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Alternative uses for 100V output trafo's
Alternative uses for 100V output trafo's
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Old 30th March 2020, 02:16 PM   #11
Kay Pirinha is offline Kay Pirinha  Germany
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If you connect those dual 100 V windings in series, you'll yield an impedance of 133 ohms. Still too low as a PP tube output transformer.
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Old 31st March 2020, 04:06 PM   #12
Bill Coltrane is offline Bill Coltrane  Netherlands
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Old 1st April 2020, 11:41 AM   #13
trobbins is offline trobbins  Australia
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Quote:
Originally Posted by Bill Coltrane View Post
The other 2 trafo's ... have 5 cables coming out. 2 of them are connected to the amp output, the other are the 0V, 70V and 100V outputs.
The website does not identify anything about the line output transformer except speaker side voltage and power ratings. If the amp side of the OT was connected internally, and presented an 8 ohm loading at 250W, then an estimate of the OPT turns ratio is primary voltage of sqrt(8 x 250) = 45V, to 100V, or 1:2.2 where the speaker side impedance is 40 ohm. You could do a simple turns ratio voltage test to confirm what the actual turns ratio is.

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Originally Posted by Bill Coltrane View Post
The 2 bigger trafo's are rated 100V at 33Ohm and have 1 primary winding connected to the output of the amp. The 100V windings are dual.
You probably can't tell if the two windings are connected in series or parallel for a 100V output ?

These transformers are effectively what is seen inside any solid-state PA amplifier from the last few decades - they have been designed for very low impedance matching. As such, they are pretty impractical to use for 'typical' valve amplifier applications. You would need to be fairly experienced to utilise them in a valve amp, such as in an output stage that uses multiple parallel tv line output valves that would be happy with driving a low impedance, and even then the speaker would likely need to be an effective 16, 32, or 48 ohm combination of series connected speakers.

I've had a go at designing up some solid-state pa amps for valves (as the amps are cheap as chips and have a chassis, front panel, power transformer, and output transformer all ready in place), but not yet made a practical conversion, as there are a lot of design and construction issues to work through.

Last edited by trobbins; 1st April 2020 at 11:45 AM.
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Old 1st April 2020, 11:47 AM   #14
Bill Coltrane is offline Bill Coltrane  Netherlands
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The windings are parallel.

What other uses are there for these trafo's, as tubes are very impractical?
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Old 1st April 2020, 12:01 PM   #15
wg_ski is online now wg_ski  United States
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100 volt line transformer, if rated down to 30 or 40 Hz, could in theory be used as a power transformer. The caveat is that you don’t know how well it’s insulated.

Many of the tube amp designs that use line transformers are just a few watts. The little 5 to 15 watters you find on the back of ceiling speakers work pretty well for that, given the cost (usually free) - and the fact that you drive it with something dirt cheap on relatively low B+ (ie, 50C5). Unfortunately, higher power doesn’t help here unless you use exotic tubes which are “impractical”.
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Old 1st April 2020, 12:10 PM   #16
trobbins is offline trobbins  Australia
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Quote:
Originally Posted by Bill Coltrane View Post
What other uses are there for these trafo's ...?
The options as I see it:
- a solid state PA amp
- a door stop
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Old 1st April 2020, 02:14 PM   #17
Kay Pirinha is offline Kay Pirinha  Germany
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Are you able to dismantle these transformers? Do you have winding skills and can source magnet wire and insulation foil? Then you might wind suitable output trannies, using just the core laminations and bobbins.
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