Watkins Dominator conversion

[SweetSpot]

Greetings,
My name is Mick & I'm crazy about this site!
I need your help please.
Currently working on a blue/white, V front Dominator attempting to
18 Watt-ise it. Main issues have been to sort out the B+ & the PI.
PT 2ndary is 283v.dc, after trying several EZ81s a Mullard is now giving
320 plus v.ac (close enough for me). 2nd. filter shows 302v & 276v at
3rd. filter. With most other changes to the circuit completed this thing is
starting to breath fire ! REALLY hefty - especially the normal ch.
So, "Where's the problem ?" I here you ask.
Well, my last task is to replace plate resistors where necessary (most are way out of spec) problem is I NEED A VOLTAGE CHART bad,have searched the site but can't find one & am currently using a Watkins drawing as a guide.
As I've said, the amp sounds great but some voltages make me wonder-
for instance 180v on V1 pin 1 ?, (this is with 276v into an accurate 100k plate res.)I'd kinda expected 150-160. Without pin out voltages I'm not sure if this thing sounds so right because it IS right or because it's about to vopourise - I,m hoping it's option one !
Can someone please put me out of my misery ?

Plate resistors left till last because this is a later Dominator with components mounted on PCB (Aaagh!) - not much lee-way for repeated changing of parts as the track lifts from the board or disintegrates if you so much as look at it the wrong way - nightmare !
So I'm hoping that with a voltage chart I can hopefully make a semi-educated guess & get the values right with the least amount of disturbance to the board.

Was that long winded or what ?

Thanks

Mick

[Plexi]

Mick: Hello and welcome.. here is a schematic with the voltage chart.

Some things that can throw of the voltage..caps in the power supply,resistor for the choke. And as you check the plate resistors..also the cathode resistors,for the EL84..and the preampand driver tube..
If the ones on the preamp change from 820ohm to say 1k or 1,5 k.. the plate voltage will also be higher.. The tube itself can also make a bit of a voltage change.. But here is the link.. theres some other sites with very good gut shots of the WEM..
http://www1.korksoft.com/~schem/bargain ... inator.pdf

Richie

[SweetSpot]

Hi Richie

Thanks for the advice

Cathode resistor on V1 is 1.5k & is stock(reads 1.7k) Ouch!
I had this ear marked to change to 820ohm as per the schematic - on your advice it's now the first thing I'll do.

Cathode res. on V2 is 820 (reads 790) - I'll replace this too.

Replaced all resistors on cathodes of driver and EL84s.

Thanks for the link but the Watkins schematic is what I'm working with already, so do I take it that these figures would apply more or less to real world 18 Watt voltages? I realise they must be similar - just want to be sure.

Circuit on my amp is slightly different to the regular Watkins schematic, mainly in that it somehow had B+ involved with the PI cathode/bias
cicuit ? Changed to regular PI wiring and the amp gained some life,less constricted than before.

Help & advice appreciated

Mick

[Plexi]

As you said, this schematic may be a bit different than your amp. You may be able to look at the 18 watt layout,and see the differences..Theres a few of them. Once you change some of these ,you may be closer to the voltages. They aren't too far off now. A few cap values,and resistor changes. And a few wireing changes. thats about it..

Richie

[loverocker]

Hi SweetSpot - I converted a WEM, too. Mine was a different model (Custom 15, a 1x12 combo), although they all seem to have the same PCB.

I went for the Lite II circuit, so I can't help much on voltage values. I did post the output section voltages I had in a previous thread if you want to search for it. But that was purely for checking on EL84 dissipation with the amp gurus here - I didn't bother with the preamp.

By the way - does that Dominator have the WEM's conjunctive filter on the output transformer (cap and resistor between each side and the centre tap)?

[SweetSpot]

Thanks Richie,

On your advice have just changed to 820ohm cathode res. on V1 - now
seeing 140v at the anode - much nearer to what I expected (perhaps a little low now ?) haven't tried changing valve yet, will do that right now.

Have already changed component values and wiring where needed as you suggest and have been working by comparing both Watkins & 18 Watt shematics. Having sorted out cathodes res. values, only parts of circuit left to restore/mod/upgrade are the plate resistors - which is where
the expected voltages question came in.
I guess I'll use a combination of Watkins voltages, available B+, instinct & tone to get me there.

Thanks again for your interest & help.


Hi loverocker

Yes there was a filter across the PT - I removed it !
My feelings being that it tamed the sound a little and also, of course, the fact that Marshall didn't use it.
Apart from anything else it just looks so ugly !

Mick

[Plexi]

Mick: yep there were a few changes..i don't know how far off your amp is compared to the schematic link i posted.. This schem had the 820 on the V1 already. but anyway..

other things on this schematic.

Input resistors on the inputs of the trem channel.
shows 100k..
Cathode bypass cap values are different,and cathode resistor for the EL84s
The resistor between the filter stage..this one shows a 10K
The 8.2 K may brig up the voltage some to the preamp.

140 isn't too bad, maybe when you have all the changes it may come up some.
Coupling caps in the Driver...005 the 18 uses .01
Grid stoppers to the EL84s show 10k..
and again..8.2K in the 18 marshall

This schematic shows a 275-0-275 transformer, where the 18 had a 300-0-300 So you may have slightly lower voltages in the WEM.. but still should be fine, and maybe make tube life last a bit better.

I used an old set of trannys in my first 18 i built.. And it had around 307 on the Plates of the EL84s.. and about the same voltages you show with yours.. This amp sounded fine..maybe a wee bit less volume compared to the Heyboer trannys..

