Anyone know what a 5687 tube is.

[Red Planet]

Looks of the 12A family but havent figured out what it is yet.

[Riscchip]

I've had a few of these in the past, and as I recall they have a different pin arrangement than a 12ax7 or similar. They can't be swapped with a 12ax7 without some modification. It is, however, a dual triode like a 12ax7.

I reserve the right to be totally wrong here, as I'm not the tube expert some of the folks on the forum are.

[Red Planet]

It looks like a Long Plate 12AX7 and the Pin Arrangement is the same.

[Old Tele man]

...the old RAYTHEON and TUNG-SOL data sheets indicate it's NOT the same as 12AX7, ie:

12AX7A...gm = 1,600 micromhos; rp = 62,500 ohms; mu = 100; Ppd = 1.2W
5687WA..gm = 11,500 micromhos; rp = 1,610 ohms; mu = 18.5; Ppd = 4.2W

...quoting from the TUNG-SOL data sheet:

"The 5687WA is a ruggedized, general purpose medium-mu twin triode of the miniature button 9-pin all glass construction. Each triode section is electrically independent, although the two heaters have a common connection permitting either a 6.3 or 12.6 volt operation. This type has high perveance and high emission capacities which allow very high plate current pulses if a suitable short duty cycle is employed. The cathode material is chosen to minimize interface formation, thus making the 5687WA ideal for triggered applications involving long periods of stand-by cut-off service. Since it must be alble to withstand severe mechanical test specifications, the 5687WA is especially suited for use in industrial and military airborne equipment which may be subjected to severe shock and vibration."
[emphesis in red is mine]

...or, in simple words: it's designed for "pulsed" (digital?) operation, not for "linear" audio applications!

...so, from strictly a "gain" view point it's closer to the 12AU7 with mu = 17, but certainly NOT same as!

[Red Planet]

Is it safe to run in an Amp?

[Riscchip]

It looks like a Long Plate 12AX7 and the Pin Arrangement is the same.

I should have said "pin-out" not pin arrangement. The pinout is different, so don't use it where a 12ax7 is called for.

[Red Planet]

How bout splaining.

[lastwinj]

a 5687 is used occasionally in hifi amps. it gets REAL hot.

germ

[Damon]

"capacilities"

Either those T-S writers had great imaginations or that's a brand new term for me.

[Rich M]

Definitely different pin-out:

http://www.nj7p.org/Tube4.php?tube=5687

But it will take 500 V plate voltage, WOW!

[Riscchip]

How bout splaining.

I lack the expertise to give you any kind of technical explanation, I'm afraid. The fact that it has a different "pinout" means that the pins connect to / do different things within the tube than what the same pins do in a 12ax7. An EL84 or 6973 have their pins arranged the same as a 12ax7, but you wouldn't plug them in where a 12ax7 goes, right? Same idea with this tube. There are gazillions of tubes out there that look like other more familiar tubes, but can't be used the same way.

That's about as much as I can say wity any level of confidence.

[Rich M]

I think in the simplest terms, the pin arrangement refers to the design of the pin connectors. An EL84 and a 12AX7 both have the same pin arrangement and thus would fit in the same socket. The pinouts, however are different. Each of the corresponding pins between the two tubes make very different connections within the tube and thus you would never want to swap one for the other, even though they would fit.

One should also check the electrical compatibility. For example, EL34 and 6L6 types have the same pinouts and pin arrangements, but one of them (forget which) draws more heater current and thus subbing in that one in an amp designed for the other would draw more fil current, which the amp may or may not be able to take. Similar limitations can be found on factors such as max plate current/voltage, etc. I have a ton of HP dual triodes (forget #) with same pinout as 12AX7 but has max plate voltage of 250V, less than my marshalls will hash out.

Similarly, it is ok to sub a 12AT7 for a 12AX7, but not visa versa as a 12AT7 is designed to handle more current than a 12AX7.

[Old Tele man]

Either those T-S writers had great imaginations or that's a brand new term for me.

...typo!