29-06-2020, 05:22 PM
The Rod Tubes are lower voltage than the regular 1.4V valves. Most will work well to below 0.9V.
For RF where you want to feed the "cathode" the well known approach with direct filaments is a 1:1 transformer wired to f- and f+. The f- and f+ are shorted for the signal via a capacitor and either pin is the input, or two caps and feed the junction. The transformer windings are in series to the filament supply such that the DC currents cancel, but it is a choke to the common mode RF (or indeed 38 kHz or audio). The input side of the transformer, a common mode choke, has both connections to RF ground. The f- and f+ point may be tuned to ground if desired. The g3 must also be at RF ground, usually zero volts. The supply is then 0V and -LT or whatever to the filament, nominally 1.2V.
You can only use regulated DC due to the filament design. A DEAC approach on trickle charge has close to 1.5V using NiMH, it's a bit lower on NiCd (the original DEAC). There is no need with modern regulators. Though shorting the Adj pin to 0V of almost all adjustable regulators is about 1.25V, slightly high, but FAR better than a trickle charged NiMH.
But the whole point of these valves is the low battery current on LT, apart from the 1p24b, which are about 220mA each. Obviously you can design mains powered gear, but if using mains it's far better to use EF80s and ECH81s. Common and cheap. You can make a decent push pull audio amp with EF80 or ECH81. You could even make an entire AM/FM radio with 2 x EF80 for VHF preamp and Mixer / Osc. One can be the AM LO. The 1st IF FM amp can be a Pentode Mixer using LO to g2 on AM. A pair of EF80 as push-pull audio can use a small 115-0-115 mains transformer without saturation. Copy the Vidor battery AM/FM set that uses all DF97s. Use an AGC amp and high level inverted AGC on the g2 pins.
You can also make an entire AM/FM radio using ECH81. Note ECH83 is the same valve. Apart from audio out you can make an entire radio using EF89, ECH81/ECH83, ECC82 etc all with 12V heater and 12V HT.
The clamp diodes need things like 1N5401 to manage the current if filaments are disconnected and are more suitable as last line of defence safety devices. Note the 1N4001 or 1N5401 are OK for 1.2V, but for the D series valves you want the 1N4007 or 1N5408 as they have a slightly higher voltage at the same forward current. Some parallel 125mA D series UK sets did use a selenium rectifier as a shunt regulator. Using either the 1N series or selenium, the regulation is poor and voltage rises alarmingly if the o/p valve fails or is removed. The series resistor is fairly critical to the usual filament current.
For RF where you want to feed the "cathode" the well known approach with direct filaments is a 1:1 transformer wired to f- and f+. The f- and f+ are shorted for the signal via a capacitor and either pin is the input, or two caps and feed the junction. The transformer windings are in series to the filament supply such that the DC currents cancel, but it is a choke to the common mode RF (or indeed 38 kHz or audio). The input side of the transformer, a common mode choke, has both connections to RF ground. The f- and f+ point may be tuned to ground if desired. The g3 must also be at RF ground, usually zero volts. The supply is then 0V and -LT or whatever to the filament, nominally 1.2V.
You can only use regulated DC due to the filament design. A DEAC approach on trickle charge has close to 1.5V using NiMH, it's a bit lower on NiCd (the original DEAC). There is no need with modern regulators. Though shorting the Adj pin to 0V of almost all adjustable regulators is about 1.25V, slightly high, but FAR better than a trickle charged NiMH.
But the whole point of these valves is the low battery current on LT, apart from the 1p24b, which are about 220mA each. Obviously you can design mains powered gear, but if using mains it's far better to use EF80s and ECH81s. Common and cheap. You can make a decent push pull audio amp with EF80 or ECH81. You could even make an entire AM/FM radio with 2 x EF80 for VHF preamp and Mixer / Osc. One can be the AM LO. The 1st IF FM amp can be a Pentode Mixer using LO to g2 on AM. A pair of EF80 as push-pull audio can use a small 115-0-115 mains transformer without saturation. Copy the Vidor battery AM/FM set that uses all DF97s. Use an AGC amp and high level inverted AGC on the g2 pins.
You can also make an entire AM/FM radio using ECH81. Note ECH83 is the same valve. Apart from audio out you can make an entire radio using EF89, ECH81/ECH83, ECC82 etc all with 12V heater and 12V HT.
The clamp diodes need things like 1N5401 to manage the current if filaments are disconnected and are more suitable as last line of defence safety devices. Note the 1N4001 or 1N5401 are OK for 1.2V, but for the D series valves you want the 1N4007 or 1N5408 as they have a slightly higher voltage at the same forward current. Some parallel 125mA D series UK sets did use a selenium rectifier as a shunt regulator. Using either the 1N series or selenium, the regulation is poor and voltage rises alarmingly if the o/p valve fails or is removed. The series resistor is fairly critical to the usual filament current.