Postponement is a powerful supply chain concept employed to minimize inventory/capital for a business by delaying configuration of a specialized product until as close as possible to delivery to the end-user. For great examples, see Dell’s made-to-order computer business or Edcor’s made to order transformers.
In vacuum tube land, the transformer is a critical component. Tubes come in all shapes and sizes, requiring a variety of voltages for optimal operation. This has lead to many different power transformers and filter configurations for various circuits. We even have transformer companies whose entire business strategy is founded on servicing the myriad of transformer configurations and custom options.
What if we could find one power transformer that could be used with any circuit? What would it look like? Well, if I were to build one it would probably look something like this:
Looks pretty simple to be universal, doesn’t it. But what’s up with the 50V winding? It’s not a heater tap but it could be used for bias, I suppose. The use I have in mind is something like this:
In conjunction with the 300V winding, the 50V winding will allow you to create 250V and/or 350V outputs (all voltages AC of course). Using the extra winding and some filter math, you could easily tune in any target B+ from low max voltage tubes like 6V6/EL84 to higher max voltage tubes like EL34 or KT88. Careful attention would need to be paid to phase labeling and any power supply would use a bridge rectifier, but those are pretty small prices to pay for more flexible parts.
A transformer like this with a 250mA current rating might be the only transformer a builder would ever need for a variety of projects. Fewer parts means less money tied up in iron for users and fewer SKUs means more economies of scale for transformer manufacturers. That’s the beauty of postponement.
- Aikido Headphone amp is underway
- Push-push octal monoblocks are in design phase
- Working on write-up for latest peanut watt SET “El Cacahuate”