Rectified Again ~ Nest Music Theater Crossgrade 23Oct23

Well my 70 year old Sylvania rectifier died in my 300B SET amp in the NestMT.

I had the "stock" Shuguang 5Z3PJ rectifier from my original build so I was back online quickly. It's a strong rectifier too, even military "J" grade but it's only "fine" and not as open as the Sylvania and I am a bit dubious as it's like a 4th of July light show when I first turn it on. The Shuguang has resulted in multiple power fuse blowouts when I was trying to play the new NMT with center channel for Scooter. I need an alternative 5U4G design ~ for backup if nothing else.

I couldn't find another 1950's military Sylvania so I had to set my sights lower and looked for a well regarded alternative, or maybe two. Well, Tung Sol and RCA "coke bottle" 5U4G rectifiers are both touted by audiophiles however getting NOS versions was gonna cost me $100s... grrr. I set out and found used ones however that tested well supposedly. I bought one of each: a Tung Sol 5U4G and an RCA 5U4G. Interpreting the markings, the Tung Sol (322 ID) is from the 7th week in 1957 and the seller tested it very good at 110/112 (with 130 max) ~ it's a black plate, D getter version.

The RCA is seemingly more worn but tested strong as well at a similar 112/110 measurement. It also is a black plate D-getter style but from the 26th week of 1955. Neither tube was NIB so no original packaging. Just wrapped decently by the sellers and costing ~$40 each rather than $100s each. They frankly look equivalent.

As mentioned NOS NIB versions of these tube were too expensive for me given their likely affect on the system. Let's see how the used ones play in the NestMT. I've never thought rectifiers (part of the power supply, not the signal path) would make much difference in the sound an amp produced, however the Sylvania was better than the Shuguang to my ear previously. Not much difference in the SPL sweep as shown... however the RCA and TungSol were similar to my ear and both were smoother than the Shuguang and neither did fireworks like the Shuguang. I'm using the RCA to start.