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Beefing up bass amp with 2 6AQ5 ...
Beefing up bass amp with 2 6AQ5 ...
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Old 14th November 2017, 03:05 AM   #11
thoglette is offline thoglette  Australia
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Default I'm only happy when it rains......

Quote:
Originally Posted by Paul Munters View Post
I think the amp can deliver much more, at least 25 watt.
Which is a whole 4db above the nominal power of 10W. Changing your speaker would be a more effective to get 4db. (If much less fun).

The most effective way would be to put about 0.5 ohm in series with your speaker (in the ground leg) and blend the voltage generated thereon with 5% of the amplifier output voltage. Then feed that into a great, steaming pile of Class D amplification and get 15 odd db of headroom.
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Old 14th November 2017, 09:40 PM   #12
Printer2 is offline Printer2  Canada
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I have never got 10W out of a pair of 6AQ5's, maybe 7-8W.
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Old 15th November 2017, 01:02 AM   #13
Tubelab_com is offline Tubelab_com  United States
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Quote:
You do not want to go any higher on the 6AQ5's. 300V is the most
I have plenty of experience melting tubes......the easiest tube to melt is the 6AQ5. You can't squeeze these guys at all beyond their specs. The glass is just too close to the plate, and the plate tends to develop a red spot in one small place when pushed. There is a very fine line, just a few milliamps between pale red glow, and hole in the glass. I have melted enough of these guys to know......of course I had about 1000 used ones to play with, so I "tested" some of the ugly ones, but they all have the same issue, no margin for error.

Quote:
I have never got 10W out of a pair of 6AQ5's, maybe 7-8W.
I have seen 10 watts, and even 12, but don't run them at 12 watts output for long. You won't even hear the sucking sound......just silence!
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Old 15th November 2017, 10:30 PM   #14
Printer2 is offline Printer2  Canada
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I have no doubt you got that out of them, But us mere mortals...


I should have qualified that as cathode biased also.
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Old 16th November 2017, 02:19 AM   #15
Tubelab_com is offline Tubelab_com  United States
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Quote:
I should have qualified that as cathode biased also.
I used fixed bias from the old Fluke 407D. Twist the bias and plate voltage knobs until you find maximum power output with minimum glowing parts! I also had the screens hooked up to a different power supply for more knobs to turn.
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Old 16th November 2017, 08:28 PM   #16
Paul Munters is offline Paul Munters  Netherlands
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Still exploring. Assuming power transformer and output transformer would hold, putting ss rectifier in and thus have B+ of above 350, what would two 6l6s roughly deliver? And what cathode resistors value would be appropriate? Seems that putting El84s in would not give much gain compared with current 6AQ5s.
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Old 17th November 2017, 02:13 AM   #17
Printer2 is offline Printer2  Canada
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Quote:
Originally Posted by Paul Munters View Post
Still exploring. Assuming power transformer and output transformer would hold, putting ss rectifier in and thus have B+ of above 350, what would two 6l6s roughly deliver? And what cathode resistors value would be appropriate? Seems that putting El84s in would not give much gain compared with current 6AQ5s.
http://www.mif.pg.gda.pl/homepages/f...93/6/6L6GC.pdf
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Old 17th November 2017, 09:04 PM   #18
mozz is offline mozz  United States
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Before you do any of this, be sure the power transformer can handle the higher filament current and the higher plate current, or you will burn it out. I said to take out the dial lamps because that gains you 300ma filament current right there, also any unused tubes. I doubt very much you can swap to a pair of 6l6gc without damaging the power transformer.
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Old 22nd November 2017, 04:00 PM   #19
Paul Munters is offline Paul Munters  Netherlands
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Indeed, I calculated the total heater current needed, and compared with original circuit. Taking out lights will help, but EL84s will be too much. I then replaced 6aq5s with 6N1Ps. Lots of hum now. Have to take a closer look in the weekend.
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Old 24th November 2017, 04:09 AM   #20
nauta is offline nauta  Canada
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The output power of an amp is based on the PT capabilities and the OT primary impedance. In the amp as it is, these parameters are set and there is nothing you can do about it.

The only way you might get a little more power is if the amp is cathode-biased and you change it to fixed-bias. This will make the amp more dynamic BUT may not increase useful output, since full-load is still the same.

You would be more successful changing the speaker complement and cabinet positions. Use two cabinets separated by a space and let psychoacoustics work for you.
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