[HAM] Best 12AU7 - now 6550

[Keith H Clark]

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

-----Original Message-----
From: hammond-bounces at zeni.net [mailto:hammond-bounces at zeni.net] On Behalf
Of David Anderson
Sent: Saturday, March 08, 2008 3:28 PM
To: The Hammond Forum
Subject: Re: [HAM] Best 12AU7 - now 6550


All the Russian reproduction Tung Sols I've tried have been quite  
good. Based on the talk on audiophile tube sites frequented by tube  
dealers, Russian tubes have the most consistent quality these days.  
I'm running reissue Tung Sol 5881s in my 32H amp, and their 12AX7 is  
very low-noise in one of my AO-28 preamps.

My favorite 6550 for the 122 amplifier is the KT90. I'm running a  
pair of the EI brand in mine, but I hear the Electro-Harmonix version  
is good, too. The EI tube factory in Serbia is now sadly out of  
business. JJ (Slovakia) can make good tubes, but I've heard lots of  
ranting about poor quality control from them in recent shipments.

Rated at 50 Watts per tube, the KT90 should last a long time in  
Leslie amps. I swapped a few different power tubes in my 122, and the  
guy I've been playing with recently said, "Yes, that's it! Use  
those!" When I put the KT90s in.

I'm not sure there's a "best" 12AU7. I have found that the Sylvania/ 
GE plate style with a small box in the center tends to sound brighter  
than the style with large, flat plates, which tends to sound richer  
and mellower to my ears. The RCA clear-top versions are nice, but as  
Scott says, you primarily want to look for balanced triode sections.

It's best to get 6550s as a matched pair. Yes, a pair of NOS American- 
made Tung Sol 6550s would be nice, but they'd be $$$$$$$$$$. Such a  
low supply also makes it harder to get a matched pair. I've never  
liked the GE 6550A in anything, but some people do. The Sylvania  
6550A is supposed to be wonderful, but extremely rare.

David

On Mar 8, 2008, at 2:17 PM, mike p wrote:

>
> <<  Ok..what about the 6550's? any difference in these?>
>
> Certainly ,  my money is on the newly produced Tung-sol 6550's .   
> Best bang
> for your buck .  Russian made
>
> For older tubes either NOS or good tested used,  still the Tung- 
> sol  50's
> and 60's  Originals  USA made.............
>
> Mike P

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