Wem Dominator 45 Bass impedence question

[Phil Starr]

It's been a while since I worked on valve amps (30 years!) but the theory hasn't changed too much. If you run a mismatched speaker then this is less serious than running into open circuit for the reasons explained above. I don't think for example you would have any major problems running an 8ohm speaker off a six ohm tap in the output transformer.

You might find that the output transformer has other unused taps. Some manufacturers in those days used standard, off the shelf OT's but most towns had people winding transformers so there were lots of custom built OT's as well. Whether these OT taps are identifiable or not if they do exist is another matter.

It may be worth putting up another post here with 'valves' in the title. This post is probably only attracting the attention of speaker buffs rather than the valve experts, which I am not.

What you do next is up to you. I'd measure the speaker to determine its DC resistance which should give an indication of its impedance. I'd also contact Watkins to see if they have any info or advice. I'd probably then just replace it with another speaker of the nearest impedance and not worry unless it starts eating valves. I don't think this will be a problem though, in the days when I used only valve amps I did from time to time run small mismatches with no real problems other than a slight loss of power.

Axe Music in Axminster, quite near you, have a valve tech I think and are very helpful. If you get really stuck I could take a look as I am not too far away either.

Meanwhile, have you measured the inside of the cab so we can start looking for a replacement speaker?

[Christophano]

Wow, thanks for the responses and the advice chaps. Much appreciated.

I havent gotten round to measuring the inside of the cab yet. I was waiting until the Multimeter turned up and I could do both things at the same time.

I'll post up my results when the pesky mutlimeter turns up! :-)

[orangepeelneil]

[size=3]Hi,

I'd just ring or directly contact the lengendary Charlie Watkins at WEM ( Watkins Electric Music) and ask him.

[url="http://www.wemwatkins.co.uk/"]http://www.wemwatkins.co.uk/[/url]

[email protected]

020 8679 5575.

He designed and possibly even built the amp, great guy -real character and a real amplifer pioneer.

I've a got a 15W valve Dominator bass which has a 16 Ohms Celestion G15M Speaker I think.

Cheers Neil[/size]

[Christophano]

Right then, the Multimeter is saying 7.1 when I touch the speaker connections. (The amp is now in bits so the speaker isnt attached to anything)... So i'm assuming it's an 8ohm speaker as I've read that most 8ohm speakers measure at about 7ohms?

Measurements for the cab are 23 inches high, 22 inches wide and 8.5 inches deep. Take 5 inches off of the height for the amp gubbins that should be inside the cab, as I've have taken them out.

[Slipperydick]

[quote name='orangepeelneil' post='1052672' date='Dec 9 2010, 01:07 PM'][size=3]Hi,

I'd just ring or directly contact the lengendary Charlie Watkins at WEM ( Watkins Electric Music) and ask him.

[url="http://www.wemwatkins.co.uk/"]http://www.wemwatkins.co.uk/[/url]

[email protected]

020 8679 5575.

He designed and possibly even built the amp, great guy -real character and a real amplifer pioneer.

I've a got a 15W valve Dominator bass which has a 16 Ohms Celestion G15M Speaker I think.

Cheers Neil[/size][/quote]

Absolutely right, and a thoroughly nice bloke too. Helped me out a few times.

Not sure if he's still getting the phone himself, must be knocing on by now.

Website makes an interesting read, Hyde park with about 1500W for PA..wouldnt touch the sides now would it ?

[umph]

[quote name='Christophano' post='1051636' date='Dec 8 2010, 01:32 PM']Hmmm, interesting. So if it had a minimum load of 6 ohms an 8 ohm speaker could be alright. I've got a multimeter in the post so will find out for sure after i've had a play around.

Will post up my results![/quote]

needs 16ohm speaker to be ideal, although it wouldn't be hard getting another transformer put in or sending it and getting it rewound with taps for 8 and 4.

[Phil Starr]

[quote name='Christophano' post='1054081' date='Dec 10 2010, 02:34 PM']Right then, the Multimeter is saying 7.1 when I touch the speaker connections. (The amp is now in bits so the speaker isnt attached to anything)... So i'm assuming it's an 8ohm speaker as I've read that most 8ohm speakers measure at about 7ohms?

Measurements for the cab are 23 inches high, 22 inches wide and 8.5 inches deep. Take 5 inches off of the height for the amp gubbins that should be inside the cab, as I've have taken them out.[/quote]

OK the speaker is probably a bit over 8 ohms but not by enough to worry the amp. So we'll go for an 8ohm speaker. The cab will have an internal volume of about 45litres, a bit small for a 15. Its probably got a huge bass hump and doesn't go too low with the fitted speaker.

Speakers that would work in your cab might be
Fane 15-500 £68 small bass hump, f3 74hz 112db output
Fane 15-400 £54 nearly flat 115dB f3 91Hz
Celestion BN 300S (neo so light weight) £75 Small bass hump f3 92
Eminence Delta 15pro £74.96 3dB bass hump, pronounced midrange hump f3 73 Hz
Interesting and possibly not unlike the original as new, though I'm guessing here. Eminence Delta 15A loud with huge midrange and bass hump, wild and wooly Up to 120dB f3 73Hz.

