Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Oct Sat 16, 2021 4:46 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 17 posts ] 
Author Message
 Post subject: Firestone 3071 electrolytic polarity
PostPosted: Sep Thu 23, 2021 6:07 pm 
Member

Joined: Jan Thu 24, 2013 11:50 pm
Posts: 3542
Location: Bristol, Rhode Island
Hi all,

I just cracked open a Firestone R3071, and the set has had some damage. Two resistors in the power rail (the flexible wirewound type) are fried, as is a few caps. The set had been recapped and I noticed that one of the electrolytics, which I thought from the schematic should be grounded on the positive side, is reversed.
Can anyone check this over and tell me if I have this right?
It looks to me that:

1. 21 negative goes to center tap
2. 22 positive goes to ground
3. 31 negative goes to ground

Am I correct?
The resistors that burned up are 35 and 47.

Thanks,

Ted


Attachments:
firestone.jpg
firestone.jpg [ 549.35 KiB | Viewed 285 times ]
Top
 Profile  
 
 Post subject: Re: Firestone 3071 electrolytic polarity
PostPosted: Sep Thu 23, 2021 6:11 pm 
Member

Joined: Nov Tue 14, 2017 5:09 am
Posts: 4005
Location: Austin, Texas
Ted,
Yes, your connections are correct. The tricky one connects to the transformer center tap. That is the most negative point so the positive goes to ground for that cap.

Jay


Top
 Profile  
 
 Post subject: Re: Firestone 3071 electrolytic polarity
PostPosted: Sep Thu 23, 2021 6:13 pm 
Member
User avatar

Joined: Feb Sat 06, 2016 1:47 am
Posts: 3616
Location: La Mesa Califonia
You are correct with the capacitors.


Top
 Profile  
 
 Post subject: Re: Firestone 3071 electrolytic polarity
PostPosted: Sep Thu 23, 2021 6:17 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 27843
Location: Detroit, MI USA
It's really unfortunate that the draftsman back then did not bother to take 2 seconds extra to draw the 3 + signs on those electrolytics. At that time it was assumed anyone reading the diagram would know what the polarity needed to be to work properly. But I'm not sure if they actually did, there must have been some who had questions.

_________________
Dennis

Experience is what you gain when the results aren't what you were expecting.


Top
 Profile  
 
 Post subject: Re: Firestone 3071 electrolytic polarity
PostPosted: Sep Thu 23, 2021 6:23 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 13272
Location: Fernandina Beach, FL
Mr. Detrola wrote:
It's really unfortunate that the draftsman back then did not bother to take 2 seconds extra to draw the 3 + signs on those electrolytics. At that time it was assumed anyone reading the diagram would know what the polarity needed to be to work properly. But I'm not sure if they actually did, there must have been some who had questions.
As well as some that caused some rather spectacular venting of new capacitors!

_________________
Don


Top
 Profile  
 
 Post subject: Re: Firestone 3071 electrolytic polarity
PostPosted: Sep Thu 23, 2021 7:20 pm 
Member

Joined: Jan Thu 24, 2013 11:50 pm
Posts: 3542
Location: Bristol, Rhode Island
Thanks for the confirmations, folks. Was sure I had it right but what I thought/think did not jibe with what I saw on the set, which turns out was obviously an error on the part of whoever last looked at it in the 60s, from the style of caps installed.

Thanks.


Top
 Profile  
 
 Post subject: Re: Firestone 3071 electrolytic polarity
PostPosted: Sep Thu 23, 2021 7:23 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 6336
Location: Minneapolis, MN USA
During the design, development, and production of a new radio design back then, I wonder how many people would actually read a schematic ? I question if the people on the production line needed know, I speculate they would be trained by component illustrations, drawings, photos or the supervisor or maybe even mock ups--aka looking at the markings on the cap itself. Presumably radios went thru a pre production setup process...did they need to know polarity on a schematic ?


Top
 Profile  
 
 Post subject: Re: Firestone 3071 electrolytic polarity
PostPosted: Sep Thu 23, 2021 7:42 pm 
Member

Joined: Nov Tue 14, 2017 5:09 am
Posts: 4005
Location: Austin, Texas
I've known people who worked on radio and TV production lines and they didn't even need to know the correct names for the components. They were only instructed to install a part and didn't need to know anything about how it functioned. On lady told me the interesting names that the assembly line workers called the parts. Ceramic disk caps were red pancakes.

Jay


Top
 Profile  
 
 Post subject: Re: Firestone 3071 electrolytic polarity
PostPosted: Sep Thu 23, 2021 11:15 pm 
Member

Joined: Jan Thu 24, 2013 11:50 pm
Posts: 3542
Location: Bristol, Rhode Island
Hi all,

There is some other strangeness going on with the radio that I could use some help understanding.
My issues first, then questions:


Issue one:
The schematic shows (and radio has) an 8/450 cap (#31) running positive to 6K6 screen grid (4) and negative to chassis.
However there is a second 8/450 running positive to 6K6 pin 4 in this chassis. This one is negative to center tap. I've never seen two caps at different potential at the same positive node ...
This second 8/450 is not shown on the schematic. But the parts list (which is pretty unclear to be honest) shows (I think?) two #31 8/450 caps. Hard to tell.

Issue two:
Also in the parts list, electrolytic # 22 is also shown twice (I think?) . I only found one, the 25v, running positive to ground from center tap. There is only one on the schematic.

