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Old 21st June 2003, 11:13 PM   #1
akersa is offline akersa  United States
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Default Tube headphone amp problems

I am working on building a variation of an Antique Sound Lab Tube headphone amp, and I am wanting to get away from using an output transformer, my problem is when I build the circuit without the transformer, I end up with high voltage on the audio outs. What am I doing wrong? Do I need bigger filters than you do if you have the transformer. I have attached the schematic, hopefully somebody can help me with my problems.

Thanks,
Adam Akers
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Old 21st June 2003, 11:39 PM   #2
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Default AC/DC.

Hi,

You did what?

Suppressed the OPTs?

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Old 22nd June 2003, 12:08 AM   #3
Colt45 is offline Colt45  Serbia
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When you drop the transformer, there is no real plate load.. so youll need a plate resistor or choke

but this output will be really high Z..

better use a trafo or do a CF. straight r/c-coupled is gonna have a real high Z
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Old 22nd June 2003, 12:41 PM   #4
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Hi,

From what I can tell there should be a headphone jack behind C11/R?.

That will probably be still quite high impedance but it does bypass the OPT.

Another option, assuming you leave the OPT in place or use a proper plate load, is to take the signal from the cathode of the 6BQ5 using a good quality coupling cap as Colt45 suggested.

Do you happen to know the input impedance of your cans?

Cheers,
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Old 22nd June 2003, 02:51 PM   #5
akersa is offline akersa  United States
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Thanks for the help. My cans have a 600 ohm Z. Can anybody be more specific on the values of coupling caps, or a plate resistor value. I am new to Tubes, and sometimes my experimentation with different values is a shot in the dark.

Thanks again,
Adam Akers
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Old 22nd June 2003, 05:17 PM   #6
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Hi,

The PSU of that schematic has a really low B+, 160V.

If you could make it around 270V you could than easily run the trioded 6BQ5 in class A using a 3K5 anode resistor and a 270R cathode resistor.

The input stage needs revision also to accomodate the higher B+ but I feel it would be much better off that way.

For 600 R cans a 80 uF cap should be ample, you could even use some // filmcaps to reach that value.

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Old 28th June 2003, 02:09 AM   #7
akersa is offline akersa  United States
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Default Still having problems

Thanks for all of the suggestions guys. But I am still having problems with my amp. Would anybody be willing to take the attachement that I am posting and draw in the missing parts. I have been playing with a cathode follower circuit, but I do not think that I am doing it correct. My headphones are 600 ohm. Thanks again for all of your help. I am enjoying this project, but finding it difficult to finish. Help!!

Adam Akers
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Old 28th June 2003, 07:38 AM   #8
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Default this is probably close...

Ok, I took the circuit and made a cathode follower so you could see what was meant... I don't know what to do with the screen grid, so i left it unconnected. Others here who know their stuff moreso than I can help you out more and make fun of my circuit. I admit- I don't know a lot about tubes.BUt, I got the basic topologies down. hehe MGHead as cathode follower: (not totally complete though...)

EDIT: Ignore pin numbers- I threw this circuit together using the objects I had in my schem program, which were 6L6GC and 6SL7. So, pin numbers are wrong. Part numbers and values not shown on purpose. (because I don't know them hehe)
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Old 28th June 2003, 01:26 PM   #9
akersa is offline akersa  United States
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Thanks for the help. Can anyone else fill in any more of the missing peices? Values, what to do with the plate etc.

Thanks

Adam Akers
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Old 1st August 2003, 05:35 PM   #10
akersa is offline akersa  United States
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I am still having a really hard time trying to incorporate this circuit. I am in need of some one that understands this stuff better than I do to help me. If anyone out there would spend the time to draw the schematic like it should with the Cathode follower circuit in place I would be willing to pay you. This is a project that I am really wanting to finish.

Thanks,
Adam Akers
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