NOS 12AX7 tubes for Cathode follower ?

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bandit2013

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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.
 
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.
 
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.
 
I've been using Russian 12AX7 tubes (12AX7EH and 12AX7LPS) in Mesa Dual and Triple Rectifier Solo heads for years with no problems.
 
3124+ said:
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?

http://www.forum.grailtone.com/viewtopic.php?f=4&t=25102&start=16
 
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.
 
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.
 
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).
 
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.
 
Utilizing NOS (New Old Stock) 12AX7 tubes in a cathode follower enhances the vintage allure of audio systems. The NOS tubes, known for their rich harmonics and character, can impart a warm, classic sound. This combination of a time-tested design and premium components elevates the cathode follower's performance in high-fidelity audio applications.
 
Utilizing NOS (New Old Stock) 12AX7 tubes in a cathode follower enhances the vintage allure of audio systems. The NOS tubes, known for their rich harmonics and character, can impart a warm, classic sound. This combination of a time-tested design and premium components elevates the cathode follower's performance in high-fidelity audio applications.
Welcome to the forum.

My $0.02 on NOS/VOS.

I’ve been down the NOS rabbit hole many times, and any ‘benifit’ from NOS tubes really depends on the amp’s circuit. Most times it is a very negligible difference that gets lost in the mix of a live band. IMO the benefit of NOS tubes in cathode follower use is their ability to handle the higher voltages used in that position yet remain their composure.

Guitar amps (and their speaker cabinets) are far from high-fidelity audio systems, they are a narrow bandwidth system with a lot of clipping stages, they work in a specific frequency range designed to compliment the guitar’s frequency range and blend with other instruments and their frequency ranges.

This is quite a difference from a full bandwidth, ultra low distortion audio amplifier that is designed to be played in isolation, which will reveal these intricate changes in sound, especially with a great set of headphones.

If someone is happy with using NOS tubes in their gear that is really all that matters. But for me and my experiences, I’ve been through dozens of NOS/VOS tubes in multiple amps over the past few decades, and of all the amps I currently own and play, only one has an NOS tube still in it, my TC-100.

I’ve still got a box full of them…

IMG_0460.jpeg


Dom
 
It can be hit or miss when it comes to NOS as they are not tubes you find at every resource like you would get with current production. The added cost due to limited resources, is it worth the risk?

I had bought a few (NOS): RFT12AX7 and some EiCV492 (these were commonly used as Mullard counterfeit tubes, they are good tubes though). Neither of these ever made its way into any of the Dual Rectifiers I have. They found their home in two amps, Royal Atlantic RA100 Head and Combo. RFT in V1 and Ei in V2 and Ei in the phase inverter. Rest remained the same stock tubes. I will say the Hi gain and lo gain never sounded better. Both amps completed with NOS Mesa STR442 SED =C= EL34. I bought a few sets of those, also had some I bought from the Tube store just when Svetlana Electron Devices stopped making the 6L6 and EL34 tubs. Not the same tube as the new production Svetlana as they are made by Reflektor (New Sensor that makes the TungSol EH, and so on).

Never thought about using the RFT in the Roadster, if I did and may have done so, it may not have been that rewarding or ended up with too much low end. The RFT has an interesting characteristic, when used in a typical triode circuit with 100K plate resistor, it will sound very similar to the Mesa 12AX7 (JJ ECC83s). However, when it gets driven into hard clipping it takes on a new characteristic with an aggressive tone that is not the same as the JJ ECC83s. Sub-harmonic content is evident. It emulates the cold clipper circuit used in the Dual Rectifier usually in the V2 position. Enough said. Different amp.

I had in my possession 10 of the Mesa 12AX7 tubes from 1990. Tube removals from the Mark III I held onto when I was changing all tubes every 8 months. The preamp tubes were all in good shape, some with less than 3 months and some with a bit more. Every single one of them tested really good. Where to use them? A few years back, Doug's tubes and some inventory of the Ruby Square Foil getter tubes of that era, claimed not to be used in the V1 position but will work everywhere else. Bought 10 of those. Tried them mostly in the Mark V90 as I was struggling to get to bond with that amp. I gave up and installed all original Mesa (JJ ECC83s) tubes in the amp as I was considering selling it. Tubes on the left are the Mesa branded 6N4-J Military grade Chinese Beijing tubes. Tubes on the right are the one's brokered through Ruby Tubes (trade name used to sell the goods, not the manufacturer)
20180624_070447.jpg


I recently cleaned up the Roadster, chassis removal, inspected around each preamp tube socket for aluminum dust caused by the rotation of the tube shields. That usually happens when installing the shields while the chassis is in the head shell. If I pull the chassis out, and change tubes then, no dust.

