SonicArt Posted August 18 Share Posted August 18 Some of the forumers will remember Tube Technology, drift your minds back 30 years to the glorious 90's and the local Melb shop Acoustic Images in Glenferrie Rd near the Malvern town hall... Frenchie loved his audio, sold some of my speakers and cables in the shop and over time he became a good friend. He had a nice range of gear from the UK and France, Tube Technology, Trilogy, Rose, Micromega, Pierre Lurne to name a few. To cut a long story short in the late 90's I ended up with mildly used Tube Tech UNISIS power amp, and a SEER preamp. I did it up over the years, caps, connections, the amp really was a lovely sounding unit. For some reason I also took photocopies of all the schematics and documents that Tube Tech had faxed over to Acoustic Images, like a good hoarder I put all this paperwork away with all the other copies of stuff I had been collecting. Anyway late last year someone in a FB group posted the question about Tube Tech, he had a UNISON Integrated amp, his late fathers amp, it was dead and he was looking for help. I answered him at the time, then his post was lost in the ether. Early this year I reached out to see how he had gone, the amp was still sitting in the box unloved, so as he was in Melb I offered to take a look at it. He told me a friend had looked at it, drawn out some of the circuit and discovered the little toroidal that powers the preamp was dead. Talk about an unobtainum part! It was looking rather neglected, the plating was not chrome but I believe nickel, or nickel chrome, to get that slight bronze tint to it, lovely when new but they all get pitting, this one rather bad unfortunately... A little detail on the design: The UNISIS was a power amp, four EL84 tubes in push/pull parallel per channel, 12AX7's in front of them, transformers were substantial and the whole amp was really well built. The SEER was the bread n butter preamp, it ran 12AX7's in the linestage and the board could accommodate a phono stage as well. The chassis used the same front panels, so were the same basic size. The UNISIS Integrated was a UNISIS and a SEER put into the one chassis. TT took the UNISIS main chassis, added an extra enclosure on top at the back, this lifted the transformers up out of the main chassis, he then put a blue plate across the hole where the transformers would usually hang down, creating a shielded main chassis. The SEER preamp board was mounted right up the back of the main chassis, like it was in its own preamp case, with all the inputs at the back, it all fitted as the speaker binding posts were moved up into the second compartment where the transformers were. So its rather crowded inside the main chassis, essentially a complete UNISIS inside with the SEER pre sitting where the transformers would usually have hung down. Now the SEER pre section was powered by a little 56mm toroidal transformer, this was put into a plastic case and bolted to the back of the chassis, a clever way to fit the preamp in and power it with its own transformer! The Tranny was pretty small, got pretty warm when in operation and this one had failed internally. Above you can see how the transformers are raised, the little toroidal bolts on next to the IEC socket. Its a UK made tranny, the company appears long gone, and there are exactly zero schematics, manuals or forum posts online to help anyone replace one of these! So I began the search for my old paperwork, I told the owner I would fiddle around with the amp in my own time, and it was going to take months, in fact it took me a couple of months before I found all my papers from the 90's, and there was a crapload of it! (some interesting brochures and articles from locally made gear too, I am going to scan some of it to post up in a nostalgia thread, who remembers the Contan tube amps?) Next post, dealing with the dead toroidal... 6 Link to comment Share on other sites More sharing options...
SonicArt Posted August 19 Author Share Posted August 19 On to the transformer problem.... I thought about seeking out someone to rewind it, but that would likely be very costly here in these post covid days, plus we would simply end up with the same transformer, and potentially the same risk down the track of failure. So I got stuck into my old paperwork, sorting through all the schematics and notes I finally found the details for all the early variations of this amp. The copies were a bit sketchy having been reproduced from faxes that were not 100% in the first place! I scanned in the relevant schematics and spent some time in photoshop editing the hard to read values and instructions so as to preserve these documents as much as possible. There appears to be no one out there online who has anything of the early Tube Tech designs on paper, the last version of the amp is available in user manual form, but it has a completely different bias setup and setting procedure to the early amps. So I decided to contact a Chinese factory and see what we could make from scratch, luckily I had found one page which had the power supply for the SEER preamp, and it included the secondary voltages for the transformer! No current ratings, but that's not too hard to calculate, we are driving a pair of 12AX7 tubes, the heaters are connected in series so they draw 150ma per tube, the SEER uses a DC heater circuit with 7812 regulator, 300ma current draw. I specced the windings for 2A as I wanted the design to handle both the linestage and the line/phono version. Hi voltage winding was specced at 30ma but its likely a bit more, as the smallest toroidal they could make me was 78mm diameter! Above we see the new transformer, really nicely made, they even potted a plastic tube and blind nut into the centre so it can be mounted multiple ways! And it has quite a bit more mass than the old one! I wired the transformer primaries into position inside the amp, connected meters up to the secondaries (being very careful with the HV winding) and brought the power up to the pre with the variac, at 240v the secondary voltages were spot on, the factory got the wind perfect. I then grabbed a piece of 80mm delrin and machined it out, a lot! rather than use 90mm and make the ID larger than needed (the transformer is not perfectly round due to the windings tucked down either side, creates a slight oval shape) I decided to make a thin wall cover that would flex to the shape when fitted. I drilled a new hole in the back of the chassis that just missed the post mount for the pre board and allowed the transformer to sit over the original wire entry point. Quite happy with the end result, the transformer while big, fits neatly enough, and should provide years of operation. Next up is to wire it into the circuit. Both power transformer primaries connect to the same spot on the board after the switch, secondaries connect to the pre board, wiring was shortened and fitted up, then the internals were re-assembled, tubes cleaned and refitted inside, and power applied with variac again while monitoring the voltages. At 240v the circuit measured perfect, as per the schematics! Time to put the baseplate on and get the power section up and running and then check bias and bench test.... 2 Link to comment Share on other sites More sharing options...
