EL81 vs EL84 as audio output valve

[dougietamson]

Originally Posted by kalee20

They are - no doubt as a result of the aligned grids. With the grid wires of g2 effectively in the shadow of the grid wires of g1, they'll trap fewer electrons from the stream.

BT's are also less consumptive of heater power for the same overall output- compare EL84 pentode (6.3V 0.76A, 4.79W) against the 6V6 or 6AQ5 or 6BW6 (6.3V 0.45A, 2.84W) yet both are rated 65mA maximum cathode current, and both can give very similar output powers (5.7W for the EL84 and 5.5W for the 6V6).

The EL81 is much higher than either, at 6.3V 1.06A (6.68W), but as already noted, it can pass nearly 3x the current - 180mA.

Curious circuit, using ECC85 as phase inverter! Why not ECC81, 82, or 83? (Though I like the neon / LDR automatic level control )

I've got a couple of used Mullard ECC85 pulled from a scrapped stereo radiogram (FM radio). They tested good in an audio amp, just got to watch the filaments are on 4&5 and gnd the screen on pin 9. Mu is similar to an ECC81.

Doug

[Ed_Dinning]

Hi Folks, if anyone wishes to swap between E, U, P series valves, a simple auto transformer can be wound to do this and is quite compact.
Most (but not all) of these valve series use a constant heater power across the different letters, so no danger of overloading the heater windings

Ed