Help High Line voltage - 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 20th July 2012, 12:39 AM   #1
diyAudio Member
 
HarryOOOO's Avatar
 
Join Date: Apr 2005
Location: Illinois
Default Help High Line voltage

So the line voltage at my Condo is 123.7 volts and my tube amps power transformer is rated at 120 volts but when I measure the lvoltage at the plate pin number three its 626 volts and it should be 580 volts which I would not think important except that when I bias the amp to 250mv the plates in the KT88 tubes begin to glow red which I can not imagine is correct. Anybody have any suggestions on what to do I have checked all the parts and resistors and they all seem to be within spec.
__________________
HarryOOOO
  Reply With Quote
Old 20th July 2012, 01:01 AM   #2
tomchr is offline tomchr  United States
diyAudio Member
 
tomchr's Avatar
 
Join Date: Feb 2009
Location: Greater Seattle Area
Even though it seems the B+ is "dramatically off", it's really only 8 % high. Your mains voltage is 3.1 % high. Both don't sound to be within reason. The line voltage in the US is supposed to be 120 V +/- 5 % so your mains voltage is within spec. You'll have sporadic dips and peaks outside this tolerance band, though. The B+ will droop a bit when the amp is delivering higher power to the speaker.

You don't mention where you measure 250 mV for your biasing circuit. Would you post a schematic?

~Tom
__________________
21st Century Maida Regulator, Universal Filament Regulator, Damn Good 300B, Novar Spud, and more...
Neurochrome : : Audio - http://www.neurochrome.com/audio - Engineering : : Done : : Right
  Reply With Quote
Old 20th July 2012, 01:39 AM   #3
diyAudio Member
 
HarryOOOO's Avatar
 
Join Date: Apr 2005
Location: Illinois
Tom that measurement is taken through a Bias meter that is mounted on the face of the amp and it is from pin 8 to ground this is done for each tube via a selector switch.
__________________
HarryOOOO
  Reply With Quote
Old 20th July 2012, 03:41 AM   #4
diyAudio Member
 
PlasticIsGood's Avatar
 
Join Date: Mar 2012
Location: Bradford
Assuming pin 8 is the cathode, the important information required is the current from cathode to ground. Your test circuit must use a resistor to sense the current, and you need to know the value of that resistor. There may be one for each cathode, or just one switched between each.

First, reduce the current to a level at which the anodes are not red. Overheating is bad even for a short while.

Then verify the bias meter readings by checking with your multimeter, cathode to ground, for each selected valve in turn.

Then switch off and wait for the amp to discharge before selecting each valve in turn on the bias switch and measuring the resistance from cathode to ground.

Assuming the cathode circuit is sensibly simple:

Cathode current = cathode voltage * cathode resistor value
Power dissipation = anode voltage * cathode current (more or less)

If you find out what the max power is for the valve from its datasheet, you then have all the information you need. If operating conditions are within limits and the anodes still glow red, the valves are not to spec. Adjust for balanced, reduced current so they are not too hot.
  Reply With Quote
Old 20th July 2012, 04:02 AM   #5
6J6 is offline 6J6  Australia
diyAudio Member
 
Join Date: Feb 2012
Wow, 3.7 volts over is miniscule and shouldn't cause that much of a B+ increase.

Where I live in Australia, the code is 230 volts +10 -7%. I was receiving 267 volts for years and had to make a lot of noise to get the power company to lower the transformer tap on the entire street to bring it down. I wasn't even at the start of the transmission line either.

Got so sick of all my appliances failing, but they paid compensation after the fact so it was some outcome.

So yes, 3 volts is nothing to worry about. And like tomchr said, it will drop under load anyway. Rebias and all should be fine

6J6.
  Reply With Quote
Old 20th July 2012, 06:36 AM   #6
diyAudio Member
 
trobbins's Avatar
 
Join Date: Feb 2009
Location: Melbourne, Oz
6J6 - are you in WA?
  Reply With Quote
Old 20th July 2012, 11:50 AM   #7
6J6 is offline 6J6  Australia
diyAudio Member
 
Join Date: Feb 2012
Hi trobbins. I am in Country Tasmania on the SE coast. Appaling electricity here!!
  Reply With Quote
Old 20th July 2012, 12:11 PM   #8
diyAudio Member
 
trobbins's Avatar
 
Join Date: Feb 2009
Location: Melbourne, Oz
Between Bicheno and Hobart I guess. Bloody hell - must be too much water passing through those hydro turbines to get 267V !!! Are you sure they haven't wired you phase-to-phase (snigger).

BTW, I'm pretty sure its 240V nom (not 230V). I think WA used to run a lot of 250V nominal many years ago.

Ciao, Tim
  Reply With Quote
Old 20th July 2012, 01:07 PM   #9
diyAudio Member
 
zigzagflux's Avatar
 
Join Date: Oct 2006
Location: Charlotte, NC
ANSI/IEEE 141 -1993 states voltage range A for a 120V system is 114-126 at the service, with utilization equipment down to 110V. Voltage Range B is 110-127, with equipment down to 106V. If your equipment cannot operate satisfactorily within range A, your equipment needs modification.

You can buck it down with a little 5V transformer to 118.8, but then you have to consider the effects when the utility drops the service voltage to 115V. Then you'll be frustrated with how low your secondary is.
  Reply With Quote
Old 20th July 2012, 01:42 PM   #10
Einric is offline Einric  United States
diyAudio Member
 
Einric's Avatar
 
Join Date: Feb 2011
Location: Bozeman, MT
You could always pick up a line conditioner.

Panamax makes quite a few that range from cheap to WOAH!!!
  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
Why high voltage Fets when low voltage types gives less distortion? Circlomanen Pass Labs 21 9th December 2009 09:43 PM
High voltage, high current super regulator, possible group buy peranders Group Buys 54 2nd June 2009 09:43 AM
Wanted - High Power, High Voltage, Audio Frequency Transformer Manual. kimbal Tubes / Valves 4 11th May 2009 08:05 PM
Akai GX 265D line voltage on line outs? ShorBird Solid State 11 26th January 2009 11:44 PM
6BY5 High Voltage & High Current Choke Input Design P.S. snoopyma Tubes / Valves 7 28th June 2006 01:32 PM


New To Site? Need Help?

All times are GMT. The time now is 10:11 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