Aikido loses power? - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 19th September 2008, 01:08 PM   #1
lazyfly is offline lazyfly  Australia
diyAudio Member
 
Join Date: Jun 2004
Location: Melbourne
Default Aikido loses power?

Hi,

I've built an Aikido 6SN7 based on Broskie's boards and some parts from 8 Audio such as:

Transformer:
Output:
0-250-280V (100mA)
0-6.3-15V (2A)
0-6.3V (2A)
0-10V (0.3A)

Choke:
5H 100mA

PS:
B+ and up to 3 sets of independently regulated filament power source to tube heaters.

The problem is that the heaters just dim out and the music fades away after around 5 minutes of play time.

I believe 2A shared among the four heaters is a little under rated but thought it just wouldn't work to its full potential and not actually just fade out.

Any suggestions would be greatly appreciated.

Thanks for your time.

Cheers
Kendal.
  Reply With Quote
Old 19th September 2008, 03:39 PM   #2
diyAudio Member
 
Join Date: Jul 2006
2A is insufficient to heat four 6SN7s, which are rated at 600mA per tube. You're underspecced by almost half an amp AC.

If you're rectifying the 6.3V winding and feeding your heaters DC, you're looking at even steeper requirements. I had this exact same question when I built my Aikido, and John kindly responded to my email with an explanation.

Basically, the upshot is that the current rating on the filament winding is for AC operation. If you're rectifying it, the rule of thumb to use is to divide the AC current rating by 1.8 to arrive at its DC current rating. 2 / 1.8 = 1.11A, almost enough for two 6CG7s.

All that said, is your power transformer getting hot? I expect that it is; you may be exacerbating some type of thermal instability in your transformer by wringing too much power out of it. I'd check the AC voltage across each of your 6SN7s - if it's not within 10% or so of 6.3V, you're probably damaging your tube's cathodes anyway. My suggestion is to purchase and use a separate filament transformer with at least 3A current rating. I'm relatively certain Rat Shack has something serviceable if you're looking to get it playing, like, tonight.

--k
  Reply With Quote
Old 19th September 2008, 04:50 PM   #3
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Sounds like in addition to the under rated winding issue your filament regulators are under heatsinked, (if I understand your comment about regulated filament supplies) and going into thermal shutdown - this might actually be saving your grossly overloaded power transformer from burning out its filament winding.

Use both sets of heater windings if possible, consider ac heating, or add a separate 4A 9V transformer (Do not double) to run the regulator.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 20th September 2008, 12:05 AM   #4
diyAudio Member
 
Join Date: Jun 2007
I feel your pain! Let me give you my version. I've been bench testing filament PS for the last week and a half. I'm running 4, 6sn7's and it's a heck of a load with DC. I've ended up using a trannie with 2 secondarys rated at 12vac 2.33amp. I rectify with a 10 amp bridge and then drop the voltage with a string of 5w power resistors rated at .2 ohm. I filter this with a 5000uF electrolytic. All of that is to feed the input of a LM338k, TO-3 variable voltage regulator. I adjust the reg to 6.3vdc and feed all the heaters in parrallel. The regulator is mounted on a 3"x 5" heatsink. I drop the voltage to the reg with the resistor string to limit how much the reg has to dissipate. It only has about 9.5 volts input and limits the heat buildup. I can run this for days w/o any problems from any component.

freecrowder
  Reply With Quote
Old 20th September 2008, 10:07 AM   #5
diyAudio Member
 
Geek's Avatar
 
Join Date: Sep 2004
Hi Kendal,

Easy fix!

Have one 6SN7 as the Aikido bottom tube, the other as the top tube. Same for the other channel.

You have two windings each with 6.3V @ 2A. Use one secondary to power the bottom tubes, the other the top tubes. Each secondary only needs supply 1.2A.

Cheers!
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Sonic Impact T-amp loses one channel jives11 Class D 3 13th February 2009 07:01 PM
T-amp loses one channel, power off/on resets ? jives11 Class D 1 26th December 2008 05:51 PM
H-K AVR3000 loses memory among other things Flyier Solid State 13 17th January 2007 01:03 PM
NuForce loses their head designer... kuribo Class D 16 2nd August 2006 08:30 PM


New To Site? Need Help?

All times are GMT. The time now is 07:14 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2