Triode Dick/FdeGrove 2A3 PP amplifier - diyAudio
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Old 11th March 2005, 07:07 PM   #1
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Default Triode Dick/FdeGrove 2A3 PP amplifier

In another thread Frank (fdegrove) showed the schematic for a 2A3 based push-pull amplifier, derived from an original created by Triode Dick. I would like to build it, but need to find suitable transformers readily available in the USA. I am asking for assistance from the more experienced tube people.
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Old 11th March 2005, 07:08 PM   #2
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Default The output transformer

Stepping backwards, I thought about using the Hammond 1645 as the output transformer.

http://www.hammondmfg.com/1608.htm

The primary impedance of the Lundahl in Frankís schematic is 5K6 but the Hammond 1645 has a nominal 5K. Can I use the Hammond 1645? Is any adjustment to component values necessary?

Hammond suggests the 1615 for use with the 2A3, but since the price difference is small, I thought that the 1645 would give me more options to re-use it in a future project.

Hammond 1615
Audio power: 15 W
Primary impedance: 5K
Secondary impedance: 4, 8, 16
Max D.C. per side: 100 mA

Hammond 1645
Audio power: 30 W
Primary impedance: 5K
Secondary impedance: 4, 8, 16, 70V
Max D.C. per side: 128 mA
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Old 11th March 2005, 07:10 PM   #3
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Default The power transformer

Frank also posted a power supply to use with the proposed amplifier.

Hammond offers one model, the 369AX, that provides a 125-0-125V secondary and a 6.3V, 2A filament winding. Could I use the Hammond 369AX for the power supply?

http://www.hammondmfg.com/300series.htm
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Old 11th March 2005, 07:13 PM   #4
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Default The 2A3 heaters

Now I need a transformer for the 2A3ís 2.5V, 2.5A requirement. I could not find any readily available. Would anybody have a suggestion?
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Old 11th March 2005, 09:50 PM   #5
EC8010 is offline EC8010  United Kingdom
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Default 2.5V 2.5A

Buy a cheap 6V toroid, unwind the 6V windings (counting the turns as you go). Using new wire, wind 4 off 1.25V windings. It won't be very many turns, so it's easy to do. Finding 2.5V CT is really hard. If you're feeling posh, you could add an E/S screen, but make sure you don't accidentally create a shorted turn.
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Old 11th March 2005, 10:09 PM   #6
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That is a good idea and I will definitely try that.

Thank you!

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Old 12th March 2005, 05:03 PM   #7
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The 1645 should work- the difference between 5600 and 5000 ohms p-p is totally swamped by the real-world variations in speaker impedance with frequency.
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Old 12th March 2005, 05:33 PM   #8
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A much better schema from Dick is the Mupp Amp.
See: http://members.home.nl/triode.dick/2...p_project.html
I've also build this amp with the 2A3's from JJ.

Guido
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Old 13th March 2005, 12:34 AM   #9
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Hi,

Quote:
A much better schema from Dick is the Mupp Amp.
Better in what respect?

Both can easily be improved but my choice would still be the original one with the ECC88 paraphase for its sheer musicality.

Cheers,
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Old 13th March 2005, 07:18 AM   #10
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Have you buiild both amp's Frank? I did. I find the Mupp amp better, the amp has a better bass-response, also a better soundstage, more correct. I recently build a second pair with a C-core with a lamination thickness of 0,05mm. I used top components as Riken Ohm resistors and Mundorf Silverfoil in oil caps. Also completly build with silver wire. I found this amp better than the Big C from Dick. And the Big C is a SE amp. This are off course only my humble expierience .

Guido
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