2A3 OTL 800 Ohm Speaker

desperateaudio · 15th June 2007, 01:48 PM

Hey Guys. Just got a noce pair of NOS Philips 10w 800 ohms fullrange speakers. I would like to build a 2A3 OTL amp. Possible? Any suggestions? Thanks in advance.

Tom Bavis · 15th June 2007, 02:14 PM

4 2A3s in parallel? That would give a decent match... parafeed direct to the speaker.

Why not use the Philips amp circuit that was DESIGNED for this speaker? See Tung-sol 6CW5 data sheet for an example: http://datasheets.electron-tube.net/...127/6/6CW5.pdf

desperateaudio · 15th June 2007, 11:10 PM

Thanks Tom - I did not know there was a specific amp made for these speakers. I did some searching on the web and in the forums with no luck. Why the 4 2a3's in parallel? Thanks again.

desperateaudio · 15th June 2007, 11:13 PM

I saw the circuit it looks good. I just like the triodes plus I have about 10 2A3's. Can you elaborate on the parafeed idea? Appreciate the help.

Tom Bavis · 16th June 2007, 12:11 AM

The 2A3 likes a plate load of about 3K, so four of them should be happy with 800 Ohms...

You don't want B+ on the speaker wires, so use a choke for the DC load on the tubes and a coupling capacitor to the speaker.

desperateaudio · 16th June 2007, 12:32 AM

Thanks Tom.

So say 70H to 100H choke between the B+ and the plates and a 2uf to 8uf cap from the plates to the speakers?

Might also try a 6AS7 with both stages paralleled to see the results.

poynton · 16th June 2007, 12:47 AM

Parafeed is not OTL.

You might as well use them in PP with a transformer.

Andy

desperateaudio · 16th June 2007, 12:53 AM

I here ya. Could just load it with a resistor.

15th June 2007, 01:48 PM	#1
desperateaudio diyAudio Member Join Date: Dec 2004 Location: NE USA	2A3 OTL 800 Ohm Speaker Hey Guys. Just got a noce pair of NOS Philips 10w 800 ohms fullrange speakers. I would like to build a 2A3 OTL amp. Possible? Any suggestions? Thanks in advance.

16th June 2007, 12:47 AM	#7
poynton Magneto the Gravity Man diyAudio Member Join Date: Mar 2005 Location: A life on the ocean waves when I'm not at home in N. Wales (but I'm not Welsh so no sheep jokes!)	Parafeed is not OTL. You might as well use them in PP with a transformer. Andy __________________ If it ain't broke, break it !! Then fix it again. It's called DIY !

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15th June 2007, 02:14 PM	#2
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	4 2A3s in parallel? That would give a decent match... parafeed direct to the speaker. Why not use the Philips amp circuit that was DESIGNED for this speaker? See Tung-sol 6CW5 data sheet for an example: http://datasheets.electron-tube.net/...127/6/6CW5.pdf

15th June 2007, 11:10 PM	#3
desperateaudio diyAudio Member Join Date: Dec 2004 Location: NE USA	Thanks Tom - I did not know there was a specific amp made for these speakers. I did some searching on the web and in the forums with no luck. Why the 4 2a3's in parallel? Thanks again.

15th June 2007, 11:13 PM	#4
desperateaudio diyAudio Member Join Date: Dec 2004 Location: NE USA	I saw the circuit it looks good. I just like the triodes plus I have about 10 2A3's. Can you elaborate on the parafeed idea? Appreciate the help.

16th June 2007, 12:11 AM	#5
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	The 2A3 likes a plate load of about 3K, so four of them should be happy with 800 Ohms... You don't want B+ on the speaker wires, so use a choke for the DC load on the tubes and a coupling capacitor to the speaker.

16th June 2007, 12:32 AM	#6
desperateaudio diyAudio Member Join Date: Dec 2004 Location: NE USA	Thanks Tom. So say 70H to 100H choke between the B+ and the plates and a 2uf to 8uf cap from the plates to the speakers? Might also try a 6AS7 with both stages paralleled to see the results.

16th June 2007, 12:53 AM	#8
desperateaudio diyAudio Member Join Date: Dec 2004 Location: NE USA	I here ya. Could just load it with a resistor.

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