NAD: WEM Dominator MKIII with the real old Mullards in there, question about EL84 pinouts

De_Batz

Slight punt on this one from eBay - I've wanted a Dominator for a while (had a MKII twenty years ago, and still have the earlier PowerBass one in the 'Scout' livery) but not prepared to pay £500 for one. 

The punt - if all those Mullards work well, they're worth half to 3/4 what I paid for amp. 

If they're shot to balls, I've overpaid (a bit). 

Got it to the rehearsal place last night, all three of the preamp valves working well and all four EL84s seeming to do something. Ch 1 works, after a bit of jury-rigging the input socket. Ch 2 works really well. Annoying to have to mess about to connect it to a speaker (see the flying wires poking out of the back!), and it was crackly before the liberal application of a switch cleaner to the pots. 

I'd rate this as a bit of a score, actually. The three I63 preamp valves sound fantastic and have already been cherry-picked for other amps where they do more of a job. The EL84s may well be a bit tired, who knows. They're going in the box for special occasions. 

I haven't checked it with a set of modern EL84s yet, but I understand that I might have to bridge pins 1 and 2 on the EL84 sockets to make them work. Has anyone done this mod? It looks simple enough - once the chassis is off the board, you can get at the socket easily. 

It's not humming madly, which is a bonus, as well. 

As a further point for discussion, I'm going to get a head box made for it. What do we think in terms of colour scheme?

I'm currently leaning black/cream/black along the lines of its older brother the Warrior... (that's not my actual amp, BTW!). 

LastMantra

I've built a dominator into a head. Mine is just natural wood with Danish oil.


https://photos.app.goo.gl/PM45UV4aeRL23Sf1A

LastMantra

sorry don't think I can do pics 

springhead

Why do you think you'd have to link pins 1 & 2?  EL84 pinouts haven't changed over the years.  I've put new ones in old amps and vice versa.  Pin 1 is shown as an internal connection, so shouldn't be connected to anything.  Pin 2 is the control grid. 

De_Batz

springhead said:

Why do you think you'd have to link pins 1 & 2?  EL84 pinouts haven't changed over the years.  I've put new ones in old amps and vice versa.  Pin 1 is shown as an internal connection, so shouldn't be connected to anything.  Pin 2 is the control grid. 

I read - and bear in mind I haven't tried and I also haven't taken the amp apart to check - that the old Mullards have the grid (pin 2) internally connected to pin 1, so they work without issue, but modern EL84s have no internal connection. WEM connected pin 1 but not pin 2 (again, so I read), relying on the internal connection present in the old EL84s but not the new ones. 

The mod is supposed to be tie pin 1 to pin 2, then you can use any modern or old EL84. 

De_Batz

LastMantra said:

I've built a dominator into a head. Mine is just natural wood with Danish oil.


https://photos.app.goo.gl/PM45UV4aeRL23Sf1A

I can see it if I follow the link. Nice stuff!

JezWynd

LastMantra said:

I've built a dominator into a head. Mine is just natural wood with Danish oil.


https://photos.app.goo.gl/PM45UV4aeRL23Sf1A

Very nice!

De_Batz

JezWynd said:

LastMantra said:

I've built a dominator into a head. Mine is just natural wood with Danish oil.


https://photos.app.goo.gl/PM45UV4aeRL23Sf1A

Very nice!

While we're on the subject, what is bolted to what? It looks like the chassis bolts through the front marry up to the two through the side. Have you got a couple of fat braces / battens in there to hold it all together? 

My 'plan' would be to have the panel up as close to the top as possible (perhaps under a little lip like the combos) and rest the bottom wooden tray on the box or on a couple of battens on the inside. 

With 'plan' being very much the operative word...

Dodge

De_Batz said:

springhead said:

Why do you think you'd have to link pins 1 & 2?  EL84 pinouts haven't changed over the years.  I've put new ones in old amps and vice versa.  Pin 1 is shown as an internal connection, so shouldn't be connected to anything.  Pin 2 is the control grid. 

I read - and bear in mind I haven't tried and I also haven't taken the amp apart to check - that the old Mullards have the grid (pin 2) internally connected to pin 1, so they work without issue, but modern EL84s have no internal connection. WEM connected pin 1 but not pin 2 (again, so I read), relying on the internal connection present in the old EL84s but not the new ones. 

The mod is supposed to be tie pin 1 to pin 2, then you can use any modern or old EL84. 

