23-05-2024, 06:35 PM
Because the PCL82 was designed for TV use the triode section is larger than needed for an AF pre-amp. The ECL82 was developed from it and has the same oversize triode.
An interesting experiment would be triodising the pentode section (connect g2 to anode) and use a 100V to 150V HT and a mains transformer that's for 220-240 or 110-120 and wiring that as push pull. Adjust the series resistor on each cathode for about 1mA to 5mA, adjust the antiphase drives so output level the same on each part. The bias currents cancel, so no transformer saturation. The 6V to 12V (or 2 x 6V windings) secondary drives speaker.
However quite a few "signal" valves can do 500mW, or even 2W push pull. EF80, either section of an ECH81/ECH83 (same valve). But not ECC81, ECC85 etc.
An interesting experiment would be triodising the pentode section (connect g2 to anode) and use a 100V to 150V HT and a mains transformer that's for 220-240 or 110-120 and wiring that as push pull. Adjust the series resistor on each cathode for about 1mA to 5mA, adjust the antiphase drives so output level the same on each part. The bias currents cancel, so no transformer saturation. The 6V to 12V (or 2 x 6V windings) secondary drives speaker.
However quite a few "signal" valves can do 500mW, or even 2W push pull. EF80, either section of an ECH81/ECH83 (same valve). But not ECC81, ECC85 etc.
