I was looking at this page

http://www.jaycar.com.au/power-products-electrical/power-conversion-transformation/ac-ac-transformers/c/405D?q=%3Arelevance%3Aprice%3A%240-%2419.99&text=#

and wondered if any of them could be pressed into service as a replacement speaker transformer?

I don't really care about the output impedence, 2 to 16 ohm is fine, just as long as the output valve is happy with the load.

My understanding of coil turns and ratios is lacking, so hoping that a knowledgeable member can do a few calculations and pick the transformers that are suitable.

Thanks!

Hi Rob, theres a web site that covers using power trannies as output transformers, cant remember but just google around and you will find it.

I have used power trannies for radio and guitar single end amps when I was too slack to wind one.
The output transformers used in radios and small guitar amps are nothing special. Usually just one primary winding and a tapped secondary winding just exactly what a Jaycar small wattage transformer is.

So long as the iron area can handle the magnetisation (pretty small in push pull, not so small in single end) and wattage so it does not saturate, the coppers sizes are not overloaded by current and the turns ratio is in the ball park you are already there!

For instance have a look at my "Vogue" radio restoration in tne articles and tutorials. In this I matched a single end 6V6 to a Jaycar 12" party speaker and used a MM2155 power tranny. In the article I go into the ins and outs of turns ratio, interleaving laminations and stuff.

Before any audio types (free oxygen cable/ class A output triodes/Ultralinear PP outputs/golden ears) start coughing and spluttering yes I know, when you are striving for bandwidth, efficiency, response, or high power then output transformers are a technical area. I have wound multisection coil high class EI stacks for HiFi and even higher power "C" core outputs for 500 watt plus and 700volt PP amps so have a bit of practical experience.

For a radio if you strike the turns ratio somewhere near 25: 1 ( say 240v : 9v) square that = 625 x VC ohms say 8, = about 5000 ohm to the valve and juggle that about for the actual valve data book value, and the original power wattage rating is about twice the music wattage you want its going to work in some way and good enough for little valves. It is very simple if you don't think about it too much beause valves are very elastic in their matching and speaker impedances also more so!

Cheers, Fred.

There are also some Altronics options put forward by Valve Heaven.
Their lamington amp uses an Altronics M1115. (http://www.valveheaven.com/)
Other circuits they have use other Transformers, although I think they are push pull
I used an Altronics M1115 in a Philips 10W valve PA amp with success
I cant see why 100v line transformers cant be used for output transformers non push pull
Here is a site with a list of 100v Line transformer impedances (down the page)

http://members.iinet.net.au/~cool386/6bm8/6BM8.html

Also, a Video of the Philips amp with the Altronics transformer as an output transformer

https://www.youtube.com/watch?v=N8os8PXhjvI

Josh

Hi Rob,

Hi Rob,

As an alternative might I suggest the multi-tapped 3.5W audio output transformer from Radio Spares. To quote them

"From OEP, this multi-tapped transformer is suitable for matching 3Ω to 15Ω speech coils to the high impedance output (4kΩ to 15kΩ) of audio amplifiers. This chassis mounted transformer is suitable for various of amplifier configurations."

http://www.rsaustralia.com/

Part number is 2106475, I have had success with this on a number of radios.

Joe

Jaycar MM1900., Alltronics M1109 , Alltronics M1112 , Wagner Electronics LT05 . These are all recommended by the HRSA . I have used the Jaycar model with great success after a minor modification . Email me if you want pictures and text.

The reason I asked about Jaycar is that there's a store about 10 km "down the road" and I can be there and back in an hour.

Wagner's is an hour by train each way, so it becomes almost a day wasted. And Altronics is a 1.6km walk from the nearest station. Also I do not use a credit card.

The MM1900 http://www.jaycar.com.au/5w-line-speaker-transformer/p/MM1900 seems quite reasonable at $10. I don't really want to spend more than $20 as many radios are barely worth that much.

Thanks Tallar Carl for the suggestion.

I have sent Brad some photos in regard to the minor modification you will need to do to the Jaycar transformer. This is exactly what the HRSA has recommended . You need to pull the outer cover off then put the transformer into a vice at a angle so as to break the lacquer bond for the metal E pieces and I pieces. Then pull all the Es and Is out and put all the E pieces together one way and have them facing to the bottom of the transformer then place a piece of paper to cover all of the bottom and then line all the Is up together and place then sideways on top of the paper and then put the cover back on the transformer and you are finished. The piece of paper creates enough of a air gap so as to prevent the core being saturated and the sound will be undistorted.

I also removed the terminal block on the transformer just to make it look the part.

I bought 2 transformers from Jaycar yesterday. Then I attempted to modify one of them as per your instructions.

Putting it in a vice did nothing, so I used a hammer to get a lamination loose. Then found that all the laminations were glued together, including down the middle. It took ages to get it fully apart. Then the fun of getting the E-shaped ones back in without it flying to bits. The last part, putting the paper in followed by the I-shapes was easy. The whole thing took at least an hour and a half, and I'm dreading having to do it again.

Then over to the radio, which is some brown plastic HMV with 5 7-pin valves and shortwave. The valves are the usual, 6BE6, 6BA6, 6AV6, 6AQ5, 6X4. Underneath was a bunch of shrivelled-up mud capacitors with no markings. Fortunately the values are obvious considering their circuit positions. These caps look something like those dreadful Techno mud types. The power electros were made in England, so I left them in. There were a few dry joints too. I decided to remove the 25μF feedback capacitor and just use a miniature 33μF 16V going directly to ground. Replaced the 6AV6 load resistor, as the old one measured 891K. Replaced the old black-tar transformer with the newly reconstructed one.

Did a few continuity and voltage checks, all seemed fine so in went the rectifier, and we had a working radio. Remaining faults are that shortwave doesn't work, tone control doesn't work (someone butchered the circuit there and left another dry joint), and the SW/MW/PU switch is extremely touchy, the sound keeps dropping out even just by tapping near the switch.

Now, although we had sound, the level of it wasn't that great, and the 6AQ5 got very hot. I had originally used the 2W position on the transformer, so I changed it to the 1W position, and this improved both matters.

The other test radio is a small square-shaped bakelite Philips with octal valves, which has the dial pointer sticking out the top. Naturally, the dial is missing. I'll look at that one next week.

LOL the transformer should have only taken a half hour. When its in the vice you must have it at a angle and give it a couple of good goes. I do remember a few cuss words being uttered when I was doing my first one lol but it gets easier.

I found this on ebay:

http://www.ebay.com.au/itm/201614272267

Just modified the other transformer, it took 2 hours and 10 minutes. I was going to fit it to a Philips 112A, but not going to bother now. The Philips is missing the dial glass, the front is damaged and the special knobs are missing. It would be a waste of my time.