V1 = Mesa branded 6N4-J Beijing tube, the phase inverter has a Mullard reissue 12AX7 long plate and the rest of the tubes except for the reverb (stock mesa tube) are the Ruby Beijing tubes.

That worked out really well. Still running with the STR440 tubes. Roadster is much tighter in tone, CH3 is closer to the MWDR character, and for the first time I was able to run a 7-string guitar without any drone or mud. That was epic.

I have tried the Chines 7025, not sure what factory makes them, brokered through Ruby tubes. They would be equivalent to Groove Tubes. Not a tube manufacturer, more of a broker/distributor just like Mesa branded tubes are not manufactured by Mesa, they are certified and tested/ approved by Mesa. The Sino 7025, or in western culture, the Chinses 7025 could be made by Psvane, Shuguang, Linlai, or Guiguang (now owned by Psvane). The word Sino is not a company name, it is a reference. Sino means Chinese.

I think I experimented with them a couple of years ago. However only with V3 and V5 in the Roadster.
 
I'm not sure you'd be getting the best "mileage" out of an NOS tube in the cathode follower position, though it does only use one triode. I generally want "expensive" tubes in locations that I'll be able to hear their desirable overdrive characteristics, and a cathode follower is a different type of circuit. I think it is used mainly to drive / buffer the tone stack.

Looking at schematics for the OG rectifier, the V3B cathode follower is putting 415V on the plate and 216V on the cathode. Both of those exceed the design parameters of the 12AX7, which is 330v on the plate and 200V cathode to heater voltage, which also is affected by whether it's positive or negative. You need a solid tube to withstand that type of use, which NOS tubes can usually do easily. The spiral filaments on the new production Russian tubes cannot handle running over spec, which is why they burn up.
 
Precisely. And that’s the schematic voltages when the amp is expecting 117VAC. Now with modern AC voltages, those numbers will be even higher.
 
The issue is generally with the voltage difference between the heater and the cathode. The other problem arises in Songy mode with the reduced voltage. The tubes cannot handle it but do not recall the side effect of what happens.

Some tubes cannot handle the specified voltage between the cathode and heater element. Some can exceed it. Chinese tubes like the 6N4-J or the JJ ECC83s will operate fine with the DC coupled cathode follower that is used as the tone stack driver. The cathode follower used in the FX send is not as damaging since it is not a grid to high voltage connection to the DC supply. That circuit can also degrade tubes but will take longer I suppose.

Mesa used the 6N4-J tube during that time period the Rectifier amps came out. Mark III from 1989 was equipped with them. I have used them as that was all I could get from Mesa at the time. Before that it was Tungsram tubes. Not sure when the inventory dried up on the Chines versions. I know the 12AT7 were Shuguang but they were constructed differently than the Military grade Beijing Square Foil getter tubes from the 1990s. Not as stable.

Anybody know here that Mesa memo information got too? I did not see it when I was looking a while back.
 
The issue is generally with the voltage difference between the heater and the cathode. The other problem arises in Spongy mode with the reduced voltage. The tubes cannot handle it but do not recall the side effect of what happens.

Basically, your amp gets very quiet, as the tubes don't get hot enough for proper emission. I had some spiral filaments tubes in my Tremoverb and could not figure out for the life of me why it got so quiet, or why my reverb was totally dead in spongy mode. Then I noticed if I started in "bold" and went to spongy, it was fine for a while. Then my caveman brain finally realized it was because the plates in the preamp tubes were actually at proper temperature for a while. I replaced the reverb driver and phase inverter and all was well.

So yeah, not sure it really "damages" anything, but the spiral filament tubes, while quiet, were not designed to the same conservative specifications that the traditional filament tubes from Sovtek were. They don't tolerate high filament to cathode voltages, and don't like under voltage conditions. I don't recall hearing of people having issues with the workhorse Sovtek 12AAX7WA/B/C in these applications. I definitely like the tubes, but they can be finicky depending on which amps you use and how they are designed.
 
Perhaps that was the cut-out issue. I only read the memo once so my recall is not all that good on the subject. Oh wait, part of it was cut-off. Found it again.

edit (I deleted the attached image of the document as it was marked with confidential, did not want to risk any legal action).
 
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Perhaps that was the cut-out issue. I only read the memo once so my recall is not all that good on the subject. Oh wait, part of it was cut-off. Found it again.
YEP. I wasn't aware of that second part, so I had all the Russian tubes in the correct spots, but wondered why my Tremoverb was so quiet and had no reverb in spongy mode. Mystery is solved now.

However, I have also seen some Mesa tubes labeled "Russian 2", which I assume are different than the EHX / RUSS / Russian marked tubes?
 

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