Antique Radios Forum

This is the temporary home of the Antique Radio Forums while a new server to host it is being found. You will have to register here to post. Please Note: None of these topics will be preserved when the original forums are back.
 
HomeCalendarFAQSearchMemberlistUsergroupsRegisterLog in

Share | 
 

 RCA 811K grounding questions.

View previous topic View next topic Go down 
AuthorMessage
dynadude

avatar

Posts : 51
Join date : 2010-10-13
Age : 61
Location : Chapel Hill, NC

PostSubject: RCA 811K grounding questions.   Sat Oct 16, 2010 5:33 pm

I'm currently rebuilding the chassis on this 811K, as it was pretty well butchered. The SW was disabled, and there where some pretty bad "repairs" done at some time.

http://www.nostalgiaair.org/PagesByModel/152/M0015152.pdf

The condohm resister was partially burned out at the two 90 ohm points, and the connection points were bypassed with a large power resister with a tap. I want to replace all of the points with individual resisters, as I don't trust what's left of the condohm, but I want to be sure to ground them correctly.

Can I ground these separate resisters directly to the chassis?
The main reason I ask, is that there are 6 resister points on the condohm, but there is one extra point that seems to possibly be a separate ground. I'm not sure if there was a resister built into this point or not, as it seems to be one of the damaged points. I do get about an 85 ohm reading from this point to chassis ground, but I'm not sure if it's from the previous damage or what.

Also, I am having some trouble determining the proper orientation of the electrolytics as far as polarity. I think I can figure them out, but I don't want to make any greenhorn mistakes and ruin other parts. This set is already pushing my patience and knowledge to the very edge. Shocked

Thanks for any advice,
Bryan
Back to top Go down
View user profile
pred



Posts : 18
Join date : 2010-10-14

PostSubject: Re: RCA 811K grounding questions.   Sat Oct 16, 2010 5:55 pm

+ side of lytics go to either side of field as in diagram,
- sides of lytics go to center tap of transformer,
So in diagram you have above, + is up and - is down.
Peter


Last edited by pred on Sat Oct 16, 2010 6:05 pm; edited 1 time in total
Back to top Go down
View user profile
Johnnysan



Posts : 64
Join date : 2010-10-12

PostSubject: Re: RCA 811K grounding questions.   Sat Oct 16, 2010 6:05 pm

pred is not correct.

+ side of C57 (25uf) goes to the input of the field coil; negative to the center tap of the HV winding. + side of C58 (16uf) goes to the output of the field coil; negative goes to chassis ground. Between the center tap of the transformer and chassis ground is the two 90 ohm resistors from the candohm. Center tap is not grounded.
Schematic is in Riders 8-153.
Back to top Go down
View user profile
pred



Posts : 18
Join date : 2010-10-14

PostSubject: Re: RCA 811K grounding questions.   Sat Oct 16, 2010 6:09 pm

Johnnysan wrote:
pred is not correct.

+ side of C57 (25uf) goes to the input of the field coil; negative to the center tap of the HV winding. + side of C58 (16uf) goes to the output of the field coil; negative goes to chassis ground. Between the center tap of the transformer and chassis ground is the two 90 ohm resistors from the candohm. Center tap is not grounded.
Schematic is in Riders 8-153.
You are right and I should have been more specific in my response,
When I look at the diagram, I see the CT, Some resistors and the lytics both there, I know there are resistors and the ground,,,,,
I will take this as an educational expirence and slow down a bit.....
Usually in diagrams, Lytics and + side up.
Peter
Back to top Go down
View user profile
dynadude

avatar

Posts : 51
Join date : 2010-10-13
Age : 61
Location : Chapel Hill, NC

PostSubject: Re: RCA 811K grounding questions.   Sat Oct 16, 2010 7:18 pm

Ok, I think I can deal with the caps now, but I think I may have the wrong idea about the candohm. Never had to deal with replacing one before.

Can I think of a candohm as one long resister with taps at different points, or is it individual resisters with a common ground?
Back to top Go down
View user profile
dynadude

avatar

Posts : 51
Join date : 2010-10-13
Age : 61
Location : Chapel Hill, NC

PostSubject: Re: RCA 811K grounding questions.   Sat Oct 16, 2010 8:06 pm

~crickets chirping~

Churrrrrrrrip churrrrrrip churrrrrrip
Back to top Go down
View user profile
Dale Saukerson



Posts : 6
Join date : 2010-10-12

PostSubject: Re: RCA 811K grounding questions.   Sat Oct 16, 2010 8:27 pm

It's a mixture of both. Long reply coming....
A Candohm is a series string of resistors, with shared taps (lugs).
Consider it a tapped resistor.

They may or may not share a ground. It depends on how the Candohm is wired.

A lug may have a wire running to the chassis. This lug is grounded.
A lug may be connected internally to the body of the Candohm which is fasted to the chassis. This lug is automatically grounded.
It may be that none of the lugs connect to the body and no lugs have a wire running the chassis. Then none of the Candohm is grounded.

Thus parts of a Candohm may or may not have a shared ground.

But a Candohm will never have a common ground for ALL sections of the resistor.

Your Candohm has six resistor sections and seven lugs.
Counting from the right:
Lug 3 is grounded.
Lug 2 should read about 90 Ohms to the chassis.
No other lugs should read zero Ohms to the chassis.



Last edited by Dale Saukerson on Sat Oct 16, 2010 8:51 pm; edited 1 time in total
Back to top Go down
View user profile
dynadude

avatar

Posts : 51
Join date : 2010-10-13
Age : 61
Location : Chapel Hill, NC

PostSubject: Re: RCA 811K grounding questions.   Sat Oct 16, 2010 8:39 pm

Uh oh. Neutral

Is this going to be scary? ~biting nails~

I know this was covered in the old forum, but I didn't have the foresight to copy it or learn it.
Back to top Go down
View user profile
Tony Wells

avatar

Posts : 69
Join date : 2010-10-12
Age : 57
Location : the Lone Star State

PostSubject: Re: RCA 811K grounding questions.   Sat Oct 16, 2010 8:52 pm

Here's an old page from the Real Forum:

http://webcache.googleusercontent.com/search?q=cache:iLQM9-8fHAMJ:antiqueradios.com/forums/viewtopic.php%3Ft%3D4925+site:antiqueradios.com+candohm&cd=2&hl=en&ct=clnk&gl=us&client=firefox-a
Back to top Go down
View user profile
dynadude

avatar

Posts : 51
Join date : 2010-10-13
Age : 61
Location : Chapel Hill, NC

PostSubject: Re: RCA 811K grounding questions.   Sun Oct 17, 2010 10:48 am

Thanks for the replies everyone. I'm gonna give it my best shot. Wink
Back to top Go down
View user profile
Sponsored content




PostSubject: Re: RCA 811K grounding questions.   

Back to top Go down
 
RCA 811K grounding questions.
View previous topic View next topic Back to top 
Page 1 of 1
 Similar topics
-
» Driver Hotswap to AI Questions
» New to the game: questions/comments
» 40k Tournament sportsmanship questions
» V8 Supercars Series 2012 Questions
» New To Dark Eldar and full of questions

Permissions in this forum:You cannot reply to topics in this forum
Antique Radios Forum :: Antique Radio Forums :: Electrical/Mechanical Restoration-
Jump to: