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I have restored this R-142A console Stewart Warner radio and would like to add bluetooth. Mr. Carlson had mentioned at the beginning of the year that he might do a video on this topic. Until then, I have attached a link to the schematic (if that works). My question is, where is the best place to inject the bluetooth signal? Many discussions on this topic suggest either directly to the speaker (bluetooth with amp) or at the volume control. In this set the speaker uses a field coil so I’m not sure how to make that connection. And, on this set the volume control is on the antenna input so that would not work. Any suggestions?
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Electronics Old and New by M Caldeira.
try this guy, might suit you.
Just as a wild guess as I have not done this, but I would think you would input it to the grid of the 6F6 output tube.
I would thing you would need a switch to here to turn off the grid from the radio.
I am not sure if this is what you have here.
Remember it is just my guess.
Larry – N7LUF
@larry_n7luf Thanks Larry, I’ll do some experimenting and give that a try. Also, thanks for posting the schematic. I need to figure out what I did wrong in my failed attempt.
@smartin Regarding your failed attempt to post a link to a picture. I assume it was your very first post and that’s the reason it was not approved according to what MCL has stated on Patreon. But if you try again on your next post chances are it would work. 😉
@smartin As there is DC voltage here, make sure you have a blocking capacitor between you bluetooth and the grid.
Also the grid I believe you want is the grid that comes from 6j7, but I do not see the pinout.
Here is where I found the schematic.
chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/ https://pacifictv.ca/schematics/sw32data.pdf
Looking up of the pinout of the 6F6, pin 5 would be the grid you need.
Again this is my guess.
I would make the break after the copastor 21 that is a .2Muf at 400 volts. Remember the high DC voltage here.
Larry – N7LUF
To protect you bluetooth device you might think about a device in Pateron number 36 video about a DC blocking circuit.
Larry – N7LUF
@larry_n7luf Just to update, I did insert the bluetooth signal just before the .02 uF cap going to the grid of 6F6. This works really well. Using my Iphone at full volume the radio is just loud enough. I thought maybe if I went in front of the 6J7 I’d be able to get more volume but then concluded that since the radio volume control is out of the picture, I really don’t want the possibiliity of turning it on too loud and overdriving everything. So, I’m happy with this solution. I ran it through a switch so I can always go back to the receiver if I want. I’m also trying to post another picture to see if my link approach works. The instructions from Mr. Carlson say to use a BBcode link but I can’t find that option in Imgur so I’m just using the direct link.
@smartin I found that every time i need to post a picture here using IMGUR picture service I “successfully” choose the “Direct Link” option. This way, the picture is always shown directly within the post “itself” instead of just a link that needs to be clicked in order to get you to it. But…feel free to experiment with all other link types should you wish to.
Here is a conclusive example:
PS: the link that you chose in your post doesn’t appear to be of Direct Link type
@smartin I am so happy it worked for you.
You may think how to increase the output of the bluetooth to give you more drive.
Also may to look how the grid is being controlled for the drive of the 6F6.
For the pictures here is what you need in red and to get there look at the top right of imhur where you login and find the images link.
Larry – N7LUF
@larry_n7luf Thanks Larry. I think I found the link page. Let me try this first with the BBcode link.
[img] 
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Now with the direct link