SLO Build
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Re: SLO Build
Red/Green and Red/Yellow 124v I'm glad i have a usable Transformer and tapping the HV is the course. So I'm guessing the tap point, which I've draw in orange is at the filter cap B+ point? and the other area of confusion is this fill/1 fill/2. In the drawing there is no connection point. I assume 6.3 goes to the heaters 4-5 in the picture it's just bridged in V-2-3-4 and non evident on V-1 Thank you so much for answering my very naive questions and enduring this "Too many requests" issue the site is having.
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Re: SLO Build
Red/Green and Red/Yellow 124v I'm glad i have a usable Transformer and tapping the HV is the course. So I'm guessing the tap point, which I've draw in orange is at the filter cap B+ point? and the other area of confusion is this fill/1 fill/2. In the drawing there is no connection point. I assume 6.3 goes to the heaters 4-5 in the picture it's just bridged in V-2-3-4 and non evident on V-1 Thank you so much for answering my very naive questions and enduring this "Too many requests" issue the site is having.
Re: SLO Build
If taking the bias supply from the B+ rail, I'd take it directly from the point where the red HT supply wire connects to the rectifier. I'd start with typical Marshall values You are shooting for bias range around -37V.
If this were my build, I'd probably use the 125V supply you'll get from the Red/Green. Same basic bias circuit, but lower value dropping resistor. You can tinker with the voltage divider (15K, 47K 25K pot) to dial in an appropriate bias voltage range.
This is a good resource. About 50% down the page you'll see the bias supply, though it is not what he's discussing, it's there in the schematic. https://robrobinette.com/How_the_Marsha ... _Works.htm
Heater supplies. Do you have a schematic from the donor organ? My thought is that the 12V supply was used for the preamp tubes and you can do the same. To wire the 12A?7 family of tubes at 12.3V, use only pins 4 and 5. Nothing on pin 9. It is typical to omit heater wiring on both schematics and layouts to reduce clutter, as this is a commonly understood thing. Wire the preamp tubes in parallel. Imagine a ladder, where the rails are the heater supply wires and the rungs are pins 4 and 5 of each tube. All heaters get equal access to the supply wires. I'd reserve the 6.3V heater supply for the power tubes -- same idea, wire in parallel. Here is a decent piece on heater wiring and there is an excellent picture of a heater wiring harness about 30% down the page: https://www.diyaudio.com/community/thre ... ly.211731/ It shows 6.3V wiring, where pins 4 & 5 are bridged and the harness goes to 4/5 and 9.
If this were my build, I'd probably use the 125V supply you'll get from the Red/Green. Same basic bias circuit, but lower value dropping resistor. You can tinker with the voltage divider (15K, 47K 25K pot) to dial in an appropriate bias voltage range.
This is a good resource. About 50% down the page you'll see the bias supply, though it is not what he's discussing, it's there in the schematic. https://robrobinette.com/How_the_Marsha ... _Works.htm
Heater supplies. Do you have a schematic from the donor organ? My thought is that the 12V supply was used for the preamp tubes and you can do the same. To wire the 12A?7 family of tubes at 12.3V, use only pins 4 and 5. Nothing on pin 9. It is typical to omit heater wiring on both schematics and layouts to reduce clutter, as this is a commonly understood thing. Wire the preamp tubes in parallel. Imagine a ladder, where the rails are the heater supply wires and the rungs are pins 4 and 5 of each tube. All heaters get equal access to the supply wires. I'd reserve the 6.3V heater supply for the power tubes -- same idea, wire in parallel. Here is a decent piece on heater wiring and there is an excellent picture of a heater wiring harness about 30% down the page: https://www.diyaudio.com/community/thre ... ly.211731/ It shows 6.3V wiring, where pins 4 & 5 are bridged and the harness goes to 4/5 and 9.