Modding a Transformer (Doing a CJ -Badly)

[sahib]

I've had these Triad TX-3X and a pair of A-133X auto transformers lying about at the workshop for years. As they were primarily made for CRT TV sets, I offered them on the BM at a give away price for experimentation but they did not receive any attention. So, today I thought I would modify them with separate primary-secondary and see if they would amount to something.

I knew that TX-3X would not amount to anything, as it tolerated 950mA DC in the primary and had winding resistance of half an ohm. More like an inductor than an audio transformer. It indeed turned out to be the case and had a lower cut-off of 1.5kHz. So, straight into the scrap metal box.

But with A-133X I hit the jackpot. To my delight it responded to 15Hz-25kHz flat, and had a turns ratio of about 10:1. So, I thought of documenting what I've done. In case you come across one or two at a reasonably good price, just grab them, do the mod and you'll have a nice pair of output transformers.

For those who do not know what an auto transformer is, it is just a normal transformer but with primary and secondary sharing a common tap. So, the modification involves separating the primary and secondary. The red wire in the below picture no 1 is the common tap. Yellow is primary and blue is secondary.


In the below picture no 2 the ends of the secondary are clearly visible. Be careful here as the wire is much thinner than the primary. So, when cutting up the insulating paper and removing the fly leads take great care.




Below picture no 3 shows it opened up. The blue arrows are the thin secondary wires. The yellow are the primary which are much thicker and easier to work with. When you solder a fly lead (shown in picture no 4) immediately secure it using a glue. I have used low melt glue for this. Do not try to solder all of the fly leads at once and then secure them as there can be a risk of breaking the secondary wires. Solder one, glue it and then move onto the next one. I do not know what generally people do for removing the enamel from the copper wire. I use a surgical scalpel to scrape it off. This again requires extreme care for thin wires as you can easily scrape the whole wire off. (I have a modelmaking background, so I am good at doing things like this.)


Picture no 5 below shows all the fly leads soldered and secured. Once this was done I bent the fly leads upwards as I wanted them to exit from the top, as shown in picture no 6. This also brings additional security in case they are pulled unintentionally.


I then sealed the whole thing with low melt glue as shown in picture no 7 and 8. It does not particularly look pretty, and I am not sure if it would get me to be accepted to apprenticeship with CJ, but it functions well. I may put an insulation tape all around to secure it further as hot glue may release itself in time.



A nice pair of (about) 10:1 output transformers.

 

[Tubetec]

Necessity(to save the planet from destruction ) will become the new mother of invention ,
Thats really cool what you did Sahib ,but I'll bet you've sent the used price of A-133x up a bit ,ahaha

A cursory check shows these things are over 400 bucks a piece right now

 

[sahib]

Thank you Tubetec.

I am keeping them for myself for future use.

But the transformer prices in general have indeed gone crazy.

 

[sahib]

My finds continue.

A friend of mine had given me some studio flash power packs that had received pretty bad water damage. He also had some flash units that developed faults. So, I parted out the power packs and used the capacitors and rectifiers to fix the flash units. However, I also removed these transformers and for fun tested them for frequency response. To my total surprise they tested incredibly well. I also had some power transformers that I had removed from professional Tascam and Aiwa tape recorders over 10 years ago. I thought, hmm, how about them? The result is below.

The transformers were driven from an unbalanced 600 ohm source. Secondary was loaded with 4k7 resistor and drove into a balanced load (OP275). Tests were not surgical. So, there is a bit of give and take in the numbers quoted.

These are the transformers removed from the flash power packs. They have core sizes of 65mm x 50mm x 20mm. They have 6 independent taps giving good practical turn ratios. They measured 15Hz -19kHz flat.




This one came from I think Tascam 112R. It has two independent centre tap secondaries with normally with 15.8 - 0 -15.8 and a single tap at 8V. I used one of the centre tap secondaries and it gave almost 7:1 turns ratio. 15Hz -20kHz flat. Between 30kHz and 65 kHz there is a slight rise in amplitude with about 1dB hump, and starts to roll of at 65kHz.



This one came from Tascam 133. It has one independent centre tap secondary and one single 8V. I tried the center tap secondary and it gave about 8:1 turns ratio. It is 50Hz - 15kHz flat. Slight drop between 50Hz and 20Hz. From 15kHz the response starts to climb up and there is 1dB rise in amplitude at 28kHz. From 28kHz starts to climb steep and there is 5dB rise at 55kHz and then rapid roll-off.



Now this came from an Aiwa cassette deck. Actually there were two of them one with additional secondaries. They were externally mounted to the rear panel. At the time I thought it sounded like an audiophile hype but it really surprised me. This thing gave 10Hz - 60kHz flat. There is a negligible rise from 60kHz and at 110kHz there is about 0.6dB increase in amplitude. The amplitude response starts to climb and there is 3dB rise at 160kHz then rapid roll-of. However, I would not get too excited about the frequency figures after 60kHz as the fly leads are bundled together at termination and the capacitances between them are taking effect, hence possible cross talk.



I have no idea what you make of these but I was really surprised. I have a number of these transformers but I am not counting my chickens yet as I would also like to test them subjectively. At the same time they made the transition from power transformer shelf to audio transformer shelf..

 

[sahib]

Finds continue.

This time I parted out some old electromechanical mains voltage stabilisers which were based on auto-transformer/variac. However, the servo circuitry had three mains transformers for providing supply and reference voltages. The servo circuitries utilised a couple of 741 and transistors to drive the relays for controlling the synchronous drive motors. Two of the stabilisers also had Mullard 150B2 rectifier tubes. Again the transformers gave surprisingly good results. Here we go;

This is one of the two smaller auto txs The stabilisers were rated at 1000W. The other three were much larger and rated at 1500W.



These are the two 150B2 rectifiers.



This has two independent primaries and a centre tapped secondary. The turns ratio is 1+ 1: 0.5. Frequency response 20Hz-30kHz flat. Amplitude response starts to rise from 30kHz and at 73kHz it is 3dB up. Then it rolls off.


This also has two independent primaries and a single secondary, though there is a solder tab in the middle. The turns ratio is 1 + 1 : 0.1. Frequency response 20Hz-50kHz flat. Amplitude response starts to rise from 50kHz and at 88Hz it is about 10dB up. Then rolls off.



These have single primary and a centre tapped secondary, though one has fly leads and the other solder tabs. The turns ratio is 1 : 0.5 + 0.5 Frequency response 20Hz-22kHz flat.. Then rolls off.





These have two independent primaries and a centre tapped secondary. The turns ratio is 1 + 1 : 0.025 + 0.025 . Frequency response 20Hz-55kHz flat.. Then rolls off.



These have single primary and single secondary. The turns ratio is 10 : 1. Frequency response 20H - 35kHz flat. There is an insignificant rise between 35kHz and 65kHz then rolls off. For all practical purposes the frequency response is 20Hz 65kHz.


I would not imagine anybody would come across these particular transformers, but the main purpose in posting these here is to remind you to check before thinking that they are mains transformers and may not be any use.