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Old 7th April 2012, 06:09 PM   #1
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Default Tube Preamp turn on circuit

I have built an Aikido amp (12BH7 output). I use a 555 timer to turn on the fiiments first followed by B+ ~30 sec later, and then connect the power amp after another 5 sec automatically.

Question: Can I short the output of the preamp until I finally connect the power amp (~5 sec with B+ applied)? This helps with the thump, but I don't want to do any damage.
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Old 7th April 2012, 09:43 PM   #2
zkri is online now zkri  Croatia
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Quote:
Originally Posted by macdelf View Post
Question: Can I short the output of the preamp until I finally connect the power amp (~5 sec with B+ applied)? This helps with the thump, but I don't want to do any damage.
Yes, you can. Make it 10-15 sec.
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Old 8th April 2012, 04:01 AM   #3
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Thank you. I'm a yube newbie.
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Old 8th April 2012, 10:49 AM   #4
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All of my Aikido's power up with the filaments and B+ at the same time.

If you allow the line stage to warm up and then turn on the power amp there will be no thud. I have used my Aikido's with both SS amps and tube amps. I have no thud period. There is NO need to power up the filaments and delay the B+ at all. There is not going to be any cathode stripping to worry about so why make it any more complex than necessary.
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Old 8th April 2012, 11:31 AM   #5
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Cathode stripping..... There is a fraternity that believes that this can happen. But this is usually only a problem in High Power amps.

It is contraversial and I don't want to get into an argument in this guys thread.

Valve longetivity can be helped along by slowly applying the heater current.

When do your light bulbs blow - when you first turn them on normally.

We went overboard on this one but it was only an experiment.
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Last edited by KatieandDad; 8th April 2012 at 11:34 AM.
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Old 8th April 2012, 09:39 PM   #6
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Not really trying to argue but is it really necessary to go to the trouble of making the circuit to possibly add a few hours to the life of a $5 tube.


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Cathode stripping..... There is a fraternity that believes that this can happen.

Given the right circumstances it can happen. But not with the circuit in the Aikido with the plates voltages it runs on.
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Old 10th June 2012, 12:33 PM   #7
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Default New issue

This is a 9-pin dual mono. I'm using a 2.2 uF output cap and driving two power amps in parallell (about 100K each, and a subwoofer crossover (~75 Kohm)). Recently I disconnected the sub, and the protection circuits on the main amps went off. I hooked the preamp up to a scope and observed some faitly random, but smooth subsonic noise whith rare peaks (~0.1 v, usually around 20 mv). I am currently using PS1 from glassware with a choke. I look at the input to the grid in the PSR circit and I see sharp spikes where the largest swings take place but not following the smoot nature of the noise. Qestions:
1) Is this a power supply issue?
2) should I go to a regulated B+?
3) Have I just used too large of a coupling cap?
4) Should I increase the size of C6 in the PSR leg?
4) Has anyone seen this before?
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