magic smoke pilot aa903 - 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 28th November 2007, 07:39 AM   #1
diyAudio Member
 
Join Date: Sep 2007
Default magic smoke pilot aa903

I just let the magic smoke out of one of my pilot AA-903 amps. Does anyone have any specific information/advice on inproving these amps?
5Y3, 2X12ax7, 6c4, Ecc82, PP-6v6
cgater
  Reply With Quote
Old 28th November 2007, 08:44 AM   #2
diyAudio Member
 
Join Date: Apr 2003
Location: Portland,Oregon
Blog Entries: 4
Send a message via AIM to DigitalJunkie
I hope it wasn't transformer smoke.
  Reply With Quote
Old 29th November 2007, 01:17 AM   #3
diyAudio Member
 
Join Date: Sep 2007
Not transformer smoke thankfully, was resistor between 5y3 and capacitor. Pretty sure 5y3 is toast now too, considering it lit the room up when it happened.
  Reply With Quote
Old 29th November 2007, 01:45 AM   #4
diyAudio Member
 
TubeHead Johnny's Avatar
 
Join Date: Jan 2005
Location: The emerald city, Seattle, WA.
You should have this amp refurbished, completely if possible. At the very least, you're going to need filter capacitors, (sounds like one or more of the old caps have shorted) plus you will need the rectifier tube. You're lucky the PT didn't go south as well! I would invest in a Variac and reform the old caps for the next amp you buy, but for this one, it's too late.

~~John~~~
  Reply With Quote
Old 29th November 2007, 03:48 AM   #5
diyAudio Member
 
Join Date: Sep 2007
Your're right Johnny, one cap had shorted. Been running strong for last year pushing Klipsch (right side).
  Reply With Quote
Old 29th November 2007, 12:17 PM   #6
diyAudio Member
 
Tom Bavis's Avatar
 
Join Date: Jun 2002
Location: Macedon NY
If you want a scan of the Sams folder, give me a buzz. tbavis(at)rochester(dot)rr(dot)com
  Reply With Quote
Old 1st December 2007, 07:07 AM   #7
diyAudio Member
 
Join Date: Sep 2007
Thank you for the offer Tom, but I have a schematic I made (with actual and indicated values), and photofact. Do you have any suggestions that might take some of the "smear" out of the bass during heavy passages?
Rob
  Reply With Quote
Old 1st December 2007, 02:19 PM   #8
diyAudio Member
 
Tom Bavis's Avatar
 
Join Date: Jun 2002
Location: Macedon NY
Bass distortion can be due to mismatched output tubes - even a small current imbalance will reduce the primary inductance of the transformer, and bring the core closer to saturation. Of course, even a properly working amp will run out of headroom with inefficient speakers...
  Reply With Quote
Old 26th December 2007, 06:42 AM   #9
zobsky is offline zobsky  India
diyAudio Member
 
zobsky's Avatar
 
Join Date: Mar 2002
Location: Dallas, Tx, USA
Quote:
Originally posted by coyotesgator
Thank you for the offer Tom, but I have a schematic I made (with actual and indicated values), and photofact. Do you have any suggestions that might take some of the "smear" out of the bass during heavy passages?
Rob
I own a pair of the same amplifiers, . both decided to quit on me over the last year. Need to refurb them.

I recapped one of them (signal caps only) a few years ago, but the smear you speak of remains (though I'd describe it as tubby bass) . It only really bothered me on inefficient speakers though (less than 90dB)

Two things I could think off
1. beefing up the power supply
2. implementing the williamson circuit mods. detailed on the chimera labs page http://www.chimeralabs.com/williamsmod.html .


Some audio enthusiasts have noticed that the amplifiers sound better when they are connected to efficient speakers. In fact when they are connected to less efficient speakers, two design flaws surface. At higher output levels they exhibit high levels of distortion and instability. In 1961, Talbot M. Wright published an insightful analysis of the circuit in Electronics World, highlighting these two problems. Fortunately he also told us how to fix them and his recommendations form the basis of this article.

Hope that helps.
__________________
"Any fool can know. The point is to understand" - Albert Einstein
  Reply With Quote
Old 26th December 2007, 06:59 AM   #10
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Quote:
Originally posted by zobsky



2. implementing the williamson circuit mods. detailed on the chimera labs page http://www.chimeralabs.com/williamsmod.html .

This b%%^&*t travels from forum to forum, from topic to topic...
__________________
The Devil is not so terrible as his math model!
  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
Pilot LED for my new car Amplifier raghs Car Audio 11 27th March 2009 05:03 PM
Pilot SA 260 bias baltimoreblues Tubes / Valves 1 3rd February 2008 06:00 PM
Flame On!: Tragic loss of magic smoke KBK Solid State 28 29th October 2006 05:26 PM
pilot 264 jaron Tubes / Valves 17 13th March 2006 03:32 PM
Magic Smoke (smells bad works good)(long) Stocker Chip Amps 0 28th February 2005 11:44 PM


New To Site? Need Help?

All times are GMT. The time now is 07:28 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