SWR Workingman's 15 blow fuse

[agat38]

Hello from France,

I just buy a not working SWR Workingman's 15 from 1996 (pre FMIC), when i power on the first time the main fuse blow (1 1/2 A),
i replace it, I disconnect the secondary winding from transformer, power on a second time the fuse blow again.

With my multimeter i can read around 2 ohms on primary winding, 1.8 on secondary, this values are ok ?
or i need to replace the transformer

thanks

[Jazz P Bass]

If the secondary leads are disconnected from all circuits & the transformer all by itself blows the fuse, then, yes, it is bad.

[J M Fahey]

Check that you don't have a 120V (USA model) amplifier.

[agat38]

It's an export model (240v), the transformer part number is 560013-240, it's that i need in France.

[J M Fahey]

Ok, try to get a new one from factory or distributor.

Might not be available, because of the triple handicap of being 18 years old, the company having changed hands and not being in USA; but in that case you might source a similar ratings transformer and mount it inside, maybe with a little surgery (different bolt hole spacing, etc.).

Only possible problem is that the old model "head"/ chassis is quite small, not much free space there.

Post a couple gut pictures and transformer size (in cm will be fine, in fact I prefer that .

[Jazz P Bass]

You will have to go with an 'after market' transformer.

Something such as this maybe?

266L48 Hammond Manufacturing | Mouser

Workingman 15.zip

[agat38]

Thanks, i 'll try to find a transformer locally, i need 2 x45v 400VA ?
For surgery work is no problem for me

[J M Fahey]

Sorry, the hammond one suggested in post #6 is way too low power (98VA) and voltage (48V ct).

2x45VAC is way too high, and no way you can fit a 400VA transformer there.

Following an annoying tendency which I find everywhere, the amplifier or power supply does not show rail voltages which I find CRAZY STUPID .

They always show the +/- 15V by the way, unnecessary because they always come drom a 78xx or Zeners.

This amp is 100W RMS into 8 ohms, which means +/- 45/50V DC rails, the classic transformer voltage for that is 36+36V at 2.5A , some 180VA .
You might fit a 250VA there but doubt any larger will fit.

Please measure the EI iron core dimensions, in cm (not legs, bolt holes separation nor bell covers, I'm interested in the business end which is the iron)

And post some gut pictures, it's tight in there.

[Jazz P Bass]

Ooops.
It appears that the amp is 160 watts output into one 8 ohm speaker.
200 watts into 4 ohms.

wm15_specs.pdf

[J M Fahey]

Ooops.
It appears that the amp is 160 watts output into one 8 ohm speaker.
200 watts into 4 ohms.

[ATTACH]33308[/ATTACH]

That's the modern (2015) version, made by Fender.

The one we are talking about is the 1996 one.
The tech notes you posted mention adjusting bto 100W RMS into 8 ohms ... the amp might have furnished, say, 120W RMS nominal way back then.

2 ways to notice which is which

1) only cosmetic:
* old speaker grill: cheap rhomboidal "slit and pulled metal" grill , don't know the English name, cheap bacause metal stretches 2 or 3x original length
* new metal grill: punched sheet metal, more work, more machine wear, 1 yard=1 yard (no0 stretching)

2) more than cosmetic:

* new chassis is as deep as the cabinet, lots more space

* old cabinet" small head on top of larger cabinet look, tight space.

OLD:


intermediate/transition:


modern:

[agat38]

At the back off my amp i can read 360 watt, i know it's power consuption. in practice i see power out is half then power consuption.

For the transformer dimensions are (millimeters) : A :87 b: 71 c: 28 d: 14 e: 14 f: 43 g: 57 thickness : 27 weight : 1,56 kgs

[J M Fahey]

At the back off my amp i can read 360 watt, i know it's power consuption. in practice i see power out is half then power consuption.

For the transformer dimensions are (millimeters) : A :87 b: 71 c: 28 d: 14 e: 14 f: 43 g: 57 thickness : 27 weight : 1,56 kgs
[ATTACH=CONFIG]33311[/ATTACH]

First of all, thanks for measuring , and you measured with good precision

2) I am amazed, I almost spit my morning coffee all over my keyboard.

That transformer is way too small

I use that core size for my 100W RMS SS amps .

And for 120/140W RMS use the next larger core size ... which by the way is what GK, Peavey, Crate, Laney, Marshall, etc. use .

Is that the original one?

Or maybe it was already replaced once, to adapt it for 220V ... and there you have the result, a burnt transformer .

For reference, I'm posting a standard EI core size table.

