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-   -   Over-Spec'd PT as replacement. (http://www.diyaudio.com/forums/tubes-valves/207776-over-specd-pt-replacement.html)

MellowTone 29th February 2012 12:31 AM

Over-Spec'd PT as replacement.
 
A friend of mine has a Line 6 Spider Mk II tube head, which is USA-spec. Using this in Australia requires a stepdown transformer. He would like to be able to use this straight off the mains without need for lugging around a stepdown.
I have confirmed the transformer is NOT universal primary (supports 115/120V operation, but not 230/240V)
He'd be looking at around AUD$220 for replacement Line 6 tranny at 240V, which is higher than he wanted to pay. I happen to be doing an order of transformers soon (probably from Edcor) and thought I might get a custom replacement for the PT in his Line 6. Line 6 have declined to divulge
Secondaries required are 6.3V (heaters) 9.8V (on board solid state effects) 60V (bias) and 340V (B+)
Which brings me to my question. Looking over the amp, I can estimate what current required on each tap, and I was planning to simply take my estimate, then add something in the order of 30-50% as a buffer to ensure it has enough current.
To my knowledge, this should not have a detrimental effect on the amp (having the correct voltages but at higher than required amperages) - can anyone confirm?

leadbelly 29th February 2012 03:46 AM

Quote:

Originally Posted by MellowTone (Post 2927174)
To my knowledge, this should not have a detrimental effect on the amp (having the correct voltages but at higher than required amperages) - can anyone confirm?

It can if you overdo it. Google "transformer regulation curve" to understand why. If you don't overrate too much you should be fine.

EDIT: if it were me I would probably try to fit a 240:120 autoformer inside. Reversible, cheap, lower risk. Of course you have to find one sized correctly first.

MellowTone 8th March 2012 11:16 PM

Quote:

Originally Posted by leadbelly (Post 2927339)
It can if you overdo it. Google "transformer regulation curve" to understand why. If you don't overrate too much you should be fine.

EDIT: if it were me I would probably try to fit a 240:120 autoformer inside. Reversible, cheap, lower risk. Of course you have to find one sized correctly first.

Interesting read.
Yes, we're currently trying to decide which option is best.

Although it did just occur to me that I do have access to the amp, so I'll connect up a dummy load, crank it and check how much current it's pulling on each winding.

Why I did not think of this before, I do not know.....

counter culture 9th March 2012 01:46 AM

Tube instrument (guitar) amplifiers get their tone (partly) from having mildly underspec PTs.

Look for the Hartley Peavey Whitepapers on the Peavey site under support/technotes. I think 'Transtube' is the relevant one.


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