18Watt.com

picked this ex-mod test unit up on ebay for £22 free delivery,the frame & panels are aluminium and it has switches,pilot lights,fuse holder etc that i'm going to use to build a ecl86 amplifier with. i've cut the box to size and painted it,inside was a fibre board 14mm thick! used a piece of it for my vvr board. the amp is going to be 18W specs for the phase & power section with vvr and switchable rectifier,not sure on preamp yet,probably lite2 or TMB.

Couple of pics against my 112 combo to give you an idea of the size,because it’s old stock the threads in the flanges are bsf or unf so going to drill & tap those out to 3mm.
I’ve got some stainless mesh for the back plate and going to use tinted Perspex at the front.just waiting for my sheet of 3mm aluminium to get here then now lockdown has eased of I can visit my local friendly sheet metal shop and bend the chassis up,going to be tight in there about 11 X 5 inches so i’m using tag strips for this.

Burning in the new electrolytics,even though there is an allowable amount of leakage with electrolytics it always surprises me how much brand new ones have until burned in! one thing I hate about carbon composites is their tolerances,I bought these 6 1W 100K’s to try the “mojo” on the phase plates and look at these measurements- 92K,95K,105K,109K,114K,115K, what do you have to do to actually get 100K buy 100 of them and hope you get 2!

Holy moly! Those are the longest terminal strips I've ever seen! Is that a current product, or something you have that's NOS? I wouldn't worry about the values of those 100Ks for PI service. If you want the PI to be balanced, it's the ratio that matters. You could use a 100K and a 115K. If you want the PI unbalanced for extra even-order harmonic energy, pick two that are similar. This looks like a fun project!

Jack

28 lugs Jack,i got these from one of the suppliers i get resistors/capacitors etc from but i've seen them on ebay as well.
yeah not worried about the comps,can always use films if i need to be exact.

geoff 1965 wrote: ↑

Thu 05/06/21 6:16 am

C958D657-402B-43CB-A814-FF48B6E78C62.jpeg
Burning in the new electrolytics,even though there is an allowable amount of leakage with electrolytics it always surprises me how much brand new ones have until burned in!
E8FA3B98-3A10-42E3-8C10-BC7E3140E6D5.jpeg
one thing I hate about carbon composites is their tolerances,I bought these 6 1W 100K’s to try the “mojo” on the phase plates and look at these measurements- 92K,95K,105K,109K,114K,115K, what do you have to do to actually get 100K buy 100 of them and hope you get 2!

for better balance, 100k and 92k would be close to ideal - but we don't want better balance in our non-Hi-Fi world

the OT primary resistance is pretty equal at 162-168 ohms whereas my lite2 18W has 345-306,a good 40 ohms difference so even if i have a perfect matched pair of tubes there is some imbalance.
i'm not going to bias the ecl's at 13W max,my target voltages for the anodes is 275-300 on the pentodes,220 on the phase and around 150 preamp.i'll have to see what i get under load.

geoff 1965 wrote: ↑

Thu 05/06/21 11:34 am

the OT primary resistance is pretty equal at 162-168 ohms whereas my lite2 18W has 345-306,a good 40 ohms difference so even if i have a perfect matched pair of tubes there is some imbalance.
i'm not going to bias the ecl's at 13W max,my target voltages for the anodes is 275-300 on the pentodes,220 on the phase and around 150 preamp.i'll have to see what i get under load.

The difference in winding resistance is due to the fact that one set of windings is on top of another. For an equal number of turns, the outer winding will consist of a longer run of wire. When you're thinking about the imbalance this might cause, consider that 40 ohms DCR is really insignificant within a winding with a reactance of thousands of ohms. It's also a tiny portion of the anode resistance of most tubes used to drive it. You can't count on this to deliver much even-order distortion.

Jack

thank's for explaining that Jack,i was dubious of the evenly matched windings. anyway that poor little OT has spent it's life in a HiFi amp with zero distortion,it's time to experience some overdrive!!

Tricky part of cutting the chassis shape to fit in the frame done,the local sheet metal workers bent the plate up,that’s the second they’ve done for me and they won’t accept payment! good lad’s!

Awesome project Geoff!!!

My current profile pic shows my 13W LIte IIb combo, based around a pair of ECL86/6GW8s. I re-used the cab and metal work from a crappy Marshall 2060 Mercury combo I bought on FleeBay. Kind of big for a lunch box I got Nik from Ceriatone to build me a custom board for it - his first ever non-F*nder board! The OT is one of Ingo Gorge's famous RS replica OTs. Ingo uses all of the exact same materials as RS did, even down to the paper. I also put a vintage G12H30 speaker in that cab. That amp has a beautiful creamy overdrive tone with a solid low end and is super loud! I've been told so many times to turn it down by people who couldn't believe it was only 13W! It was a favourite gigging amp of mine, until my brain surgery and then the lockdown.

cool! steve who gets the valvepower transformers made recently had some exact repro RS output transformers for sale on ebay,they've all sold but if he lists anymore i'll post it the ad,he helped me out with the 275-0-275 PT's i had made.
the description of your amp inspired this build ZP,all the demo's of ecl86 guitar amps on youtube sound terrible except one guy who made a mini plexi which had really good tone and breakup.

Transformer cutouts done,just enough room for the 5 tubes,tubes & pots are going to be at the front.

Drilling and test fitting done,next strip it and sand the scratches out ready for a couple of coats of etching primer.

geoff 1965 wrote: ↑

Sat 05/08/21 10:55 am

Transformer cutouts done,just enough room for the 5 tubes,tubes & pots are going to be at the front.
16F5C06D-7A77-4E43-AA80-5CF3C8AF60FE.jpeg

Five tubes?? My Lite IIb only has three tubes, with solid state rectification

My 18W is lite2/cascade,and my 6V6 amp has the trinity plexi mk2 preamp so i’m going to do some experimenting with this one ZP, I know the tone & breakup is in those ecl’s and i’ve got the rectifier switchable between ez81 and solid state.the extra preamp tube gives me options as in TMB etc. I might try the hiwatt tube buffered effects loop with the extra triode?

zaphod_phil wrote: ↑

Sun 05/09/21 4:28 pm

geoff 1965 wrote: ↑

Sat 05/08/21 10:55 am

Transformer cutouts done,just enough room for the 5 tubes,tubes & pots are going to be at the front.
16F5C06D-7A77-4E43-AA80-5CF3C8AF60FE.jpeg

Five tubes?? My Lite IIb only has three tubes, with solid state rectification

ZP... is that a SE output amp?

Bieworm the ecl86’s have one pentode and 12ax7 triode in them,if you use those for the phase inverter you only need one more preamp tube for a lite2.

geoff 1965 wrote: ↑

Mon 05/10/21 6:25 am

Bieworm the ecl86’s have one pentode and 12ax7 triode in them,if you use those for the phase inverter you only need one more preamp tube for a lite2.

ok.. my bad