• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Tube Technology Unisys

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I think it's basically a matter of output transformers. TT may be willing to supply the upgraded ones. They're easy enough to fit.
However, as an owner of a Unysis power for a while now, I would say that you're much better off doing the following:
-add valve regulated power supply
-convert to triode mode
-new old tubes, esp. for input (Tele, Mullard)
Yeah, I meant the feedback circuit from the o/p trans. Simply disconnect. This is best done if you triode strap the el84s, as no-feedback UL operation is likely to produce too much distortion. And the downside of triode mode is, of course, loss of power and theis brings into play factors such as speaker efficiency, room size etc. This wasn't a problem for me. In fact I use the amp with just four el84s (one p/p pair per channel). This reduces power to about 7W, but it does mean you can use better valves for the money. As it happens, the Unisys was my first valve amplifier, bought with Insurance money. Having since got into the technical side, it's pretty obvious that the Unisys is designed as a kind of valve/transistor compromise, and a lot of money goes into build quality (for the export market apparently). Component quality is nothing special. Everything I've done has got the sound back to a more trad valve sound. I much prefer it now, but if I had to start again I'd probably sell it and buy something else or build from scratch.
I'll try to disconnect the feedback ! But honestly i haven't know an amp (tube amp) with no NFB ! Can u till me were can i find some info about this ? And i agree with you that my amp TT Unisis it look very high class but inside using a lot of cheap stuff ! Dull circuit board design ,cheap component and ugly soldering ! this is why i want to upgrade it . But it is good to talk to you at least i learnt something !
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