Question about why the mains transformer in my amp might've blown......

[Brow]

Hey guys, just a quick question........

As I posted on here a few weeks ago, my Marshall JTM60 combo stopped working and I later found out that it was the power transformer that blew.

Would using a Boost pedal (such as a Fulltone Fat Boost) in the amps series FX loop have caused the Transformer damage over time?

As this was something I've been doing on occasion for the last few months, and just wondered if this may be 1 of the causes for the mains transformer suddenly blowing.

Thanx for any info.

Craig

 

[Lake Placid Blues]

Re: Question about why the mains transformer in my amp might've blown......

I don't think it's anything you did. This particular model has a reputation for that kind of thing. I love Marshalls, but this amp wasn't one of their better efforts....

 

[kmcguitars]

Re: Question about why the mains transformer in my amp might've blown......

Do a forum search on the JTM60. There was a post about them having AC heaters, And a mod to convert them back to DC a few months ago. But it sounds like you've passed that point? I guess it's a inherent design flaw?

 

[TheArchitect]

Re: Question about why the mains transformer in my amp might've blown......

Hey guys, just a quick question........

As I posted on here a few weeks ago, my Marshall JTM60 combo stopped working and I later found out that it was the mains transformer that blew.

Would using a Boost pedal (such as a Fulltone Fat Boost) in the amps series FX loop have caused the Transformer damage over time?

As this was something I've been doing on occasion for the last few months, and just wondered if this may be 1 of the causes for the mains transformer suddenly blowing.

Thanx for any info.

Craig

I doubt it but why would you put it there?

 

[The Golden Boy]

Re: Question about why the mains transformer in my amp might've blown......

You've ruled out an impedance mismatch? You were using just the speakers in the amp, and not to a 4 or 2 ohm extension cab?

 

[Burnin_UP]

Re: Question about why the mains transformer in my amp might've blown......

Impedance mismatch could blow the Output Transformer, but not the mains.

The most common reasons for main transformer blowing are deffective tubes (if the B+ is not fused, I doubt this is your problem), incorrect tubes (drawing too much heater supply current, a limited resource), or the most likely culprit in your predicament:

Cheap parts.

There is no way putting even a Herzog in your effects loop would blow your power transformer.

Good luck,

Mickey C.

 

[Brow]

Re: Question about why the mains transformer in my amp might've blown......

Thanx for the posts guys

I think I did mean the Output transformer, not the mains transformer as I mentioned in my original post :smack:

I doubt it but why would you put it there?

I sometimes use the Fat Boost in the FX loop for a pure volume boost for solos. Nothing too OTT, just enough to lift my volume up a little for solos etc

You've ruled out an impedance mismatch? You were using just the speakers in the amp, and not to a 4 or 2 ohm extension cab?

I always just use the internal 16ohm speaker with this amp. When I have in the past used my Orange 4x12 with it, I've always unplugged the internal speaker and just used the 16ohm extension out for my Orange.

Craig

 

[Burnin_UP]

Re: Question about why the mains transformer in my amp might've blown......

Output transformer is a completely different story!

Some amplifiers require the internal speaker jack to always be connected, regardless of whether or not you have an extension cabinet or not, in order for the transformer to see the load properly. Some amps include a dummy load on the switched terminal of the input jack, in case somebody plays it accidentally without a speaker.

So if you hook up just the extension jack, you are actually running the wrong impedance, into a resistive load (as opposed to a speaker's reactive load). This incorrect load reflects back across the secondary so the tubes see "some other" load.

With most fenders this is no problem. In my experience, however, this is a huge problem for UK transformers.

Sorry about the bad luck.

Once again, the most likely cause, in my opinion, is still cheap iron.

 

[Brow]

Re: Question about why the mains transformer in my amp might've blown......

Thanx for the post.

Output transformer is a completely different story!

Some amplifiers require the internal speaker jack to always be connected, regardless of whether or not you have an extension cabinet or not, in order for the transformer to see the load properly. Some amps include a dummy load on the switched terminal of the input jack, in case somebody plays it accidentally without a speaker.

So if you hook up just the extension jack, you are actually running the wrong impedance, into a resistive load (as opposed to a speaker's reactive load). This incorrect load reflects back across the secondary so the tubes see "some other" load.

With most fenders this is no problem. In my experience, however, this is a huge problem for UK transformers.

Sorry about the bad luck.

Once again, the most likely cause, in my opinion, is still cheap iron.

Both the internal and extension speaker sockets on this amp are labelled as 16ohm.

On the very rare occasion that I did use my 4x12 instead of the internal amps speaker (I only did it once or twice), I recall using the 'internal speaker' output jack on the amp. As both were labelled as 16ohm, and I wasn't using the internal speaker at the same time.

Like I say, I can't see this being the cause of the problem as I only did it twice at the most

 

[Scott_F]

Re: Question about why the mains transformer in my amp might've blown......

My only comment to add is that the AC versus DC heaters are not a big issue to me. Unless the amp's wiring is just routed poorly this shouldn't be a big deal. And even then, it's only a noise issue.