Tuac Amplifier modules

[Trevor]

In My youth
I used to see often the Tuac modules advertised in the electronics mag,s
Does any one out there have any information re these as I most keen to study the circuit
The unusual feature of these amplifiers was that they used a driver transformer
best regards for now
regards Trevor

[Adjuster]

I would guess that they used only one polarity of output transistor, like the NPN 2N3055, driven via a dual-secondary driver transformer (as opposed to the centre-tapped variety). That sort of arrangement was fairly common at one time, a sort of half-way house between earlier push-pull amplifiers with driver and output transformers, and later truly transformerless types using complementary PNP/NPN transistors.

The transformer probably didn't do much for the sound quality, but perhaps at the time good complementary output transistors were not available, or at least not cheap. When exactly did these TUAC units date from?

[Aub]

I remember the TUAC units being advertised in PW & other mags from about 1974 - 1976. They also made sound to light units. The same unit, or at least one very similar, was used in an amplifier we had in our mobile disco. That was bought from a shop in Croydon. It was called a "Baker 100" and had 4 inputs with a gain control on each, as well as bass & treble. The module in it certainly looked the same as the TUAC ones, with the driver transformer. It used, IIRC, 4 x 2N3055 in the output stage. It sounded pretty good at the time, but the benchmark for disco quality back then seemed to be the HH series of amps.

Cheers

Aub

[AlanBeckett]

On the contrary. Arthur R Bailey argued, and demonstrated, that a well designed and constructed transformer was better than the usual (transistor) phase splitter.
Alan

[dseymo1]

If it's any help, I believe the name was an acronym of Transistor Universal Amplification Company.
I don't think they were directly connected with Baker / RCS (I'd have expected a Baker - badged amp to use an RCS module), but am willing to be proved wrong!

[Trevor]

Many thanks for the replies so far!
I think I have a Bailey designed transformer coupled amplifier in my collection and I tend to agree with Baileys findings .There are in fact some people that say their is no such thing as a complimentary matched pair
I have in my collection a no of transformer coupled amplifiers by Rogers I also have designed a simple 4 transistor amplifier of about 15 watts that sounded nice
My interest in the Tuac is re the driver stage I think that the driver transformer is in the collector circuit where as Baileys in his early Radford was in the emitter of the driver
I would be willing to pay a reasonable price for a module so that I can study it or pay a reasonable deposit for a loan of 1
regards Trevor

[kalee20]

Originally Posted by AlanBeckett

On the contrary. Arthur R Bailey argued, and demonstrated, that a well designed and constructed transformer was better than the usual (transistor) phase splitter.
Alan

I'd agree.

Of course, the transformer would have to be properly driven, and a suitably low impedance drive (emitter follower perhaps?) may itself introduce more distortion under certain conditions than a non-transformer-circuit.

Care has to be taken, but as AlanBeckett implies, there is no justification for dismissing an amplifier as inferior on the basis that it has transformers in its signal path.

[Adjuster]

It would be interesting to see that proven. Unfortunately I would need to see the proof, as due to deafness I cannot judge what anything really sounds like these days. Does anyone know of a relevant article, perhaps available on the web?

[AlanBeckett]

Arthur Bailey "High-Performance Transistor Amplifier" (20W) published Wireless World Nov, Dec 1966, p542

[roffe]

From PE june 1975

[kalee20]

And those driver transformers look as though they have plenty of iron in them!

Distortion figure not brilliant, but not bad either. The circuit looks simple so probably not a lot of extra gain to sacrifice in NFB. Frequency response very credible. I see the blurb makes mention of sectionally-wound transformers, so some thought has gone into the design.

[Trevor]

Roffe
Thanks very much for your post I appreciate the information !
I just wonder if anyone has a schematic
To me the main attraction is the potential to make a reliable amplifier that does not blow seven or eight devices under fault conditions
best regards Trevor

[Trevor]

Originally Posted by kalee20

And those driver transformers look as though they have plenty of iron in them!

Distortion figure not brilliant, but not bad either. The circuit looks simple so probably not a lot of extra gain to sacrifice in NFB. Frequency response very credible. I see the blurb makes mention of sectionally-wound transformers, so some thought has gone into the design.

Do you have a circuit? or are you looking at the pcb etc
The circuit is what I am looking for
best regards Trevor

[roffe]

Sorry,no schematic.
But if you want to examine this totem pole configuration with driver transformers,there were several amps using this like AR,Grundig SV50,Arena GF1225,Philips GH925,Heathkit AA-22E and many,many more.An example,the Arena GF1225(note that it needs no output cap due to the use of a symmetrical power supply as in modern amps):

[Lucien Nunes]

Hmm. TUAC. Brings back memories.

I've attached a couple of pics of a Baker Major 100W amplifier. This PA looks like a close relation of the ones in the PE ad. IIRC there's no mention of TUAC on the PCB but I've seen other TUAC PCBs with their name in the foil somewhere. The Baker Major has the customary 4-input 2N3819 mixer on the front, which is the same as the one in an RTC although that power amp is completely different (Quasi-comp, I think). I don't know whether the 1973 date on the driver transistor is original - it had been messed about with inside, hence the few other later components such as the white power resistors that were replacements I put in.

The transformer-coupled design is rather basic but it has worked perfectly in it's lo-fi way since I fixed it in about 1990, during which time it has travelled far and wide, been shorted and overdriven once or twice, but not lost a transistor. The simplistic global NFB goes a bit funny on the approach to DC - the damping runs out at a couple of Hz. If you input a single pulse you can watch the speaker cone wobble gently in and out for a few seconds afterwards. I have not measured any audio parameters, but you can hear that they're not great!

I can't get at the amp at the moment as it's 200 miles away but the numbers on the board suggest I drew a sketch schematic back in 1990. That might still be here.

Lucien

Edit - something odd about that driver transformer - only seems to have 5 ends!

[Trevor]

What a wonder-full unit this is what I am after!!!
this is a rebadged TUAC
I would love top see the schematic if you can get it
I have longed believed in the reliability advantage of transnformer coupled amplifiers
please send me the schematic if at all possible
regards trevor

[Aub]

Yes that's the Baker we had in our mobile disco.

[Trevor]

I have managed to to buy a tuac power amp and made a successfull bid I will let you know if it is a transformer coupled unit
This is the only reason I have purchased it !
regards Trevor

[kalee20]

Originally Posted by Trevor

I have longed believed in the reliability advantage of transnformer coupled amplifiers

I'm not convinced of this - that a transformer-coupled amplifier is any less prone to failure than a DC-coupled amplifier.

However, I am TOTALLY with you if you infer that when something in a transformer-coupled amplifier fals, it doesn't ripple right through the whole circuit, taking out 75% of the transistors, overstressing the others and shifting their characteristics, burning out most of the resistors and popping any electrolytics!

[AlanBeckett]

I learned that lesson a long time ago. The Fairchild Salesman gave me a couple of kits of brand new Silicon Planers and a (dc coupled) circuit to try. One whiff of oscilation or prod in the wrong place and it destroyed itself in microseconds. The only repair possible was to replace all the transistors.
Alan