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Old 25th March 2013, 06:32 PM   #1
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Default Welding on an output transformer

I bought a used and abused broken Peavey Tour VB-2, which uses 6 EL34's to make 225 watts. Or would, if it worked.

It looks like the output transformer broke loose, and flew around and broke tubes etc.

So somebody welded it back on its mounting plate (while uninstalled). Which sounded crazy to me until I found out that Peavey also welds them to the same plate.

The funky output transformer it the only thing that 'looks' wrong, except the middle keyed phenolic pin is broken out of most of the EL34's (which really shouldn't matter).
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Old 25th March 2013, 06:37 PM   #2
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I would have thought they used a laminate core not just for assembly but to prevent eddy currents in the core. Wouldn't welding across the core in multiple places be a bad thing? I'd imagine there's also a big risk of cooking off the insulation, or even melting some copper windings! Or inducing enough current to blow thin wires?

I can't imagine why someone would decide to weld a transformer core instead of just
putting a plate across the top and 4 long bolts.
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Old 25th March 2013, 07:46 PM   #3
Enzo is offline Enzo  United States
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But it doesn't shunt the core. Peavey has welded on mounting plates for many years, no problems have come from it.
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Old 25th March 2013, 09:13 PM   #4
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Peavey has extensive experience. Yet their weld didn't hold, their weld broke, and the transformer went flying, wreaking havoc. And now I have very very low confidence in the unauthorized repair welds. Unfortunately, really thorough testing of an output transformer is very difficult. I still can't see the sense of welding it, when better mounting methods seem simple. Then again, I'm prejudiced by looking right at a catastrophic failure.
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Old 25th March 2013, 09:29 PM   #5
sreten is offline sreten  United Kingdom
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Hi, So do some drilling and add nuts, bolts and washers, rgds, sreten.
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Old 25th March 2013, 09:56 PM   #6
Enzo is offline Enzo  United States
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THAT weld broke. Tens of thousands of their amps did not break the weld. There is a limit to the abuse something can take before it breaks, even a well made something. There is nothing you can make that someone else cannot destroy.

That is a big heavy piece of iron. Bolt it down, and someone can drop the amp, and the momentum of that iron can pull the bolt nuts right through the chassis metal. But whatever horor story we can come up with, 99.99% of them will never face it.

The welded plate is reliable and sturdy - even if one broke. Bolts and clamps are reliable and sturdy too. They will work fine instead of welding. There is no need to try to reweld it unless you are a professional welder.

Not all failures are systematic or due to a design flaw.


In my 27 years running a Peavey service center, I have had one broken weld plate. I contacted my inside guy at the factory and told him I didn;t feel it should have come apart, as ther was no sign of abuse on the cab. He agreed and sent me a replacement transformer. The amp was long out of warranty, but they covered it anyway.
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Old 25th March 2013, 09:56 PM   #7
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Welding a transformer core without TIG and some application specific experience is bound to come out messy. Besides, welding it a second time would usually occur after a varnish dip which would make a clean, strong weld impossible. I'd mount it mechanically if I could.. Or replace as suggested is probably better if the original mounting is still possible.

Last edited by Andrew Eckhardt; 25th March 2013 at 10:08 PM.
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Old 25th March 2013, 10:45 PM   #8
JMFahey is offline JMFahey  Argentina
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Agree.
The original Peavey welding looks TIG made by some automated machine, looks *very* clean and smooth, doubt a human could easily do it that way.
Well, maybe he could if he had to weld 1000 transformers a day and had some device to guide the torch.
I've tried to rewind such transformers and gave up, could not pull them apart in a clean way, so I chose to wind a new one on a fresh conventional core.
And mounted conventionally with L brackets and bolts.
By the way, I also contact cement the core to the chassis if possible, helps a lot against vibration.
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Old 28th March 2013, 03:20 AM   #9
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I'm really reluctant to use the output transformer that's been re-welded by some shop that was too incompetent to finish the repair, yet the real Peavey part is expensive.

What's the load impedance an EL34 likes to push, as opposed to what a KT88 likes to work out into? I have a brand new output transformer meant for a 400 watt Trace Elliot V6 with 6 KT88s, instead of this 225-watt Peavey's 6 EL34's. Mechanically there's mounting issues again, but electronically would it be likely to work?
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Old 28th March 2013, 07:23 PM   #10
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At the least, welding across the core laminations makes it nearly impossible to rewind.

The 400-watt transformer from the Trace Elliot V6 isn't much bigger, but the core is thicker with more laminations. I figure that's a good thing for bass.
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