I'd go for the fane 15-400 for a cheap uncoloured sound or the Celestion Neo. Both would match a drummer but might need a little help from the PA in a medium sized venue. The Delta might be enough on its own for small and medium gigs. There's other alternatives especially if you want to pay more. Prices are from Blue Aran. Blue Aran you owe me.
[quote name='Slipperydick' post='1054109' date='Dec 10 2010, 02:48 PM']Absolutely right, and a thoroughly nice bloke too. Helped me out a few times.

Not sure if he's still getting the phone himself, must be knocing on by now.

Website makes an interesting read, Hyde park with about 1500W for PA..wouldnt touch the sides now would it ?[/quote]

When I was doing PA in the olden times the WEM PA anp was the most desirable thing going, 100W of pure transistor power and made for PA with a flat response instead of a borrowed guitar amp. Pink Floyd were so proud of theirs they put them on the album sleeve. Google Ummagumma

[Christophano]

[quote name='Phil Starr' post='1054424' date='Dec 10 2010, 07:35 PM']OK the speaker is probably a bit over 8 ohms but not by enough to worry the amp. So we'll go for an 8ohm speaker. The cab will have an internal volume of about 45litres, a bit small for a 15. Its probably got a huge bass hump and doesn't go too low with the fitted speaker.

Speakers that would work in your cab might be
Fane 15-500 £68 small bass hump, f3 74hz 112db output
Fane 15-400 £54 nearly flat 115dB f3 91Hz
Celestion BN 300S (neo so light weight) £75 Small bass hump f3 92
Eminence Delta 15pro £74.96 3dB bass hump, pronounced midrange hump f3 73 Hz
Interesting and possibly not unlike the original as new, though I'm guessing here. Eminence Delta 15A loud with huge midrange and bass hump, wild and wooly Up to 120dB f3 73Hz.

I'd go for the fane 15-400 for a cheap uncoloured sound or the Celestion Neo. Both would match a drummer but might need a little help from the PA in a medium sized venue. The Delta might be enough on its own for small and medium gigs. There's other alternatives especially if you want to pay more. Prices are from Blue Aran. Blue Aran you owe me.


When I was doing PA in the olden times the WEM PA anp was the most desirable thing going, 100W of pure transistor power and made for PA with a flat response instead of a borrowed guitar amp. Pink Floyd were so proud of theirs they put them on the album sleeve. Google Ummagumma[/quote]

Hey Phil,

That's a crackin' bit of info. Thank you very much.

Your right, bit of a tiny combo to have a 15 inside. Also right when you said about it not going down too low... Packs a might punch, but not a low one!

I've got two 10 inch delta's in one of my cabs, I like the sound that they chuck out... So I might go for one of those. They sound pretty decent on break up with my big muff and tech 21 xxl. Plus I'm a bit of an eminence fan boy.

I've got my eyes on some lovely looking el84's at the tube amp doctor, some of their TAD matched ones.

I'll get some pictures up when I get it all sorted out.

Thanks again.

[Phil Starr]

Liking the Delta 10's is interesting, they have the pronounced midrange hump that is common to a lot of eminence speakers so I'd cross off the Fanes, they'll sound too polite for you.

I wasn't thinking you'd do major surgery to the cab. If you want a 10 in the cab you'll have to make a new baffle ( the board the speaker fits on to). If you want to keep the original look or might want to go back to original then you could always cut a panel and screw it onto the back of the existing panel, then it could be easily removed if these ever become collectors items.

You might like the sound of the Delta 15. The Pro would be similar to the sound of the 10's but louder than a single 10 and with noticeable extra bass in this cab, which is a bit big for a single delta10. I think the Delta15 might be a sound you'd love. If you can afford it the Celestion Neo looks made for your cab and is designed to be 'fast' sounding. It would be my choice. Do you want me to model the Eminence Neo 15's?

It might be worth pm's to Stevie (another from this end of the country) and LawrenceH to get their suggestions, they both know at least as much as I do, probably more.

[Christophano]

I was rightly or wrongly comparing the delta 10's I have to the delta 15, I don't think I could bare to rip the Dominator to shreds, it means quite alot to me as i've owned it for 17 years.

The delta pro seems like it might be the best bet in terms of the sound I would want to get, but if you think the Celestion Neo is the most promising, it might be worth considering? Might save my back a little bit too....

If you could model the eminence neo's, it would be most appreciated. :-)

Chris

[Phil Starr]

The deltalite 2515 will give you a small bass lift, just noticeable and it has a small midrange peak centred around 2K. This peak is fairly broad and flat suggesting the breakup modes are well controlled. F3 is fairly high at 93Hz but you will still get 95 dB at 40Hz so I think you'll be happy with the bass. It has very similar characteristics to the Celestion and i think they would probably sound very alike, the only minuses are price £92 and it has an aluminium voice coil. It's a personal thing probably but I have had a couple of failures with Eminence and it has always been the aluminium coils corroding at the junction with the lead out wires. Always with quite old speakers though (10 Years)