I am building a Fender Bassman type amp. There is 3x ECC83s + PP stage.

I have a two options in my anode transformer. Either use 12,6 V with center
tapping or 6,3 V.

Would it be best to connect 12,6 V to heaters, tube heaters fed in series
(in each tube). But should I then connect the common heater pin (pin 9) into
ground in each tube or is it best leave the pin 9 unconnected and only
ground the CT on the transformer ?

What I have seen in original factory made amps, they only use 6,3 V and
hetares fed in parallel in each tube and heater feed is grounded only on
xfrmr side balanced with two low value resistors.

Best regards from Finland,

George

"Aku Ankka"

I am building a Fender Bassman type amp. There is 3x ECC83s + PP stage.

I have a two options in my anode transformer. Either use 12,6 V with
center
tapping or 6,3 V.


** Your output tubes need 6.3 volts at several amps - you would need a
separate, low current winding for 12.6.


Would it be best to connect 12,6 V to heaters, tube heaters fed in series
(in each tube).

** No.


What I have seen in original factory made amps, they only use 6,3 V and
heaters fed in parallel in each tube and heater feed is grounded only on
xfrmr side balanced with two low value resistors.


** This arrangement means the heater voltage is only 3.15 volts relative to
chassis ground and induces the less hum in the pre-amp tube cathodes.

You can also use a 100 or 200 ohm pot to do the heater voltage balancing and
so adjust it for minimum hum - as is done on many other Fender amps.





........... Phil

It shouldn't be a problem either way but make sure you twist the wires and
dress them away from signal circuits. However if you detect any hum and all
else fails you can try DC on the filaments.
Hank WD5JFR
"Aku Ankka" wrote in message
...
I am building a Fender Bassman type amp. There is 3x ECC83s + PP stage.

I have a two options in my anode transformer. Either use 12,6 V with
center
tapping or 6,3 V.

Would it be best to connect 12,6 V to heaters, tube heaters fed in series
(in each tube). But should I then connect the common heater pin (pin 9)
into
ground in each tube or is it best leave the pin 9 unconnected and only
ground the CT on the transformer ?

What I have seen in original factory made amps, they only use 6,3 V and
hetares fed in parallel in each tube and heater feed is grounded only on
xfrmr side balanced with two low value resistors.

Best regards from Finland,

George

"Henry Kolesnik"


It shouldn't be a problem either way


** Bull**** !!!

Why do you imagine 6.3 volt CTs are so widely used ??

Why do amp makers like Fender fit hum balance pots ???

It reduces the damn hum.




............ Phil

"David R Brooks"


One point that may matter (depending on your circuit topology) is
fail-safe operation. Most double triodes (for example) have a separate
heater for each half, wired in series (with centre tap) at the pins.
If you use the series connection, & leave the centre floating, an open
heater (the most common failure mode) will shut down both triodes. If
the tap is grounded (or the heaters are paralleled), only the open-ed
side will fail.


** Once the heater is open the tube stops - ie no more sound.

There is no safety issue at all.



............... Phil