12B4 Pinout Question (pin 6 & 8)
Posted:
Mon Nov 01, 2010 11:12 amby Shannon Parks
Working on a 12B4 design and am wondering if I can always count on pins 6 and 8 to be not connected to anything? The datasheets from a couple manufacturers label them as no connects. Checking my GE 12B4s that I have, indeed, the pins go up to the mica spacer and dead end - easy to visually verify. If someone could check a few manufacturers for me and visually ID this, I would be grateful. Basically, I'm thinking of piggy-backing a 12B4 on a standard twin triode B9A footprint and looking to do as few cuts and jumpers as possible.
--Shannon
Posted:
Mon Nov 01, 2010 3:43 pmby EWBrown
I have a quantity of both GE and RCA 12B4As, and indeed, pins 6 and 8 are truly "no connection". So they could be used as tie points, or other wise disregarded.
I got the little 12B4A SET "Darling Killer" r amp unning and it sounds pretty doggone good, with TF103-48 OPTs, and about 250V B+. I wired the filaments for the 12B4As and driver as 12 V, so I can also use 12DT8s, which BTW sound very good, as well, for a cheap "plinker".
Its ouptpu section uses nearly identical basic circuitry and plate voltages / curent as the 1626 "Darling", but with 2X the output power and lower 2HD and 3HD. With a bigger chassis I could have made it 12B4A / 1626 "convertible".
12B4As also make for a really nice sounding linestage, I've seen and heard Gary Kaufman's design, and it is very nice. He gave me one of the B+ regulator PCBs and two of the plate load CCS boards (10M45S). so I have the major parts, including two of the Hong Kong 100K ladder step attenuators from E-bay. The rest of it is ppretty simple, just run 12B4A "grounded cathode" VA stage on Tube CAD with B+ of 250V, and IP of 10 mA.
/ed B
Posted:
Mon Nov 01, 2010 4:14 pmby Shannon Parks
Thanks for the confirmation, Ed. Indeed, I'm planning on doing a 10M45S loaded 12B4 linestage as 'an extra' thrown on top of the phono board I'm working on. Didn't see any reference to it on Gary's page last I looked (yesterday). Cool you got to hear it. Looks like a fun tube - and a cheap one!
--Shannon
Posted:
Mon Nov 01, 2010 4:20 pmby EWBrown
He doesn't have it posted, on his URL and I saw it well over a year ago. He updates that website about as often as a total solar eclipse
/ed B
Re: 12B4 Pinout Question (pin 6 & 8)
Posted:
Sun Aug 13, 2017 1:56 pmby EWBrown
Speaking of a total solar eclipse, in 8 days from now, 21 August, 2017 we will be in the path of full totality!
