Phase Inverter tubes can wear pretty quickly and if not replaced when they're ready to be it can affect your tone more than you think. If the Power tubes of your amp determine the flavor and overall tone then the PI tube plays a huge part as it is the last stop in the preamp section before it is sent to the power tubes. Since every channel in your amp sees this tube it's a good idea to play around with all the tone possibilities of different tube types and brands.

Power Tubes: JJ 6CA7s
1:35 - JJ ECC83s Gold Pin
2:03 - JJ ECC803s
2:32 - Tung Sol 12ax7
3:01 - Telefunken ECC83 Gold Pin

The master volume is maxed at 100% to get the most drive from the phase inverter tube to an ear bleedingly loud level even with headphones on (notice the camera shaking). There is virtually no pre or post production. Sound was captured with my preferred blend of an Audix i5 & sm57.

Verdict:
The JJ ECC83s Gold Pin is the thickest sounding tube of the bunch and JJs usually are. It has great midrange response in my H&K and has smooth breakup. The JJ ECC803s
is the brightest of the four tubes and has the least low end response. It took a lot of the punch out of the amp and you can hear its breakup isn't as smooth as the other tubes. The Tung Sol 12ax7 has more of a thicker tone but doesn't have the midrange response that the JJ ECC83s does. It sounds more mid-scooped and warm and the breakup is a little crisper than the JJ ECC83 Gold Pin. The Telefunken 12ax7 Gold Pin has a sonic response in this amp somewhere between the JJ ECC83 and the 803s. It has the midrange of the ECC83 but the low end response is weaker and it has the crisp high end response of the ECC803 but not as much and is much smoother.

Thanks for watching.

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