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Old 24th December 2005, 12:22 PM   #1
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Default transformerless amp help plz ...

hi
i heard that i can build a tube amp without transformer ...
it so hard and almost impossible for me to find a tube output transformer here ...
so how can i build a transformerless version amp with 2 el34 ?
i have another 2 gz34 tubes r they useful ? can i use all tubes ( 2xEL34 and 2xGZ34 ) together ?
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Old 24th December 2005, 03:08 PM   #2
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Even 3 GZ34 won't help you

What you want just can't be done. At least not with normal speakers.
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Old 24th December 2005, 03:40 PM   #3
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Default Transformerless or OTL amplifiers...

Those valves you have are just not suitable for an OTL type amp, except maybe a headphone amp, and even then it probably wouldnt be very good.

The most popular OTL type O/P valves are the 6C33C-B, PL/EL 509, EL/PL 504, 6C41c, 6C19C, 6AS7.

Valves driving speakers directly isnt a normal act for a valve to do, as it requires current to drive a speaker, while a valve is basically a voltage amplifying device..........

This calls for special design considerations and rather specialised valves--The most common one would be the PL509/EL509 as these were used in thousands of early colour TV sets in the early 80's--Most older TV repair places may still have a few around....
The 6C33C-B is a Russian Voltage Regulator easy to get off Ebay and very popular for OTL's

Try a search here for 'OTL' and for 'Futterman' and 'Circlotron' There are various designs of OTL some guys prefer one type over another--My fave at the moment is the Circlotron type.

Alternatively, if you have the time and can get the parts, its not impossible to wind an out-put transformer yourself. Have a look at Yvesm Transformer calculator It does more or less everything except wind it for you.............
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Old 24th December 2005, 04:04 PM   #4
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hi and thnx alot ...
i donno if i can find the parts to wind a transformer myself ... should i find special parts for a output transformer or the parts for regular transformers will work ???
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Old 24th December 2005, 04:10 PM   #5
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You can get cheap and good opts here: www.tubesandmore.com

Forget OTL! And iŽd say forget transformerless power supply too, its way to dangerously.
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Old 24th December 2005, 05:00 PM   #6
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Quote:
Originally posted by Ahmad_tbp
hi and thnx alot ...
i donno if i can find the parts to wind a transformer myself ... should i find special parts for a output transformer or the parts for regular transformers will work ???
you can build a nice amplifier with good output without output transformer
if you use transistors instead of tubes

how about this bright idea

PS. it might even have better performance than tube amps
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Old 24th December 2005, 05:14 PM   #7
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Don't consider for a second ANY amp (tube or SS) without a power transformer.

If O/P transformers are too difficult to obtain, build a hybrid power amp that uses tubes for voltage gain and FETs for the "finals".
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Old 24th December 2005, 07:50 PM   #8
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tube voltage gain and FETs for final ?
sounds great , how ? :P
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Old 24th December 2005, 11:25 PM   #9
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Winding a push-pull output transformer involves more or less the same parts as for a 'regular' mains transformer, but requires more work with the winding - the setup of the windings is much more complex. Even so, if you can get a transformer wound per your specification, you can make output transformers. Granted, high quality output transformers require more than a few tricks to make but these are the tricks that make an ordinary transformer into a top-notch one. A patient winder will still be able to make a more than decent transformer just by following instructions, without the need for extra special core materials or winding techniques. You can stretch this all the way up to excellent if you can have transformers wound on C cores. Keep in mind I am talking about PP transformers - single ended is a rather different story.

Also, if you can get toroidol transformers wound to order (or sometimes even some standard types), you can use these with some tube types as surprisingly good PP output transformers - what is required is a fairly low plate-to-plate impedance, and very good idle current balance in the two push-pull output tubes. For instance, a 115 + 115VAC primary into 6.3V secondary toroidal transformer will give you a ~10k plate-to-plate load on the two primaries connected in series, when an 8 ohm load is connected to the 6.3V secondary, but this is pushing things, unless the toroid has something like two 6.3V windings for the secondary, which you can connect in parallel. Just keep in mind that you will need a 50Hz mains toroid transformer rated at least 100VA in order to get a decent 20W at 20Hz (and even that might be pushing it).

Finally, you may look at the problem from a different perspective - that of the loudspeaker. If you are into line arrays, you can connect them so they have a relatively high impedance, and in this manner considerably widen the choice of tubes you can use in a output transformer-less (OTL) type amplifier.
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Old 26th December 2005, 01:35 PM   #10
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thnx a lot
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