29-12-2016, 06:18 PM
Hi Trevor,
The EFM1 soon became obsolete and there was a time when Mullard simply suggested that the valve should be replaced by an EF39. just leave the tuning eye out of the circuit. This is not satisfactory and later on Mullard came up with this modification by using the vari-mu EF39 and the EM34, the latter is now becoming scarce and expensive. The EM4 is electrically identical and has the side contact base the same as the EFM1, this might be a good thing for the Tandberg because it maintains almost near originality. Other Philips-Mullard tuning eyes are the EM1/TV6 and EM3, the former requires only -5volts and the latter -21volts for 90 degrees defection. Other tuning eyes to consider would be the American 6G5 and 6U5 but these are not very sensitive tuning eyes, requiring -21 volts for full deflection.
The Solvsuper must be the only non Philips set to use the EFM1
The attachment shows the information found in the 1958 Mullard Maintenance Manual about replacing the EFM1 with the EF39 and EM34. The EM4 was not suggested as a replacement because it was considered obsolescent 1958.
Interestingly, at least one vari-mu audio amplifier valve was made, the EF83.
From the Radiomuseum: http://www.radiomuseum.org/tubes/tube_ef83.html
EMI-Capitol used the EF89 in certain record players, by varying the cathode bias in a differential manner to adjust the stereo balance, not nice really.
I do have some funny valves upstairs so it might be worth a search for an EFM1, I know there is an ELL1 up there, even Mullard doesn't list it in any publication.
Geordie McBoyne.
The EFM1 soon became obsolete and there was a time when Mullard simply suggested that the valve should be replaced by an EF39. just leave the tuning eye out of the circuit. This is not satisfactory and later on Mullard came up with this modification by using the vari-mu EF39 and the EM34, the latter is now becoming scarce and expensive. The EM4 is electrically identical and has the side contact base the same as the EFM1, this might be a good thing for the Tandberg because it maintains almost near originality. Other Philips-Mullard tuning eyes are the EM1/TV6 and EM3, the former requires only -5volts and the latter -21volts for 90 degrees defection. Other tuning eyes to consider would be the American 6G5 and 6U5 but these are not very sensitive tuning eyes, requiring -21 volts for full deflection.
The Solvsuper must be the only non Philips set to use the EFM1
The attachment shows the information found in the 1958 Mullard Maintenance Manual about replacing the EFM1 with the EF39 and EM34. The EM4 was not suggested as a replacement because it was considered obsolescent 1958.
Interestingly, at least one vari-mu audio amplifier valve was made, the EF83.
From the Radiomuseum: http://www.radiomuseum.org/tubes/tube_ef83.html
EMI-Capitol used the EF89 in certain record players, by varying the cathode bias in a differential manner to adjust the stereo balance, not nice really.
I do have some funny valves upstairs so it might be worth a search for an EFM1, I know there is an ELL1 up there, even Mullard doesn't list it in any publication.
Geordie McBoyne.
