Using a 12at7 in place of 12ax7 in dual rectifier

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MrBoggles
Mark I
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Joined: Thu May 29, 2008 10:44 am
Location: Perth, Australia

Using a 12at7 in place of 12ax7 in dual rectifier

Post by MrBoggles » Tue Jan 24, 2017 5:24 am

Just wondering if anyone has experimented with using 12at7's in a dual rectifier..
Either replacing V1,2&3 or replacing just one..
Given they are a lower output,
I'm wondering if they would tame the fizz and gain or just push it back further requiring you to turn up the dials?
Any thought or experiences?
Mesa DR, TC G Maj, Berg F/Sw, PRS Cu24, EJ Strat, Ibanez RG7620 w EMG 707 781, fender HRDlx

bandit2013
Triple Recto
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Re: Using a 12at7 in place of 12ax7 in dual rectifier

Post by bandit2013 » Sat Feb 04, 2017 8:50 am

Yes, I have used an NOS (RFT as well as JAN-GE) in my Roadster. I only ventured into the V1 or V2 positions. Never try a 12AT7 in a cathode follower circuit as it will not work well. I was impressed with a NOS JAN version of the 5751 in V2. Actually sounded much better than using current 12ax7's.

MrBoggles
Mark I
Posts: 28
Joined: Thu May 29, 2008 10:44 am
Location: Perth, Australia

Re: Using a 12at7 in place of 12ax7 in dual rectifier

Post by MrBoggles » Wed Oct 24, 2018 10:25 am

Thanks for the reply bandit,.. Last year.. Oops.. It's been a while on here..
I ended up changing V12&3 to At7's and it tamed the amp pretty nicely.. It's a subtle change didn't really drop the volume much but tamed the gain a little.. I get a little more range from the gain before it hits the fizz spot..
Still frustrating though.. I've now tried different power tubes, preamp tubes, pickups, volume settings, tone settings, mic placements.. and still when the gain control gets to the point where any sort of usable gain and sustain gets introduced, the high frequency fizz comes in at the same time.. I'm now thinking it must be a bias thing..
Mesa DR, TC G Maj, Berg F/Sw, PRS Cu24, EJ Strat, Ibanez RG7620 w EMG 707 781, fender HRDlx

bandit2013
Triple Recto
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Joined: Fri Feb 22, 2013 7:31 am
Location: North Carolina

Re: Using a 12at7 in place of 12ax7 in dual rectifier

Post by bandit2013 » Sat Oct 27, 2018 9:30 am

I have not done this with the Roadster yet (however I have had done so but did not impress me so I forgot about it), but have with the JP-2C. 12AT7 in the phase inverter position. Another tube you can try out is the JAN/GE 5751. Has more gain than a 12AT7 and is closer to the 12AX7 characteristic just lower gain.

I would also keep one of the tubes in V1 or V2 as a 12AX7 and see if the 12AT7 in V1 or V2 makes much of a difference. Stock tube in the cathode follower position is best. I have tried the Chinese tubes there as well. I actually preferred the character when using a JAN/GE 5751 in V2 and a stock tube in V1 (reference to the Roadster). I think the standard Dual recto is a bit different than the Roadster.

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