Adding a Tube Recto? WEM Dom amp.

[Sea Chief]

Chaps-
Ive heard of of my WEM dominator (mk1 bass) with a tube rectifier mod addition. Anyone know anything?

The best thing: the chassis has -an el84 size- hole cut in exact rectifier spot (surely likely for a tube rectifier itself in the 'next-up' amp?) so perhaps made to accomodate a gz81 is it? tube/ socket.

Id have thought at say £20 tube & socket it would be a damn good affordable upgrade & without too much faff as hole already cut. I guess its just how/ whether the PT taps etc etc.

Anyone have any info/ thoughts?

[YTube clip/ go to 3.40 Watkins Dominator: Tube Rectifier versus Solid State! - YouTube ]

thanks SC.

[mhuss]

More likely it's an EZ81 sized hole. :-) The original Dominators used these, changing to SS was likely a cost saver later on. The only question is, did they reduce the PT secondary voltage when they changed this? (I would have, because the EZ81 drops a chunk of B+. Also, it requires a separate 6.3 volt heater supply, does your Dominator have one?)

You can get much of the tube recto vibe by placing a 10w 330 ohm resistor inline after the SS diodes.

--mark

[Sea Chief]

Hi Mark-
ez81 is it- ok afaict its an el84 sized tube anyway/ the hole cut in 'rectifier place' is so.
Im interested in the 10w resisitor addition, but if this is so effective/ cheap, why was it not in the amp to begin with?

Assuming the PT does have the neccessary wiring (if the YTube one is done so, then the PT must have/ he wouldnt have changed out the orig PT for losing the essence of the amps tone) I wonder how simple it would be to do.

[Bruce / Mission Amps]

Doesn't the EZ81 have separate filament elements from it's cathode? If so, and the PT high Voltage secondary is Full Wave... and it can handle another 1 amp on the 6.3v winding, ...you should be able to just wire it into the existing 6.3v filament line and run B+ instead of using the SS rectifiers.
And it makes perfect sense to me to use SS rectifiers for a bass amp....

[Sea Chief]

Hi Bruce-
is the reason I see most often a separate pair of (usually yellow iirc) 6.3v heater wires going to the rectifier, because this additional tube is generally too much for the other (usually green iirc) heater wires going to other tubes? or is it because usually a different voltage pair of heater wires is required for the rectifier?

[g1]

The yellow wires are usually a 5 volt heater winding. Rectifier tubes that run on 5V heater are more common than 6.3V types. Green windings are 6.3V, yellow 5V (maybe some rare exceptions to this rule).

[Sea Chief]

So do ez81 rectifiers run on 6.3v heater wires then? I assume the el84's and the ecc83's/12ax7's are doing so in my Dom amp.

[Jazz P Bass]

The EZ81 heaters run on 6.3 Vac.
The current requirement is 1 amp.
Link: http://www.hifitubes.nl/weblog/wp-co...ilips-ez81.pdf
What are you trying to accomplish with this mod?

[Ted]

The EZ81 heaters run on 6.3 Vac.

The clue is in the "E" of EZ81

Mullard?Philips tube designation - Wikipedia, the free encyclopedia

[Sea Chief]

Good links chaps- extremely useful those. Now I can guess why my 5AR4 starts with a 5 then. So the mod is made easier still with both a hole ready in recto spot, and the heater supply covered. So even if results are miimal it still makes much sense to do, IMHO.

"What are you trying to accomplish with this mod?".. good Q. Well, from amps Ive played backed up with video evidence (a good eg a: 'Fender Super Sonic 22 vs Fender DRRI'/ effectivey same circuit but SS vs tube recto) or similarly the SS vs tube recto link in #1.. the slightly 'hard' edge of a SS rectifier IS made slightly softer/ richer/ more organic tone and feel overall with a tube rectifier. Not massive difference I admit but clear/ significant enough to me. (For £20 + few hrs work even with minimal positive difference it seems verging twds 'no-brainer' mod, does it not? or maybe Im missing a trick here? Im open to be put right tho).

[Steve Conner]

The whole point of the "E" series rectifiers is that the heater is well insulated from the cathode and can run off the same 6.3V winding as all the other tubes.

This is in theory, in practice the heater-cathode insulation was none too reliable so some designers used a separate heater winding anyway.

You also have to question whether the heater winding can withstand the extra 1 amp of load. Maybe Watkins kept on using the same PT after eliminating the tube rectifier (old stock to use up?) or maybe they downsized the heater winding to save manufacturing cost.

Finally, American transformers used different colour coding to British ones. No green heater wires here.

[Sea Chief]

Ah yes I didnt see any green wiring you're right.. I can of course locate the heater wires to the '1st' pwr tube and put these onto the ez81, then adding 'green' pair as it were from there to the 1st pwr tube.

I might pluck up the courage to ask Mr Watkins himself re the extra load: I was lucky to rcv an email directly from the man himself (so he reads this excellent site- not so surprising as Id bet none come close to MEF); he was concerned over my innitial Q regarding what I thought the seller had (not) done [ie rejigging the pwr tube wiring for pins 1&2 for a modern pair of el84's] and gave me the new reissue maker's number. How good is that? Seller had done the rejig ok btw.