I have made a real bonehead mistake this time. Hope someone can help. I am trying to determine where this wire in question will connect bak to when I reistall the RF unit. I had numbered it but forgot to note where I removed it from. As you'll see from the 2 attched photos(the best I could do), the wire in question is connected to pin 8 of the 6A8G and that pin is also strapped to pins 7 and 8. That wire is hard to see but it is yellow and at the very top right hand corner. While I am still a novice, I determine pin 8 as the first pin to the right of the keyway counting clockwise as viewed from the bottom. Unfortunately, I am just not sharp enough yest to determine where that wire should connect to in the chassis. It almost looks like it should go to a ground point but I am not sure.
You haven't given us the model number of the set so I looked up the 6A8 pin assignment. Pin 8 is the cathode and pin 7 is a filament connection. Check your schematic and you'll probably find the cathode is grounded and so is one side of the filament.
I was correct with the 6A8 pin connection's, 7 and 8 are connected to ground as well as the tube shield (the broken line surrounding the tube in the schematic). If the 6A8 is a metal tube then pin 1 Wil be connected to the metal shield and should also be grounded.
(This post was last modified: 11-28-2024, 02:46 PM by RodB.)
Maybe this is starting to make some sense in my hard head. Is this why the wire in question was not in the great Ron Ramirez video of 37-640 of the wires to disconnect the IF unit? My 6A8 tube is a metal one and maybe his was glass. Does all this mean that I could connect the wire in question to any ground point? Perhaps my radio is a later production run since it also has aa Muter variable resistor for a bias instead of the large tubular Bias Resitor--Thanks John
You'll have to forgive me, I am not sure what you mean. Can you explain what you are really saying. If anyone does not know where the wire should connect, I would rather they just say so---Thanks, John
I'm not sure why that wire wasn't covered in the video. I'm pretty sure the 6A8 won't work until that pin is grounded. You should be able to check with an ohmmeter to see if it is already attached to ground. Maybe the wire is sending a ground connection to another point.
It's not like we are good friends with that wire and can tell it from other ptetty identical looking wires.
Why'n't you just trace it, where it goes, and then see in the sch what the possible connections are, and see which one is missing.
I see no big deal in doing it.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
I don't have this radio, but I can supply some info:
Based on your pic, pins 7,8 and 1 are used together, go to the wire in question and are also grounded to the sub-chassis. This would be correct for the 6A8 as pin 7 is one leg of the heater, pin 8 is the cathode and pin 1 is the shield for metal or coated tubes. For the non-coated glass tube, Pin 1 has no internal connection in that tube. The fact that pin 1 is grounded and a glass tube is used does not have a negative effect. However, if the tube does not have an internal shield, an external shield must be used if called for.
Attached is a base diagram for the 6A8 and 6A8G from the RCA Receiving Tube Manual RC14 (ca 1940).
In the RCA Receiving Tube Manuals, the pin numbering is from the chassis side (worm's eye) view. Where the ground is connected is important in an RF section, since, I believe, that this is sub-chassis is mounted to the main chassis by rubber insulators. However, since the pins 7,8 and 1 of the 6A8 are already grounded to the sub-chassis, this may make where the ground wire is attached to the main chassis to be less important. It seems to me that this should be connected to whatever filament lug is grounded for the 6K7 IF tube or whatever tube supplies the "hot leg" 6Vheater voltage to the sub-chassis. I cannot tell from the schematic whether pin 2 or Pin 7 of the IF tube is at ground potential. Pin 1, the shield of the 7K7 IF tube is grounded or should be, especially if a metal or Zenith (Sylvania) Metal-Glass (their brand for a glass tube employing internal shielding) is used. The cathode, Pin 8, is not grounded like the 6A8; there is a cathode bias resistor and a bypass condenser.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
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Excellent information. It is all starting to come together now and your explanation really helped since I noticed that the 6A8 tube in the schematic had a G suffix for glass which is what they originally used and then apparently a change was made sometime in 1937 where they started using the metal tube version. probably was cheaper--That's my guess anyway. -thanks so much--John
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