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Old 10th March 2011, 04:12 PM   #1
GoranB is offline GoranB  Poland
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Default AC or DC heathing?

Does anyone have an experience about difference in sound using AC or DC heathing?
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Old 10th March 2011, 04:22 PM   #2
kevinkr is offline kevinkr  United States
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You need to be a little more specific posing your question, are you talking about DHTs or indirect heated tubes?

I and many others here have lots of experience with both..
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Old 10th March 2011, 04:40 PM   #3
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Hi!

Here is my take:

DHTs as output tube:

45, 2A3 : AC
all others : DC

DHTs as driver or in preamp : DC

IDHT in power amp or linestage: AC
IDHT in phono stage : DC

Best regards

Thomas
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Old 10th March 2011, 04:48 PM   #4
GoranB is offline GoranB  Poland
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Precise for double triode PCC88 (indirect heathed) like a gain stage and 12BH7 (Im not sure but i think its also indirect heathed) like catode follower stage.
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Old 10th March 2011, 04:51 PM   #5
GoranB is offline GoranB  Poland
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Quote:
Originally Posted by Vinylsavor View Post
Hi!

Here is my take:

DHTs as output tube:

45, 2A3 : AC
all others : DC

DHTs as driver or in preamp : DC

IDHT in power amp or linestage: AC
IDHT in phono stage : DC

Best regards

Thomas
Hi Thomas,

Im using PCC88 and 12BH7 in my preamplifier. Till now heathing was AC i would like to try DC heathing using LM317T.
Any suggestion will be welcomed.
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Old 10th March 2011, 04:58 PM   #6
M Gregg is offline M Gregg  United Kingdom
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GoranB,


There is a difference with AC or DC heaters. AC seems more open than DC. Regards the LM317T. Remember that tube heaters are very low resistance at startup! The 317t will probably shut down in thermal or current limit without a soft start!

Regards
M. Gregg
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Old 10th March 2011, 05:02 PM   #7
GoranB is offline GoranB  Poland
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Quote:
Originally Posted by M Gregg View Post
GoranB,


There is a difference with AC or DC heaters. AC seems more open than DC. Regards the LM317T. Remember that tube heaters are very low resistance at startup! The 317t will probably shut down in thermal or current limit without a soft start!

Regards
M. Gregg
A very usefull information. I should look for a proper circuit for DC heathing.
Any impressions about difference in sound between DHT and NDHT?
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Old 10th March 2011, 05:04 PM   #8
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Hi!

Quote:
Originally Posted by GoranB View Post
Im using PCC88 and 12BH7 in my preamplifier. Till now heathing was AC i would like to try DC heathing using LM317T.
Any suggestion will be welcomed.
Depends on the level your preamp needs to amplify. If it is linelevel or above, don't bother with DC. AC, possibly biased slightly positive is fine.

Otherwise the sound impact with IDHT is insignificant. There are 100 other things which are way more important

Best regards

Thomas
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Old 10th March 2011, 05:06 PM   #9
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Quote:
Originally Posted by GoranB View Post
A very usefull information. I should look for a proper circuit for DC heathing.
Why? Do you have an issue with hum? If not AC is fine

Thomas
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Old 10th March 2011, 05:07 PM   #10
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by M Gregg View Post
GoranB,


There is a difference with AC or DC heaters. AC seems more open than DC. Regards the LM317T. Remember that tube heaters are very low resistance at startup! The 317t will probably shut down in thermal or current limit without a soft start!

Regards
M. Gregg

Not a problem at all with these particular types using an LM317 in my experience.

I don't think IMLE with an IDHT there is any difference at all except in terms of potential hum and noise pick up. With DHTs I use AC with 2.5V tubes in output stages, but based on George's (tubelab) recent comments about IMD on AC may not continue the practice. I'm using some of Rod Colemans DHT CCS in new projects and that will probably be the case going forward. Historically I've used monolithic based CCS, combined with VREGs in some cases and VREGS with chokes to heat DHTs. All seem to work well and sound good if properly implemented. YMMV
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