Heater String Wiring order? - Page 1
Forum section: electronics / beginners

author: Wil_Bloodworth
author_rank: Regular Contributor
timestamp: December 22, 2023, 03:52:07 pm
content: Finally got all of the replacements parts in and updated my first radio... also got in the isolation transformer, variac, and dim-bulb tester. After one mis-wiring issue, the radio came to life and is receiving stations. I'm now in the IF alignment phase BUT... while examining the schematic (not the correct one I might add but close enough), I noticed that the actual wiring (of the heater string) in the radio differs from the specified order in the schematic.Below, I have eliminated everything except what is relevant to this conversation. What concerns me is that the heater string starts (as it should) at pin 7 of the 35Z5-GT tube and is supposed to go to pin 7 of the 35L6-GT (in my case it's a 50L6-GT but I'm not sure that matters).My issue (shown in red with the big red arrows and dotted red line on the far, top right) is that the actual wiring is going from pin 7 to pin 2... instead of going to pin 7 of the 35LS as is shown in the schematic.Question: Does it matter whether you go to pin 7 or to pin 2 when wiring up the heater sting since they're all connected anyway?Thank you,- Wil

author: PlainName
author_rank: Super Contributor
timestamp: December 22, 2023, 04:17:44 pm
content: No idea, sorry, because I can't be arsed making my browser window fit your idea of an appropriately scaled image.Try using the forum tool to do it as above.

author: Wil_Bloodworth
author_rank: Regular Contributor
timestamp: December 22, 2023, 05:05:29 pm
content: Quote from: PlainName on December 22, 2023, 04:17:44 pmSorry you're having a hard time using a web browser. I have resized the image so you can potentially figure out how to view it now.- Wil

author: PlainName
author_rank: Super Contributor
timestamp: December 22, 2023, 05:59:02 pm
content: Well done

author: PlainName
author_rank: Super Contributor
timestamp: December 22, 2023, 06:07:26 pm
content: I'm not even a bulb beginner, but the heater isn't polarised. The datasheet specifies max voltage (positive or negative) with respect to cathode, but not which end. I would think it doesn't matter.Edit: forgot to say the heater voltage is AC or DC, so that's a big clue I reckon.

author: MarkT
author_rank: Frequent Contributor
timestamp: December 23, 2023, 02:46:34 pm
content: Quote from: Wil_Bloodworth on December 22, 2023, 03:52:07 pmI'm glad there's an isolation transformer because that circuit is dangerous without one - there should never be any mains current flowing to earth as shown. Chassis should be earthed or the whole device double-insulated.Are you building an isolation transformer into the unit though?These early two-pin valve circuits were and remain killers and should always be converted to three-pin safe configuration.

author: radiogeek381
author_rank: Regular Contributor
timestamp: December 23, 2023, 04:56:04 pm
content: For many tube nomenclatures, the digits before the letter group designate the nominal filament voltage.With a 35Z, 50L6, and the 4 12XXX in series the filament stackup is 133 V.With a 35Z, 35L6 and the 4 12XXX in series the filament stackup is about 118V.if the stack up is 50 L6 and 50 Z5 then it makes sense to wire the two 50 V filaments in parallel to get a 98 V loop.Did they wire the two 50V filaments in parallel?