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Aikido All-In-One Octal Heater Troubles
Aikido All-In-One Octal Heater Troubles
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Old 6th February 2010, 01:19 AM   #1
ultrachrome is offline ultrachrome  United States
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Default Aikido All-In-One Octal Heater Troubles

I'm using all 6SN7GTB.

Initial readings:
HV AC input is 236.3VAC
B+ voltage is 307VDC
Heater voltage is 6.2V
Slight hiss from both speakers, slight buzz from right channel.

Sounds really good playing music but when I stop the music after a few minutes to switch to a new song, I notice the hiss volume is much louder and my left woofer is oscillating. Immediately shut off the power amp (did not wait to see if right speaker was doing it too) and measure voltages.

Now my heater voltage is 2.1VDC and the filaments are no longer visibly glowing. I did notice the regulator heatsink (1.5"Wx1"Dx2.5"H) gets really hot. My IR thermometer sees temps well over 180F.

Looking at the documentation, I'm confused. There's a Filament Jumper Wire Schedule that shows the configuration for a 12.6V PS with 6.3V tubes. I've jumpered that configuration.

On the next page is a table of typical part values. I've chosen the parts in the 6.3V Heater Voltage column.

For Vac Input, 7-8Vac@ 5A and 12-12.6Vac @ 2.5A options are listed.

I'm using a toroid on which I wound a 20 gauge 12V secondary. Max RMS current density is 4.9A/mm2 (=2.53A) and DC current density is 2.4/mm2 (=1.29A).

What did I do wrong?
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Old 6th February 2010, 03:19 AM   #2
john65b is offline john65b  United States
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I have the exact same setup. Your issues are most likeley around your heater circuit.

First question i do you have AC or DC on heaters? Regulator? A 7806? I beleive a Regulator is usable only with DC, not AC.

How did you ground your heater? I floated mine with a cap as suggested in the Aikido Octal manual.

If DC Heaters, check your rectifier-smoothing cap arrangement...

Actually, I also initially had a 7812 regulator on my 6SN7 heaters, but current was too much and got hot, and burned up, so I put in a resistor ( I was using Rat Shack 12VAC Trannies -> DC on heaters). I bet you fried your regulator due to filament currents, just use Ohms law to figure resistor instead of regulator.

Keep it simple - Tranny, Full Bridge rectifier, 10,000uf 16v cap, resistor, to heaters.
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Last edited by john65b; 6th February 2010 at 03:28 AM.
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Old 6th February 2010, 03:32 AM   #3
ultrachrome is offline ultrachrome  United States
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LD1085V. The filaments are being fed with DC.

I'm using the all-in-one kit that has both power supplies and the preamp circuit on a common PCB. The only connections are heater ac, hv ac, input and output.
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Old 6th February 2010, 03:39 AM   #4
ultrachrome is offline ultrachrome  United States
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I'm composing an email to JB and it occured to me that I could configure the heater supply and filament wiring in multiple ways.

Currently, my 12Vac is being turned into 6.3Vdc by the regulated supply and the heater socket pins are jumpered for a 6.3Vdc supply.

But perhaps I should configure the supply to produce 12.6Vdc and change the filament wiring for a 12.6Vdc supply feeding 6.3Vdc to each tube.
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Old 6th February 2010, 04:18 AM   #5
rknize is offline rknize  United States
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It sounds like maybe your heater supply regulator went into thermal protection and shut down. Is it working now? It probably needs a better heatsink.
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Old 6th February 2010, 04:31 AM   #6
ultrachrome is offline ultrachrome  United States
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I adjusted the regulator to output 12Vdc and rewired the filaments to suit and have a much cooler and happier regulator.

Much better. Now I just have to hunt down the source of that buzzing in one channel. For the time being, I can ignore it.

Thanks.
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