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Old 24th May 2003, 08:33 PM   #1
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Default SE 6L6 amp (missile amp)

I have been looking into building a nice, simple, cheap 6L6 amp for a while. I have heard that the 6L6 is a nice sounding tube, and it seems as though a complete stereo SE amp could be put together for fairly cheap. The missile amp really appeals to me, as it is very simple. Does it look like it would perform well? I know that the tubes shown in the schematics for this amp are not 6L6's, but they are related. Output irons will be Hammond 125ESE's, resistors will be 1W Vishay/Dale, coupling caps will be polypropylene Orange Drops, ecetrolytics will be either Nichicon or Panasonic FC.

I have only a few questions...

If I use a 100k log pot at input (I don't have a preamp and will need volume controls) I then scale the input resistor up to 1M, correct?

How much power would this put out, approximately, with 6L6's running off of +300V supply?

About what mA rating will I need for SE 6L6's?

I will not be making a separate bias supply. How will I go about adjusting the bias of the 6L6's, then? Just put the resistor to ground? Will 470k give me the needed bias at this tube's input?

Thanks in advance
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Old 24th May 2003, 11:53 PM   #2
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Quote:
If I use a 100k log pot at input (I don't have a preamp and will need volume controls) I then scale the input resistor up to 1M, correct?
or leave it out...

Quote:
How much power would this put out, approximately, with 6L6's running off of +300V supply?
About 2-3 watts

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About what mA rating will I need for SE 6L6's?
100 - 125 mA should be plenty for the transformer

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I will not be making a separate bias supply. How will I go about adjusting the bias of the 6L6's, then? Just put the resistor to ground? Will 470k give me the needed bias at this tube's input?
Ground cathode through a resistor of about 270 Ohms, 2W, bypassed with a 47-100 uF capacitor - will provide the bias.
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Old 25th May 2003, 03:04 AM   #3
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Default Its ok for starters

Don't expect too much from this amp as it is only a starter design. But you can get a couple of watts out of it.
Electrolytic caps as cathode bypasses are only tolerable, other types will perform better.

Hope this helps.
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Old 25th May 2003, 04:16 AM   #4
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Revision 3 (6L6GC SE) gets 5W output from 330V 60mA (269AX power tranny). A little NFB to clean up the distortion and it's a sweet little amp.

Omit the 1st stage and tone circuits and use the free 12AX7 section for the other channel, or skip it and use a 6AV6 if you're making monoblocks.

Tim
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Old 25th May 2003, 06:12 AM   #5
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Tim, could you please post some wattage ratings for the resistors in your amp? If I use Ohms Law on some of those I end up needing 100W resistors... that would be both impossible to obtain, and extremely expensive if I could. I am targeting for not much at all. 125ESE's will cost me about $60, then another probably $40 for power transformer, and $20 for inductor, so I am looking at less than $30 for parts. If you will... please provide me with the wattage ratings that work best and the voltage rating on the electrolytic caps. Thanks
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Old 25th May 2003, 10:03 AM   #6
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The OPT is a P-T31, meant for 6V6s but seems to work, albeit with a bit of distortion on the bass (the least you can expect). Sounds fine, and seems to take NFB well.

All the 'lytics are rated except for the 6L6's bypass, which has about 20V on it in use; a 35V cap will be fine. It doesn't need to be 470uF either, but I had it around, so I used it.

All resistors are 1/2W 5% carbon film RS resistors ... that's why a few are paralleled. The 6L6's cathode bias can be replaced with a 330 ohm 2 to 5W resistor and the 3x15k in the supply would be 4.7k 1W or so.

Tim
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Old 25th May 2003, 06:42 PM   #7
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Default 5 watts???

Do you want to specify if that is 5 watts RMS or Peak or Music power?
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Old 25th May 2003, 10:51 PM   #8
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Measured into 4-10 ohms, at clipping as seen on 'scope.

Tim
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Old 26th May 2003, 02:25 AM   #9
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Default Watts are watts

Engineering watts are the things that heat components rather than engineers. They do not know about marketing watts (peak, music, Sinclair), they only know about watts derived from RMS values of voltage and current with due regard for phase angle.
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Old 26th May 2003, 08:17 AM   #10
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