# 1985 JCM800 Output transformer repair ?



## Louis (Apr 26, 2008)

Hi guys ,.....I have a blown JCM800 output transformer here and would like
to have it fixed,.....anyone knows someone in Canada that could do this ?

Thanks


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## greco (Jul 15, 2007)

You might want to contact Hammond Mfg. in Guelph, ON.
If they don't offer the service, they should be able to make some suggestions.

Good Luck with repair/rebuild!


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## Budda (May 29, 2007)

Any reason not to just replace it?

A new hammond was around $130 a few years ago. I imagine a repair would easily double that due to bench rate and time.


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## Lincoln (Jun 2, 2008)

$120 at Next Gen!

Hammond 1750N


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## StevieMac (Mar 4, 2006)

If it's a question of maintaining value on the amp, I'd advise simply replacing it and hanging onto the original unit for resale down the line. In most cases, repairing a blown transformer doesn't restore value on an amp as it becomes "non-original" at that point. Just a thought...


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## nonreverb (Sep 19, 2006)

You can have it rewound by Mercury Magnetics....it will cost you a fortune though.


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## pipestone62 (Nov 14, 2013)

Louis said:


> Hi guys ,.....I have a blown JCM800 output transformer here and would like
> to have it fixed,.....anyone knows someone in Canada that could do this ?
> 
> Thanks


Just replace it, I just had one replaced on a 1985 jcm 800, L&M tech did it, works great. Wasn’t too bad of a bill either, think it was around $300.00 all in.


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## Louis (Apr 26, 2008)

Thank you guys !,.......seems that you all agree on a replacement
so I'll change my plans !

Really appreciate !


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## Latole (Aug 11, 2020)

Louis said:


> Hi guys ,.....I have a blown JCM800 output transformer here and would like
> to have it fixed,.....anyone knows someone in Canada that could do this ?
> 
> Thanks


MP send.

Louis , how do you know OT is blow ?
We need to read OT impedance to know.

Often read on many forum, member thinking they blow OT ant it was not.


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## Louis (Apr 26, 2008)

Latole said:


> MP send.
> 
> Louis , how do you know OT is blow ?
> We need to read OT impedance to know.
> ...


It is my amp tech that blew it by mistake,......he made a bad move and blew his
scope and the Output transformer but doesn't know what happened.

Thanks for the link ,...I won't go for 900's trannys though.


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## Latole (Aug 11, 2020)

Anybody can make a mystake.
He must pay for a exact replacement, not a hammond

"...but doesn't know what happened ..." 
I would wonder about the qualifications of this guy. I know a guy named Lacombe in Acton Vale, is that your guy?


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## nonreverb (Sep 19, 2006)

Latole said:


> MP send.
> 
> Louis , how do you know OT is blow ?
> We need to read OT impedance to know.
> ...


900 series won't fit. They're laydown where the 800's are stand up transformers. 900 quality isn't as good either.


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## greco (Jul 15, 2007)

Louis said:


> ....blew his scope and the Output transformer....


OUCH! ...Expensive error!


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## nonreverb (Sep 19, 2006)

Heyboer makes one that is very close to OEM and is reasonably priced.




__





Tweed Twin High Power 5F8-A Output Transformer 45268







www.mojotone.com


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## Latole (Aug 11, 2020)

nonreverb said:


> 900 series won't fit. They're laydown where the 800's are stand up transformers. 900 quality aren't as good either.


Sorry I make a mistake with 900. I delete.


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## Latole (Aug 11, 2020)

It is a 100 watts or 50 watts amps ? 

Hammond 1750N for JCM800 50 watt
1750U for 100 watts JCM 800 





__





Transformer - Hammond, Output, replacement for Marshall | Antique Electronic Supply


Replacements for Marshall Amps Designed for drop in replacement of original units. Physically, parts were designed to look similar to original factory units (where possible). Material used & design specs. were kept as close as possible to the original part to preserve the stock "tone".




www.tubesandmore.com


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## nonreverb (Sep 19, 2006)

If it's any consolation, I find I replace more output transformers from Marshall than any other amp combined.


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## Latole (Aug 11, 2020)

See next Gen Guitar in Ottawa.
I order often from them






Amp Transformers & Chokes - Canada


Transformers and chokes for building or repairing guitar, bass, and other amplifiers.




nextgenguitars.ca


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## Louis (Apr 26, 2008)

greco said:


> OUCH! ...Expensive error!


Yes indeed !