Usually there's no "any" random size at will but designers must pick one of these; for any desired power you start by selecting a "square" core if possible (same stack thickness as center leg width) , because it's most efficient; if not enough you stack more iron to increase core surface, until after 1.5X or 2X it's better to choose the next higher size:



your measurements match perfectly standard lamination #112 , whose center leg C , called A in my table is 28.6 mm .

A square core would also be 28.6 mm , what you have, so I'm satisfied that it's core #112 and not other.

To boot, the weight of such square core alone is 1 kg (1030g) , you measured 1.56kg for the complete transformer which accounts for somewhat over 1/2 kg copper plus mounting legs, bell covers, bolts, etc.

So size is confirmed in more than one way.

Now to available power or VA .

In the "old days" (think Blackface Fender, Ampeg V4, early Marshall, etc.) such a core would have been used (VERY conservatively) for 70 VA

No way, no matter how daredevil SWR designers are , thay they are pulling some 250VA out of it.

Being wild is one thing, but you can't beat Physics, that's for sure, at most push them to the limit but not beyond.

I can guess only 2 explanations for what you found:

1) SWR expected only Jazz players , maybe Country, which would routinely use that amp at, say, 70 to 100W tops, definitely not Rock Musicians, (which is not impossible but very unlikely) or:

2) somebody replaced the original 120V transformer with a too small 220V one.

Please post a picture showing it in its place, (no need to connect it) , just to check available space, and also a closeup of mounting holes punched in the chassis, maybe that tells us something.

Anyway you will need a real 250VA or larger (if it fits) to be comfortable powering that amp.

A real mystery.

For reference: a Marshall Valvestate 8080 or 8100 or a GK MB200 (100W RMS) , 2 well known amplifiers and rated for 100W RMS , use transformers with larger square stacked lamination #125 , go figure (core 32x32mm) .
100/120W Peavey, Laney, Crate, etc. use about the same.

[agat38]

That transformer is way too small

Is that i said when i see it

I can guess only 2 explanations for what you found:

1) SWR expected only Jazz players , maybe Country, which would routinely use that amp at, say, 70 to 100W tops, definitely not Rock Musicians, or:

2) somebody replaced the original 120V transformer with a too small 220V one.

Please post a picture showing it in its place, (no need to connect it) , just to check available space, and also a closeup of mounting holes punched in the chassis, maybe that tells us something.

Anyway you will need a real 250VA or larger (if it fits) to be comfortable powering that amp.

A real mystery.

Or the people at Mercury Magnetics who make the final assembly take the good stiker (560013-240) but take the unit in the bad basket may be workinman 12 or 10...

this afternoon i try with another transfomer who give +- 30v, +-HV 41V, the amp work fine, i can't test it very loud now,
just have +15 and -10v, zener problem i expect.
And another surprise i put my meter on speaker and he give 4,2 ohms expected 8 ohms, the speaker look like on all workinman's 15 first séries pictures i can find.

[J M Fahey]

Is that i said when i see it

Or the people at Mercury Magnetics who make the final assembly take the good stiker (560013-240) but take the unit in the bad basket may be workinman 12 or 10...

So that is an MM made transformer?
Who bought it, you or the former owner?
If the measurements you gave me correspond to an MM labelled power transformer, catalog#560013-240 (by the way, their online catalog Mercury Magnetics -- The Guitar Amp Transformer Company only shows:

PT 560013-220

Old Workingman 15 / 160 -- #0067197000 -- 220V

then it's plain WRONG, neither MM (nor me) nor anybody can safely power a 160W RMS amp (which will need some 50% extra VA rating, around 250VA) with such a little core.
No way.

So if they sent an improperly labelled transformer (only explanation because they do know how to make it right), they must send you another and apologize for the inconvenience.

No need to send the burnt one back, just a couple pictures with a ruler by it to confirm bad size, freight is more expensive than copper/iron cost .

If possible, I'd still like to see a couple pictures but mainly the transformer inside the SWR chassis and the mounting holes, I find it impossible that SWR originally fit such a small one, primary being 120V or 220/240V is irrelevant, problem here is magnetic saturation.

Unfortunately, MM catalog shows no pictures or measurements.
On the contrary Hammond does , maybe that means something


this afternoon i try with another transfomer who give +- 30v, +-HV 41V, the amp work fine, i can't test it very loud now,
just have +15 and -10v, zener problem i expect.
And another surprise i put my meter on speaker and he give 4,2 ohms expected 8 ohms, the speaker look like on all workinman's 15 first séries pictures i can find.

[J M Fahey]

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