Just started to put together an alternate build of Bottlehead's Crack. Enjoying the current stock build of the Crack with the Speedball upgrade has been great. But my itchy building fingers wants to try to build one from scratch. By using the Speedball upgrade, the build becomes incredibly simple. The main component that needs to be thought through is the PSU. Taking advantage of the fact that I have someone working, means that there is more scope for experiementation in the new build.
My basic design premise is to stick to the basic design, with a potential substitute for the driver tube. At the moment, the choices are: 5687 family, 12SN7/12SX7 (I have a stash), 6n6p and 12BH7 in the dual triodes. But more experimentation to try to use a single triode or a single triode strapped pentode. This could definetly open up more options, but this will have to be made soon, as heaters and bias points are a consideration.
The PSU will be a choke input in common mode, followed by a LC stage and then a seperate RC stage for each channel. But again, I might decide later on to do a LC instead for the last stage, to provide that inductive seperation between channels. The transformer should be a 240VCT to produce around 170V at the B+.
So far, I have committed to parts for the resistor side only and had the various PSU caps already on hand. Going to try the Charcroft metal foil for the shunting resistors at the output and using Kiwame 5W (in parallel) for the bleeder and RC filters. Also got some Amtrans carbon for the grid stoppers if I use a higher Gm tube. The PSU caps will be Obbligato oils, and tenatively using 70uF for the common stages and 30uF on the individual channel stages.
More details to follow.
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