Inspire 6FLV Tube combinations, what are your favorites?

[Kruds]

I recently picked up a used Inspire 6FLV (2020) and I am exploring it's capabilities. I have seen some of the various comments about 6SN7 vs 6SL7, 5AR4 vs 5U4, NOS vs New, Chinese tubes, etc. but what I am looking for are any suggestions relating to your favorite tube combinations for this specific Inspire (FLV vs KT88) variant. Any ideas out there?

My current collection of tubes include 5AR4 (Sovtek & Tung-Sol), 5U4G (Sovtek), 5U4GB (ElectroHarmonix), GZ34 (Mullard), 6SL7GT (Tungsol), 6SL7GT / VT-229 (Sperry), 6F6G (Sylvania), 6L6GC STR (Tungsol), 6V6GT (Mullard), EL-34 (Mullard) & KT-77 (JJ). I’ve also have a NOS Raytheon 6SN7GT & some Shuguang KT-88-Z Treasures on order.

I generally like small combo Jazz, Acoustic Guitars, Reggae, some Pop, etc. I run a small DAC/Pre into the Inspire out to some small Klipsch 2-Ways. Sources are mostly digital streams.

 

[zackthedog]

Don't forget the 807 (with adapter socket). That's what a friend of mine likes best in his. You would want to use the 5U4 rectifier, as with a 6L6G.

 

[Kruds]

Don't forget the 807 (with adapter socket). That's what a friend of mine likes best in his. You would want to use the 5U4 rectifier, as with a 6L6G.

Thanks I'll check into that.

 

[FlaCharlie]

I recently picked up a used Inspire 6FLV (2020) and I am exploring it's capabilities. I have seen some of the various comments about 6SN7 vs 6SL7, 5AR4 vs 5U4, NOS vs New, Chinese tubes, etc. but what I am looking for are any suggestions relating to your favorite tube combinations for this specific Inspire (FLV vs KT88) variant. Any ideas out there?

My current collection of tubes include 5AR4 (Sovtek & Tung-Sol), 5U4G (Sovtek), 5U4GB (ElectroHarmonix), GZ34 (Mullard), 6SL7GT (Tungsol), 6SL7GT / VT-229 (Sperry), 6F6G (Sylvania), 6L6GC STR (Tungsol), 6V6GT (Mullard), EL-34 (Mullard) & KT-77 (JJ). I’ve also have a NOS Raytheon 6SN7GT & some Shuguang KT-88-Z Treasures on order.

I generally like small combo Jazz, Acoustic Guitars, Reggae, some Pop, etc. I run a small DAC/Pre into the Inspire out to some small Klipsch 2-Ways. Sources are mostly digital streams.

Keep in mind that any amp that promotes the use of such a wide variety of tubes in all the various positions (rectifier, input, output) cannot possibly be operating them all optimally.

Some of their operating points will be compromised. It's possible that, in order to accommodate the use of so many choices, that none of them are actually being operated optimally.

Designs like this make good sense from a marketing perspective, not so much from a performance perspective.

Just as an example, the rectifiers you list have very different voltage drops, which will result in much different voltages being supplied to the rest of the circuit. The 6L6 draws twice as much heater current than the 6V6, and the EL34 draws more than three times as much. The various output tubes also have different bias requirements and, probably, different output transformer primary loads.

 

[Kruds]

Keep in mind that any amp that promotes the use of such a wide variety of tubes in all the various positions (rectifier, input, output) cannot possibly be operating them all optimally.

Yes, I understand that point, but DH makes a point of suggesting that a lot of configurations are possible. Here is a table from his instruction manual sent with his units which pairs the various output tube "families" with suggested rectifiers. He also suggests that you can can use either 6SN7 or 6SL7 as input tubes.

Right now I am running the Tung-Sol 5AR4, Tung-Sol 6SL7GT & JJ KT-77’s. I am just curious if any other Inspire users have any other preferred combinations.

The former owner suggested I try the Sovtek 5U4, Tung-Sol 6SL7GT & Sylvania 6F6G’s (which I will try soon).

I am just looking for other ideas so I can budget my future acquisitions.

 

[FlaCharlie]

Yes, I understand that point, but DH makes a point of suggesting that a lot of configurations are possible. Here is a table from his instruction manual sent with his units which pairs the various output tube "families" with suggested rectifiers. He also suggests that you can can use either 6SN7 or 6SL7 as input tubes.

Right now I am running the Tung-Sol 5AR4, Tung-Sol 6SL7GT & JJ KT-77’s. I am just curious if any other Inspire users have any other preferred combinations.

The former owner suggested I try the Sovtek 5U4, Tung-Sol 6SL7GT & Sylvania 6F6G’s (which I will try soon).

I am just looking for other ideas so I can budget my future acquisitions.

I don't doubt they are "possible". The question remains, are any of them optimal ?

The 6SN7 and 6SL7 are both dual triodes with the same pin configuration but the rest of their specs are quite different. If you were designing an amp to use one or the other the parts used, and the resulting operating points, would not be the same.

https://tube-data.com/sheets/127/6/6SN7GT.pdf

https://tube-data.com/sheets/127/6/6SL7GT.pdf

So the amp is either designed to use one of them and subbing the other results in operating points that are way off . . . or the amp uses parts that result in operating points that are not quite as radically wrong for either tube, but neither tube is being operated correctly.

This same scenario applies to the entire amp.

As a result, once you find a combination you like, it's a safe bet that it could be made to sound much better with a few parts changes. Just something to consider if you want to get the best possible sound out of the amp.

 

[cdfac]

the 6SN7 will give your amp less gain. i'd stick with good 6SL7's -- my understanding is that's what these amps were designed flor (the 6SN7 is more Dennis saying that it won't hurt anything to try, as other folks have done it). you should try a black glass 6SU7GTY.

you might also consider trying 6CA7's for the power tubes at some point. supposedly EH makes a pretty good reproduction these days, because the original Sylvania's are pretty pricey (but worth it if you like the sound).

it's true that some of these tubes are likely being operated outside of their optimal range. that doesn't mean it will necessarily hurt them. i think of the different tube types as fixed tone settings. you might just like the sub-optimal frequency response in your system.

 

[Palustris]

As FlaCharlie has stated, the 6SN7 and 6SL7 require very different operating points. The operating point defines the Mu (amplification factor), Gm (transconductance ) and Rp (plate resistance). So as cdfac implies, if the operating points are engineered specifically for a 6SL7 it will have more "gain" than a 6SN7 at its correctly engineered operating points. If the operating points are engineered for a 6SN7, the 6SL7 might not even have much gain or it might not operate very long.

Here's the real world application: both Eric Barbour ( in Vacuum Tube Valley) and Morgan Jones (in Valve Amplifiers) determined empirically that lowest distortion for a 6SN7 or 6J5 occurred when the plate current was 6mA. Here's the real world challenge: use the Triode / Pentode Loadline Simulator (or draw out the load lines yourself) to find a 6mA operating point for a 6SL7 that does not cause the tube to self destruct.