Like you said, your amp has some different values compared to the schematic,maybe a different early/late model.
So Alot of things you'll just have to look and see or compare to the 18.

Richie

But looks like you've just about got it..lets us know how it turns out/sounds.

Richie

[zaphod_phil]

Currently working on a blue/white, V front Dominator attempting to 18 Watt-ise it.

Hey Mick, if it's not already too late, could I suggest you not 18W-ise your Dominator. Those V-front ones are very collectable and worth some good money. It would be tantamount to sacrilage to mod one of those. I would recommend you put it into as close to good original form as possible and sell it. Then buy yourself a MkII or MK III Dominator and mod that into an 18watter instead. You'll probably end up with a small profit. Loverocker has recently modded a later model Dominator into an 18watter.

[SweetSpot]

Whoops! Sure didn’t intend to offend anyone’s amp-sensibilities.

Thanks for the suggestion Phil. Sorry, but the deed is done........

Yes they are "collectable and worth some good money".
So here’s how I see it

This amps’ appeal is visual, it’s not renowned as a tone-machine like for instance the JTM 45, AC 15 or, Marshall 18 Watt, so I really don’t see the problem with making the Watkins sound better.

While the 45, 15 & 18 etc. sound fantastic in their natural state the Dominators don’t!............they LOOK fantastic ........ but, in my humble but considered opinion, sound mediocre to OK-ish at best. I’ve not heard of anyone craving “that unique Dominator distortion toneâ€

[loverocker]

I wouldn't worry. Like you, I had no worries about modding my WEM, but as a pennance I did go out and buy a completely stock Custom 15 - including the world's most ugly grille! Thinks: I really ought to do an A-B listening test of it against my 18W conversion...

Of course, the Dominator got a boost from the Oasis connection. People who had ignored WEMs checked them out and - surprise, surprise - they found they sounded just like thrashy '60s Brit amps. Perfect for retro/indy recording, so up went their value and rep as people started buying them up (ignoring the other WEMs with near/identical circuits).

Hey, they're only amps! Now, who here is going to own up to putting a Floyd Rose on their old Strat in the '80s? Swapping out PAFs for Dimarzio Super Distortions? I know you're out there, come and 'fess your sins to Rev Loverocker...

[zaphod_phil]

Hey Mick, no need to go overboard on it! No you haven't offended my sensibilities in the first place, as I'm not a WEM fanatic in any case. Without knowing the amount of amps you have owned/bought/sold etc, I was giving you the same friendly advice as to anyone else who may have asked the same question. Yes, of course the visual aspect is a big thing with the V-fronts, and yes, I know they sound mediocre. But collectors it seems are prepared to pay good money for them. I was only suggesting a more economic alternative. And actually, some of the later Dominator models aren't bad-looking either in my opion, although the one that is much taller than it's wide, the half PA column one is one obvious excpetion. Good luck with the build.

[ampkits]

Hello,

Hi Sweetspot. Your last message must be the the one with the most emoticons used in a single message on this forum, or anywhere I've seen!! :) Congratulations!

Anyways, on the matter of trashy Brit amp, I had a brief encounter with a Selmer Mercury 5. Not collectable or anything but the I really liked the tone. It sounds thick, yet chimey/brilliant, but maybe that was because I auditioned it thru a 66 Strat.

Didnt get the amp, nor the strat (selmer was bad cosmetically, and strat no longer for sale).

Point is: Some of these Brit amps really rock! Although they are not collectible today, it just takes a band or two that make it big using em. And prices would slowly rise up...

About WEM, maybe they are abundant over there in UK. They are getting rarer here, as people start to wise up on tube amps and collectibility. Heck, even the Copycat echos are so expensive nowadays here!

Thanks!

Nik

[SweetSpot]

Okay Phil

Just reviewed my last post

You’re right..................didn’t I go on & on?

Guess the Watkins / WEM thing must’ve hit a nerve with me.

The amps/bought/sold part was purely to make the points about having heard more than one Watkins & having experienced the indifference of prospective users as to how they sound.
In hindsight, I can see that it could possibly read as trying to impress –certainly wasn’t intended that way.
Didn’t imagine for a minute that a few Watkins owned or sold over the years might particularly impress anyone, especially on a site dedicated to such a venerable Marshall.
But yes, I agree ....... does waffle on a bit.

Well, really wouldn’t like to get off on the wrong foot with a fellow tone fan. Gained so much practical knowledge on this forum.....very informative & very addictive stuff........Magic!

Btw did I mention how amazing this conversion sounds?.....
Just can’t stop raving about this thing!
Can’t leave it alone!

Contrary to any impression possibly implied in last post ....... all
& any interest, advice or help, appreciated and welcomed.



Peace, love & the right B+

Mick




Hi ampkits

Thanks for the award, Nik, but the emoticon thing...........it’s over.

I’ll quit while I’m ahead.

[SweetSpot]

Whoops.........should've stuck to regular font size




(Rev) Loverocker

Any issues with OT on your conversion?
Seen some with a stock 12ohm G12.

Mick

[loverocker]

No OT issues - it's about the same size as the Heyboer I've bought for my 2nd 18Wer. I've left the conjuctive filter off - it's not fizzy, even with my extra triode on the front-end.

Mine's in a cab with a G12M, but the stock WEM Custom 15 has something else - an odd-looking Audiotrine or something (tucked in the back of the 'toy room', so I can't check it easily). I've taken to leaving it plugged into a '70s Marshall 4x12 (via a HotPlate) - far better for the classic rock sounds I like.