Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Jun Thu 21, 2018 7:15 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 4 posts ] 
Author Message
 Post subject: Fisher 500C - Service manual for #70222
PostPosted: Feb Fri 23, 2018 11:32 pm 
Member

Joined: Aug Thu 27, 2009 7:47 am
Posts: 2778
Location: Seattle 98125
Anyone have a Fisher service manual for the 500C, covering serial 70222? The published manuals I find easily online cover 30001 - 49999. It's pretty close, but there are some different values in the bias circuit and the unit I'm working on has been "messed with" in that area before I got to it, and it isn't clear what's original and what's new.


Top
 Profile  
 
 Post subject: Re: Fisher 500C - Service manual for #70222
PostPosted: Feb Sun 25, 2018 2:35 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 4963
Location: Rochester NY USA
Add four 10 Ohm resistors - cathode to ground for each output tube so that you can measure current. The bias circuit resistors can be changed to get 300-350 mV - 30-35 mA per tube. If you get that, the resistors are RIGHT, regardless of what any manual says. (of course, if they're not equal, you need some new output tubes).


Top
 Profile  
 
 Post subject: Re: Fisher 500C - Service manual for #70222
PostPosted: Feb Mon 26, 2018 3:08 am 
Member

Joined: Jul Sun 09, 2006 3:11 am
Posts: 5435
Location: Aurora, CO
Tom Bavis wrote:
Add four 10 Ohm resistors - cathode to ground for each output tube so that you can measure current. The bias circuit resistors can be changed to get 300-350 mV - 30-35 mA per tube. If you get that, the resistors are RIGHT, regardless of what any manual says. (of course, if they're not equal, you need some new output tubes).

+1. I just had a 500C a few months ago and added the resistors. It was a lower serial number than yours so I could use the online manual.

_________________
ex nihilo nihil fit


Top
 Profile  
 
 Post subject: Re: Fisher 500C - Service manual for #70222
PostPosted: Feb Wed 28, 2018 4:50 am 
Member

Joined: Aug Thu 27, 2009 7:47 am
Posts: 2778
Location: Seattle 98125
Yeah, sounds good, I'll do that and then adjust the fixed resistor to give a reasonable current across the 10 Ohms. Thanks for the notes.


Top
 Profile  
 
Post New Topic Post Reply  [ 4 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 3 guests



Search for:
Jump to:  
























Privacy Policy :: Powered by phpBB