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## Louis (Apr 26, 2008)

nonreverb said:


> If it's any consolation, I find I replace more output transformers from Marshall than any other amp combined.


Thanks !!


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## Louis (Apr 26, 2008)

Latole said:


> It is a 100 watts or 50 watts amps ?
> 
> Hammond 1750N for JCM800 50 watt
> 1750U for 100 watts JCM 800
> ...


2204 50 watts,.............I think I'd prefer an Heyboer over a Hammond over what I've read.


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## Latole (Aug 11, 2020)

Marshall owner forget to plug speakers or use the wrong impedance or Marshall transformers are cheap ?


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## Louis (Apr 26, 2008)

Latole said:


> Marshall owner forget to plug speakers or use the wrong impedance or Marshall transformers are cheap ?


Dont understand your question ?


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## Latole (Aug 11, 2020)

Louis said:


> 2204 50 watts,.............I think I'd prefer an Heyboer over a Hammond over what I've read.



Why not.

Did you tech pay for or you pay ?


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## Paul Running (Apr 12, 2020)

Hammond 1750P - Output Transformer - 126/500/2K, 2/4/8/16 OHM, PP, 50W CLEARANCE 
If you are operating 2 X EL34, this tranny should work for you. $65...at that price, you could buy two to experiment. 3400 ohm prim., EL34s will like that.


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## Louis (Apr 26, 2008)

Latole said:


> Why not.
> 
> Did you tech pay for or you pay ?


Yes he did


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## Louis (Apr 26, 2008)

Paul Running said:


> Hammond 1750P - Output Transformer - 126/500/2K, 2/4/8/16 OHM, PP, 50W CLEARANCE
> If you are operating 2 X EL34, this tranny should work for you. $65...at that price, you could buy two to experiment. 3400 ohm prim., EL34s will like that.


That's cheap !........I'll do some more reading ,.........always read that Hammond was a little modern sounding
for Classic Marshall tone


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## tomee2 (Feb 27, 2017)

nonreverb said:


> If it's any consolation, I find I replace more output transformers from Marshall than any other amp combined.


Any reason why? Are the owners just more abusive on them, or do they have undersized output transformers? Or circuits that are a bit off?
This isn't the first time I've heard this said but not sure I've ever understood why it is.


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## nonreverb (Sep 19, 2006)

tomee2 said:


> Any reason why? Are the owners just more abusive on them, or do they have undersized output transformers? Or circuits that are a bit off?
> This isn't the first time I've heard this said but not sure I've ever understood why it is.


No one has ever officially said however, it's interesting to note that it is not unique to either Drake or Dagnall transformers ....they both blow...and not just output transformers either although they are the ones that blow most frequently.


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## nonreverb (Sep 19, 2006)

Latole said:


> See next Gen Guitar in Ottawa.
> I order often from them
> 
> 
> ...


+1. Jonathan is a great guy to deal with....and being based in Ottawa myself, SUPER convenient too.


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## loudtubeamps (Feb 2, 2012)

nonreverb said:


> No one has ever officially said however, it's interesting to note that it is not unique to either Drake or Dagnall transformers ....they both blow...and not just output transformers either although they are the ones that blow most frequently.


Agreed, It seems they are designed to run close to the edge for some strange reason.

I had a JMP 100 watter in the 70's. 
Half way through a set it would shut down, cool down then fire up again.
Embarrassing to say the least!
It took me a few days of head scratching and poking around with my very limited knowledge.
Back then all I knew was how to turn them on and make noise.
It turned out to be a thermistor buried in the first few windings of the mains transformer.

That was a turning point for me : 
My motivation to maintain and repair my own gear as best I could (when your amp quits ..... in the middle of January in Kirkland Lake.)


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## Paul Running (Apr 12, 2020)

nonreverb said:


> No one has ever officially said however, it's interesting to note that it is not unique to either Drake or Dagnall transformers ....they both blow...and not just output transformers either although they are the ones that blow most frequently.


Many guitars amps push the boundaries of the max. operating specs for tubes without safe guard circuitry...it's the pursuit of that tone. Catastrophic failure of an output tube can and will test the output tranny, sometimes both are defeated.


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## Paul Running (Apr 12, 2020)

loudtubeamps said:


> Agreed, It seems they are designed to run close to the edge for some strange reason.
> 
> I had a JMP 100 watter in the 70's.
> Half way through a set it would shut down, cool down then fire up again.
> ...


I came across the same move with a Peavey. Have to wonder about the reasoning...concealment of parts, how many trannies have been trashed without this knowledge and it does question the morals of design.


