Cheapest power supply transformers?

[Gregg]

It's true toroids are most efficient when full wave bridge rectifier is used but I've used at least a dozen of toroids with multiple secondaries where the bias and the bipolar opamp supply were half wave rectified without any problems. The HV supply and preamp tubes heaters were always bridge rectified.

[printer2]

Cheap amp.



Used a 120V isolation transformer that has two windings to run off of 240V. You do not get 240V maybe like 210 but that is OK with me. If I wanted to I could have used a doubler running 120V. Around $18 around here. The heater transformer is a 12V wall adapter that I have been picking up at thrift stores. The output transformer is a 10W 70V line transformer, scrounged a bunch out of the 43VA. trash at work. Will not compare to a Twin but for home use not a bad little amplifier. To do cheap little amps I would use 12L6's or the like so the high voltage will not be more than 200V. Will need a higher heater current ratting though but the tubes are cheap and sound ok.The higher grid sensitivity will make up for the loss of headroom you get from running your preamp tubes at a lower voltage.

[J M Fahey]

Dear Austin.
If you want to build tube power amps forget doublers/switchers/backward_transformers and any unconventional solution.
You will already have your hands filled of amp building and tweaking, plus the big "mechanical" problems (chassis, panels, cabinets) to add the extra load of worrying about unsuitable PSUs.
If you can get transformers which supply 6.3V + suitable HV voltage, with adequate power, fine.
If not .... wait until you can.
And let's be realistic, you are trying to shave 30/35 bucks from the cost; how many hours of work are you ready to spend to get that?
jm2c

[J M Fahey]

Dear Austin.
If you want to build tube power amps forget doublers/switchers/backward_transformers and any unconventional solution.
You will already have your hands filled of amp building and tweaking, plus the big "mechanical" problems (chassis, panels, cabinets) to add the extra load of worrying about unsuitable PSUs.
If you can get transformers which supply 6.3V + suitable HV voltage, with adequate power, fine.
If not .... wait until you can.
And let's be realistic, you are trying to shave 30/35 bucks from the cost; how many hours of work are you ready to spend to get that?
jm2c

[Enzo]

There are cheaper transformers available that do exactly the job you need done.

But another source is dead amps or retired amps. SOme old BOgen PA amp from a grade school gets tossed out, but it still can be the basis of a guitar amp. We have a whole section on this forum for conversions even. And even if you don;t feel like rewiring an old Bogen into a guitar amp, well, take the power transformer from it and start from there.

SO much better than cobbling something together.

I have to say, if you want to build amps for your friends for the pride in making something, great. If you think you are making money selling an amp you made for $50 over the cost of goods and including your labor, you are working real cheap. Even ignoring that if you SPEND $50 on parts, you really want those parts to make some money when resold, if you make $50 profit on your labor and it took 10 hours to build it, you made a whole $5 an hour. You can make more than that working in a restaurant, and they feed you as well. Most of us can;t build an amp in an hour or two.

[printer2]

My sister is an artist. I doubt she makes $5 an hour. But she is going to do her thing anyway so at least she gets her costs covered and hopefully a few extra bucks to help support herself.

Now I am not building amps to sell, some I just give away. This is just a hobby to me something to keep my mind occupied. The extra time it took me to take the transformer out of a wall adapter and mount it really does not matter. It actually makes it more of a challenge. Nothing wrong with voltage doublers either. If you are using a desktop PC then you are using one also. It all depends on what it is your intent is in making amps and your choices in parts reflect that.

[Austin]

Wow, thank you all for the replies. It is wonderful to have a great resource like all of you on this forum to interact with. Nobody I know is interested in this stuff, I think about building amps and how they work pretty much all day everyday (silently to myself) and it is nice to be able to share my ideas crazy or not with other people. Ideas some of which I am a little shy about telling even you guys.. I wouldn't want you all to think me too far out there...

Like this one: I have collected seven or eight microwave oven transformers. They can produce about 2000 volts with something like a 17:1 turns ratio. If you sepparate the E and I and unwind a buncha turns from the secondary the volts of course come down to a more usable level. They also have little pieces of metal for shunts that are easily removed. An additional secondary provides an isolated supply of typically 3 V at 15 A for the magnetron heater and this could be rewound to give 6.3 volts easy enough I think. I would guess they weigh about 15 lbs., so pretty huge. One modified like this could be a power transformer and one as is could be a output transformer with a 17x17=289 289x16= 4624 ohm primary into 16 ohm speaker for a single ended bass amp. I say bass guitar amp because it is unlikely a mot for an output transformer is going to have very good frequency response for treble.. But they are free on the side of the road very often. Microwave oven transformer - HvWiki This idea is probably not a very safe thing to build so please don't try this at home unless you are absolutley sure you know what you are doing. (People do far more dangerous things with mots on youtube tho. )

To build a bunch of little amps out of stuff lying around can be fun and challenging in making something work, it tests your understanding of the forces at work and I think can help keep your mind pliable or flexable. I could ask somebody if this or that will work but either nobody seems to know or they just think that I'm a little crazy and turn there nose up. So I want to build this stuff reversed engineered and cobbled to further my understanding and to test the limits of everything.

Like: How much grid current can a 12at7 tube handle before it melts or has catastophic failure or something? It seems like nobody knows!!! It might even sound really good pushed like this. Probably not, but there is only one way to really know for sure...

