Transformer failure - common?

Squidward

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How common is it for transformers in a tube rig to fail, and what are the most likely causes? Is it the same in vintage gear as modern? Should I worry about the output transformers in an amp if they are say, vintage Dynaco, due to age or other factors? How about the power tranny? That always seemed to be the most logical place for something bad to happen, in my little brain: It gets real hot, and that's scary!

Comments, experiences, etc. appreciated.
 
Not very common at all I rebuild amps every day and I believe I have maybe 6 bad transformers here. It just doesn't happen often at all.

Craig
 
Squid,

The only caveat I have is if the transformers in question are being transplanted from one amp to another. If left alone in the amp they came in, as Craig mentioned they will by all accounts be just fine. :thmbsp:

BUT, if they're being transplanted for a DIY project-be careful! On a lot of vintage transformers the insulation on leads has seen a lot of heat over the years, and insulation from 40+ years ago isn't what it is today. Bending, twisting, re-routing dried and cracked insulation into a new chassis can very easily lead to breaks near the core-breaks that can lead to shorts, destroying the transformer. If they break they *may* be fixable, but maybe not, at least not ever well enough for my peace of mind. :no:

Left alone, as Craig said, there should be no worries. If you're planning on using them for a DIY, you'd might just be better off buying new.

Best,
mojo
 
I've only seen blown transformers, in cases where other components have shorted, somewhere. Had one output transformer blow- ostensibly, because of a shorted speaker wire. Mind you, it didn't even blow immediately- but not long afterwards, even though the short was corrected.

Other than that, and the occasional "power zap" from a surge taking out a power transformer, those transformers should pretty much last nealy forever, IME...

Regards,
Gordon.
 
Insert a fuse in the primary circuit. Size it to about 1 1/4 as much current you expect the amp to draw off the line. Slo blow. So if a filter cap shorts out the fuse will protect the transformer.
 
hi,

I'ver read the advise of putting a fuse in the primary very often.
this is the fuse between (here) 230v ac to the primary of the transformer??

isn't this a 'normal' procedure or does a lot of tube equipment not use this fuse???
(because almost all other equipment does)

or am i talking about the wrong fuse?
 
Some gear is not fused and more have the fuses under the chassis where you can't see it. Since gear isn't made with reversable plugs anymore the fuse should be on the primary that is hooked to the hot side, something to pay attention to if you install IEC plugs in vintage gear.
 
Squidward said:
How common is it for transformers in a tube rig to fail, and what are the most likely causes? Is it the same in vintage gear as modern? Should I worry about the output transformers in an amp if they are say, vintage Dynaco, due to age or other factors?

Depends on how much money the original manufacturer was willing to spend to prevent the problem in the first place. Certain models of vintage gear are notorious for blowing transformers, eg: Seeburg jukeboxes and cheap Knight-Kits.

The most likely transformers to blow in Dynacos are PA774's in SCA35's and PA211's in PAS2/PAS3's. PA135's seem to blow a lot too. PA060's in ST70's blow once in a while but often they're replaced because some varieties of PA060 run alarmingly hot.

Output transformers are the least likely to fail as they aren't passing as much power in relation to their size as power transformers and therefore don't get as hot.

The biggest enemies of transformers are heat & humidity, which cause corrosion and insulation breakdown. Ie: if you live in Louisiana and play your amp outside all year long, you'll be more likely to blow a transformer than someone who lives in Arizona and plays their amp in an air conditioned (preferably not with a swamp cooler) house.
 
Welcome Uncle Ned!! Glad to see you aboard :)

Thanks again for the 12AV7's and 12BH7's the other day. You guys get the ECC99's in yet?
 
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