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## Latole (Aug 11, 2020)

tomee2 said:


> Any reason why? Are the owners just more abusive on them, or do they have undersized output transformers? Or circuits that are a bit off?
> This isn't the first time I've heard this said but not sure I've ever understood why it is.
> [/QUOTE
> 
> Are Marshall owner forget to plug speakers or use the wrong impedance or Marshall transformers are cheap ?


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## Latole (Aug 11, 2020)

Louis said:


> Yes he did



He is very honest


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## tomee2 (Feb 27, 2017)

Paul Running said:


> I came across the same move with a Peavey. Have to wonder about the reasoning...concealment of parts, how many trannies have been trashed without this knowledge and it does question the morals of design.


The transformer safeguard might have been a UL or CSA requirement at the time.


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## jb welder (Sep 14, 2010)

Paul Running said:


> I came across the same move with a Peavey. Have to wonder about the reasoning...concealment of parts, how many trannies have been trashed without this knowledge and it does question the morals of design.


Agree with @tomee2 , has to do with the transformer meeting safety/fire requirements. It may be a cheaper method of meeting those standards, but they must be met. The part is thermal, so it's not being 'concealed' so much as it has to be sensitive to the internal temperature of the transformer.
In any case, it is illegal to replace the thermal fuses in transformers. It would have to be re-wrapped to factory spec. and re-certified, which would not be cost effective.

As far as the discussion on why Marshall transformers (OT) are more prone to failure, a couple more points. 
-They don't have a shorting jack at the speaker output like most tube amps do, so if you forget to connect the speaker it can be a quick death.
-I think Marshall users are more prone to overdrive the power amps than, for example, Fender users. (and maybe also more likely to 'tinfoil' the fuses  )
-EL34's run higher screen grid currents and seem to fail more than 6L6's because of it. In addition to this, Marshall typically uses 5W screen resistors where typical Fender is 2W. The 5W screen resistor is less likely to fail and act as a fuse for the tube. So you end up being more likely to have a short drawing big current through the OT on an amp running EL34's with 5W screen resistors.


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## Paul Running (Apr 12, 2020)

Louis said:


> Hi guys ,.....I have a blown JCM800 output transformer here and would like
> to have it fixed,.....anyone knows someone in Canada that could do this ?
> 
> Thanks


I encourage you to learn more about the operation and maintenance of your amp; the information is easily accessible now with the cyber world however, information can be false or misleading so, check many sources to discover the truth. Once you feel confident with your knowledge of the amp, begin to experiment...it may peak your interest.


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## Louis (Apr 26, 2008)

Paul Running said:


> I encourage you to learn more about the operation and maintenance of your amp; the information is easily accessible now with the cyber world however, information can be false or misleading so, check many sources to discover the truth. Once you feel confident with your knowledge of the amp, begin to experiment...it may peak your interest.


Hi Paul,......can you be more specific ,........I don't understand what you are saying !


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## Paul Running (Apr 12, 2020)

Read much information about amplifiers. Technical articles are a wealth of knowledge...an example of your situation: Tech Corner


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## Paul Running (Apr 12, 2020)

Try to spend more time on the bench as you absorb knowledge...get that practical experience in...like shop in high school.


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## Frenchy99 (Oct 15, 2016)

Paul Running said:


> Try to spend more time on the bench as you absorb knowledge...get that practical experience in...like shop in high school.


I tried that with women and i still dont understand a thing !


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## jb welder (Sep 14, 2010)

Paul Running said:


> Read much information about amplifiers. Technical articles are a wealth of knowledge...an example of your situation: Tech Corner


That MM page is a perfect example of your earlier remark of there being both great tech info and total BS on the web. Both types appearing on the same page.


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## Louis (Apr 26, 2008)

Paul Running said:


> Read much information about amplifiers. Technical articles are a wealth of knowledge...an example of your situation: Tech Corner


Thank you ,............I'm a house builder and if I had a chance to start things over,
I'd take the electronic class that was offered at school ,...never too late to learn ,
bringing my amp to an electronic engineer was the best thing I could do for my lack
of knowledge but ,....something went wrong .

Thanks for the link !


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## Paul Running (Apr 12, 2020)

Louis said:


> Thank you ,............I'm a house builder and if I had a chance to start things over,
> I'd take the electronic class that was offered at school ,...never too late to learn ,
> bringing my amp to an electronic engineer was the best thing I could do for my lack
> of knowledge but ,....something went wrong .
> ...


Okay, let us know how you fair-out with the transformer.


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