We've been supplying quite a number of WE 212 (STC 4212) output transformers to DIY folks. This tube is really getting us curious as we have not got a chance to try it ourselves. We tested our 212 output transformers with 845 in parallel to mimic the 212 tube electrical parameters all this while and that alone, is already quite scary (845 paralleled).
212 SE is already quite massive and powerful, and now comes the extreme - 212 PSE (that is FOUR 212's in a single amp!!!!)! We have even got a 212 PPP (Parallel Push Pull, this is EIGHT 212's, how crazy (oops) is that???) quote in progress! In audio world, the sky is the limit!
The 212 replicas from PRC are getting less costly and it is getting easier to reach for most people now. We've seen more and more guys online making them and showing off to the DIY community!
Unfortunately I'm a fan or NOS tubes, or else I would have considered making one for myself. The NOS 212, as I understood from one of my customers, is that I should forget about it due to the rarity and not being as rich as the collectors to bid for it.
Below is a modified 212 PSE power amplifier (monoblock) for my customer. This original schematic was obtained from online / website, which I believe should be designed by Sakuma-san. This modified version is not a full blown design yet as it was just a simple conversion from 212 SE to 212 PSE, for transformer quotation use.
If I'm the one designing it, then the B+ won't be at 1KV but higher to fully utilize the power of the 212 tube, and some other J&K proprietary tweaks would be included. Since this version is not tested nor totally verified usable, use with care please.
I did not include the minor details too since I presume users that would embark on making 212 amplifier would have enough knowledge to extrapolate from the schematic.
The transformers associated with this design will be as follow:
- Input transformer - not done by J&K
- Interstage transformer for 845
- Level 3 Nanocrystalline Double C core, potted - U$1900/pair
- Level 3 EI Z11, U$1390/pair
- Level 2 Super Hi-B Double C core, U$990/pair
- Pri: 5K 80mA, Sec: 10K
- Output transformer for 212 PSE
- Level 3 Nanocrystalline Double C core, potted - U$1790/pair
- Level 2 Super Hi-B Double C core, U$1490/pair
- Level 2 EI Z11, U$1090/pair
- Primary: 5K, 300mA, Sec: 8/16
- B+ inductor
- Level 3 - not doable
- Level 2 Super Hi-B Double C core, potted - U$690/pc
- Level 1 EI Z11 - U$340/pc
- 2.5H 800mA for choke input, HV usage
- Driver stage inductor
- Level 3 Nanocrystalline Double C core, potted - U$440/pc
- Level 2 Super Hi-B Double C core, potted - U$340/pc
- Level 1 EI Z11 - U$190/pc
- 10H 150mA
- 845 filament inductor
- Level 1 EI Z11 - U$190/pc
- 0.1H 5A
- 212 filament inductor
- Level 1 EI Z11 - U$190/pc
- 0.01H 9A
- Power transformer
- Level 2 EI Z11 - U$490/pc
- Level 2 EI Z10 - U$690/pc
J&K Audio Design
9/13/2015
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