However I think I am at a point where I want to build things normally and am just trying to figure out what it would take dollar wise to do it. So I was hoping I could do it for 50 bucks in parts before but now I realize that is wishful thinking; I do however think I can build an amp safely with real parts bought online for about $100 though, including a new "store bought" chassis. If I can make one amp with parts easily bought online and drill the chassis and figure out the layout then to duplicate that for 5 of them built assembly line style seems like it would be no problem. I was excited about the 11 dollar isolation tranny as a power supply when I started this thread but the Antek toroids are better and still very inexpensive! Higher voltage and heater windings.. 25 bucks gets one that would work ok, 35 bucks gets a much better one with dual secondaries. The output transformers from edcor are pretty cheap and also there are lots of generic champ type opt for like 20 bucks on various sites. A nice aluminum chassis with no fancy birdcage top is about 15 bucks. That leaves about 25 bucks for filter caps and resistors and sockets.

My friends want me to build them amps and I want to give them amps that are safe to use and also sound good. I am trying to figure out how much the parts will cost so I know about how much to charge, but I'm basically working for free I know and don't mind. If I could just break even and learn and have fun that will be good enough.

[Enzo]

The original poster, starting this thread, opened with the statement he planned to sell them and make some money, $50 in his example. Absolutely nothing wrong with making them for fun, giving them away, selling them just to cover parts, whatever. But when the stated purpose is to make money at it, I figure those are legitimate things to consider - return on parts investment and labor compensation.

[NorCalTuna]

These transformers are amazing. They're most likely from another certain canadian transformer manufacturer. I have a few of them out in the field, and the price isn't bad. Check the fifth one down, you could make a little 6v6 single ender with that and be happy as a bearded clam!

Transformers - Power Products from Allied Electronics

[tedmich]

those "Allied" trannies are cheap!
this one is $54
and the spec. sheet is from Hammond!
http://www.alliedelec.com/images/pro...s/70008996.pdf

its a 274X

[Zozobra]

For cheapness then the obvious choices are antek and magnetic components stuff. I've also priced up some custom wound toroidal PTs over here in euroland and they have been very cheap! Under 50 euros for something that will run a pair of KT88s and a handful of pres without breaking a sweat! You obviously have a much lower voltage and current requirement and generally custom winding toroidal transformers is pretty cheap as they're quick and easy to wind.

[Austin]

You obviously have a much lower voltage and current requirement

No don't get me wrong, maximum bang for the buck I can get would be best. Lower volts just means I have to try to compensate by running more current so that it hopefully it is still able to play over a bass and drummer with the right speakers. Output tubes I have are 6f6 6g6 6k6 6w6 6y6 6550 el34 6l6 6v6 5881 etc. These are all tubes collected from playing with the Univalve in the last couple of years. Also I havn't decided for sure yet but stereo could be an option to get more power since it doesn't add much to the final cost of the amp if can share the power supply with both channels. If I were to run parallel output tubes for more power instead at around 60 ma each, the output transformer has to be able to handle 120ma and that means big $$$. So two channels and two little output transformers for max bang for the buck I figure. Theres also lots of cool things a stereo amp can do that a mono amp can't like: loop station and a/b switch with one channel playing the loop and then playing over the other side, mp3s through the amp, stereo effects, plugging a microphone into one channel and the guitar into the other, letting my girlfriend or somebody else play into one channel etc...

I don't really know how much power this would need but I guess about 200 ma and 500 volts would be ok.

[Zozobra]

I suppose to put it into perspective I priced up 2x and 4xKT88 PTs

Spec 1 (2X ~ 250VA):
400V @ 550mA
6.3V @ 5A
41 euros

Spec 2 (4x ~ 410VA):
400V @ 900mA
6.3V @ 8A
49 euros

Bear in mind the HT secondary doesn't include power factor but thats a lot of bang for buck! They offer a shrouded 'audio grade' PT option where were 58 euros and 75 euros respectively but I can't see it making a lick of difference to the performance. Also adding additional secondaries wasn't too bad either. I'll probably specify a bias winding when I'm ready to order some bits.

Certainly the HT requirement you've spec'd there is only 100VA and the heaters will only be another 20-30VA or so on top of that. Certainly sticking the whole thing on a 200VA core will probably be fine (although it always pays to do the maths ) and it should be quite compact and cheap too.

[Austin]

I suppose to put it into perspective I priced up 2x and 4xKT88 PTs

Spec 1 (2X ~ 250VA):
400V @ 550mA
6.3V @ 5A
41 euros

Spec 2 (4x ~ 410VA):
400V @ 900mA
6.3V @ 8A
49 euros

Bear in mind the HT secondary doesn't include power factor but thats a lot of bang for buck! They offer a shrouded 'audio grade' PT option where were 58 euros and 75 euros respectively but I can't see it making a lick of difference to the performance. Also adding additional secondaries wasn't too bad either. I'll probably specify a bias winding when I'm ready to order some bits.

Certainly the HT requirement you've spec'd there is only 100VA and the heaters will only be another 20-30VA or so on top of that. Certainly sticking the whole thing on a 200VA core will probably be fine (although it always pays to do the maths ) and it should be quite compact and cheap too.

Those are quite impressive specs for the price. Is the shrouded option to allow you to place the transformer in closer proximity to the output transformers or the preamp tubes without introducing mains hum? Like for a smallish chassis with high gain maybe?

[Zozobra]

I'd assume its largely cosmetic to be honest. Toroidal transformers aren't usually as noisy when it comes to coupling EM interference so I wouldn't worry about that. I made a preamp unit with a toroidal PT pretty close to the tubes that was pretty quiet (everything was contained in a small hammond chassis).