08-06-2018, 12:12 PM
(This post was last modified: 08-06-2018, 12:14 PM by Geordie McBoyne.)
If fact the metal valves were first valves to have the international octal base, the glass ones followed shortly after.
According to the data in the Brimar valves and teletubes book No 6 the screen grid voltage applied to a 6K7 should not exceed 125V. In the TRF radio we're discussing the screen grid is supplied direct from the HT line. So it follows it might be a good idea to supply G2 from a potential divider across the HT supply.
Info about the 6K7 from the Radiomuseum: https://www.radiomuseum.org/tubes/tube_6k7.html
The diagram shows a 47Kohm resistor in series with feed to the screen grid. This is not good practise because the screen grid volts will rise when the grid bias is increased. Much better to use a potential divider.
The same rule about screen grid volts applies to the EF89.
https://www.radiomuseum.org/tubes/tube_ef89.html
Geordie McBoyne.
According to the data in the Brimar valves and teletubes book No 6 the screen grid voltage applied to a 6K7 should not exceed 125V. In the TRF radio we're discussing the screen grid is supplied direct from the HT line. So it follows it might be a good idea to supply G2 from a potential divider across the HT supply.
Info about the 6K7 from the Radiomuseum: https://www.radiomuseum.org/tubes/tube_6k7.html
The diagram shows a 47Kohm resistor in series with feed to the screen grid. This is not good practise because the screen grid volts will rise when the grid bias is increased. Much better to use a potential divider.
The same rule about screen grid volts applies to the EF89.
https://www.radiomuseum.org/tubes/tube_ef89.html
Geordie McBoyne.
