Console Amplifier Pull:Voltages over Spec - 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 27th August 2012, 05:20 PM   #11
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Quote:
Originally Posted by TheGimp View Post
Kevinkr, they specify a VTVM for measurements. The input impedance would have been greater than 1MEG ohm, so readings are accurate.

Measurements would have been taken with a line voltage of 115VAC. Modern lline voltage of 125VAC would result in an increase in voltages of 1+((125-115)/115)=1.08 or 8% increase in all readings.


Not having the original schematics I didn't know about the VTVM, but good to know. Most of the Sams (and other) schematics I have seen in this time frame specified an analog volt meter.

Line voltage has crept up quite a lot since this amp was designed, and this can cause all sorts of problems with marginally specified components in the power supply. My line voltage never drops below 117V and usually hovers around 123V except during the dinner time hours where it tends to drop. (Always horribly distorted sine wave.. )
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 27th August 2012, 06:11 PM   #12
TheGimp is online now TheGimp  United States
diyAudio Member
 
TheGimp's Avatar
 
Join Date: Aug 2009
Location: Johnson City, TN
There is a note at the bottom of the multiplex adapter section. It threw me at first as well till I saved the schematic and looked at it expanded.

That is a good point about some schematics using low Ohms/Volt meters. It is easy to forget a time when they were common.

WOW! I just looked up the venerable Simpson 260 and it is only 20Kohms/Volt.

Last edited by TheGimp; 27th August 2012 at 06:14 PM.
  Reply With Quote
Old 17th September 2012, 05:15 AM   #13
heyraz is offline heyraz  United States
diyAudio Member
 
Join Date: Jan 2011
Greetings again,
As anticipated (thanks again for explaining the calculation) a 22k resistor from R37 to ground made up for the missing tuner section resulting in voltage measurements more closely matching the schematic.
There is however, one thing I'm not clear about, and that's what voltage/Pin I should be targeting when using the Output Tube Bias Control, Pin 2 (G2) or Pin 3 (K1,G3). The only time the voltages will match the schematic values is when line voltage is 112VAC. At my available 117VAC, if I set Pin 2 to 21V, Pin 3 will be greater than 33V. Conversely, if I set pin 3 to 33V, Pin 2 will be less than 21V. A conundrum for this newb.
That being said, I think this amp sounds incredible. It's rock solid, clear as a bell and fun to listen to. I've rolled a couple of different sets of input and output tubes and am currently enjoying Tele ECC83's and Amperex EL84's.
A real pleasant surprise. Thank you all again for your help.
Rich
  Reply With Quote
Old 17th September 2012, 02:54 PM   #14
20to20 is offline 20to20  United States
diyAudio Member
 
20to20's Avatar
 
Join Date: Jun 2010
Location: W-S, NC
Quote:
Originally Posted by heyraz View Post
Greetings again,
As anticipated (thanks again for explaining the calculation) a 22k resistor from R37 to ground made up for the missing tuner section resulting in voltage measurements more closely matching the schematic.
There is however, one thing I'm not clear about, and that's what voltage/Pin I should be targeting when using the Output Tube Bias Control, Pin 2 (G2) or Pin 3 (K1,G3). The only time the voltages will match the schematic values is when line voltage is 112VAC. At my available 117VAC, if I set Pin 2 to 21V, Pin 3 will be greater than 33V. Conversely, if I set pin 3 to 33V, Pin 2 will be less than 21V. A conundrum for this newb.
That being said, I think this amp sounds incredible. It's rock solid, clear as a bell and fun to listen to. I've rolled a couple of different sets of input and output tubes and am currently enjoying Tele ECC83's and Amperex EL84's.
A real pleasant surprise. Thank you all again for your help.
Rich
With higher voltages all around it makes sense that your cathode to G1 will also be different from the schematic. The important ratio for them is to be slightly wider apart now. The G1 needs to be at least 12v less than the cathode, as designed. As the B+ for everything is higher the current through the tube will be higher, too, so under these conditions it would be advisable to have 13v -15v lower for G1 than cathode. So if you have 20v and 34v that's good.
  Reply With Quote
Old 17th September 2012, 03:16 PM   #15
jane is offline jane  Norway
diyAudio Member
 
jane's Avatar
 
Join Date: Jul 2004
Location: Norway
Quote:
Originally Posted by heyraz View Post
Between R37 and chassis ground : I measured 353 instead of 275 (implying to me that R37 is shorted)
It indicates that a tuner is not connected to the amplifier (no tuner no current through R37).
__________________
Life is hard - Then you die.
  Reply With Quote
Old 17th September 2012, 04:54 PM   #16
heyraz is offline heyraz  United States
diyAudio Member
 
Join Date: Jan 2011
Rich,
Thanks for that advice. I'm analytical by nature, so I like to understand why I'm doing something before I do it. As mentioned, I still consider myself a newb and only realized just a few moments ago that this is a "fixed bias" design. The "output tube bias adjust" control on the amp mislead me.
A difference of at least 12 volts exists no matter how much voltage is applied to the cathodes, so I assume all is well. Since the wiper of the bias adjust is connected to the control grids, I assumed that was the point of measurement and became concerned when I noticed the cathodes were slightly hotter. I guess I'll have to play with different levels to decide what sounds best.
Thanks. Richj
  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
Western Electric console pull Pano Full Range 10 4th May 2011 04:46 AM
Amplifier power supply voltages audio_tony Solid State 10 18th December 2010 05:54 PM
Need help/advice on a problem with console amplifier IG81 Tubes / Valves 39 22nd September 2010 06:05 PM
Oddball Console Amplifier kevinkr Tubes / Valves 17 29th July 2008 11:16 AM
Amplifier operation voltages Eccu Solid State 3 7th February 2002 03:12 PM


New To Site? Need Help?

All times are GMT. The time now is 02:23 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