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What do I bias KT 77 tubes at?

 
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hmic10
RM100


Joined: 22 Apr 2012
Posts: 225

PostPosted: Sat Dec 16, 2017 8:24 pm    Post subject: What do I bias KT 77 tubes at? Reply with quote

Are they the same as el34"s
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warmachine67
RM20


Joined: 20 Apr 2017
Posts: 41
Location: Alabama

PostPosted: Sat Dec 16, 2017 9:50 pm    Post subject: Reply with quote

You can bias them like regular EL34's, but they will be running a little cool.

I ran some kt77's for a while and I think my research turned up 35-40mV so that's what I set them at and they seemed to be fine.

This was in an RM50 btw

You may already have or already know, the EL34/KT77s need a 400mA fuse where a 6L6 type tube used a 250mA fuse. Jaded faith told me a 500mA will do no harm if they are easier to find than a 400mA.
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hmic10
RM100


Joined: 22 Apr 2012
Posts: 225

PostPosted: Sun Dec 17, 2017 6:37 pm    Post subject: Reply with quote

Did not know about the fuse
I will double check
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tschrama
RM100


Joined: 04 Jun 2014
Posts: 201
Location: Netherlands

PostPosted: Mon Dec 18, 2017 4:13 am    Post subject: Reply with quote

Why would a different fuse be needed for a different tube? The maximum current is determined by the HT and Plateload, not the tube.

As for bias: bias them you output tubes as ow as possible without sounding awfull. This will prolong their life multiple times and keep your amp, and the rest of your rack, cool runing, prolonging the live of al your gear.
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Patsakornut
RM20


Joined: 26 Jan 2018
Posts: 2

PostPosted: Sat Jan 27, 2018 3:39 am    Post subject: Reply with quote

I agree with you I'm biased too. I really like
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joey_truelove
RM100


Joined: 08 May 2006
Posts: 409
Location: Dales district, Sweden - heartland of Swedish folkmusic

PostPosted: Thu Feb 15, 2018 4:52 pm    Post subject: Re: What do I bias KT 77 tubes at? Reply with quote

hmic10 wrote:
Are they the same as el34"s

Well, not quite. The EL34 has an absolute max of 27W, which means that a minute drift or biased prior to warming up properly may blow them.

The KT77 has an absolute max of 32W and typically they are more rugged than comparable true pentodes, particularly those made today.

I would personally go as hot as 85% of 25W, which equals 70% of 30W. The KT77 mellows out pretty well at this point and exhibits various shades of semi-clean overtones, perhaps similar to the KT66.
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