06-07-2017, 09:53 AM
Knowing that the Marconi-Osram Z66 pentode has similar characteristics as the Mazda SP61 it makes sense to fit an international octal base to the still readily available Mazda valve.
It proved to be a rather time consuming job. Nevertheless, the substitute valve works very well in the HMV1804. Just need to work out a more time efficient method of rebasing the SP61.
It would seem that the EHT transformer will need rewinding. After 15 to 20 minutes the picture becomes dim and overscanned, a sure indication that the EHT voltage is reduced and measurement proves that the voltage has become reduced to 3KV. Correct figure for the EHT is 4KV.
Geordie McBoyne.
It proved to be a rather time consuming job. Nevertheless, the substitute valve works very well in the HMV1804. Just need to work out a more time efficient method of rebasing the SP61.
It would seem that the EHT transformer will need rewinding. After 15 to 20 minutes the picture becomes dim and overscanned, a sure indication that the EHT voltage is reduced and measurement proves that the voltage has become reduced to 3KV. Correct figure for the EHT is 4KV.
Geordie McBoyne.
