Just ordered $500 worth of tubes

[JazzRules]

15 GT 12AX7-M
pair Philips NOS JAN 7581A (6L6 family)
pair SED 6L6
pair NOS GE 5751 (lower gain 12AX7)
1 NOS GE 6072 (12AY7)
1 NOS GE 12AY7

from KCA NOS.


Figure I'd retube the Mark IIC+, Mark IV and Formula Pre.

 

[screamingdaisy]

Nice.

The way I setup my amp chews through tubes, so I can't be bothered with NOS.

 

[Grandor]

*ouch* on that price.

Let us know how they sound!

 

[Boogiebabies]

Wait until half of those 12AX7M's go bad !!!!

I have had about 8 out of 18 go down from the first three batches.

The 7581A's are a 35 Watt tube, so when you bias them take that in to
consideration. A great choice. I run them in the SLO 100 and any Simul Boogie I can.

 

[JazzRules]

Wait until half of those 12AX7M's go bad !!!!

I have had about 8 out of 18 go down from the first three batches.

The 7581A's are a 35 Watt tube, so when you bias them take that in to
consideration. A great choice. I run them in the SLO 100 and any Simul Boogie I can.

Hopefully they all came from a bad batch. I haven't heard anything along those lines yet. I might have shelled out some serious dough on some NOS RCAs or Mullards if I had known, instead of the GTs.

So far so good with the GT 6L6GEs. A bit microphonic though, but very nice tone from the IIC+.

 

[JazzRules]

Wait until half of those 12AX7M's go bad !!!!

I have had about 8 out of 18 go down from the first three batches.

The 7581A's are a 35 Watt tube, so when you bias them take that in to
consideration. A great choice. I run them in the SLO 100 and any Simul Boogie I can.

"so when you bias them" ??????


I think you've been visiting other amp websites. Boogies with adjustable bias?

Boogie tubes have to be "plug and play". No big deal to screen some tubes.

 

[Boogiebabies]

Ahem, when you put a 35 Watt tube in and it draws 18ma at -56 volts it is
Not running anywhere near the tubes potential. In an amp that has 480 volts at the plates, these would need to draw 54ma to be at 75% MPD.
I bet they didn’t tell you that when you bought them. If you do not get a 7581A that draws enough natural plate current you will be in grainy, notchy crossover land. For example, a GT 6L6GE in a #5 and a GT 6CA7GE in a #6 will draw around 22ma-25ma at 480 plate volts in a Simul-Class IIC+. This is 40% of MPD. Most tubes do not appear to smooth out until 60-70%. I have been using a Svet 6L6 and Svet EL34 from Triode in a 32-34 range. They bias up at around 35ma. Very smooth.
Learning about these things is how you avoid bad sounding tubes and how to get around the plug and play mentality. Hopefully you are used to crossover distortion and rationalizing that the high dollar tubes you just bought sound great.


Good luck to you.

 

[JazzRules]

Ahem, when you put a 35 Watt tube in and it draws 18ma at -56 volts it is
Not running anywhere near the tubes potential. In an amp that has 480 volts at the plates, these would need to draw 54ma to be at 75% MPD.
I bet they didn’t tell you that when you bought them. If you do not get a 7581A that draws enough natural plate current you will be in grainy, notchy crossover land. For example, a GT 6L6GE in a #5 and a GT 6CA7GE in a #6 will draw around 22ma-25ma at 480 plate volts in a Simul-Class IIC+. This is 40% of MPD. Most tubes do not appear to smooth out until 60-70%. I have been using a Svet 6L6 and Svet EL34 from Triode in a 32-34 range. They bias up at around 35ma. Very smooth.
Learning about these things is how you avoid bad sounding tubes and how to get around the plug and play mentality. Hopefully you are used to crossover distortion and rationalizing that the high dollar tubes you just bought sound great.


Good luck to you.

"32" was written on both boxes.

You'd be more convincing to this EE if you had some load line calculations to back up your claims.

 

[Boogiebabies]

Oh, I see we have an EE geek sniffing cork with that load line hockey.
Well, if I were a hooligan I would tell you to cram the cork you sniffed in your
tradesmans entrance. It also took you a month to craft a witty retort.
WTF !!!

I will scope them all for you and then report back on the load line chart.