@ICBM will be along in a minute to confirm. I think you're right though, I'm sure i read there's something to be done to make these work with modern EL84s.

impmann

Dodge said:

De_Batz said:

springhead said:

Why do you think you'd have to link pins 1 & 2?  EL84 pinouts haven't changed over the years.  I've put new ones in old amps and vice versa.  Pin 1 is shown as an internal connection, so shouldn't be connected to anything.  Pin 2 is the control grid. 

I read - and bear in mind I haven't tried and I also haven't taken the amp apart to check - that the old Mullards have the grid (pin 2) internally connected to pin 1, so they work without issue, but modern EL84s have no internal connection. WEM connected pin 1 but not pin 2 (again, so I read), relying on the internal connection present in the old EL84s but not the new ones. 

The mod is supposed to be tie pin 1 to pin 2, then you can use any modern or old EL84. 

@ICBM will be along in a minute to confirm. I think you're right though, I'm sure i read there's something to be done to make these work with modern EL84s.

I'm sure there is a problem here too... a chap I work with had problems putting modern valves in his WEM. I can't remember the ins-and-outs but I'm sure there was some kind of difference.

springhead

Mullard datasheets show Pin 1 as "IC", internal connection, but don't show what it's tied to. I can't see why WEM would use that for grid, assuming that it is internally tied to Pin 2.  However JJ's data sheet shows nothing on Pin 1.

Actually, just occured to me my office hifi Leak Stereo 20 has 4 old Mullard EL84's in.  I've just pulled one and lo and behold pin 1 is a dead short to pin 2!

I'd say have a look at the underside of the valve bases in your Dominator and if they've wired the grid connection to Pin 1 then just move it to Pin 2.

Edit:  Further just occured to me that I've also got a Fender Pro Junior sitting behind me with a pair of JJ EL84's in.  Pulled one of those and yes, no connection between Pin 1 and Pin 2.

So If WEM have used Pin 1 for Grid then it won't work with JJ EL84's so it needs to move.

LastMantra

De_Batz said:

JezWynd said:

LastMantra said:

I've built a dominator into a head. Mine is just natural wood with Danish oil.


https://photos.app.goo.gl/PM45UV4aeRL23Sf1A

Very nice!

While we're on the subject, what is bolted to what? It looks like the chassis bolts through the front marry up to the two through the side. Have you got a couple of fat braces / battens in there to hold it all together? 

My 'plan' would be to have the panel up as close to the top as possible (perhaps under a little lip like the combos) and rest the bottom wooden tray on the box or on a couple of battens on the inside. 

With 'plan' being very much the operative word...

Ah thank for the pic @JezWynd ;;;and comments much appreciated 


To be honest I can't totally remember  the amp is being stored at my parents house at the moment. The box was basically just glued/screwed together with some strengthening battens in the corners. The chassis is just held by the bolts at the side which are into rubber mounts. Kind of floating. I think as it was originally. Pretty solid anyway but heavier than I was expecting. 

I stripped it right back to the bare circuit board and rebuilt it with new components. All that's original are the valves and transformers really. Two greenbacks in the cab.

Sounds great though IMHO. 

RiftAmps

De_Batz said:

springhead said:

Why do you think you'd have to link pins 1 & 2?  EL84 pinouts haven't changed over the years.  I've put new ones in old amps and vice versa.  Pin 1 is shown as an internal connection, so shouldn't be connected to anything.  Pin 2 is the control grid. 

I read - and bear in mind I haven't tried and I also haven't taken the amp apart to check - that the old Mullards have the grid (pin 2) internally connected to pin 1, so they work without issue, but modern EL84s have no internal connection. WEM connected pin 1 but not pin 2 (again, so I read), relying on the internal connection present in the old EL84s but not the new ones. 

The mod is supposed to be tie pin 1 to pin 2, then you can use any modern or old EL84. 

The Laney VC30 also has this problem, Steve Rowse explains...

I bought NOS EL84s for my Laney VC30 but when I plugged them in they went pop. Wassup?

The sockets in the VC30 are wired up to accept only one type of EL84. They use a pin that has no connection on some valves as part of the circuit – however other EL84s do have a connection there – and pop they go when you plug them in. Not too hard to rewire the sockets if you have this problem.

springhead

According to my old 1970 Mullard Data Book Pins 1, 6 and 8 are internal connections.  I'd move the grid to Pin 2, not link 1 and 2. And while you're there make sure that 6 and 8 aren't being used as a tie point, e.g. for screen resistor.

