Tubes for a Conrad Johnson 17LS?

Get to know the preamp in your system with the stock tubes then venture into NOS. Can get a bit pricey, but its hard to go back to the stock Sovteks.

Amperex 6DJ8s offer a touch of the romantic, with superb mids and airy highs - these were the ones I kept coming back to in my Premier 16. 6DJ8 Telefunkens are also wonderful but getting harder to come by. 7308s are a tad more neutral, not quite as seductive, with slightly firmer bass and clear highs. I could never use more than one Siemens 7308 per channel without bordering on the strident, but 7308 Valvos (Amperex Heerlen made) work great.

And Joe's right - unwise to cross mix types (not to be putting a 6922 in the same channel as a 6DJ8 or 7308). Brand mixing is where you'll find the 'blend your own' fun. Try for '60s thru mid-70's vintage. The nice thing about the 17 is you only need 4 and can begin to experiment with just 2. Check out the 'Joe's Tube Lore' FAQ on the Asylum to get one guys opine on many varieties out there.

Regarding the use of different tube types (2 of each), you're on your own here. I was told by someone I trust and respect in this area that there is no problem in doing so, and I've tried various combinations with no ill effects. I guess I'd like to see a definition of "unwise," Jtimothya -- what is the real downside?

I agree that you should get the measure of the stock tubes first, and they're really not bad. But I don't plan to go back to them anytime soon! Dave

Hi Dave - The different types have different electrical characteristics - which is why they are different types. (For example a 6922 draws less heater voltage than a 6DJ8.) The circuit design of the 17LS creates a single 'composite' triode from the combination of the four triode sections in each channel. My suspicion is that the preamp performs better when that composite is created from tubes with similar versus different electrical properties. Other types of preamps may act differently - so the context here is the Premier 17/16/ART lineup which share a common topology. (The ACT2 is in the same family but its tube rolling opportunities are much more limited.) I do know that CJ told me they do not recommend mixing types in the same channel for those preamps.

If you've had no ill effects using different types in the same channel then that's great as you've got a broader range of combinations open to you! (Imo thats where the fun is.) Is your experience with the 17LS?

Jtimothya, thanks for the info. I take it to mean that best results would come from using the same tube type in positions 1&2 and 3&4 rather than 1&3 and 2&4, assuming you have only two tubes of the same type. My unit is a 17LS2. Dave

just a note of caution,be sure to use the shortest interconnect with this preamp as the output impedence is very high at 1000ohms,or the base will drop off quite a bit,also be sure your amp has at least an imput impedence of 20k,or you will be very unhappy.

mike,