[HAM] Best 12AU7 - now 6550

[Keith H Clark]

Dave,
    Let's hope this sheds a little more light on this for you. 
In general they work a bit better in a 122 than a 147. In a 147 driven hard,
Jon Lord style, they tend to sound dark or muddy,if driven very hard they
suck the power supply right down. KT-88's are brighter and retain that even
on overdrive.
I'm sorry if I don't supply theory behind each of my posts, I just get
annoyed at times with mis-information posted.Also the tests we did were 10
years ago, I think the new 90's are somewhat different,older ones pulled
current real hard when overdriven.

-----Original Message-----
From: hammond-bounces at zeni.net [mailto:hammond-bounces at zeni.net] On Behalf
Of David Anderson
Sent: Saturday, March 08, 2008 6:46 PM
To: The Hammond Forum
Subject: Re: [HAM] Best 12AU7 - now 6550

On Mar 8, 2008, at 4:11 PM, Keith H Clark wrote:

> Kt-90's are not a particularly good match for that circuit. KT-88's  
> are much
> better.

As I've noticed is the norm with you, Keith, we get a critical  
response with no technical explanation whatsoever.

In my 122 amplifier, KT90s draw the correct bias and sound good. They  
draw the same heater current as a 6550.

Al Goff sells them on his site as a "high performance 6550 replacement."

What's the problem?

David Anderson




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