ICBM

RiftAmps said:

I bought NOS EL84s for my Laney VC30 but when I plugged them in they went pop. Wassup?

The sockets in the VC30 are wired up to accept only one type of EL84. They use a pin that has no connection on some valves as part of the circuit – however other EL84s do have a connection there – and pop they go when you plug them in. Not too hard to rewire the sockets if you have this problem.

The fault is with amp designers not reading the original spec for the EL84 correctly, misinterpreting 'IC' (internal connection) as 'NC' (no connection) and using the valve socket terminal for pin 1 as a component support, usually for the screen resistor. This then feeds the full HT voltage into the control grid of the valve, which will immediately kill it. Even if it's the grid stopper resistor, a valve with pins 1 and 2 connected internally will then effectively bypass the resistor which may cause instability.

De_Batz

EL84 socket wiring... https://imgur.com/gallery/Z8sfM2P

Let's see how we get on with this... 

De_Batz

Balls. Not working on the images at the moment. Amp off wooden base, looking at EL84 sockets. Currently look like nothing wired to pin 1, so we might not have to arse about with these sockets.

Please check whether I am an idiot or not. Could go either way, really... 

De_Batz

springhead said:

Mullard datasheets show Pin 1 as "IC", internal connection, but don't show what it's tied to. I can't see why WEM would use that for grid, assuming that it is internally tied to Pin 2.  However JJ's data sheet shows nothing on Pin 1.

Actually, just occured to me my office hifi Leak Stereo 20 has 4 old Mullard EL84's in.  I've just pulled one and lo and behold pin 1 is a dead short to pin 2!

I'd say have a look at the underside of the valve bases in your Dominator and if they've wired the grid connection to Pin 1 then just move it to Pin 2.

Edit:  Further just occured to me that I've also got a Fender Pro Junior sitting behind me with a pair of JJ EL84's in.  Pulled one of those and yes, no connection between Pin 1 and Pin 2.

So If WEM have used Pin 1 for Grid then it won't work with JJ EL84's so it needs to move.

Great stuff in this post. Looks for all the world as though this amp was originally wired to pin 2 across the board, so either is an anomaly or late enough to have been corrected at the time of manufacture. 

De_Batz

RiftAmps said:

De_Batz said:

springhead said:

Why do you think you'd have to link pins 1 & 2?  EL84 pinouts haven't changed over the years.  I've put new ones in old amps and vice versa.  Pin 1 is shown as an internal connection, so shouldn't be connected to anything.  Pin 2 is the control grid. 

I read - and bear in mind I haven't tried and I also haven't taken the amp apart to check - that the old Mullards have the grid (pin 2) internally connected to pin 1, so they work without issue, but modern EL84s have no internal connection. WEM connected pin 1 but not pin 2 (again, so I read), relying on the internal connection present in the old EL84s but not the new ones. 

The mod is supposed to be tie pin 1 to pin 2, then you can use any modern or old EL84. 

The Laney VC30 also has this problem, Steve Rowse explains...

I bought NOS EL84s for my Laney VC30 but when I plugged them in they went pop. Wassup?

The sockets in the VC30 are wired up to accept only one type of EL84. They use a pin that has no connection on some valves as part of the circuit – however other EL84s do have a connection there – and pop they go when you plug them in. Not too hard to rewire the sockets if you have this problem.

From what I read last night, it's the exact opposite problem, in that they wire something to pin 1 that doesn't belong there, and if you put Mullards with 1 and 2 connected (internally), it either cabbages the amp or the expensive valve.

Would be happy to be corrected, though. 

De_Batz

ICBM said:

RiftAmps said:

I bought NOS EL84s for my Laney VC30 but when I plugged them in they went pop. Wassup?

The sockets in the VC30 are wired up to accept only one type of EL84. They use a pin that has no connection on some valves as part of the circuit – however other EL84s do have a connection there – and pop they go when you plug them in. Not too hard to rewire the sockets if you have this problem.

The fault is with amp designers not reading the original spec for the EL84 correctly, misinterpreting 'IC' (internal connection) as 'NC' (no connection) and using the valve socket terminal for pin 1 as a component support, usually for the screen resistor. This then feeds the full HT voltage into the control grid of the valve, which will immediately kill it. Even if it's the grid stopper resistor, a valve with pins 1 and 2 connected internally will then effectively bypass the resistor which may cause instability.

Just read this after posting reply to @RiftAmps. As ever, thanks for your wisdom! 

De_Batz

Thanks for all the replies, technical info and support. Brilliant stuff all round.