimed all the time anyway..

SO those would be just general precautions when using old eqipment at any given time.. Did you get you grounding issue sorted out??

-NOCD
 

Siegler

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Joined
Jul 21, 2001
Messages
956
Taken out of context, your comment "you'd probably not want to run a JTM 45 fully dimed all the time anyway" could be heard to mean the amp can't take it. However, as you said you think I'll be fine, I guess you mean because it would just be very loud.

What I like to do is find a setting where I can use my volume control on the guitar (along with the 680pf cap) to go from Jazz" (neck at 4.5 volume, 2.0 tone) thorugh country twangy (volume 6) through normal crunch (volume 7.5) to lead at 10. In the case of my Fender Super, I put the volume at 6.75 for this. This Marshall seems to do it at 7.5. So, I want to put the Marshall on 7.5 and play through it all day (I play my Fender all day and never think about it).

Also, is there any extra burden placed on the amp by plugging into the upper left input and using a second cable from lower left to upper right; the blending this amp affords this way is incredibly intuitive and useful: I usually find what I want in no time at all.

And thanks a lot Dave. Also, no, I didn't here from Ted about the grounding/polarity thing -- he probably thought the stream was over.
 

NewOldCokeDave

Active member
Joined
Jul 16, 2001
Messages
4,945
I can see what you mean about context.. No I didn't mean the amp couldn't take it, but like, say, an older car, you'd probably want to keep an eye on it for signs of stress when run at extremes. Nothing you've described so far would be a sign of stress to me, and I can appreciate your attention to detail. Hey, you've probably got a sizeable investment here and they're not just down around the corner at your local guitar shop. (If they *ARE* I want to know where you live!! :) ) You siad you're running it at 7.5, that's not dimed. I'm talking 10 across the board. 1) I don't think that sounds too good, and 2) Yeah it'll be a little loud, and 3) if it's gonna fail, it'll probably fail in this scenario as you are running full bore maximum.

What I mean by all of this is insulation on wires breaks down over the years, components and parts dry up and get brittle, metal gets fatigued, etc.. So in that vein, yeah it'll probably go like a bat out of hell, but just keep an eye out for anything that may appear to get "funny".

Also try it with a straight Y cord too.. into both HI inputs.. I like that better.. IMHO

-NOCD
 

Siegler

New member
Joined
Jul 21, 2001
Messages
956
Just a short "thank you" for now as I am going ahead with normal operation (amp on 7.5) for a couple of days before I turn it up to 10 (vol 10, pres 5, bass 4 mid 7 and treble 7) for a couple of hours and really crank the guitar through it. Again, "thanks" for now and we'll see what happens!
 
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