help/clarification for a new guy [resolved]

squirrelworks · 1473

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Offline squirrelworks

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on: July 07, 2015, 09:11:34 AM
Howdy all!
(Disclaimer: I am completely new to tube amplifiers... This question may have been asked, but my search-fu completely failed me)
So, I have a 1yr old Crack, and I've recently upgraded the tubes to an RCA 6AS7G power tube, and a Raytheon 6FQ7. The power tube warms up just fine, and the stock 12AU7 works as well. The 6FQ7, however, does not.

How does one go about testing a tube? Does this have anything to do with the following on the specs page "with a little care taken to do the proper tube socket wiring for the heater pins", and if so, how do I go about verifying that everything is correct?

Any assistance would be greatly appreciated.
« Last Edit: July 07, 2015, 02:30:59 PM by Caucasian Blackplate »


Offline fullheadofnothing

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Reply #1 on: July 07, 2015, 09:29:08 AM
The 6FQ7 would require rewiring the socket to work.

Joshua Harris

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Offline galyons

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Reply #2 on: July 07, 2015, 09:35:28 AM
The pin out is different for the 6FQ7. Although it is a good replacement, (6SN7 in 9 pin small bottle), you will need to make some simple changes to the heater wires.  The 12AU7 uses a 9A Base and the 6CG7/6FQ7 uses a 9AJ Base. The only difference is the connection of the filament voltage.

In the 9A, (12AU7), base one leg of the heater voltage is connected to the number 4 and 5 pins and the other leg is connected to the number 9 pin. To convert to the 9AJ base, (6FQ7), simply move the 4 and 5 leg to the number 4 pin and move the number nine leg to the number 5 pin.

From your post, I am assuming that you didn't build the Crack.  If you are not comfortable around tubes, high voltages and soldering, I suggest putting the 12AU7 back in and enjoying the Crack for awhile.  Then, if you want to do some mods, after you are comfortable, it is a pretty easy, and reversible process.

Cheers,
Geary

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Offline mcandmar

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Reply #3 on: July 07, 2015, 09:42:20 AM
http://www.ebay.com/itm/1pc-gold-plated-6cg7-6fq7-TO-ECC82-12AU7-tube-adapter-6-3V-heat-/201083377532?

Buy one of these adapters as they work perfectly.  Personally i much prefer the 6CG7/6FQ7 over any 12au7 variant, and from memory there is a thread here somewhere about modding the speedball board to run the tube optimally.

M.McCandless

Offline squirrelworks

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Reply #4 on: July 07, 2015, 09:50:03 AM
Thank you, both.

I actually did build the Crack, but it's my first high voltage/tube build, and I wasn't sure where to begin. I figured the fix would be a relatively simple one, just needed the obvious pointed out.

Thanks again.


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