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.
Attachments
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 Frank’s 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
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 Frank’s 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
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
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
Attachments
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.
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.
A much better schema from Dick is the Mupp Amp.
See: http://members.home.nl/triode.dick/2a3_mupp_project.html
I've also build this amp with the 2A3's from JJ.
Guido
See: http://members.home.nl/triode.dick/2a3_mupp_project.html
I've also build this amp with the 2A3's from JJ.
Guido
Attachments
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
Guido
Hammond 302AX power transformer
Hi Guys,
This transformer is best suit for building of 2A3. It provide 2 sets of 2.5V for 2A3's filaments, 5V for rectifier tube and 6.3V for driver. You don't need extra filament transformer even you build this Push Pull or Stereo SE 2A3 amplifier.
It's really cool.
Johnny
Hi Guys,
This transformer is best suit for building of 2A3. It provide 2 sets of 2.5V for 2A3's filaments, 5V for rectifier tube and 6.3V for driver. You don't need extra filament transformer even you build this Push Pull or Stereo SE 2A3 amplifier.
It's really cool.
Johnny
Somehow I missed this one when I first looked at the Hammond catalog.
Hammod 166S2, 2.5 VCT, 10 A
* Primary 115 VAC, 60 Hz.
* Center tapped secondary.
* Open style, channel bracket, two hole chassis mount.
* Dual bobbin design - no electrostatic shield required.
* Class B insulation (130 degrees, C)
* Hi-Pot test of 2,000 V RMS.
* UL listed (# E50394) & CSA certified (# LR3902).
It seems like a viable option to feed the 2A3s. The question now is what would be the best way to get 2.5V D.C. out of it? Unwind it until I get about 1.75V A.C. or use a regulator?
Hammod 166S2, 2.5 VCT, 10 A
* Primary 115 VAC, 60 Hz.
* Center tapped secondary.
* Open style, channel bracket, two hole chassis mount.
* Dual bobbin design - no electrostatic shield required.
* Class B insulation (130 degrees, C)
* Hi-Pot test of 2,000 V RMS.
* UL listed (# E50394) & CSA certified (# LR3902).
It seems like a viable option to feed the 2A3s. The question now is what would be the best way to get 2.5V D.C. out of it? Unwind it until I get about 1.75V A.C. or use a regulator?
I use a currentregelator . See :http://members.home.nl/triode.dick/tekeningen/stro_br.gif
The second LM 317 is the currentregelation. It's easy to build and works very good. You can regelate is perfectly on 2.5 volt. With a resistor its alway's difficult to make it exact 2.5 volt.
Guido
The second LM 317 is the currentregelation. It's easy to build and works very good. You can regelate is perfectly on 2.5 volt. With a resistor its alway's difficult to make it exact 2.5 volt.
Guido
The Lundahl output transformer noted in the schematic is also for sale in the USA. http://www.kandkaudio.com, just thought you might want to know.
Cheers,
Bas
Cheers,
Bas
Frank,
I have never built a power supply using CMC. KYW addresses the same issue here:
http://www.diyaudio.com/forums/showthread.php?postid=576995#post576995
Is that what you have in mind? If so, could you help me with the specs for the common mode choke?
I have never built a power supply using CMC. KYW addresses the same issue here:
http://www.diyaudio.com/forums/showthread.php?postid=576995#post576995
Is that what you have in mind? If so, could you help me with the specs for the common mode choke?
Guido,
Thank you so much for your input. That is what I had in mind initially, however, as this is a project to help me learn about tubes and their use in amplifiers, I am thinking about trying the PSU suggested by Frank since I have never built one like that before. If that does not work out, I’ll go for the LM317 based one, as you suggested.
Thank you so much for your input. That is what I had in mind initially, however, as this is a project to help me learn about tubes and their use in amplifiers, I am thinking about trying the PSU suggested by Frank since I have never built one like that before. If that does not work out, I’ll go for the LM317 based one, as you suggested.
Bas,
It was nice of you to point that out. I was aware of the availability of the Lundahl transformers in the USA, however, due to the falling Dollar exchange rate and I believe the FOB price in Sweden and also shipping expenses, the final cost is prohibitive. Compare the price of $195 for the LL1623 to $51.92 for the 1645 and you will see what I mean. Thanks anyway.
It was nice of you to point that out. I was aware of the availability of the Lundahl transformers in the USA, however, due to the falling Dollar exchange rate and I believe the FOB price in Sweden and also shipping expenses, the final cost is prohibitive. Compare the price of $195 for the LL1623 to $51.92 for the 1645 and you will see what I mean. Thanks anyway.
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