What a difference a tube makes!

[Thatch_Ear]

I was messing around with amps and had warmed up a SE 6BQ5 stereo I built to get it back in line.
Sounded good but as I was picking up tubes and stuff off the desk so I could put them up one of them was an RCA 5751 black plate and even though it had lower test numbers than the Mullard 12AX7 that was in there I decided to roll them.
First of all was the shock of higher gain and then everything just bloomed. Cleaner, quieter, and a real tightness that wasn't there before.
Jazz sax, Josh Grobin, Diane Reeves and now Steely Dan. Amazing how loud 3 watts will get these old Stromberg Carlson coax drivers going.
I definatly need to get a new potentiometer for the gain.
This is like getting a whole new amp! Woopee! Now for some rectifier and power tube switching!

[MikE]

That's the military-grade version of the 12ax7. Not familiar with the 12ax7 family I did find similar results with the 5814 and 5963 in place of the 12au7 or 12at7. In fact, the very best "12au7" I found while rolling tubes for three (3) years in my VAC were the 1953 Hytron / blk-plate / d-getter 5814's. I read somewhere (after the fact) that they are one of the very best 12au7s. All I know is I loved that tube (still have them) and hope to use them again in the future.

I don't seem to have the listening impression notes handy but if memory serves, the reason for the preference had to do with a degree of "rightness" with that tube that made all other input tubes I had sampled in the amp sound like distortions. I found many tubes I enjoyed, some that were highly-touted, but I always found myself eventually listening to the tube, and not the music. With the Hytron 5814, that effect was drastically reduced. It did everything well, if not everything as well as some tubes. The Mullard's still had more air surrounding images and a greater impression of venue atmosphere or ambience. This tube reminds me of the current output tube I use - the 45 - and while the result or effect is even greater with the 45 the two same samilar presentations.

MikE

[Thatch_Ear]

I got my RCA recieving tube manual out and double checked the pinout, pulled a Japanese 5U4 and started trading out 5V4s. A bit of a hum audible with no input. 2 RCAs the same, a Syl Jan and the hum is still there but you have to listen close.
The bass seems a bit fuller but still has the snap to it. This is a NOS so I am going to run it a day or 2 and then get out some US made 5U4s and see where that goes.
The 5V4 would be preferable because of the soft start but better sound will win out.

[hurdy_gurdyman]

This looks like a good place to mention an experience I recently had in tube substitution. In my old Heath W5-M I changed the wires around on the 12AU7 sockets and converted to 6CG7's. This was one of the biggest improvements in sound quality I've ever heard in an amp mod. Makes me wonder why they ever bothered to make 12AU7's. Wonder if there is a similar conversion that can be done for 12AX7's.
Dave:)

[Rob]

Originally posted by hurdy_gurdyman
Wonder if there is a similar conversion that can be done for 12AX7's.
Dave:)

Dave,

I think the pinout is different but I've heard the 6DJ8 is a very good audio twin triode. It is listed as a special high quality type for critical applications in the GE tube manual. Also consider the 12AY7. This is listed as a specially low microphonic twin triode.

I have no experimental experience yet with either. I have a pair of NIB GE 6DJ8's to play with on my desk recently acquired in a bulk tube purchase. Inside they look completely different to the normal 12AU7, 12AX7, 12AT7 series'.

Rob

[hurdy_gurdyman]

Thanks for the tip about 6DJ8's. As for 12AY7's, these have much less gain then a 12AX7, and may not work without some circuit mods.
Dave:)

[gonefishin]

What a difference a tube makes!

yes indeed!!!!!!!!!!!!!!