Black Plate NOS 5U4 - why does it matter?

[Shottky]

Why do NOS black plate rectifier tubes go for a significantly higher price than NOS rectifier tubes of the same spec? I do realize that this is similar to questioning the difference between NOS 12AX7s and new ones, but at least with those tubes I can understand the impact of the getters, plate shape, etc.

It seems to me that a rectifier tube's main job is to rectify AC into DC and provide enough capacity to allow the current draw. I haven't been able to find a solid explanation as to which properties of the 5U4G/GB/GA make the NOS ones more expensive. Is there an actual difference in the output DC? Less/more ripple? Less/more sag under load? Or is it largely in the imagination of the tube purchaser?

[Pressed_Rat]

Simply supply and demand. I don't know why either, probably a general perception that the remaining NOS tubes are better than all current production tubes. It is driving demand as the supply keeps dwindling.

A friend of mine gave me a few to try out and frankly I couldn't measure a difference - voltage drop was consistent among all three - around 25 to 30 volts (a Sovtek, a NOS GE, and a used unknown brand - all 5U4GBs). He said they were popular tubes in television sets - lasted forever.

[zaphod_phil]

It's common knowledge that any tube with a "BLACK PLATE" has much better sonic qualities - and by that I mean TONE! I have some RCA blackplate tubes that BLOW everything else out the WATER tone-wise! Black is electrically such a STRONG color. Come to think of it, I also have some Germanium transistors in black cans, and I'm sure that if I did an A/B test with them, they would sound WAY BETTER in FX pedals than the ones in plain old silver cans.

[morcey2]

It's common knowledge that any tube with a "BLACK PLATE" has much better sonic qualities - and by that I mean TONE! I have some RCA blackplate tubes that BLOW everything else out the WATER tone-wise! Black is electrically such a STRONG color. Come to think of it, I also have some Germanium transistors in black cans, and I'm sure that if I did an A/B test with them, they would sound WAY BETTER in FX pedals than the ones in plain old silver cans.

But that only applies if you use purple-insulated oxygen-free unobtainium-plated copper wire.

[Shottky]

I knew it. That also explains why many chassis are painted black.

[rjgtr]

I thought it was because with a black-plate less electrons can escape, thus being channeled into the enhanced tone creating properties of the tubes.

[dotfret]

I have tried to evaluate this effect before, and come to these conclusions.

Assume that a modern rectifier valve, delivered yesterday, is $10 retail.

Now, you are looking at a valve of similar type on eBay -

1) Is it NOS? Start from $20 if it is.

2) Is it made in the west? Add $40 for RCA or Philips group, $30 other European makers (including Tesla / Tungsram), $25 for US made, $15 for RFT/VEB or for Jap makes.

3) Is it a type designated for a very popular guitar/hifi amp? Yes? Add $15.

4) Is it a Russian equivalent type? Deduct $11.

5) If it has black plates, add another $10.

Usually, the sound differences are undetectable. Rectalfication - "the public gets what the public wants", even if they are taking it where it hurts.

[Shottky]

I found a local vintage radio guy in town who sells used, old-stock 5U4s for $10 bucks a pop, tested to within a reasonable range. I figure I might pick one up for my next build. If my understanding of rectifier tubes is correct, I won't be needing to replace it for many more years.

[Phil_S]

I think (I'm not home at the moment and can't check) I've got two Mullard made 6CA4's, one labeled RCA, the other GE, both of which rattle and are only useful for testing stuff. If you hold them up to your ear and tap them, you can hear the vibration, so I'm sure something is loose inside. I don't have them here with me, but I'm pretty sure at least one of them has black plates. Since these are Mullard brand I'd be willing to part with them for $20 each. After all, everyone knows if it's Mullard and black plate (even if it says GE Made in Great Britain), it's worth whatever the seller says its worth. Any takers, feel free to PM me.

[tbradshaw]

I bought the Ruby for mine because it was cool looking. I've checked it against the two older 5U4s that came with my AO-39 and can't tell a lick of difference tone-wise. So the looks win this one.