Fisher Tube Tuner Restoration Walkthrough - 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 13th March 2009, 11:30 PM   #1
diyAudio Member
 
Join Date: Aug 2008
Thumbs up Fisher Tube Tuner Restoration Walkthrough

Hi, Tube folks,

For anyone who is interested - I wrote Fisher 400 tube tuner/amplifier restoration walkthrough. Your comments and suggestions are very welcome. Upon request I can add/edit stuff which may be valuable for the next creative tube junkies and vintage lovers.

http://www.starlett.com/~web5_macgur...ration_en.html

PS. Next restoration walkthrough is coming soon - tube integrated amplifier Pioneer SM-83.
  Reply With Quote
Old 14th March 2009, 12:14 AM   #2
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Default Re: Fisher Tube Tuner Restoration Walkthrough

Quote:
Originally posted by LinuksGuru
Hi, Tube folks,

For anyone who is interested - I wrote Fisher 400 tube tuner/amplifier restoration walkthrough. Your comments and suggestions are very welcome. Upon request I can add/edit stuff which may be valuable for the next creative tube junkies and vintage lovers.

http://www.starlett.com/~web5_macgur...ration_en.html

PS. Next restoration walkthrough is coming soon - tube integrated amplifier Pioneer SM-83.
Fine, except grid leak resistors called grid stoppers, and your explanation why their values need to be reduced is wrong.

Also, "on schematic diagram it was 15V, main was 10v.", did you mean mine instead of main? And "lethal charge" should be called "lethal voltage".

__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 14th March 2009, 03:31 AM   #3
diyAudio Member
 
SpreadSpectrum's Avatar
 
Join Date: Nov 2007
Nice walkthrough. I have a Fisher X-101-B that I refreshed, then the power transformer went up in smoke. According to the Photofact, the power transformer was rated for less than the quiescent current draw. Since I want a bigger power transformer (for obvious reasons) and there is no room on the chassis, I am considering a separate power supply chassis.

The grid stoppers are the 1k resistors that connect directly to the grids of the power tubes.
  Reply With Quote
Old 14th March 2009, 05:45 PM   #4
diyAudio Member
 
Join Date: Aug 2008
Default Re: Re: Fisher Tube Tuner Restoration Walkthrough

Quote:
Originally posted by Wavebourn
Fine, except grid leak resistors called grid stoppers, and your explanation why their values need to be reduced is wrong.
Ok, thanks, was is correct explanation?
  Reply With Quote
Old 14th March 2009, 06:54 PM   #5
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Default Re: Re: Re: Fisher Tube Tuner Restoration Walkthrough

Quote:
Originally posted by LinuksGuru


Ok, thanks, was is correct explanation?


There are 2 x 330k grid resistors (so called grid stoppers) and 2 x 0.047 ukF coupling capacitors which need to be replaced with 180k - 220k and 0.1 - 0.22 ukF respectively. Grid stoppers act as high-frequency low-pass filter, cancel possibility of parasitic oscillation on the tube itself, suppress radio frequencies on the input stage plus prevent blocking distortion. New tubes have sligthly different plate/plate-grid curves, and therefore, sometimes may not work stable with 330k grid stoppers




There are 2 x 330k grid resistors (so called grid leak resistors) and 2 x 0.047 ukF coupling capacitors which need to be replaced with 180k - 220k and 0.1 - 0.22 ukF respectively. NOS tubes can have more gases inside so voltage drops on this resistors may cause positive shift of bias causing higher idle current that causes more gases that causes higher bias shift and so on, until anodes are red and melted down. When values of resistors are lower the same currents cause lower voltage drops, so run-away is less possible.
Since values of resistors are smaller to preserve the same time constant values of coupling capacitors must be increased accordingly, otherwise roll-off will start on higher frequencies affecting bass reproduction.

However, my English is not perfect, but my explanation may help.
__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 14th March 2009, 07:00 PM   #6
diyAudio Member
 
Join Date: Aug 2008
Default Re: Re: Re: Re: Fisher Tube Tuner Restoration Walkthrough

Quote:
Originally posted by Wavebourn



There are 2 x 330k grid resistors (so called grid leak resistors) and 2 x 0.047 ukF coupling capacitors which need to be replaced with 180k - 220k and 0.1 - 0.22 ukF respectively. NOS tubes can have more gases inside so voltage drops on this resistors may cause positive shift of bias causing higher idle current that causes more gases that causes higher bias shift and so on, until anodes are red and melted down. When values of resistors are lower the same currents cause lower voltage drops, so run-away is less possible.
Since values of resistors are smaller to preserve the same time constant values of coupling capacitors must be increased accordingly, otherwise roll-off will start on higher frequencies affecting bass reproduction.

However, my English is not perfect, but my explanation may help.

Thanks a LOT! My English is not perfect either - it is not my native tongue.
  Reply With Quote
Old 15th November 2011, 01:48 PM   #7
diyAudio Member
 
Join Date: Nov 2005
Default Grid resistor mod clarification question

Quote:
Originally Posted by Wavebourn View Post
There are 2 x 330k grid resistors (so called grid leak resistors) and 2 x 0.047 ukF coupling capacitors which need to be replaced with 180k - 220k and 0.1 - 0.22 ukF respectively. NOS tubes can have more gases inside so voltage drops on this resistors may cause positive shift of bias causing higher idle current that causes more gases that causes higher bias shift and so on, until anodes are red and melted down. When values of resistors are lower the same currents cause lower voltage drops, so run-away is less possible.
Since values of resistors are smaller to preserve the same time constant values of coupling capacitors must be increased accordingly, otherwise roll-off will start on higher frequencies affecting bass reproduction.

However, my English is not perfect, but my explanation may help.
Hi, Fisher X101-b resistor mod, are you saying the both 330K on each tube are to be replaced, 8 resistors total. If yes, then maybe I am thinking wrong, but would not .68 uf be closer to preserving the 3dB point for the filter formed
by 2 grid resistor in series and coupling cap?
  Reply With Quote
Old 15th November 2011, 03:15 PM   #8
diyAudio Member
 
Join Date: Aug 2008
Restoration walkthrough have been moved to:
Fisher 400 Vacuum Tube/Valve Tuner/Amplifier Restoration | MacGuru HQ
  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
Fisher 800 restoration pixpop Tubes / Valves 31 5th December 2011 02:35 AM
Walkthrough: Pioneer SM-83 Tube Amp Restoration LinuksGuru Tubes / Valves 1 21st March 2009 06:09 AM
Fisher 400 Tube Tuner/Amp fpr Sale (in Europe) LinuksGuru Swap Meet 3 14th December 2008 08:49 PM
Old Tube Radio - Restoration Project Algar_emi Tubes / Valves 21 5th June 2008 12:53 AM
Fisher 500c - Trouble shooting tuner section ALBQ Tubes / Valves 0 6th May 2004 11:40 AM


New To Site? Need Help?

All times are GMT. The time now is 11:43 PM.


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