I just ordered a buncha 6p14p-eb from deep inside a bunker full of fanatical ruskies . . . . 20 of them.
Well, it might have been just an ordinary merchant now that I think about it.
Anyway, I can't really match them properly with my Hickock 6000 and 6000A testers, but I am going to give it a try and then run them in my scott 222c that would prefer 7198 tubes.
I'll post back what I find. I have old stock 6bq5 in there now and they are wearing out fast but sounding great anyway. +400 volt plate seems to confront them.
Anyone know if the EH EL84M are new production? Or simply relabeled 6p14p-EB tubes?
Dan
EL84M
ARE in current production, branded Sovtek. In fact, the last 2-3 years of production of those tubes are much better than the earlier era of tubes sold with the same number. I highly recommend the last few years Sovtek EL84M.
The 6P14P-EB is the EXACT SAME TUBE as the EL84M. The only difference would be
when the tubes were produced. EL84M is a designation applied to the tubes by New Sensor via the "Sovtek" brand.
The EL84M = 7189, not 7189A. If you use them in 7189A applications you may have to do a bit of rewiring, and whether they will perform well is going to be dependent on the application. Me, I'd probably look at dropping the screen voltages a bit and keeping the dissipation at or under 7189 limits to use an "M" in a 7189A hole.
Also remember that EL84/7189/7189A tubes were often used in cathode bias circuits. To find the plate or screen voltages you have to deduct the cathode voltage - for example, you might measure:
- 400 volts from the plate to chassis ground
- 20 volts from the cathode to chassis ground
Since the tube only "sees" the difference between plate and cathode, the plate voltage is actually 380 volts.
Finally,
higher voltage in and of itself does not cause a tube to wear faster! You could have 600 volts on the plate and screen of an EL84 and if the current is zero, the tube will not wear at all. The failure mode of excessively high voltages is arcing, either from pin to pin at the socket or from element to element within the tube envelope.
On the other hand, if an increase in voltage causes the tube to have to dissipate more wattage (meaning heat), then the increased voltage can
contribute to a failure for sure. A tube run at 300 plate volts and 40 ma will have to dissipate .04 x 300, or 12 watts. Raise the voltage to 400 (with no other changes) and the dissipation increases to .04 x 400 or 16 watts. That dissipation increase may be enough to kill a tube by itself - but the increase from 300 to 400 volts probably will also cause the tube to pass more current (unless you change something else like the bias voltage to prevent that from occurring). If the change to 400 volts from 300 in our example also causes the tube to pass 50 ma. (up from 40), then the dissipation becomes .05 x 400, or 20 watts! That's a 60+% increase - that can kill a tube for sure!
When thinking of why/how tubes failures occur, remember:
1. Excess current - even with dissipation in the specs - can deplete the cathode and cause the tube to wear out more quickly. There is a finite number of electrons the cathode can emit, and excess current depletes them more quickly.
2. Excess voltage does NOT wear out a tube more quickly (if the dissipation and current are unchanged). Excess voltage can cause arcing. But excess voltage
alone cannot "wear out" a tube.
3. Excess dissipation - caused by any combination of voltage and current - can cause a tube to wear out more quickly. Keep in mind that voltage and current could both be in spec, but the tube could still be required to dissipate more wattage (heat) than it is capable of regardless! Localized overheating inside the tube can occur.
I hope this helped...
