what to do with a 12W 600ohm to 4/8 ohm output transformer? - diyAudio
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Old 18th September 2012, 07:57 PM   #1
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Default what to do with a 12W 600ohm to 4/8 ohm output transformer?

Hey guys,

I recently ripped apart an old build, and now have a hammond 119DA spare... i was using it in an SE 1/4 watt application where it wasn't really used to its full potential, so my question is, what could i do with it? what tubes could i use it with? and what configuration?
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Old 18th September 2012, 08:10 PM   #2
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OTL with impedance matching transformer output.
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Old 18th September 2012, 09:29 PM   #3
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Hello,

The “Ear” is a headphone amplifier made by MapleTree Audio, it uses that transformer. The amplifier output is a 12B4A cathode follower with a 30uf capacitor followed by that Hammond transformer.

I built a bootleg copy. it works well!
DT
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Old 18th September 2012, 09:43 PM   #4
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OTL with impedance matching was what i was thinking, I think il leave the headphone amp. i'd rather have 2 channels, for a low power HiFi, 1 channel is usable, or even a Mic pre maybe...

Any schematics for anything?
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Old 18th September 2012, 11:40 PM   #5
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another twisted way to use this transformer is to tie the output in series to the negative feedback network and use the primary as a DI output (to pins 2&3 on a xlr connection)

if you need less voltage on the xlr, use the 4 ohm tap on the primary. If you still need more build an "O" type attenuator on the 600 ohm secondary (xlr side).
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Old 18th September 2012, 11:47 PM   #6
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Hmm, I think i would like to use as much of the 12 watt potential as i can, but i cant see an easy way of doing that. im thinking a push pull output between 2 cathode followers? but then whats an ideal output, 12BH7?

The idea of using it the other way for a line out is interesting, could do a better job at speaker emulation than a dummy load.
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Old 20th September 2012, 02:04 AM   #7
Fenris is offline Fenris  United States
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You could try something like I did here:

New amp: 13DE7 SE hybrid
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Old 20th September 2012, 07:29 AM   #8
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Good idea, a MOSFET output would be much more efficient, and i think i have a few IRF MOSFETs laying around, though i may try with a lower voltage and a pushpull configuration of N and P type MOSFETs, at +/- 40v with an ECC82 to drive it.
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Old 20th September 2012, 09:40 PM   #9
pilovis is offline pilovis  Italy
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Click the image to open in full size.

The audio transformer is 600-800/8 ohm 10W (600 ohm suggested)
L = 4-5 turns diam.0.5 mm around the 82 ohm 2W resistor.
Supply voltage: min 50Vcc - max 110Vcc (90V suggested)
Heaters voltage: min 24Vac/Vcc - Max 29Vac/Vcc (27V suggested)
Cathode resistors = 39 ohm 2W
Note: a bypass capacitance of 470uF 50V could be added in parallel to the cathode resistor of each tube.

Click the image to open in full size.
Power supply for 50Vcc.

Last edited by pilovis; 20th September 2012 at 10:02 PM.
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Old 20th September 2012, 10:28 PM   #10
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Better do a PP with PL84's, at about 250 anode voltage.
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