Brom onderdrukking in Philips radio's (Algemeen)
door Pandu Rajan 
, 15.07.2016, 05:54 (3055 dagen geleden)
Dear Members
With reference to the thread Remarkable Modification BX520A dated 1.7.16 I have some queries to ask which are as follows:
1. Is it necessary that in all cases where a +ve voltage is applied to one end of to the filament of EBC41/ECH21 for reduction of HUM, one end of the filament winding of the main transformer is not Grounded?
2. In the set BX765X one end of filament of the valve ECH21 ( B4) is connected to the cathode through a resistance R109. Is this also going to serve the same purpose as in 1 above?
3. In the set BX716X the filament winding of the main transformer for the valve B3 only (EBC41) is given through a choke S51 and the filament itself is shunted by variable resistance R64?
4. In the set BX806X one end of the filament of the valve B6 only i.e. EF40 is grounded. Why?
5. What is the amount of + voltage given to the filament for HUM reduction?
Regards
P.Rajan
Brom onderdrukking in Philips radio's
door John Hupse † 
, Schoonhoven, 15.07.2016, 08:20 (3055 dagen geleden) @ Pandu Rajan
1. Is it necessary that in all cases where a +ve voltage is applied to one end of to the filament of EBC41/ECH21 for reduction of HUM, one end of the filament winding of the main transformer is not Grounded?
if the DC voltage of the filament is lifted (i.e. when a DC voltage is applied to the filament) then you cannot "ground" the filament at the same time. If you "ground" the filament the DC-voltage will be zero, if you "lift" the filament the DC-voltage will have a positive value.
2. In the set BX765X one end of filament of the valve ECH21 ( B4) is connected to the cathode through a resistance R109. Is this also going to serve the same purpose as in 1 above?
yes
3. In the set BX716X the filament winding of the main transformer for the valve B3 only (EBC41) is given through a choke S51 and the filament itself is shunted by variable resistance R64?
R64 is a conventional "hum" potmeter. S51 blocks mains noise. No DC-lifting here.
4. In the set BX806X one end of the filament of the valve B6 only i.e. EF40 is grounded. Why?
all filaments are connected here in parallel, so not only the filament of B6 is connected to the null. The EF40 is a high quality tube with respect to hum suppression, and no further measures were taken here to prevent hum.
5. What is the amount of + voltage given to the filament for HUM reduction?
in most cases 30 to 60 volt DC
Brom onderdrukking in Philips radio's
door Pandu Rajan , 15.07.2016, 08:42 (3055 dagen geleden) @ John Hupse †
Dear Mr. John Hupse
Thanks your reply. Against point no one my question was if the +ve voltage is applied to one terminal of the filament eg: pin no 1 of ECH21 then the the other end of the filament i.e. pin no 8 will be grounded or not? If it is grounded then apart from the AC current flowing will not a d.c. current also start flowing through the filament?
Regards
P.rajan
Brom onderdrukking in Philips radio's
door John Hupse † , Schoonhoven, 15.07.2016, 12:15 (3055 dagen geleden) @ Pandu Rajan
Against point no one my question was if the +ve voltage is applied to one terminal of the filament eg: pin no 1 of ECH21 then the the other end of the filament i.e. pin no 8 will be grounded or not?
the resistance of such a filament is low (approx 19 ohm). If you apply 50 volt DC on one end, and zero volt to the other end there will be only a very low DC voltage left. So a "lifted" filament is never connected to the null.
Brom onderdrukking in Philips radio's
door Pandu Rajan , 16.07.2016, 12:22 (3054 dagen geleden) @ John Hupse †
Dear Mr. John Hupse
Thanks your reply.
Regards
P.Rajan