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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

Take a look at my transformers

Hey guys

Take a look at these transformers that I got. I got them for free from the shop where I work. The smaller one is made by Stanley, and the bigger one is made by a company called Freed. They are both 750v center tapped with 5.0 and 6.3 volt taps as well. The cases are metal and are sealed with solder. The big one weighs about eighteen pounds and the smaller one about twelve. One of the pictures has an ipod in frame to give you an idea of scale. Take a look at the pictures and let me know If you think they are going to be good power transformers. I have just started a project to build my first tube amplifier. I think I want to build a mono single ended class A amplifier. I have a feeling that I have some really nice transformers and I think I would like to optimize my amplifier to utilize the transformer to it's full ability. The tubes I have collected are two 12AX7 tubes that are matched, an EL84 tube and a 5Y3GT rectifier tube. If any of you have any suggestions of schematics I could use with these tubes, or if you know a design that would work better with additional or different tubes let me know, I would love to have some input. Also, the small transformer that has some sort of a rating on the side that is given in units of W.V. do any of you know what this means, I can't figure out what that unit is.

[IMGDEAD]http://tapa.tk/mu/18a44c7f-2bc1-d645.jpg[/IMGDEAD]

[IMGDEAD]http://tapa.tk/mu/18a44c7f-2be9-67f4.jpg[/IMGDEAD]

[IMGDEAD]http://tapa.tk/mu/18a44c7f-2c10-90ff.jpg[/IMGDEAD]

[IMGDEAD]http://tapa.tk/mu/18a44c7f-2c2d-270a.jpg[/IMGDEAD]

[IMGDEAD]http://tapa.tk/mu/18a44c7f-2c50-4057.jpg[/IMGDEAD]
 

gain wire

Member
2004-11-27 4:04 am
NCR
Never heard of them. Probably junk. Send them to me for proper disposal.

Ha HA HAA! Good one.. yeah!
Virtually all Transformers can be adapted to any design, at least, as output transformers.

Proper disposal... really:rolleyes:

seriously I have nothing to suggest other than that you could use the twp 12AX7 tubes as differential stereo preamplifiers. That would be quite the thing with a single ended output stage. All you need is two output transformers now.
 
Mill transformers

They're quite common in old test equipment and commerecial radio or receiving equipment. But use caution with transformers of that age, because they are rated for 115 volts, and not 120 volts, so they will have a slightly higher output (actually most of that designs that age were rated at 110 v, so 115 may not be far off from today.). Don't be fooled by size either, because they are big due to the potting design. I'v seen many of those paired with 5Y3 and the odd 5V4. Keep in mind that an amplifier can demand alot more from a power transformer then a receiver would. I would not gamble with 5AR4s or larger. But those transformers are worth it.
 
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mace1337

Member
2005-08-21 11:21 pm
So, would it be possible to use the bigger one for the power transformer and the smaller one for the output transformer? If so, how would I wire it up as an output transformer?

Unless you have two of those smaller ones you can only make a mono amplifier, so it's better to just get some separate OPT's, or maybe even go OTL (output transformer-less), but that's usually not for beginners. :)

edit: oh you said you want to build a mono amp, I missed that. :)
 
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I think I want to build a mono single ended class A amplifier. The tubes I have collected are two 12AX7 tubes that are matched, an EL84 tube and a 5Y3GT rectifier tube. If any of you have any suggestions of schematics I could use with these tubes, or if you know a design that would work better with additional or different tubes let me know, I would love to have some input.

What's the intended use of the amp you build? How many watts do you need?

A SE EL84 will be about 2-5 watts depending on operating conditions. SE EL34/6L6GC/KT88's will be 5-10 watts or so depending on operating conditions.

Are you planning on Triode operation or Ultralinear?

Do you have any output transformers yet? The power transformers appear to be appropriate for EL34/6L6GC/KT88 operation; the B+ voltage that you end up with may be a little high for SE EL84.

Do a search here for SE EL34, SE KT88, etc. The Simple SE and Mikael Abdellah's KT88 come to mind, but I'm sure that there are more. You could build 1 channel of these for your mono application.

The 5Y3 looks like it will work for a mono application, and maybe even for a stereo application, depending on current draw. Your 12AX7's will be a little light on current drive for the above outputs.....

The larger transformer could also work in a stereo SE application, although 125ma may be a little low depending on your choice of output tube.

You can get an idea of typical operating conditions for the various output tubes and the rectifier on duncan amps TDSL pages:

http://tdsl.duncanamps.com/tubesearch.php
 
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gain wire

Member
2004-11-27 4:04 am
NCR
So, would it be possible to use the bigger one for the power transformer and the smaller one for the output transformer? If so, how would I wire it up as an output transformer?

Well, this isn't a simple thing. You need to know the type of amplifier you want to build (that's easy though) and what tube you want to use. Then you look at the tube data and discover what load impedance that tube wants to see. Knowing the load you will put on it (example: 8 ohms) you then simply find the impedance ratio (Zamp/Zload). In most cases it will range between 3000 and 15000. To fidn the impedance ratio of the transoformer you must first find its voltage ratio (so choose the longest winding on the secondary) and then by means of the turns ratio to impedance ratio, find the impedance ratio. Zp/Zs= (Np/Ns)exp2

this page explains another manner of doing this: Output Transformer Impedance
 

gain wire

Member
2004-11-27 4:04 am
NCR
I also have another question, could I use two 12AX7 tubes in series before the EL84 tube to get either more power or a better signal, or does it not work that way.

It doesn't exactly work that way. You can put single tube stages in series, so I don't know if that's what you were referring to. But it won't give you more power, if you design it well, using the maximum gain from each triode section.

there are so many am designs floating around on the internet so just search a bit there, or here, there's lots of proposed and "filtered-by-diyer's" on diyaudio. Just search for "single-ended amp" or something like that.

good luck!