SORTED - Mullard ECL86

Castro

Good afternoon

I took delivery of some NOS 12ax7s today and the seller accidentally included an extra tube, a Mullard ECL86.

I know nothing about these and would be interested to know what their use might be.

Thank you.

ICBM

It’s a combination pentode/triode which can be used as a power valve with its own driver stage or half of a phase inverter. The pentode is similar to an EL84 but with slightly lower ratings and the triode is basically a 12AX7, from memory.

It’s not often used in guitar amps but two which do are the Marshall Popular and some versions of the WEM Dominator, although I think the WEM was designed for the similar ECL82. Both of these will need a pair though, unless you’ve got one with an obvious failure in one valve and the other is OK.

ecc83

The ECL86 belongs to a group of triode pentodes. ECL80, ECL82, ECL83*,ECL86. The 86 is the best of the bunch being used in the more upmarket record players and radiograms. The "Blue spot" RG was a famous must have for the regge boys,  ECL86 in pp per side and four, iirc, ten inch speakers to woomp well!

*A truly awful valve. Compact but that was its undoing it got very hot and cooked everything around it.  The PCL83 was the CTversion and was similarly unreliable. (there was a PCL84. Not sure if there was ever a 6volt heater version?)

Make nice little practice amp would an ECL86.

Dave.

ICBM

ecc83 said:

Make nice little practice amp would an ECL86.

That was my first thought... if you have no use for it, send it to @4114Effects . I think it would need another gain stage though - all the one-stage-preamp amps I know of use an EF86, which has more gain - so a single-valve amp is probably not going to work.

exocet

ICBM said:

ecc83 said:

Make nice little practice amp would an ECL86.

That was my first thought... if you have no use for it, send it to @4114Effects . I think it would need another gain stage though - all the one-stage-preamp amps I know of use an EF86, which has more gain - so a single-valve amp is probably not going to work.

My first valve guitar amp used ECL86. It wasn't actually a guitar amp but I used it anyway driving a Celestion G12 -100. Got some good tones out of it...at least that's what I thought at the time.

ecc83

ICBM said:

ecc83 said:

Make nice little practice amp would an ECL86.

That was my first thought... if you have no use for it, send it to @4114Effects . I think it would need another gain stage though - all the one-stage-preamp amps I know of use an EF86, which has more gain - so a single-valve amp is probably not going to work.

Oh! Bugger! I have just done a massive (gigs) cleanup of this laptop and now I have just quoted ICBM I have got some coding ***t in the box I have NEVER seen before! Anyhooos ! Was going to say, VERY cheekily and pointedly that the ECL86 could have a nice little TL072 20dB or so booster affront it! (now, where have we seen that idea before?) Actually will lookup the data on the 86. I reckon the triode is, as you say, 1/2 an 83 and the pentode has a pretty high gm so if gain is not wasted in complex tone stack? Could be hot enough. Dave.

ecc83

Phew! 's ok. Dave.

ecc83

http://www.r-type.org/articles/art-003g.htm ^ Shows a Mullard amp design and give a sensitivity of 50mV for 3W (and that is B loud out of a guitar speaker!) . Note, that is without the negative feedback but us gitamp folk don't bother with such niceties DO us! Dave.

ICBM

ecc83 said:

http://www.r-type.org/articles/art-003g.htm ^ Shows a Mullard amp design and give a sensitivity of 50mV for 3W (and that is B loud out of a guitar speaker!) . Note, that is without the negative feedback but us gitamp folk don't bother with such niceties DO us!

Aha! Plenty . A typical guitar output is about five to ten times that, so you should be able to get useful overdrive as well, as you say as long as you don't use a tone stack with a big insertion loss. I would guess for this kind of project it would be either just a volume or at most with a treble cut/treble pass single tone knob.

ecc83

The sting in the tail in the Mully design these days is a suitable output transformer IC. Must of course be a "gapped" stack intended for single ended operation and they tend to be expensive . Had a very quick look at Sowters...Wheee! a nifty. Of course these are "hi fi" traffs so it might be possible to use a Fender Chap SE component.  Anytime any of you are looking round car boots etc , don't pass up old radios if cheap enough. Even if well battered and dead the SE optraff is very unlikely to be faulty.  The mains traffs in the bigger radios were also very reliable but if you use one for a project amp you must get it PAT tested.

Dave.

Castro

Cheers people  your responses have at least clarified that I have no current use for it.

springhead

Phil at Bluebell Audio sells Hammond transformers.  A 125BSE, 5W, 45mA, £27 would do it. 

http://www.bluebellaudio.com/ 

 

4114Effects

Or of you want even cheaper I've used a few of these in low wattage builds https://www.google.com/url?sa=i&source=undefined&cd=&ved=0ahUKEwino6HMsa7gAhUz8-AKHTdkCxEQzPwBCAM&url=https://uk.rs-online.com/web/p/audio-transformers/2106475/&psig=AOvVaw1El76bbrmJ3zcd0Rflay4C&ust=1549792633398189

ICBM

4114Effects said:

Or of you want even cheaper I've used a few of these in low wattage builds

[RS 3.5W OT]

Formerly known as the ‘Midget’ Output Transformer .

They’ve been selling those since at least the 1960s - I’ve got one with the old Radiospares ‘running man’ logo on somewhere.

ecc83

Cor! Never thought Rad Spad were still doing those transformers! Used to be called the "Universal Output Transformer" I think and I have a bigger one on a chassis in the loft for PP EL84s and EL34s.

There were a few radios (and tellies) that had rather feeble OPTs and the RS ones were used and I never knew one to fail.

Dave.