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Old 8th April 2007, 10:22 PM   #1601
SRMcGee is offline SRMcGee  United States
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Default Aikido Preamp

And an interior shot of the preamp enclosure:
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Old 8th April 2007, 11:30 PM   #1602
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Default My attempt at an Aikido

I think it looks OK. My wife reckons that I should stain the pine a darker color? However, the camera has picked out scratches.

I am using diode rectified power. The rear tube is an Amperite 30 second delay. I have a separate 6.3VAC heater transformer, which is rectified and regulated using a Welborne Labs kit.

At some point, I'll upgrade to 12VDC and expermiment with 12V tubes.

Charlie

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Old 9th April 2007, 07:47 PM   #1603
gertk is offline gertk  Netherlands
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Smile My First EL84 PP

This my very first self built Tube Amp (actually I have built two of these since they are monoblocks)
It is based on a design in Radio Electronica from 1962
I replaced the power and output transformer by a set of Amplimo toroids (one inside the case and the other outside, stacked on a single M6 thread)
The tubes are 2 x EL84(of course) and an ECF83 as input stage and phase splitter.
All built into a Hammond cast aluminium box (quite small... I had to use some surgical handyness to get it all in...) the box runs quite hot though when it runs for a few hours :-( No chance i can close it up the way it was meant to be :-) (that's why its floating above the lid)
I planned to put 4 EL84 on the box since the output transformer is only 4 k anode-anode but the amplifier gets unstable with 4 tubes. Might be that the power transformer can't keep up but all voltages read quite OK. I also had a problem with the ECF83 generating some HF oscillation when driven with a large signal. For now I blocked it with a (too large) styroflex cap of 200 pf between anode and kathode.
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Old 17th April 2007, 07:11 PM   #1604
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Hi all,

This is my most recent work: a trivial ultralinear amp, 60WRMS/channel.
Input tubes 6922 and power tubes 6550C (or KT88), continuously variable neg. feedback on front panel knob, overkill (almost...) output stage power suplly, independent input tubes power supply (cap/choke/cap), also separated for bias and for the input stage DC heaters.
3 steps manual power on sequence and HT standby switch.
Fixed bias and 0, 4 and 8 ohms speaker taps
All aluminum chassis and piano black hand buffed front panel.

Sounds very very natural and cristal clear.

[ ]s
Ricardo

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Old 17th April 2007, 07:34 PM   #1605
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Nice job RW. I like the clean wiring inside.

Looks like you can check the output tube bias current from the top but you need to go inside to adjust it.
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Old 17th April 2007, 07:53 PM   #1606
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Quote:
Originally posted by rcavictim
Nice job RW. I like the clean wiring inside.

Looks like you can check the output tube bias current from the top but you need to go inside to adjust it.
Hi rca,

Thanks for your kind words.

No it is not that way: you can also reach the pots for bias adjustments from the top, they are (each one) just behind the bigger tubes but unfortunately the previous pics could not show them at all...

[ ]
Ricardo

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Old 18th April 2007, 06:23 AM   #1607
ddd is offline ddd  Bulgaria
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BEAUTIFUL! Like all the works of rwellerson.
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Old 18th April 2007, 12:10 PM   #1608
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Hi ddd,

Many thanks.

[ ]
Ricardo
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Old 18th April 2007, 03:11 PM   #1609
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I did not know it was possible to do such a beautiful job of point to point. I take it that those bus bars are lacquer coated transformer wire? .... Do you coat the inside of the chassis with this as well?

Also looks like plastic caps through out, except for those quality electro's on the power lines ...

Very neat, very tidy, better than factory work, a sight better than anything I have ever been able to do ...
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Old 18th April 2007, 03:49 PM   #1610
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Hi Ricardo;

nice work!
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