You only need two diodes (1N400x will be sufficient for one PCL86 or two) and two 'lytics of sufficient capacitance in a Delon doubler (courtesy of
en.wikipedia.org):
Best regards!
en.wikipedia.org):
Best regards!
But how small in size can these two electrolytics be? And do you come close enough to the required 13V (b.t.w.: there are some conflicting values for Vf of the PCL86 in the different datasheets/sources)?
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Ideally we would use a step up current source on a little pcb to turn 6.3Vac into 300mA up to 16V
Hi Robert,
true. As these P series tubes are specified for 300 mA heater current instead of certain heater voltages, the datasheet voltage readings are just estimated values.
For the Delon doubler capacitors one has to try: Observing heater current I'd start with 2 x 470 µF and increase step by step until the actual current reads 300 mA. In case of exceeding this value (as the steps between standard adjacent 'lytic capacitances are rather big) one could add an ohmic resistor in series.
Best regards!
But don't you loose some voltage (2 x 1V, or?) over the two diodes to begin with? More capacitance will not raise the output voltage if it is not there to start with, or? But my knowledge of semiconductors is very poor.
If you loose 1 of the 6.3V, you wil never get higher than 10.6V, or? That would be too low.
If you only loose 0.5 of the 6.3 V, the maximum is 11.6V. That would just do (Vf a little more than 10 % down). But is this possible in real life, with reasonable size capacitors?
A voltage tripler would do, but would be bigger in size and could be risky because it would take more heater current (little over 0,3A more?) from the existing radio than an ECL86 does.
If you only loose 0.5 of the 6.3 V, the maximum is 11.6V. That would just do (Vf a little more than 10 % down). But is this possible in real life, with reasonable size capacitors?
A voltage tripler would do, but would be bigger in size and could be risky because it would take more heater current (little over 0,3A more?) from the existing radio than an ECL86 does.
I just tried it in a Hammond AO-44 amplifer. This one was used in later versions of the A-100 and M-100 organs as the reverberation amplifier and features a pair of ECL86/6GW8's. I quickly soldered a Delon doubler with IR 30S1 diodes, that aren't even Schottkys, and 2.2 mF 25V 'lytics. With it's original power tranny the heater voltage slowly climbed 'till 12.8 Vdc, which should be sufficient for these tubes. As both the plate and heater windings are CT'ed, this heater voltage also is perfectly balanced at +/- 6.4 Vdc w.r.t. GND.
Best regards!
Best regards!
Great. Now we have closure in this thread (unless you would insist on using two tubes for the replacement...).
Not really, Robert 😉!
Due to the large internal impedance of any voltage doubler (or multiplier, of course), a somewhat higher DC voltage should be expected with just one tube. Unfortunately I didn't elaborate in this direction and all involved parts are already in their bins now.
Generally, in a Delon circuit the output voltage at a given load depends on the diodes' forward voltage and either the capacitors' ESR and value: The lower both the Vf and ESR, and the higher the capacitance, the higher the output voltage - and vice versa, of course.
I used general purpose diodes, not Schottky ones, and general purpose 'lytics, not specifically selected ones for extra low ESR.
If the heater current of one PCL86 should exceed 300 mA, I'd try capacitors of lower values first, as any other parameter has some unfavourable impact on efficiency.
Best regards!
Due to the large internal impedance of any voltage doubler (or multiplier, of course), a somewhat higher DC voltage should be expected with just one tube. Unfortunately I didn't elaborate in this direction and all involved parts are already in their bins now.
Generally, in a Delon circuit the output voltage at a given load depends on the diodes' forward voltage and either the capacitors' ESR and value: The lower both the Vf and ESR, and the higher the capacitance, the higher the output voltage - and vice versa, of course.
I used general purpose diodes, not Schottky ones, and general purpose 'lytics, not specifically selected ones for extra low ESR.
If the heater current of one PCL86 should exceed 300 mA, I'd try capacitors of lower values first, as any other parameter has some unfavourable impact on efficiency.
Best regards!
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If youre going that far to get a tube into a device just rectify the 6,3V and get a boost converter...but my original idea was not to modify the radio at all and just have a drop in replacement...two tubes it is. Waiting for the boards to arrive.
Oh boy... You clearly didn't read all the contributions in this thread, or did you?
So a PCL86 with a voltage doubler (for which you don't have to modify the radio) is 'going that far' but making an adapter for two tubes is not?
So a PCL86 with a voltage doubler (for which you don't have to modify the radio) is 'going that far' but making an adapter for two tubes is not?
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Each to his own, I'd say.
Personally I prefer the KISS principle: With an additional parts count of four a real substitution for the ECL86 tube can be achieved. As I said before, the EL84 is no direct sub for the ECL86 pentode. To decrease plate current to 36 mA you'll also have to increase the cathode resistor to 210 ohms, as per the datasheet.
Best regards!
Personally I prefer the KISS principle: With an additional parts count of four a real substitution for the ECL86 tube can be achieved. As I said before, the EL84 is no direct sub for the ECL86 pentode. To decrease plate current to 36 mA you'll also have to increase the cathode resistor to 210 ohms, as per the datasheet.
Best regards!
Which leads to a new idea : a board with a step-up circuit ( rectifier + stepup) that
allows pcl86 to be used in an unmodified amp.
allows pcl86 to be used in an unmodified amp.
Yes, but both effort and losses surely would be higher in comparison to a simple, but sufficient Delon.
Best regards!
I have read the contributions and everyone is trying to modify the radio to accept the PCL86.
With my idea no modifications are required and just plug and play and about the cathode resistor no I don't have to increase it. I have checked numerous radio circuits where THE EL84 is used withe 250V on the anode and a 150 ohm resistor in the cathode and I own one of those radios and the output transformer is comically small. The ECL86 radios I own that run 225 or 250V have a 180 ohm cathode resistor. No modifications needed.
With my idea no modifications are required and just plug and play and about the cathode resistor no I don't have to increase it. I have checked numerous radio circuits where THE EL84 is used withe 250V on the anode and a 150 ohm resistor in the cathode and I own one of those radios and the output transformer is comically small. The ECL86 radios I own that run 225 or 250V have a 180 ohm cathode resistor. No modifications needed.
Not me !
I suggested a board containing a socket for the pcl86 AND circuitry to make
the 13Volts needed to the filament, this by using the supplied 6.3V
The board has pins that fits in the amps noval socket and a socket for a pcl86
Surface mount ceramic capacitors may be useful to keep the adapter board size small. 100uF 16V capacitors are available in 1210 size and low price, see as example Kemet C1210C107M4PACTU. There are many cheap 2A Schottky rectifier with forward drop less than 500mV and DO-214AA package, such as B130LB-13-F. Both SMD packages are easy to solder with a standard soldering iron. If the components are mounted on both sides of the adapter board, it will be slightly larger than the noval socket. Two tube adapters, such as the popular ELL80 tube replacement with two EL95, are cumbersome and won't fit on many radios.