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Post subject: Re: DRRI retubed and rebiased
Posted: Sun May 01, 2011 2:39 pm
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cedarblues wrote:
My RCA 6V6GTA are rated at 14W, I run those 22-23 mA.


+1

Very similar to my vintage gray-plate GE's.

Arjay

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Post subject: Re: DRRI retubed and rebiased
Posted: Sun May 01, 2011 3:13 pm
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cedar, you mentioned your mullards were microphonic?
after i checked the bias, i tested it, i do hear a slight rattle :? , did you send them back?

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Post subject: Re: DRRI retubed and rebiased
Posted: Sun May 01, 2011 3:22 pm
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A rattle is different than a microphonic tube...

Do you know which tube it's coming from?

Here's an example of a microphonic tube

http://www.youtube.com/watch?v=QM2qWZYbInI

If I tap the Mullards, they're way too noisy, even if I touch the amp they're noisy!


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Post subject: Re: DRRI retubed and rebiased
Posted: Sun May 01, 2011 6:25 pm
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I localized the rattle snake, it was a tungsol 12ax7,
I removed each 12ax7 and connected in scxd, sure enough
I thought it was a diamondback rattler.

I wonder can I exchange it?

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Post subject: Re: DRRI retubed and rebiased
Posted: Sun May 01, 2011 8:04 pm
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Can't buy anything new that's guaranteed to work! More reason to buy NOS :)

Where do you get yours from? I got 'em from the tube store, they have a 90 day guarantee, so I will be sending the Mullards back.


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Post subject: Re: DRRI retubed and rebiased
Posted: Sun May 01, 2011 9:55 pm
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Tube depot, yeah I'm looking into RCA nos 12ax7, shopping
Around

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Post subject: Re: DRRI retubed and rebiased
Posted: Sun May 01, 2011 11:37 pm
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RCA made some of the finest tubes ever sold but I wouldn't limit my search to only one brand. Most of the mil-spec JAN's are excellent glass as well -- especially those from Raytheon, Westinghouse, and GE. JMO.

Arjay

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Post subject: Re: DRRI retubed and rebiased
Posted: Sun May 01, 2011 11:59 pm
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cedarblues wrote:
Congrats on the new tubes! Hope you had better luck with those Mullards, I just got 2 of them for my DRRI and both were microphonic :(

For 6V6 at 420 I wouldn't go higher than 20 mA, that should be right at 70%. My RCA 6V6GTA are rated at 14W, I run those 22-23 mA.

Forgot to add the link to the Weber bias calculator...

http://www.webervst.com/tubes1/calcbias.htm

6V6 (12W):

12/420=0.028
.028X.70=0.02 that's 20mA.

6V6GTA (14W):

14/420=0.033
.033X.70=0.0233 that's 23.3 mA.


See, this is where I am confused a little right now. Because some people are also treating the non GTA (NOS or new production) 6V6s as 14W tubes. (I.e. tJJs,the EH's or the RCA 6V6GT's)

But the difference in a 420V setting, as one can see above, is 3.3 ma!
Should I treat all my NOS GTs and new production tubes as 14W tubes and bias accordingly?

Thanks,
Reverend


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Post subject: Re: DRRI retubed and rebiased
Posted: Mon May 02, 2011 12:29 am
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thereverend wrote:
But the difference in a 420V setting, as one can see above, is 3.3 ma!
Should I treat all my NOS GTs and new production tubes as 14W tubes and bias accordingly?


That's been my take with 6V6's. Unless it was some low-perf import or the old metal-cased tubes as found in the K&F's or the early TV-front tweeds.

Arjay

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Post subject: Re: DRRI retubed and rebiased
Posted: Fri Jul 01, 2011 2:41 pm
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Just an update, I replaced v2 tungsol 12ax7 for TAD 7025
I actually like this tone better, to my ears, the highs with
Ts sounded a little harsher with Texas specials than the tad.
Also tad sounds clearer more articulate IMHO .
Would like to hear some opinions, maybe I'm crazy.

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Post subject: Re: DRRI retubed and rebiased
Posted: Sat Jul 02, 2011 10:50 am
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Nope, you're not crazy, I like my TAD 7025 in my DRRI :) and I'm still running TAD 6V6 in that amp and I'm very happy with the tone. Even my SR has TAD 6L6 in it, but I prefer the Mullard RI in V2 for the SR.

BTW, I did get the Mullards replaced from the tube store, much better.


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