Questions
For now I'm ignoring the extra 31 and and building per schematic.
Any ideas what's going on here or can someone interpret the parts list accurately?
I can't tell if that second #31 is a later addition or not. Its aCornell Dubilier but the part number is illegible. Kinda looks like a 50s/60s cap but I'm not sure. If it was a later addition, was it someone trying just to beef up filtering in that stage, or just making a grounding mistake while re-capping without removing the original?

Only other things that are interesting are three partially burned up flexible wirewound resistors (35,35 and 37). Two are in the ballpark ohms wise but one is open. The fabric shell is totally gone (heat?). Power transformer has seen some heat too ... big blob of wax under but so far readings are where they should be for the windings.

Thanks.


Attachments:
Screen Shot 2021-09-23 at 6.14.34 PM.png
Screen Shot 2021-09-23 at 6.14.34 PM.png [ 820.32 KiB | Viewed 244 times ]


Last edited by Diverted on Sep Thu 23, 2021 11:26 pm, edited 1 time in total.
Top
 Profile  
 
 Post subject: Re: Firestone 3071 electrolytic polarity
PostPosted: Sep Thu 23, 2021 11:26 pm 
Member

Joined: Nov Tue 14, 2017 5:09 am
Posts: 4005
Location: Austin, Texas
Capacitors 22 and 31 show two part numbers for different models of the radio. There is only one part 22 and one part 31 per radio.
The second 31 cap you found was probably added by someone doing a repair. It should not be needed.
Attachment:
Parts.jpg
Parts.jpg [ 163.67 KiB | Viewed 241 times ]


Jay


Top
 Profile  
 
 Post subject: Re: Firestone 3071 electrolytic polarity
PostPosted: Sep Fri 24, 2021 3:38 am 
Member

Joined: Jan Thu 24, 2013 11:50 pm
Posts: 3542
Location: Bristol, Rhode Island
Sorry for these long posts, but this schematic keeps confusing me.

What am I missing here? I'm seeing things that don't add up.

First:
Looking at the DPDT phono switch schematic (left).
At left side of switch, the node of R43, C15 and R45 is disconnected from 6U7 screen grid in phono mode. If switched back to radio position, that node is reconnected to the grid. Note that there is nothing else on that node.
But if you look at the original schematic at right, that node of R43, C15 and R45 goes to 6U7 grid, but there's also a leg going off to the left just above R43. This is not shown in the phono schematic.

Same thing with other side:

In radio mode, phono schematic shows high side of volume pot to left side of R34.
In original schematic, high side of volume pot goes to secondary of the IF and and R44 to eye tube grid.
How do you explain these differences?

How can I apply this phono schematic to the actual chassis/schematic? They don't appear to be drawn for each other. I would like to put one in.

Thanks.


Attachments:
Firestone phono.jpg
Firestone phono.jpg [ 484 KiB | Viewed 220 times ]
Top
 Profile  
 
 Post subject: Re: Firestone 3071 electrolytic polarity
PostPosted: Sep Fri 24, 2021 5:31 am 
Member

Joined: Nov Tue 14, 2017 5:09 am
Posts: 4005
Location: Austin, Texas
I would say the person who drew the phono switch connections made some errors.

Jay


Top
 Profile  
 
 Post subject: Re: Firestone 3071 electrolytic polarity
PostPosted: Sep Fri 24, 2021 1:46 pm 
Member

Joined: Jan Thu 24, 2013 11:50 pm
Posts: 3542
Location: Bristol, Rhode Island
Thanks, I agree.
But, my question now is how to implement a workable phono in on this set? Thanks!


Top
 Profile  
 
 Post subject: Re: Firestone 3071 electrolytic polarity
PostPosted: Sep Fri 24, 2021 11:04 pm 
Member

Joined: Jan Thu 24, 2013 11:50 pm
Posts: 3542
Location: Bristol, Rhode Island
I’m interested in installing a phono switch. How could I apply this phono schematic to the actual circuit? Thank you!


Top
 Profile  
 
 Post subject: Re: Firestone 3071 electrolytic polarity
PostPosted: Sep Sat 25, 2021 5:42 pm 
Member

Joined: Jan Thu 24, 2013 11:50 pm
Posts: 3542
Location: Bristol, Rhode Island
Hi again, can anybody tell me whether or not I can apply this final schematic to the actual Radio? They do not appear to be the same. I could use some help, thank you


Top
 Profile  
 
 Post subject: Re: Firestone 3071 electrolytic polarity
PostPosted: Sep Sun 26, 2021 4:31 pm 
Member

Joined: Jan Tue 16, 2007 7:02 am
Posts: 4711
Location: Lexington, KY USA
Someone can help with the phono input question, but now it is not clear where to post a reply.

Ted


Top
 Profile  
 
 Post subject: Re: Firestone 3071 electrolytic polarity
PostPosted: Sep Sun 26, 2021 4:35 pm 
Member

Joined: Jan Thu 24, 2013 11:50 pm
Posts: 3542
Location: Bristol, Rhode Island
Wherever you feel comfortable? I had just assumed no one could find my question, so I just restated it in another thread. I would just love an answer, regardless of where it's put .. this one, that one, a text etc. Thank you for your time!


Top
 Profile  
 
Post New Topic Post Reply  [ 17 posts ]  Moderators: Norm Leal, Marcc

All times are UTC [ DST ]


Who is online

Users browsing this forum: Majestic-12 [Bot] and 21 guests



Search for:
Jump to:  


































Privacy Policy :: Powered by phpBB