22-09-2019, 04:31 PM
The ECL80, like the ECL113 in your Grundig, is unusual in only having one common cathode for two sections with entirely different characteristics. It is common practice in Triode-Heptode and Triode-Hexode mixer/oscillator but otherwise these are oddities.
If you have an ECL82, ECL83 or ECL86 to hand, these all have separate cathodes for the two sections and can be separately biased as appropriate.
The method used by Grundig is a hangover of the days of battery valves. Here, the filament is also the cathode and can't be separated, so grid bias was the only solution. Usually, this was done with a separate battery of 6 cells, each with a brass tube to accept a wander plug. These were marked 0V, -1.5V, -3V and so on up to -9V and it was common to have several leads coming from the radio. One, of course, was ground and connected to 0V and the others were plugged into various negative voltages to suit the bias requirements of the individual stages.
Then someone came up with the idea of 'auto bias' which was a chain of resistors in series with the negative return to the battery to provide these voltages without the need for a third battery. This continued throughout the life of the battery valve radio right up to the time the transistor reigned supreme.
Some manufacturers, though, continued to use this scheme for many early mains valve receivers rather than the 'new' method of cathode bias. The HMV radio I grew up with used this method despite being a relatively mature design from about 1938.
Many valves you encounter will use the Pro-Electron coding system which tells you a lot about each valve type. You may well be aware of this already but may still find this look-up table useful.
There is one omission I've spotted which you should be aware of which is an 'O' for the first letter. It means zero volts, aka a cold cathode device such as a voltage regulator but it was later applied to transistors when they came on the market, which was quite logical.
Diodes started with OA, which is obvious and, because a transistor has three connections, it was treated as a triode - hence OC. The numbers were then allocated to indicate the type of device such as AF, RF, Power, etc.
Eventually semiconductors were given their own numbering system as the types and uses proliferated.
If you have an ECL82, ECL83 or ECL86 to hand, these all have separate cathodes for the two sections and can be separately biased as appropriate.
The method used by Grundig is a hangover of the days of battery valves. Here, the filament is also the cathode and can't be separated, so grid bias was the only solution. Usually, this was done with a separate battery of 6 cells, each with a brass tube to accept a wander plug. These were marked 0V, -1.5V, -3V and so on up to -9V and it was common to have several leads coming from the radio. One, of course, was ground and connected to 0V and the others were plugged into various negative voltages to suit the bias requirements of the individual stages.
Then someone came up with the idea of 'auto bias' which was a chain of resistors in series with the negative return to the battery to provide these voltages without the need for a third battery. This continued throughout the life of the battery valve radio right up to the time the transistor reigned supreme.
Some manufacturers, though, continued to use this scheme for many early mains valve receivers rather than the 'new' method of cathode bias. The HMV radio I grew up with used this method despite being a relatively mature design from about 1938.
Many valves you encounter will use the Pro-Electron coding system which tells you a lot about each valve type. You may well be aware of this already but may still find this look-up table useful.
There is one omission I've spotted which you should be aware of which is an 'O' for the first letter. It means zero volts, aka a cold cathode device such as a voltage regulator but it was later applied to transistors when they came on the market, which was quite logical.
Diodes started with OA, which is obvious and, because a transistor has three connections, it was treated as a triode - hence OC. The numbers were then allocated to indicate the type of device such as AF, RF, Power, etc.
Eventually semiconductors were given their own numbering system as the types and uses proliferated.
