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Old 14th March 2005, 01:42 PM   #1
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Default Different direct heating styles?

What are the main advantages/disadvantages of these two heating schemes?
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Old 14th March 2005, 02:06 PM   #2
hacknet is offline hacknet  Singapore
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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?
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Old 14th March 2005, 07:12 PM   #3
jeapel is offline jeapel  Canada
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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
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Old 14th March 2005, 07:45 PM   #4
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1 is for AC heaters where the alternating voltage balances between the two nodes, minimizing grid-cathode hum. 2 is for DC filaments.

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Old 14th March 2005, 08:50 PM   #5
jeapel is offline jeapel  Canada
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"2 is for DC filaments."

maybe but old radio use methode 2 with ac
and there is no big hum ??
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Old 14th March 2005, 11:14 PM   #6
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Hi,

Quote:
maybe but old radio use methode 2 with ac
With indirectly heated tubes and quite likely a center tapped heater xformer too....

Cheers,
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Old 15th March 2005, 12:22 PM   #7
SHiFTY is offline SHiFTY  New Zealand
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Quote:
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.
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Old 15th March 2005, 07:55 PM   #8
jeapel is offline jeapel  Canada
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i just finish my web site with photo
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