RQ: Ìethod for calculate driver transformer

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yassen

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Hello, i need methodics how calculate parameters on this driver transformer "T1" in attach file. This is principal schematic for solid state power amplifier. Just principal real methodics, no theorythical. Smilar schematics are using in early transistor amplifiers in 70' years in this case practical methodics must exsist. Sorry for bad english.
 
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Your Q1 is a backwards PNP when it shoutld be an NPN.
Your Q2 is a backwards common-emitter when it should be an emitter-follower.
Your supply voltage is much too high for such a simple circuit.

The circuit doesn't need a transformer if you make it like this:
 

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Hi audioguru, sorry for error i was posted wrong image. I'm fix this error. This is real scematic and supply voltage +60V, output power 70W/4Ohm, not a joke.
 
There were a few amplifiers like this back in the 70's, but it's difficult to make because you can't source the transformers anywhere, and the quality of the amplifier was fairly poor anyway.
 
audioguru said:
It is a horrible amplifier circuit.
Click to expand...

True! - I was presuming it's not supposed to be a full practical circuit?, but just a rough example of the principles?.
 
Hi Nigel this is real, not only for example. This is part of real amplifier - 1971 year, name him "Voxson". Honåstly i'm like him sound very, wish duplicate original sch, but not a real method for calculate transformer. This in attahed file full sch and real sch with real values.

 

Looks horrible to me, and it's going to have a truely horrible specification!

I don't see how you can source a transformer, or find how to wind your own, the transformer is absolutely critical to the design (and I use 'design' very loosely).
 
Nigel Goodwin said:
Looks horrible to me, and it's going to have a truely horrible specification!

I don't see how you can source a transformer, or find how to wind your own, the transformer is absolutely critical to the design (and I use 'design' very loosely).
Click to expand...

I measure all parameters: P out 70W/4 Ohm (sinus), FR = 20Hz - 18 000KHz (-0.5db), THD = 0.1 % for 30W (Right Mark). Sound very, very soft and dinamic - this is true. I'm have a lots sources transformers (old aparatures, radio etc., many sizes and materials). Need just metodhics HOW calculate this input transformers.
 
I find that specification very hard to believe.

It's probably tested at very low power at 1kHz.
 
Yes it's a terrible design, but the OP says he likes its performance. There's no accounting for taste. Transformer coupling and PNP power transistors are sooo 1970's. Now I'm done bashing the design, so I'll try to answer the question.

The transformer should have a primary inductive reactance near 560 ohms at the 3 db low frequency cutoff. It should have a core which is without significant loss up to the high frequency cutoff. That's a difficult transformer.

The primary of the transformer will see about 10Vrms before distortion starts to dominate. You'll want enough drive voltage to get a maximum 2V (6A) peak in the emitter resistors. That'll take approximately 2Vrms of transformer output. This makes the transformer turns ratios about 10:2:2.

Except for the high frequency response, a transformer with a 120V primary and two, 24V secondaries would do.
 
Many thanks mneary this information very practical and usefull! Many mеmbers say for this schematic bad words, yes on a paper and measuring parameters not a very good, but real sound very beautiful for unexpected surprise. For this:
You have some methodics on a paper? More info about buildings and materials for core on transformer? I' posted in attach photos on this amplifier for information:

 
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The spec on an AL102 is only 60V, 6A, and 30W - I would suggest 25W to 30W would be the maximum spec of the amp - 70W sinewave into 4A would kill the amp VERY quickly.
 
Nigel Goodwin said:
The spec on an AL102 is only 60V, 6A, and 30W - I would suggest 25W to 30W would be the maximum spec of the amp - 70W sinewave into 4A would kill the amp VERY quickly.
Click to expand...

I'm not sure in this. Original specification on amplifier 2x60W / 4 ohm. I mesured supply voltage: + 60V emty work and +55V full power. On a sinus input and 4 ohm load maximum power 70W, and 60W for not a cippling. May be transistors selected on a factory for high voltage, i not a sure but this real voltage.
 

60V is just about OK for the AL102?, but the power dissipation is rather low, like I said it wouldn't last long putting out 60W RMS - the transistors will soon toast and die, and germanium devices have a MUCH lower permissible temperature.
 
Germanium transistors are extremely vulnerable to thermal runaway, and this amplifier has no protection. It must never be operated at an elevated ambient temperature. I have some similar amplifiers and they have enormous heat sinks. (approximately 300 square inches per transistor).
 
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