T500-1 - any ideas?

[Kay Pirinha]

Hi,

years ago I've salvaged a pair of Brown Boveri T500-1 tubes, alongside with a pair (one DQ4a and one 872) of mercury vapour rectifiers, from a scrapped high frequency dental casting machine. I just found them when I was clearing my former house. But what to do with these beasts? Does there exist some reasonable usage in audio?

Best regards!

[Eli Duttman]

My word, the town you live in is a mouth full!

Let's look at the T500-1 data sheet. You use 100 W. of filament power/tube. Also, the B+ rail will be deadly dangerous. Having said that, I don't see why you can't build "monster" SET monoblock amps around the tubes. The O/P trafos will be both extremely heavy and very expensive. Talk about a PowerDrive situation, as the tubes, with their (sic) 50 W. grid dissipation rating, cry out for Class "A2" action.

[HollowState]

Originally Posted by Eli Duttman

Let's look at the T500-1 data sheet.

Looks just like an Amperex 5868 under a different name.

[Kay Pirinha]

Originally Posted by HollowState

Looks just like an Amperex 5868 under a different name.

I know that. Philips TB 4/1250 is also an equivalent. Thanks!

[Richard Ellis]

Let me know if you want to go SE............A while ago my In-laws had a custom center-tap output 220-220 Auto-transformer wound up for them for the equivalent of $300 USD.........the core is about 10" cubed & unknown weight, as I haven't tried to move it once is was set in place.

__________________________________________________ _______Rick........

[riccoryder]

The T-500-1 is also very similar to the popular 3-500Z. If not used for audio projects, they're still of value to people in ham radio along with whatever sockets, blower and power supply ran them. Even when used at low plate input power or with only the filaments lit, these types require forced air cooling to avoid failure at the seals, especially where the filament and anode connections come out. Unlike types such as the 811A and 833A having receiving tube style getters, these types should be run at red to yellow anode temperature for at least a few hours several times a year or the zirconium getter material in the anode will not remove gases. If you go too long without doing that, gas buildup sometimes may become significant enough to cause ionization, arcing, or cathode damage in a tube that could have remained healthy. Use extra care to avoid breaking these tubes. Inhaling thorium (th232) filament dust may lead to lung cancer from the radioactive decay. Even the little 4-65A carries that hazard. Typical audio and receiving types do not contain thorium.

Be well informed when designing and using these types and also take steps to insure that they do not pose a hazard to visiting children, pets or even adults that could spill a drink. At least this type doesn't appear to be one using beryllium oxide ceramics. Inhaling dust from some power devices with broken ceramics can cause drowning in your own blood from resulting internal bleeding. There are even some r.f. power transistors using those ceramics as I was reminded recently on opening up a r.f. generator that had a warning label with a skull and cross-bones. Surplus components often lack the original warning notices.

[HollowState]

Originally Posted by riccoryder

The T-500-1 is also very similar to the popular 3-500Z.

Actually no, it isn't. Aside from the obvious size difference, the 3-500Z is a zero bias triode usually used in grounded grid configurations. That's what the "Z" indicates. The T-500, like the 5868, requires considerable negative grid bias to control it's operation. It also has lower µ. And tubes like this one, along with others that use a thick heavy carbon alloy plate, should not be operated with obvious plate color. Do so and you will exceed the plate dissipation. Gettering action will still take place. This type of plate, even when operated at ICAS, will only show a barely perceivable dull red color in a darkened environment. But you are correct about the other industrial tubes with the thin style plates.

[Kay Pirinha]

In the datasheets I've found applications for push pull class AB2 operation so far, not for single ended usage. As I really do not use, or need kilowatts of AF power I think it's a good advice to offer them to ham radio operators. Thank you!