Tube Rolling w/Crack

[N72826]

If you have a Speedball in your Crack, what are the OA and OB voltages on the small board with that tube?  That can be used as a bit of a test for whether the 12AU7 is near the end of its life or is relatively fresh.

I'm getting 62.4 OA and 75.5 OB

[Doc B.]

Try a TungSol 12AU7 for a little more bass weighted sound. Don't buy $50 to $500 tubes until you buy several less expensive 12AU7s of different brands to get a feel for what you want. More educational, more bang for your buck.

[N72826]

Try a TungSol 12AU7 for a little more bass weighted sound. Don't buy $50 to $500 tubes until you buy several less expensive 12AU7s of different brands to get a feel for what you want. More educational, more bang for your buck.

Thanks Doc! That's really solid advice especially for an impulsive buyer like me. I've seen how much you advise against dumping too much money into this hobby just for the sake of it, so I just want to say I really respect your honesty.

[Paul Birkeland]

I'm getting 62.4 OA and 75.5 OB

This is a near-new 12AU7.

[Tom-s]

Oh also, my ECC82 is labeled K63 D9R, just noticed that recently as I was swapping the tubes out. Not sure what to make of that but I'm going to look around and determine what I even have because the ebay listing didn't specify the year or anything really. I think 63 means 1963 but I will set aside the speculation lol

The K63 D9R is a Philips date code.
K6 = ECC82 with 3 being the revision code.
D = The factory code for the Philips factory; Hamburg (Valvo) in this case.
9 should be 1959 but your R is probably a misread B -> feb. R doesn't exist in that years Philips code.


Here's the data to decipher a Philips factory code: https://frank.pocnet.net/other/Philips/PhilipsCodeListAB.pdf

As PB said. Is that the test result with the Valvo in the Crack? That's really good actually.
The best tester at the end of the days is the circuit the tube is used in. If it works, it works.

[N72826]

This is a near-new 12AU7.

Oh wow! I expected you to tell me it only has a month to live lol. 
And that wasn't intended as a jab at how it sounds, it sounds perfectly fine. I just felt it was impossible to get one of these that isn't on its way out for so cheap. Since I made my first post, the hiss has not only gone down significantly to where I'm not fixating on it, but now it's balanced and not primarily in the left channel which was way more distracting.

9 should be 1959 but your R is probably a misread B -> feb. R doesn't exist in that years Philips code.

As PB said. Is that the test result with the Valvo in the Crack? That's really good actually.
The best tester at the end of the days is the circuit the tube is used in. If it works, it works.

No wonder I couldn't find anything when trying to google it. I did mistake the B for an R in D9B. Thank you for identifying the tube, and yes those readings are from the Valvo 

[2wo]

A lot of these tubes have been sitting around for years and years since they were last run, if at all. You need to let them run for a good while before you know what you have... John

[watonwak]

This is a near-new 12AU7.

Any tips on deciphering these readings? what values indicate a good vs bad tube? also, can we do the same to the 6080 to check its health?

[Paul Birkeland]

Any tips on deciphering these readings? what values indicate a good vs bad tube?

With the Speedball installed, the stronger a 12AU7 is, the lower the plate voltage will tend to be (within reason).  A 12AU7 that's trending towards death will rise up more toward 100V.  This is a lot harder to do with the 6080 since the circuit is directly coupled.

[watonwak]

Thanks Paul, good to know!

[greenneedle]

Hello there.  quick question.  I have some tubes I bought as 6067 Brimar yellow Ts but can't confirm whether they are indeed 12AU7 compatible or not.  Will it hurt my crack at all to test them in the AU7 spot?  And if they are not AU7 but are actually AT7 or AX7 equivalent what should I expect to hear or find if they are indeed not AU7 equivalents?  Say I listen to an AU7 in that spot and then at the same volume what resulting difference would an AT or AX sound like.

Its not that I want to put AT7 or AX7 in that spot, just that I want to test them to see if they are AU7 or not.

[Paul Birkeland]

Hello there.  quick question.  I have some tubes I bought as 6067 Brimar yellow Ts but can't confirm whether they are indeed 12AU7 compatible or not.  Will it hurt my crack at all to test them in the AU7 spot?

Do you have the Speedball?  You'd want to see where the voltages land on terminals 1 and 5 to really know how compatible they are.

[greenneedle]

Yes its speedball and choke and crees and mundorfs etc. lol.

I tested them with the stock 6080 in and my least used headphones just in case.  They are about 25% louder than normal 12AU7s!  So I guess that solves it.  There is only one seller on the net and that is on reverb that even mentions the 3976 yellow T identification number.  They are selling them as 12AT7.

The seller I bought from swears blind they are 12AU7 but the ears don't lie   They sound OK though, just louder.

[Paul Birkeland]

They are about 25% louder than normal 12AU7s!  So I guess that solves it. 

They have the same Mu, so there shouldn't be a difference in volume.

What voltages are you observing at terminals 1 and 5?  That is what you'd want to check before listening to them.

[greenneedle]

They have the same Mu, so there shouldn't be a difference in volume.

What voltages are you observing at terminals 1 and 5?  That is what you'd want to check before listening to them.

Are you meaning testing the terminal on the back of the noval socket while it is running?  I will try an check that tomorrow.  Both of these yellow T Brimar tubes is definitely an noticeably louder though.  I tried 4 12AU7s all very similar volumes but the yellow Ts are definitely noticeably louder.  Not moving the volume knob at all between changing tubes.  It isn;t just the "brimar effect" as I tried a CV4003 Brimar as well as a '55 square getter 12AU7 and they are both similar volumes lower than the yellow Ts (and lovely sounding )

Not a problem though.  I didn;t pay much for them.  I'll use them in my guitar effects instead.