Sinclair ZX80 / ZX81 / Z88 Forums

TRACO TSR 1-2450 DC/DC Switching Regulator - pin compatible replacement for the 7805 power regulator used in the ZX81

https://www.ebay.com/sch/i.html?_nkw=TSR+1-2450

$6.99 USD buy-it-now + $6 shipping within USA from seller American Retro Shop

the listing says

Better thermal management, reducing temperatures in the case and doesn't require use of heat sinks.
- Increased power efficiency (>94%)
- Improved output accuracy (±2%)
- Short circuit protection
- Built in filter capacitors
- Excellent line / load regulation

I’ve used those in the past but found I needed to fit them horizontally rather than vertically due to lack of space in the case. This was a bit of a faff on!

I ended up using these MuRata:

https://www.retroleum.co.uk/spectrum-repairs-mods

That's quite reasonable price at Retroleum. Unfortunately they are out of stock

Appears to be muRata OKI-78SR-W36H (horizontal), but with the connector modded to be on the bottom of the board instead of the top. Also: "Can also be used in the ZX81 (splay out the outer legs slightly when fitting)"

unmodded