19-09-2017, 07:54 PM
(This post was last modified: 19-09-2017, 07:57 PM by Geordie McBoyne.)
"Hi, I have what I assume is the pre-war version, I've never restored it because of the dropper cord issue but I really should spend some time working out what I need to do, this thread is very helpful".
Hi John,
The pre-war model known as version 1 is very similar to the post-war version 2 receiver which is the subject of this topic. Version 1 employs a 6A8G pentagrid frequency changer valve whereas the version 2 model uses the 6K8G. Version 1 and 2 models use either a 25Z4 or 25Z6 HT rectifier, the valve socket is wired to accept either valve. Osram U31 is OK to use as well the TV valve rectifier PY32.
Version 1 has a tapped line cord to supply the HT rectifier anode. Version 2 the line cord supplies the heaters only.
In all events the line cord should be replaced anyway.
With regard to the capacitive dropper. Nick wrote: "Could you not hide it under the chassis and out of sight?"
Unfortunately no. The 4microfarad capacitor is too large to fit under what is already tightly packed underside of the chassis. See attachments. I did have concerns that because the heater capacitor is in close proximity to the 6Q7G top cap hum pickup might be a problem, and sure enough there is hum at maximum volume control setting. However, moving the capacitor well away from the valve didn't make the slightest difference to the hum level.
Selectivity and sensitivity is very good, five feet of wire will serve as the aerial.
Just one more job to do, fit a 1 amp fuse in series with the mains input.
Geordie McBoyne.
Hi John,
The pre-war model known as version 1 is very similar to the post-war version 2 receiver which is the subject of this topic. Version 1 employs a 6A8G pentagrid frequency changer valve whereas the version 2 model uses the 6K8G. Version 1 and 2 models use either a 25Z4 or 25Z6 HT rectifier, the valve socket is wired to accept either valve. Osram U31 is OK to use as well the TV valve rectifier PY32.
Version 1 has a tapped line cord to supply the HT rectifier anode. Version 2 the line cord supplies the heaters only.
In all events the line cord should be replaced anyway.
With regard to the capacitive dropper. Nick wrote: "Could you not hide it under the chassis and out of sight?"
Unfortunately no. The 4microfarad capacitor is too large to fit under what is already tightly packed underside of the chassis. See attachments. I did have concerns that because the heater capacitor is in close proximity to the 6Q7G top cap hum pickup might be a problem, and sure enough there is hum at maximum volume control setting. However, moving the capacitor well away from the valve didn't make the slightest difference to the hum level.
Selectivity and sensitivity is very good, five feet of wire will serve as the aerial.
Just one more job to do, fit a 1 amp fuse in series with the mains input.
Geordie McBoyne.