I'm new to tubes, like the sound, and now...

I recently purchased a Sonic Frontiers SFS-40 power amp that is using KT-90 tubes.

I also have a Eico 81 that uses EL34's and really like that sound. The tubes in the Sonic Frontiers are larger-what 'term' should I look for that will identify the larger 34 tubes if there is one?

Does one manufacturer of tubes sound better than others or have more integrity and quality? The KT-90's have an Ei in a circle and some Russian print on them (obviously dating my Russian professor in college did little to really help me learn the language, but I did get an A and had a lot of fun!) -what brand may these be and are they known for quality?

And lastly, a hum developed in the amp so I switched around the tube positions and that decreased the hum somewhat, but didn't completely get rid of it. Will dying tubes bring on this condition, or is there another problem I need to isolate (well, not me actually, but someone who does this for a living)?

Thanks in advance for answers you've probably given a hundred times,

L'wood

I'm new to tubes, like the sound, and now...

I also have a Eico 81 that uses EL34's and really like that sound. The tubes in the Sonic Frontiers are larger-what 'term' should I look for that will identify the larger 34 tubes if there is one?


FatBottle? there are FatBottle 6CA7 / El34.

I use NOS Ei Fatbottle 6CA7, the sound is exciting in my ST-70.
http://img253.imageshack.us/img253/4452/mitei6ca70326xn.th.jpg (http://img253.imageshack.us/my.php?image=mitei6ca70326xn.jpg)
http://img340.imageshack.us/img340/9006/mitei6ca70409bs.th.jpg (http://img340.imageshack.us/my.php?image=mitei6ca70409bs.jpg)

There are also EH (Elektro Harmonix) Fatbottle 6CA7 / EL34, but i don't like the Sound. Otherwise the EH EL34 are quite good tubes.

very underdog-el34 are the RFT el34. most el34 worldwide sold after 197x were from eastgerman RFT factory anyway. They were sold under a lot of international brands. I like there sound very much.. esp. for guitar and Jazz.

http://www.jogis-roehrenbude.de/EL34-Story/EL34-Story-Seite4.htm

The KT90 are just what you said , made by EI. They are a manufacturer in the former soviet controlled east europe (Yugoslavia I think). Anyway they are the only makers of that tube and of late have fallen on difficult times. You can find more about these on Jim's tube page, the link is below.
These (kt90) are incredable tubes with meritous performance and durabilty that will last a long time if taken care of.
As to your problem with HUM I would look after your balance pots both AC and DC and make sure they are adjusted properly. Look at your manual on how to do this. If not familiar ask somebody who has experience with your equipment as there are high and possibly fatal voltages present.
http://pages.prodigy.net/jimmcshane/tubes.htm

When I emailed Chris Johnson of Parts Connextion (who was one of the folks at Sonic Frontiers when this amp was designed and manufactured) he said I shouldn't be using them, but EL34's. The hum was very bad, before switched around the location of the output tubes, and then replaced two of the 6922's, now it's barely audible (I've got a couple more 6922's I'm going to add to the other channel). Thanks for the heads up on the possible fixes.