WEM Dominator MKIII project

[MARSHALL BUSTER]

Hi all

I just thought i would share my next project with anyone who is interested in Wem amp's. I'v bought it for £45 Uk pounds what i think was a bargin for one of these, from my friend and fellow band member. he says the last time it was being used, it was as a bass amp!!.

He added that it was all working fine then stoped working, the fuse had blowen. He then wraped some foil around the fuse (not advisable folks) and it still did not work, he then opened the amp up and noticed one of the Mullard el84'S glass was cracked 'hence its removed in the picture'. So it went in a cupboard and there its been for 10+years.

So thats the story behind my Wem, i just picked it up today and can't wait to get stuck in and clean it all up.

I would obviously appreciate any info-schematics-tips, or knowledge/experience anyone would wish to share.

Here are some pic's i'v just taken....

[jazbo8]

Schematic is here. Watkins Dominator Mk 3 Schematic (2)

I believe it was the inspiration for the Marshall 18Watt, so the info and repair for it should be pretty easy to get, for £45, you got a deal!

Jaz

[Zouto]

Recently I restored a similar Dominator Mk3 with a blown output transformer. I replaced all filter caps, rectifier diodes, all tubes, some resistors and OT, and got an incredible great sounding amp. A big surprise...
Zouto

[Stew904748]

Schematic is here. Watkins Dominator Mk 3 Schematic (2)

I believe it was the inspiration for the Marshall 18Watt, so the info and repair for it should be pretty easy to get, for £45, you got a deal!

Jaz

Hi Jaz, I have a MK III Dominator 60, although I believe that it is a 30w RMS amp 60w peek. My mains transformer has blown but I am struggling to find an equivalent could you help to tell me the outputs of the transformer so I can find one.....?

Many thanks Stewart

[pdf64]

What is its tube line up, especially what power tubes does it use, eg 4 x EL84, 2 x EL34?

[Stew904748]

What is its tube line up, especially what power tubes does it use, eg 4 x EL84, 2 x EL34?

4 x EL84's & 3 x ECC83's.....

[pdf64]

This schematic may be close, to the power amp / supply at least http://wem-owners.com/wp-content/upl.../04/br30b.jpeg
I guess that the operating conditions would be similar to an AC30 then, eg 300 to 320V HT.
Unfortunately an AC30 replacement PT may put out to much HT voltage when used with silicon rectification.
Something with ~225-0-225Vac at close to 200mA, and 6.3V at least 4A.
The Hammond 369HX may do at a push, especially as the 5V winding won't be loaded Power TX or play it safe with the 369KX.

[TigerAmps]

Hi:

I am going to stick with the schematic which shows: (2) EL84 and (3) 12AX7 ...
So we are looking for:
2.42 A @ 6.3 of Filament
AND
310V DC @ 120ma to 130 ma (65 ma per tube max - also in line with the Marshall 18 watt replacement transformer)

so the Hammond 369HX should work fine and provide ~315V DC to ~318V DC with 150 ma and plenty filament (6A).

Also:

the Hammond 261M6 is rated at 215V @ 269 ma (not center tapped) and 6.3V @ 4A
It would put out ~300V DC but you would have to convert over to a 4 diode full wave bridge rectifier (not a big deal).

Two things to consider:
a) The cost of the transformer options
b) Fitting them into the amp (height/width) and how it will bolt onto the chassis.
You might have to make an adapter plate or drill additional holes.
I would factor the existing PT mounting pattern into the selection of the transformer as well.

I hope that helps ...

[Stew904748]

This schematic may be close, to the power amp / supply at least http://wem-owners.com/wp-content/upl.../04/br30b.jpeg
I guess that the operating conditions would be similar to an AC30 then, eg 300 to 320V HT.
Unfortunately an AC30 replacement PT may put out to much HT voltage when used with silicon rectification.
Something with ~225-0-225Vac at close to 200mA, and 6.3V at least 4A.
The Hammond 369HX may do at a push, especially as the 5V winding won't be loaded Power TX or play it safe with the 369KX.

Thank you for your help. Forgive my ignorance but I am new to these types of transformer. I have a standard 240v input on 2 wires which is no problem. But I am not sure what the outputs from the secondary should be,I have 2 white wires that come from inside that can't see where, that go to via 2 diodes to the standby switch, and one red wire from the centre tap on the top of the transformer that goes to the chassis. Would you know which wire I would use for what if I were to use say the 369KX?

[TigerAmps]

Stew:

Are you in the US or Europe?
The Hammond mentioned transformers are generic replacement transformers.
You can find the data on them at: Hammond Mfg. - "Classic" Transformers & Enclosures

On the Hammond 369HX you would
a) Connect the 2 red wired to the 2 diodes.
b) Connect the Red/Yellow with to the chassis
c) The two green wires would go the the filaments
d) The green/yellow would go to the chassis

You would not use the yellow, yellow/black and violet wires. You would tape them up or insulate them with shrink tubing.

EDB369HX.pdf

Can you post some pictures of the transformer and the connections? It would help a great deal ...

[Stew904748]

Stew:

Are you in the US or Europe?
The Hammond mentioned transformers are generic replacement transformers.
You can find the data on them at: Hammond Mfg. - "Classic" Transformers & Enclosures

On the Hammond 369HX you would
a) Connect the 2 red wired to the 2 diodes.
b) Connect the Red/Yellow with to the chassis
c) The two green wires would go the the filaments
d) The green/yellow would go to the chassis

You would not use the yellow, yellow/black and violet wires. You would tape them up or insulate them with shrink tubing.

[ATTACH]37987[/ATTACH]

Can you post some pictures of the transformer and the connections? It would help a great deal ...

Thanks Tiger Amps, attached are some pictures......

[TigerAmps]

OK - The picture does not really jive with the schematic.

I think the picture shows (3) 12AX7 tubes and (4) EL84; is that correct.
That would make the filament draw ~4A; which is OK because the Hammond 369HX can supply 6A of filament.
Not sure if the high voltage current (150mA would be enough though; I think it should be over 200ma) ...

Another option is to have someone re-wind the transformer.
The new Hammond would cost $115 here in the US. I think the re-wind cost is around $160.00.
It might be easier to spend the extra money and have the original re-wound.
It really depends on what the amp is worth if you sell it OR if you "love it" that much.
You can Google "transformer rewind services" and ask around.
If you have it rewound, it would the be like new and still fit in the existing chassis cutout.

Just another thought ...

[mhuss]

If your pockets are deep, Mercury Magnetics (and others) can do a 'vintage rewind' of your existing burnt PT. This would, of course, 'drop right in.'

[TigerAmps]

See - Great minds think alike; only 3 minutes apart ...

[Stew904748]

Thanks guys, Tube line up is (3) ECC83's & (4) EL84's, but it is a 2 channel amp so I am guessing the power tubes are in pairs.

I am in the UK so would need to look into possible rewind cost and locality. Although I personally would prefer to just retrofit a modern equivalent if possible. I am happy to modify the chassis, in fact I was wondering if there is any issue with simply housing the PT in a box within the lower part of the cabinet and just running the wires up tot he rack perhaps via a connector for future servicing.

I love this amp and although I could replace it for £300 - £500 I'd rather sort it as cheaply as possible since I am basically broke!!!

Thanks again, really appreciate your help.....

Stewart