Tube Rolling w/Crack

Dr. Toobz · 760982

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Offline N72826

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Reply #2445 on: January 30, 2024, 06:32:35 AM
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



Offline Doc B.

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Reply #2446 on: January 30, 2024, 06:52:28 AM
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.

Dan "Doc B." Schmalle
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Offline N72826

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Reply #2447 on: January 30, 2024, 07:09:08 AM
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. ;D 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. 8)



Offline Paul Birkeland

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Reply #2448 on: January 30, 2024, 08:39:24 AM
I'm getting 62.4 OA and 75.5 OB
This is a near-new 12AU7.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Tom-s

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Reply #2449 on: January 30, 2024, 11:42:55 AM
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.



Offline N72826

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Reply #2450 on: January 30, 2024, 01:03:07 PM
This is a near-new 12AU7.

Oh wow! I expected you to tell me it only has a month to live lol.  ;D
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  :D



Offline 2wo

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Reply #2451 on: January 30, 2024, 05:46:28 PM
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

John S.


Offline watonwak

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Reply #2452 on: May 05, 2024, 09:34:31 AM
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?

Beyerdynamic DT 1990 Pros | Crack + Speedball + Alps Blue Velvet + Panasonic PP Output Caps


Offline Paul Birkeland

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Reply #2453 on: May 05, 2024, 10:26:21 AM
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.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline watonwak

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Reply #2454 on: May 05, 2024, 11:22:08 AM
Thanks Paul, good to know!

Beyerdynamic DT 1990 Pros | Crack + Speedball + Alps Blue Velvet + Panasonic PP Output Caps