believe it or not, I've been known to utilise a voltage
doubler to feed the heaters in a case like this - bulky and a
bit extravagant I know, but good ECL86's seem hard to find.
A pair of 1N5401's and, perhaps, a couple of 2200mF 16v.
cap.'s - the size of cap. can be used to adjust the final volts;
maybe a series resistor to trim.
If you have the room and the bits, I promise it works fine,
but if feeding more than a pair of valves you may need more
capacitance and watch the ripple current rating.
you only need to increase the heater voltage. You can use this circuit.
Start with 470 µF (MFD) / 10 V caps for C1 and C2. As for resistor R1, start with 2 - 3 Ohms, 1 - 2 Watts, then vary R1 to adjust to 0.3 A heater current for one tube PCL86. If you don't reach 0.3 A even at 0 Ohms, then increase the capacitors. Tell us the results you found.
If you operate more then one PCL86 in parallel, then adjust to 14 V heater voltage. Use diodes capable for the increased current.
I am just wondering if a "fire stick" power tube adapter could be fashioned for PCL86 use. Such an adapter would be quite useful since their is a great surplus of these tubes and the ECL86's are getting pricier.
In addition, maybe adapters could be made for PL84's and UL84's too.
It's not always possible to replace an Exx tube by an adequate Pxx or Uxx tube. Many of them have different characteristics, thus they can't be used as replacements.
This is the case in the relation between EL84 and PL84 / UL84.
The EL84 is designed for Vp = Vg2 = 250 V, while PL84 and UL84 are designed for Vp = Vg2 = 170 V - this is quite a difference ! But one can replace an EL86 by a PL84 !
If you're looking for a replacement for an Exx- Tube by a Pxx- tube you have to refer to a tube data book. The ratings for Vp, Vg2, Vg1, Ip and Ig2 should be equal.