Different direct heating styles?

[ktkammon]

What are the main advantages/disadvantages of these two heating schemes?

 

[hacknet]

the one with the resistors is supposed to in some way reduce the hum. i`m not really sure how it works, coud someone shed some light?

 

[jeapel]

hi

just my practical experience with my last tube driver
but no exact explication

www.loginnovation.com/jeapel

with 6sn7 double triode half for right and half for left

1-without ground on heater big hum on speaker

2-with one ground zero hum on right and hum on left

3-with 2 100 ohm 1w very low hum on both channel

4-for my very low gain 6as7 no need of ground

100ohm 1 w is typical value my 6sn7 are low noise
electro harmonic but a cheap hummy tube maybe
50 ohm or 25 ohm with good watt

 

[Sch3mat1c]

1 is for AC heaters where the alternating voltage balances between the two nodes, minimizing grid-cathode hum. 2 is for DC filaments.

Tim

 

[jeapel]

"2 is for DC filaments."

maybe but old radio use methode 2 with ac
and there is no big hum ??

 

[fdegrove]

Hi,

maybe but old radio use methode 2 with ac

With indirectly heated tubes and quite likely a center tapped heater xformer too....

Cheers,

 

[SHiFTY]

just my practical experience with my last tube driver

Nice amp! Got any pics? How many watts does it produce?

Back on topic, I have found most indirectly heated tubes have quite minimal hum.

Raising the heater supply above ground by a few volts, keeping in mind heater to cathode ratings, can also reduce hum. This is often necessary in SRPP-type designs.

 

[jeapel]

i just finish my web site with photo