Wednesday, 15 June 2022

Back to stage – a PSU for a known singing bird

Hello everybody,

in loose sequence I am posting articles about vintage audio equipment. In the last couple of month I have spend my time more with listening to music and with the support rearing of songbirds, in particular of black birds,  than with building audio equipment. To listen to the very different sound of birds is as well a exceptional training for the educated ear...

Today I am talking again about building a power supply for a British tube preamplifier with RIAA-equalizer stage. A familiar customer asked me a while ago if I will be able to make him a power supply for his Concordant Exelsior preamplifier. He pretended to have a schematic for it and as well the schematic of the amplifier itself. I said that it would not be to difficult to make one. Next he asked me if I will be able to make one with tube rectification and better components. I said I need to check, because some components are hard to find in the meanwhile and that I would need to check my stock of parts. The schematics turned out to belong to a completely different version of this preamp. As the most people might know mains transformers with split balanced HT-output and two different filament windings "don't grow anymore on trees" as it would be needed for this! A quick look in my storage gave me some overview to pulled transformers from old equipment, foremost from old radios, some were missing parts, others where winded for 4 volts filament, etc. I didn't find the right part to do it well. Next question is to find new parts, Lundahl might here the right solution, but nothing under 200 €, which was expected a lot to expensive. Next problem would be to find a matching case for all, matching in visual terms, but as well big enough to harbor all components. Not easy, but I decided to get forward with a black painted Hammond casted aluminum case of the same height and depths of the Concordant. My customer limited the cost range for all to 250 €, which is an almost impossible sporting competition to stay beyond. A rough calculation showed immediately that such amount will pay the needed parts but not the work making it. On the other hand this guy never had a chance to listen to this preamp before, since he bought it without power supply. This person normally listens to a Shindo Monbrison and other well priced and established products, so he does not know what he will become at the end, just to explain his tight money framing. To be honest with this limit a simple PSU with silicon rectification and simple filter stage for the anode rail and silicon 12 volt IC regulation will be the solution to bring the package back to life within such financial limitations. I told him about and he pleaded to get something better, smoother sounding. I told him, that there will be no guaranty that even a perfect made PSU will bring this preamp to the level he ideally might expect.

Ok, I started some research at the internet and opened the Concordant case with the result that I realized that this version is equipped with ECC82 in the output stage and ECC88 in the RIAA-filter stage. This means with ECC88 it needs a 6.3 volts filament supply – no way make a cheap silicon based regulation with penny parts only ugly rails of hated caps and resistors to drop the voltages. 

So it gets back to the start with tube rectification with EZ81, choke regulated loading and filter stage for the anode supply. I looked again into my storage list for mains transformers, where all transformers are listed, which are useful for power amplifiers with their exact output data. The most of the transformers are collected as pairs, I am always afraid to use one of them for a single project, so still a lot of them is untouched since years. So I found the right type with the right taps, just a little bit oversized for such a project, but otherwise perfect. I decided to use it because I am not getting younger and the future projects might get countable. Now I needed to order a Hammond 157G 30H/40mA smoothing choke and I found a supplier who offered a bunch of NOS double capacitors 2x100uF/400V of ideal physical size to match my selected case. The Concordant sports a luxury, a mirrored double filament support for each channel, so it says at the front plate double mono preamplifier. At the back it has two identical unusual German DIN three pole jacks for this reason. I found in my storage the matching plugs, otherwise nowdays hard to find. So I collected all necessary parts from my storage together, – switch, fuse holder, cables and wires, resistors, tubes, silicon rectifiers, oil caps, supports, screws, nuts, bolts and more. When I first time tested the size of the case with the real components, I realized that it will get tight, – exceptional tight. At the end there was not the space for one more resistor inside. I needed several times to regroup the components inside to make it work!

At the end of the day all parts were in place and the case could be closed without pressure. Before I needed to isolate delicate exposed contacts. For example the tip of the EZ81 just matched the close case because I drilled ventilation wholes into the cover, the middle whole takes the tip, underneath the octal socket I needed isolation, because there was only 1mm air left between HT contacts and the base plate!

When I connected the new preamp with PSU to my setup, I was really astonished. The sound was exceptional refined, with wide open smooth and liquid soundstage, exactly so I do like it a lot. Of course I don't have any comparison to the original version, but I must say this combination is very very good. Yes the PSU uses some basic ideas which have been established in my equipment for years. For example the push-pull choke for the filament, the low oil capacitance in the loading stage for the rectifier tube to make it fast and smooth. 

I am looking forward about the ruling of the owner when he does the compare it with his Shindo Monbrison. It might get difficult... This is definetly under all tube preamps which had a chance to listen to one of the rare singing birds.

And who is now going to pay my work? 

Friday, 21 January 2022

Revisiting own History – The classic Leak TL12+ amplifiers

As already widely shown in my earlier articles I collected in the early 1990ties during my London time a whole lot of classic Leak tube amplifiers. Foremostly I remember one visit in London in 1992 when I did buy an exceptional lot of amplifiers from London dealers. On the way back to Germany my car got stopped from French custom officers because of its obvious visible overweight in its trunk, the rear wheels already were deep hidden in the chassis with an extra 15ยบ camber. I will never forget the officers face when I did show him the tight stacked amplifiers, he had no idea what he was looking at. I don't exactly remember, but it must have been around 6 to 8 pairs of this model TL12+ and several Stereo 20 and as well some pairs TL10.1  and TL12 point one's. I tried to explain that these are historic audio amplifiers, but he hardly could believe my words looking at a wall of golden chassis.

