el34 quad tube pp guitar amp: series /parallel heater wiring for half power Q/A

[Pauld35]

hello,

I have an amp that uses series parallel heater wiring for the el34's
the left to power tubes were one wired lot and the right side were the other wired pair (please see original schematic below)

to save cost for a quad set of tubes I opted to run the amp at half power on only the two center tubes V10, V11 by wiring the heaters as a series/parallel pair, rebiasing and running the output impedance at half. this has worked fine.

I am going to pass the amp on now so I am thinking to wire V9, V12 heaters as a pair so the new owner can purchase a quad set of el34's and run the amp at full power should they choose.

My question is in the design are the V9,V10 and the V11,V12 heaters wired together for the correct voltage because the are situated close to each other to make wire routing easier and saves on wiring ....

Or is it a design rule effecting noise and interference that heater wiring in series parallel arrangement has to be at each end of the output transformer (in quad pp designs)?

please note: I am only inquiring in regards to the heater wiring arrangement,

...........to simplfy can V9,V12 be run as one heater series/parallel pair and V10,V11 be run as the other heater pair (with re wiring of course) without causing poor effects or problems?


thankyou

 

[wg_ski]

Whether or not you pick up unwanted noise probably depends more on the layout of the heater wiring than anything else. You probably want to run a twisted pair to each socket, then connect the pairs in series a bit of distance away in order to prevent a big loop. Try using the other two positions once you get it re-wired. If it isn’t any noisier than what you have now then it will be fine running either pair or both.

 

[basreflex]

with this arrangement providing 12.6V heater supply, it reduces total current and hence lowers the magnetic field of the wires running the heater current. twisting them reduces the area, and area reduction also reduces the hum field. the return wire can be best laid close to the the series wiring between the two tubes , before both twisted returning to the supply point.

 

[Pauld35]

Whether or not you pick up unwanted noise probably depends more on the layout of the heater wiring than anything else. You probably want to run a twisted pair to each socket, then connect the pairs in series a bit of distance away in order to prevent a big loop. Try using the other two positions once you get it re-wired. If it isn’t any noisier than what you have now then it will be fine running either pair or both.

Thanks, Do you think it would be possible to use the center tap of the heater transformer windings and run each pair off each half,
ie. 0/6.3v ..... 0/6.3v

 

[Pauld35]

with this arrangement providing 12.6V heater supply, it reduces total current and hence lowers the magnetic field of the wires running the heater current. twisting them reduces the area, and area reduction also reduces the hum field. the return wire can be best laid close to the the series wiring between the two tubes , before both twisted returning to the supply point.

ah yes thankyou , I should probably keep them as series parallel pairs then incase the transformer is not caple of the extra current if they are all run only as parallel