NOS 12AX7 tubes for Cathode follower ?

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bandit2013
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NOS 12AX7 tubes for Cathode follower ?

Post by bandit2013 » Sun Jun 16, 2019 12:24 pm

Is any body running a NOS 12AX7 in the cathode follower positions in their Dual, Triple Rectifier, Road King II or Roadster?

I was looking at comments on NOS tubes at tube Depot, JAN/GE 12AX7WC and noted a comment about use in cathode follower of a Marshall. I know the preamp section is very similar to the JCM800 or 2204/2203 circuit, different but similar, not so sure on the plate and cathode voltage differences between the two different makes (Mesa Vs Marshall).

Just curious if anybody is running a NOS 12AX7 tube other than a Chinese Beijing tube in the cathode follower positions. Wanted to try something different than the JJ (Mesa) or Chinese. Not sure when the coiled heater element came into play except for Reflektor /Russian tubes (Tung Sol, Mullard, EHx, Sovtek, etc....). If there is not much to gain, I can just stick with Mesa.

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Don
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Re: NOS 12AX7 tubes for Cathode follower ?

Post by Don » Sun Jun 16, 2019 7:40 pm

Any NOS 12AX7 should work fine. The issue with the modern Russian 12AX7s that can't handle being used in a cathode follower position is that they don't meet the spec for heater-cathode voltage for a 12AX7.

bandit2013
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Re: NOS 12AX7 tubes for Cathode follower ?

Post by bandit2013 » Sun Jun 16, 2019 9:02 pm

Thanks Don,
thanks for the reply. I am well aware of the Russian tube issue, but It is always good to express that as others who may read these to be well aware of that issue. I can get some 70's JAN/GE 12AX7WC tubes but was wondering if others may have used that or similar with their rectifier amps with good results. Still debating if I want to pay that much for some of the tubes.

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Re: NOS 12AX7 tubes for Cathode follower ?

Post by 3124+ » Wed Jun 19, 2019 9:51 pm

I've been using Russian 12AX7 tubes (12AX7EH and 12AX7LPS) in Mesa Dual and Triple Rectifier Solo heads for years with no problems.

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domct203
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Re: NOS 12AX7 tubes for Cathode follower ?

Post by domct203 » Fri Jun 21, 2019 10:53 am

3124+ wrote:
Wed Jun 19, 2019 9:51 pm
I've been using Russian 12AX7 tubes (12AX7EH and 12AX7LPS) in Mesa Dual and Triple Rectifier Solo heads for years with no problems.
Are you running in Spongy mode, or using the Recto tubes instead of diodes?

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Re: NOS 12AX7 tubes for Cathode follower ?

Post by 3124+ » Fri Jun 21, 2019 1:59 pm

Bold/Diodes.

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Re: NOS 12AX7 tubes for Cathode follower ?

Post by bandit2013 » Sat Jun 22, 2019 6:00 pm

I did get the JAN tubes today. Tried them in the cathode follower positions after I tested them on the Orange VT1000. They definitely brighten up the MWDR considerably in V3 and V4, think the FX loop gained some sound levels. I went back to stock tubes with the MMDR for now. However the Roadster benefited greatly in a positive way. That woke up the gain channels even more than I thought. Just in V3 and V5. I have other tubes coming in that I plan to use elsewhere.

Have some RFT 12AX7 (CV4004, depending on how they were labeled) and EI Yugo 12AX7 (CV492) due to arrive. Not sure if the Ei tube will be suitable for cathode follower, but what about the RFT 12AX7? if they are legit and not fakes. I bought them from Tubes Unlimited.

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Re: NOS 12AX7 tubes for Cathode follower ?

Post by bandit2013 » Sat Aug 03, 2019 9:36 am

follow up on the JAN/GE 12AX7WA preamp tubes I have installed in V3 and V5 of the Roadster. No issues yet. Amp never sounded better.

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Re: NOS 12AX7 tubes for Cathode follower ?

Post by domct203 » Mon Aug 26, 2019 6:00 am

FYI-
I tried an RFT in V3 of the Roadster, lasted about 5 seconds then I lost all sound on Ch 3&4. Put a Chinese back in and all is good.

Last time I used the RFT (not in a cathode follower spot) it worked, so I know it was a good tube.
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Re: NOS 12AX7 tubes for Cathode follower ?

Post by domct203 » Tue Aug 27, 2019 5:33 pm

I tried a JAN / GE 12AX7WA in V3 as well, I felt it made the amp a bit stiff, and a bit ‘too much’ in the upper mids/treble. My Roadster is modded, and is a bit brighter in the upper mids already.

So far my favorite V3 tube is the Ruby HG 7025 (Chinese). I have the same in V5.

Going to try the JAN / GE in V5 next. If I’m not tickled there I’ll give the PI a go with it (Sovtek LPS now).
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Re: NOS 12AX7 tubes for Cathode follower ?

Post by bandit2013 » Sun Sep 22, 2019 12:45 pm

Still have the JAN/GE 12ax7 tubes in V3 and V5. Also have been running this amp more since the changes. JAN/GE 5751 in V1, Mullard reissue 12AX7 in V2 and phase inverter. Stock tube in V4 and stock power tubes. Roadster is un-modified. I could not be happier with the amp. I did try the RFT in V1 and or V2 and felt that was too much for me. The Mullard in V2 and JAN 5751 in V1 keeps the response tight but not like you would get with the Multi-Watt Dual Rec. I personally found the chines tubes in V3 to be on the bright side. The stock complement of preamp tubes was just too muddy when running the Modern voice on CH4. I have not experienced any issues to date with the JAN/GE 12AX7 in the cathode follower positions. It does affect the tone somewhat so perhaps it is the 5751 I have in V1 is what is working for me. The Tung Sol 12AX7 in V1 was changing what I liked about the amp too much. Still not a bad choice but I much prefer less drone so what I have in the Roadster right now has satisfied me to enjoy playing through the amp.

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