OK, it is not an ultra linear tap as originally there was a 2.2k 2 watt resistor dropping the voltage from the tap to the screens of the output tube. I wonder why they did this instead of tapping the B+ like most circuits would do. There must be an advantage as it seems like more trouble for the transformer winders.
Such transformers were used to give additional supply voltage filtering.
The part of the primary was used as a choke.
The part of the primary was used as a choke.
Its not an ultralinear tap. It was quite common in old radios for the front end supply to be drawn off the Output transformer. I believe it either was for voltage shifting or some form of feedback - but I am not certain. It was most definiately not UL in the modern sense.
However having said that, I have used just such a SE transformer to run an UL output stage and it works very well.
Shoog
However having said that, I have used just such a SE transformer to run an UL output stage and it works very well.
Shoog
The SE OPT is from an old reel to reel tape deck. I believe it was a Norelco. if anyone has a schematic for one of those units it will probably show the tap with the 2.2k resistor on it. I am not mistaken in connecting the tap to the G2 screen? I was going to drop the voltage thru a 22v zener. regards
As artosalo says, the tap was probably for hum reduction. The OPT acts partly as a choke, and partly as an element of a hum cancellation bridge arrangement. Separate smoothing chokes and big capacitors were too expensive for an ordinary radio set, so they used these cheaper techniques.
As it is just a tap, it is up to you what you use it for.
As it is just a tap, it is up to you what you use it for.
Ultralinear is supposed to be tapped at 43% of the windings. In this case how would you know at what % of the windings the tap is ?
UL can be tapped at anything from 20% to around 50%. 43% merely maximises something (I can't remember what).
To determine the tap %, measure resistance. You can almost certainly assume that the turns ratio varies like resistance ratio.
To determine the tap %, measure resistance. You can almost certainly assume that the turns ratio varies like resistance ratio.
according to the picture, tap runs (higher) current in opposite direction... -> probably a non gap opt, made to work in SE duty
(cancelling some part of dc mag.)
if it distorts, you´ll know why 😀
(cancelling some part of dc mag.)
if it distorts, you´ll know why 😀
If you want a specific ratio then you are going to have to splash the cash. These transformers are cheap salvaged SE's and to be honest if you intend to use them for an amp you should be grateful for the chance to taste the flavour of UL at minimal cost. I would guess that you are going to get a mostly pentode result from one of these so some other form of feedback will be necessary as well.
The design I built used an ECL82 with plate to driver cathode feedback and the UL tapping and I was amazed at how well they sounded for a cheap experiment.
Shoog
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I think UL at 43% is lowest distortion point.
I did measure the resistance between the 3 taps and the bias tap resistance measures very close to the tap for the plate. So, not many windings there.
This is a gapped transformer
It is not like a "universal" transformer that can be used for push pull or SE. I am running it for el84, 6v6, and 6L6. It has excellent sound with a RH type circuit.
It is not like a "universal" transformer that can be used for push pull or SE. I am running it for el84, 6v6, and 6L6. It has excellent sound with a RH type circuit.
OK, so probably not useful for UL. In any case, the type of equipment which used a hum-bucking OPT to save money is not going to have a high quality OPT with careful interleaving to achieve good stable UL performance. Use it as a plain SE OPT, and don't expect hi-fi.DAK808 said:
If you can find the schematic for a Magnavox 196- SE (6BQ5) amp you'll see a very similar transformer where the B+ is inserted on the middle lead and the screen gets the outside lead next to it through a 4.7KR. There is only about 10R between the leads. It's a great little transformer that is higher quality than those standard SE trannies for that low wattage. The Maggie 196 is definitely HI-FI with good gain and GNFB. You may have a higher wattage version similar to that trannie but I would not assume it is more than 5W. But the B+ is supposed to go to the inside lead. Good luck with it.
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