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Chris55000 · 14th Jan 2019, 3:23 am

Hi!

EBL31 pinout & data:–

1 – i.c., 2 – h, 3 – a, 4 – ad', 5 – ad", 6 – g2, 7 – h, 8 – k, g3, cap g1

Va 250, Vg2 250, Ia 40mA, Ig2 4mA, G.B. –7.5V, gm 9.5mA/V, Ra 6500 ohms, Po 4.0W for 10% THD. Rk 150R

EBL31 circuits can look a little off–putting because they have the diode anodes on P4 & P5 connected to the 2nd IFT and A.G.C., with a meshwork of r.f. filter and detector load components that all had to be returned to pin 8 (k) with (often) a tapped cathode–bias resistor for A.G.C. bias/delay purposes, which makes the whole diagram look like a Chinese puzzle, as it was very uncommon to draw the two diodes of an EBL31 etc., type of valve separately in those days!

However, being a "short" superhet you don't have "that" cap to worry about as the top–cap grid of the EBL31 will be returned to chassis via the volume control, which normally is only connected to the diode load, so any unwanted bias will be in a negative rather than a positive direction, so altho' you might get low volume if the volume control d.c. isolating caps leak, it shouldn't put the EBL31 at risk, but do NOT run the set with the EBL31 top cap connector removed – short the top cap to chassis with a 100k resistor if you do have to remove it to test for hum etc!

Chris Williams

14th Jan 2019, 3:23 am	#8
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,874	Re: PYE 15A valve question Hi! EBL31 pinout & data:– 1 – i.c., 2 – h, 3 – a, 4 – ad', 5 – ad", 6 – g2, 7 – h, 8 – k, g3, cap g1 Va 250, Vg2 250, Ia 40mA, Ig2 4mA, G.B. –7.5V, gm 9.5mA/V, Ra 6500 ohms, Po 4.0W for 10% THD. Rk 150R EBL31 circuits can look a little off–putting because they have the diode anodes on P4 & P5 connected to the 2nd IFT and A.G.C., with a meshwork of r.f. filter and detector load components that all had to be returned to pin 8 (k) with (often) a tapped cathode–bias resistor for A.G.C. bias/delay purposes, which makes the whole diagram look like a Chinese puzzle, as it was very uncommon to draw the two diodes of an EBL31 etc., type of valve separately in those days! However, being a "short" superhet you don't have "that" cap to worry about as the top–cap grid of the EBL31 will be returned to chassis via the volume control, which normally is only connected to the diode load, so any unwanted bias will be in a negative rather than a positive direction, so altho' you might get low volume if the volume control d.c. isolating caps leak, it shouldn't put the EBL31 at risk, but do NOT run the set with the EBL31 top cap connector removed – short the top cap to chassis with a 100k resistor if you do have to remove it to test for hum etc! Chris Williams __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!