HOT Iron ? - Page 2 - 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 1st November 2006, 03:30 AM   #11
diyAudio Member
 
Tube_Dude's Avatar
 
Join Date: Mar 2002
Location: Aveiro-Portugal
Quote:
Originally posted by Vespasian
Could someone give me a step by step on how to properly set the bias? There are two pots for dc bias, and I simpy have them set so the voltage difference between the plates is 0v.
Two pots per channel or one for each channel?
__________________
Jorge
  Reply With Quote
Old 1st November 2006, 10:21 AM   #12
diyAudio Member
 
Join Date: Jan 2006
Location: Kansas
Quote:
Originally posted by jaymanaa
Most of mine get that hot, at least on the store bought stuff.
I mis-read as well. Thought it was PT. Ooops.
__________________
"Make everything as simple as possible, but no simpler" Einstein
  Reply With Quote
Old 1st November 2006, 10:26 AM   #13
diyAudio Member
 
Frank Berry's Avatar
 
Join Date: Sep 2003
Location: Midland, Michigan
The output transformers on my HH Scott model 299C run cool.
The two pots are bias balance pots. Adjust them for a plate-to-plate reading of 0 volts.

The selenium bias rectifier bridge should be replaced with a silicon bridge. The old rectifier bridge produces a lower bias voltage as it ages. This could be the cause of your hot output transformers.
__________________
Frank
  Reply With Quote
Old 1st November 2006, 11:18 AM   #14
bembel is offline bembel  Europe
diyAudio Member
 
bembel's Avatar
 
Join Date: Aug 2006
Send a message via Yahoo to bembel
I agree with DigitalJunkie, HollowState & refference.
It shouldn't be that hot ! (even with heavy bias mismatch problems, I never saw such a hot OT).
__________________
Plus je pédale moins vite, moins j'avance plus vite !
  Reply With Quote
Old 1st November 2006, 11:58 AM   #15
diyAudio Member
 
Join Date: Sep 2006
Yes, one pot per channel. A new rectifier is installed and providing -46.3, schematic calls for -45. All the coupling caps have been replaced.

Can someone describe "ultrasonic oscillation" - I am not familiar with what it is, how it is caused or what the rectification would be.

Are there ways to check the transformer's health via measuring resistance?

The amp is really sounding pretty good with the exception of a phase splitter tube that is causing some hum in one channel.

Bad transformers? That would be a real drag.

Cheers, Ed
  Reply With Quote
Old 1st November 2006, 01:15 PM   #16
diyAudio Member
 
tubelab.com's Avatar
 
Join Date: Jul 2005
Location: West Virginia panhandle
I doubt that your transformers are bad. Even if there was a few shorted turns in the transformer you would have to play it very loud for the transformer to get hot. If this were the case, it wouldn't sound good. (not the case for a bad power transformer)

Most OPT's get hot by absorbing the radiant heat from the output tubes. I have never seen them get too hot to touch though. You can check for this by puting a shiny reflective surface between the output tubes and the transformer and running the amp for an hour. If the transformers are much cooler, you can quit worrying. I have used a small mirror or aluminum foil for this test. Obviously, make sure the "shield" is not touching anything other than the chassis. The metallic surface on a mirror IS conductive!

Are the end bells getting hot, or is the whole core (laminations) getting hot? It takes a lot more energy to heat up the whole transformer core.

On amps that are crowded and get hot (including some that I have built) I often add a small fan. I use the fans that were made for computer chips. They are made to work on 12 volts. If you use a diode and a cap (1000 uF 16 volt) off of a 6 volt filament winding you get about 7 volts which will spin most of these fans enough to move some air, but not make much noise. Direct the fan at the output tubes.
__________________
Too much power is almost enough! Turn it up till it explodes - then back up just a little.
  Reply With Quote
Old 1st November 2006, 02:08 PM   #17
diyAudio Member
 
Join Date: Sep 2006
Thanks Tubelab - yeah the cores are getting hot. I'm hoping it is because I'm passing really low frequencies or it has something to do with the oscillation thing that was mentioned.

Cheers, Ed
  Reply With Quote
Old 1st November 2006, 06:17 PM   #18
diyAudio Member
 
Miles Prower's Avatar
 
Join Date: May 2005
Location: USA
Blog Entries: 6
Quote:
Originally posted by Vespasian
Can someone describe "ultrasonic oscillation" - I am not familiar with what it is, how it is caused or what the rectification would be.
It's an oscillation that generates frequencies too high to be heard. As for what causes this, it's inherent phase shift that turns intended negative feedback into positive feedback when open loop gain is still greater than unity. The best way to detect this is by o'scoping the outputs. If you don't have an o'scope, there are other ways to check for this. One thing to look out for is an amp that seems to go into clipping and overdrive prematurely. Something else to look for are finals that seem to be drawing too much current when biased to the design Q-Point Vgk. The excessive current means that there's a signal (the oscillation). Another thing to do is operate a radio receiver (preferrably a SW xcvr and check each ham band) but a BCB AM will do. If you hear noise when the amp is on that isn't there when it's off, then you can be pretty sure you have an oscillation problem.

Quote:
Are there ways to check the transformer's health via measuring resistance?
Only if you know what the design nominal coil resistances are.

Quote:
The amp is really sounding pretty good with the exception of a phase splitter tube that is causing some hum in one channel.
Could indicate an oscillation problem. Cathodyne type phase inverters are usually the first stage to overdrive since they have the least "headroom". The humming could very well be a heterodyne product from an RF oscillation if that stage is being overdriven into a nonlinear operation.
__________________
There are no foxes in atheistholes
www.dolphin-hsl.com
  Reply With Quote
Old 1st November 2006, 06:18 PM   #19
diyAudio Member
 
HollowState's Avatar
 
Join Date: Aug 2006
Location: Taxland, New Jersey
Ultrasonic is a term for a band of frequencies above the human hearing range. Typically from about 18KHz up to 50KHz or more. The quickest and easiest way to check for these is to put a scope across the amplifier's speaker terminals both with and without music.

What you do not want to see is a high level waveform without music, or overriding the music. You can't hear it but your tweeter can feel it and could burn out from too much of it. Try to borrow a scope if you don't have one.

Possible causes are internal generation from aged componets or altered wiring. It could also be passed along from the input. While this problem is rare, it's something that should be checked. A wideband AC voltmeter would also be useful.

Victor
  Reply With Quote
Old 1st November 2006, 07:06 PM   #20
diyAudio Member
 
Join Date: Sep 2006
Thanks for the input guys.

The hum I mentioned that exists in one channel, does follow the tube (6gh8's) when I swap them.

I don't hear any clipping or distortion when I turn the amp up. Sounds pretty good actually.
I will try the test with a SW.

Not really sure how to check the current draw from the power tubes. I could use some help with that one.

I do appreciate all the assistance gotten on this forum!

Cheers, Ed
  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
Gun or Iron? mashaffer Tubes / Valves 13 29th December 2007 01:22 PM
Appropriate Iron for 211 Triode SE wrenchone Tubes / Valves 50 7th December 2007 03:38 AM
Best Use For My Sansui Iron? chrisvw Tubes / Valves 13 27th May 2006 08:28 PM
soldering iron jaudio Parts 15 17th March 2006 07:22 PM
For those of you in the UK who need a new soldering iron 5th element Parts 2 26th March 2004 10:58 AM


New To Site? Need Help?

All times are GMT. The time now is 08:59 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