SonicArt Posted August 28 Author Share Posted August 28 Ok back to the UNISIS! After finishing the transformer transplant I powered the old girl up while monitoring the bias. After a few minutes to settle the bias was sitting at -17.6v or so measured at pin 2. All four pairs were sitting at the same bias point. Factory bias is recommended at -17.5v so these were pretty close! The bias pots were cranked all the way to get to -17.6, the tubes are original Saratov 6p14p which are a very strong EL84, tight specs across production, I had these in my old UNISIS. Unsure of the age or hours on these, but amp is running well so on with the base plate and off for a listen! Sounds good! Its typical of an original UNISIS amp, it does everything nicely, but its a little vague compared to all my other amps. It reminded me why I modified my own UNISIS in the first place. All the coupling caps are basic Solen metalized polypropylene, hardly the last word in detail, dynamics, or anything really...work well in speakers, I never liked them much in amplification. The caps I had used in my amp were long gone, Cardas Golden ratio film caps, very nice transparent detailed sound, but still very much a tube sound, they didnt detract from the amps qualities. Since then I have had mixed thoughts on caps, have tried many different caps over the last 20yrs or so, and I am a bit over the high priced so called audiophile offerings out there. So I decided to use something that may cause a heated debate and require its own thread! Dayton Film & Foil caps. No not the metalized MKP caps (although they are actually very good for speakers, better than solen dare I say) but actual Film & Foil, not much discussion around on these caps, but hey, lets try something different! So here we are, the power section first, 6 caps, 400v rated, now the caps in there were 630v Solens, but the circuit diagrams show 400v caps, and measuring voltages we are seeing only 330v max so I figured Zia likely used the 630v Solens as he had them and they are tiny anyway. The Daytons are huge in comparison, typical of a proper Film/Foil cap. I let it run for a few hours then sat down for a listen. Hmm detail, much more information in the recording is coming through, there is more meat to the instruments and vocals yet they are more transparent at the same time. I am impressed! For the meagre amount they cost, these caps are quite impressive.... So on to the pre section.... This was much more fiddly, the little Solen caps could fit anywhere, 0.22 and 0.47uF are almost the same size as each other. Not so with Film n Foil caps! The 0.47 are literally twice the length and diameter, luckily there was enough room to move them to one side above and below the selector switch, rated at 105 deg here's hoping they will survive the 12AX7 heat The 0.22 were a little easier, one on either side of the board fitted nicely. So back to listening, after a few more hours of running to settle them in. Result? more of the same, I think the amp has a very musical raw sound, detail that gives shape and body to the music, allows it to float in a quite decent 3D stage, and still smooth enough to allow long sessions without fatigue. In between all this work was external cleaning and polishing of the brass and plating. The chassis plate is unfortunately badly pitted, transformer covers are not bad, knobs etc still look excellent once polished up. The end result seen below, including a low light money shot 3 Link to comment Share on other sites More sharing options...
muon* Posted August 28 Share Posted August 28 @SonicArt Are the Daytons aluminium or tin foil? Link to comment Share on other sites More sharing options...
SonicArt Posted August 28 Author Share Posted August 28 Not sure, there is very little about their makeup online. I have ordered drivers from them directly in the past so have an email contact I can ask. My guess is they are aluminum foil, tin foil usually take a long time to break in, I have used the Solen tinfoil and have quite a few in my cap stock, great cap for reasonable money, but the dayton is a very good cap for stupid cheap money 1 Link to comment Share on other sites More sharing options...
muon* Posted August 28 Share Posted August 28 1 hour ago, SonicArt said: Not sure, there is very little about their makeup online. I have ordered drivers from them directly in the past so have an email contact I can ask. My guess is they are aluminum foil, tin foil usually take a long time to break in, I have used the Solen tinfoil and have quite a few in my cap stock, great cap for reasonable money, but the dayton is a very good cap for stupid cheap money Tin foil caps are usually heavy, heavier than aluminium caps. You are likely correct in them being aluminium foil. I agree with you on the Solen metalized caps, i don't like them in the signal path, in power supplies they can be good, but not in the signal path of amplifiers. Link to comment Share on other sites More sharing options...
SonicArt Posted September 1 Author Share Posted September 1 So the UNISIS is singing, and there is a little hum, the background 50hz AC hum was always present in these amps, its very faint ear against the speaker hum so no big deal, but there was another AC hum present in the amp, mainly right channel, and it was coming from the HV AC wiring that goes across the back of the main board to the rectifiers, quite close to the pre tubes. Moving it around changed the hum but there is not enough space to reposition it far enough, so I thought maybe a little shield would suffice. So I grabbed some sheet brass from the local hobby shop while I was out and about, and folded up a little shield to sit at the top of the Pre tubes, using an existing screw inside the chassis to secure it. Shield in place and the HV hum is gone, only the very faint 50hz hum remains, I think this amp is all good to go, it has settled quite quickly with all the new caps, top end is smooth and detailed, very enjoyable to listen to! 5 Link to comment Share on other sites More sharing options...
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