The classic late 1959 Leak TL12+, here already with RCA-socket and input pot.

The shown pair is one set of this batch. I did restore all of them to my highest possible standard these days. In particular this pair got the best care because of the rather rare color "champaign" and with the aim to keep them for my own collection. As regular treatment I replaced the electrolytic filter caps to oil caps. Here the old electrolytic content needed to get emptied in order to reuse their cans for originality and color with new caps glued in. Generally all coupling caps where replaced to oil caps, a expensive step these days because the only modern source for such was Audio Note, who cared about the distribution of Jensens Audio Caps, a good 20£ investment for each value which added alone to 200£ for a set. All carbon composition resistors got exchanged to new German Beyschlag 2 watts carbon composition types, each around 2 € only available in 10er belts these days. The cathode bypass capacitors generally got changed to bipolar tone frequency caps, which mainly where used as crossover parts in speakers. The religion in these days was the use of triodes in all stages, so I always changed the input stage from EF86 pentodes to ECC83 triodes in order to refine the soundstage and to reduce the input amplification factor, which is with all Leaks extremely sensitive. I brought generally the power stages of these push-pull designs to semi triode operation of the EL84 tubes. All these steps were introduced in order to achieve with this little amps a much more sophisticated and smoother operation, in contrast to the impressive, but a bit too cheaky performance of the original version. The reduction of output power from 12 watts to hardly 4 watts in pseudo triode operation emotionally perceived with efficient speakers (better than 96db) as to be a even better drivability. 

Close up of input stage in foreground, in background whole lot of modifications at the filter stage with smoothing choke (at left) and fuse holder, switch (at right) and power cord.

As some might expect the days weren't far that I decided, with almost every Leak model in daily use, the most of them in several versions, to get rid of some doublets to save space and money. Some friends of mine got within this years involved into my passion and became interested as well to use tube amplification in combination with Tannoy speakers. So I sold some amps from my collection to them. As reported in my last entry a Leak Stereo 60 of my early collection revisited me unexpected end of last year. This example found a caring new home in the meanwhile. Shortly before New Years Eve another friend visited me and brought another former pair into service, which acted for 30 years a long term companion to his Tannoy Lancasters with 15'' Monitor Golds for him. When I started to inspect this pair, I realized what 30 years of rough use with several house moves and more or less permanent plugging and unplugging can do. They were completely rocked down. Loose contacts, open wires, leaking capacitors, wax dripping from transformers, tubes run down to 20%, in one an almost black ashed rectifier tube showed the remnants of an unexpected firework, – he had treated them almost to unusable wracks. My friend decided to spend good money for another life and a total revision. At my first restoration in 1992 these amps were already 35 years old, now added on to another 30 years. I will try my best to give them another third life for the next 30 years. Maybe these little wonders will find one day when I already will be passed away the next owner who might bring them into a fourth period of living  –  this is what I will call sustainability – not the highly acclaimed class G digital amps to be so.

View of the complete mainboard, just at top edge underside of pot and the filament symmetry element

For this reason to open up for a new future I decided to change some principles I had 30 years ago. I always took extremely care to keep mechanical originality of the amplifiers, which was meant not to drill wholes or remove unused components, like the octal sockets for chaining further Leak- or other components. Today or even better tomorrow nobody really will use a Troughline tuner or a Varislope preamp, so contemporary preferences for practical use are getting more important instead of originality. A better control of the input signal, in particular with modern high output components (min. 2V or more) like preamplifiers, computers or digital streaming clients, – more or less hum- and hiss free operation and of course still the smooth and dynamic soundstage are relevant for the aficionado.

So I needed to find mechanically and electrically matching filter capacitors as paper-in oil types, not an easy job even with eBay within such sizes. Pots, switches and simple things like fuse holders are more and more difficult to be found in well known high quality, foremost made for military use in the 1970ties.

Knob inlay made from real embossed calf leather matching luxury expectations...

The Leaks got now smoothing chokes (8H/100mA) in the filter stage, NOS mil spec input potentiometers, perfect RCA-sockets, switches, optimized AC-cords and of course a set of best possible NOS tubes in every stage. So equipped this little pair will do a perfect job in the coming years and play now in the same league where best handmade tube amplifiers like Shindo, Thomas Mayer or others are bought for in difference to modern chrome monsters made to match Asian expectations. 

60 years of technological time shift to play music

Now this little amps are ready for the time which is already there, a time were music streaming has overtaken the music market and digital components are feeding their playlists into such ultra analog audio chains. After 10 years of wireless music stream into my own chain from my notebook as to be the 'jack of alle trades'. I did spend at the start of 2022 myself an actual iPad with 1Tb storage to be solely my comfortable music juke box to play from cloud services as well from my own digital collection at a finger touch. 

Stay healthy, it might find an end sooner or later, Volker