Tung-Sol RI 12AX7 vs Cathode Follower?

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I think I remember reading that Tung-Sol RI's don't like being used in a cathode follower type circuit (ie, Dual Recto). Just want to confirm if this is correct or not?
 
don't know?

Sovtek LPS is the one i've heard is a no no.
 
Are you sure about EHX? They used to come stock in Rectos before they switched to JJ. They (EHX) were also my plan B since the amp is currently full of Shuguangs and I'm not a fan of JJ preamp tubes.
 
Yeah I was under the impression that no new sensor tubes could be used in those spots. Only Chinese or NOS.
 
Crap....

Just to confirm, the V1 in a Recto isn't a cathode follower?

High gain JJ vs Chinese.... What will give me better results?

I'm currently loaded with a EHX in the V1 and Mesa SPAX7 everywhere else. From what I understand, the SPAX7 is a Chinese tube. They've been in my Recto since I traded for it last year (or maybe it was the year before... it kind of blends together). Anyway, the gain seems a little too polite compared to my previous Recto so I'm kind of eye-balling the preamp tubes. EHX were like little fuzz bombs going off in my preamp... last time I switched to JJs it cut the gain big time and darkened the whole amp up way too much.
 
Mesa says to use Chinese tubes for the cathode follower.
 
Thats what I heard:

The Tung-Sol 12AX7 is a really nice tube for some applications, but can be problematic in some stages.
They are not ideal in cathode follower stages - typical of russian tubes. They are also a bit up-front on the upper
mid and top end. Putting all TS in the amp will make it pretty shrill sounding and you may experience failures in
the cathode follower stages.
Click to expand...

http://www.vhtusers.com/forums/showthre ... #post19400

:confused:
 
I was a big fan of Tung Sol 12AX7's for a number of years as I thought they were an 'upgrade' to the usual cheapo Chinese pre's. Needless to say, regardless of the price difference between the Chinese/Shuguang and the Tung Sols, I've come to realize that Chinese are the shiznit. They're cheap, they're readily available, they're consistent, and they've got terrific tolerance in all positions.

As much as I want to upgrade the preamp section in two of my heavy hitter amps (20thA XTC and VH4S), I haven't found anything better than the Chinese - and my guess is, this goes for several other amp manufacturers.

Just my 2 cents.
V.
 
Which gain stage is usually the Cathode follower? I understand that not every amp has a cathode follower stage.

I am a big fan of the Tung Sol RI 12AX7 in general, but its not cool if I can't use them in all positions :(
 
Don't know about other amps, but I found this info in a memo released from Mesa when tube failures first reared it's ugly head.

SOUND “DROP-OUTS” / INTERMITTENT SIGNAL

One Possible Cause

Most (but not all) Mesa/Boogie amplifiers have one or two “cathode follower” tube
stages in their preamps. Tube selection is CRITICAL in these stages.

Specifically, in a 12AX7 tube used as a “cathode follower”, the voltage difference
between that present at the cathode, as compared with the heater voltage, can be
withstood or tolerated by certain types of tubes, whereas other tubes will fail. The
failure of a “cathode follower“ tube will cause sound dropouts or signal loss.

For the past few years, Mesa has been using two types of 12AX7 tubes: ones
originating in Russia (Sovtek EH), and ones originating in China. The Russian (Sovtek)
tube is NOT reliable as a cathode follower. Of the tubes we are using today (March
2008), ONLY THE CHINESE 12AX7 IS RELIABLE AS A CATHODE FOLLOWER.

In conclusion, if you are troubleshooting for signal dropout in a Mesa/Boogie amp,
suspect a cathode follower tube, and try replacing it with a Mesa 12AX7 that is marked
as “CHINESE” (silk-screened on the tube itself).

Below is a partial list of Mesa amps and cathode follower tube locations:

GUITAR AMPS BASS AMPS

Lone Star & LS Special: V3
M-Pulse: V2
Stiletto: V3 & V4
Venture: V2
Road King I: V3 & V4
Big Block 750: V4
Road King II: V3 & V5
Titan: V4
Roadster: V3 & V5
M2000: V2
Dual & Triple (2ch or 3ch): V3 & V4
Bass 400+: V2
Tremoverb: V3 & V4

ANOTHER POSSIBLE SCENARIO may occur in the “SPONGY” (or on some models,
“TWEED”) power setting: the reduced filament voltage may cause very low output from
a RUSSIAN preamp tube. Again, the recommended fix is to replace the “sagging” tube
with the CHINESE type of Mesa 12AX7 - which are more immune to this type of failure.
Click to expand...
 
Yes, the above MESA SERVICE MEMO still remains active.

Recently brought Svetlana (Russian) tubes and placed them in a Mesa Stiletto Deuce I, V3 and V4 positions.

The amp has operated in the SPONGY mode 2 months, but power seemed reduced. This week, experienced signal dropout and lost. Moving from SPONGY to BOLD mode, setting using full AC input, the signal dropout/lost cleared.

Called Mesa (great tech support), they confirmed the issue. Said, the line voltage may have been low and triggered the cathode follower problem with the amp in the SPONGY mode.

Asked about their 12AX7 tubes, they screen for this condition, end-user should not be concern with their current stock being sold (JJ 12AX7).
 
baron55":3f3rmno6 said:
Basically all the Russian Saratov tubes made at the Reflector factory. Electro Harmonix, Sovtek, Mullard, Tung Sol, all have low cathode to heater tolerances. So putting these in a cathode follower position could result in fried tubes. If the tube heaters are elevated this is less of a problem.

I have heard rumors that the Sovtek 12AX7WC can handle the cathode follower position. But I don't know that as a fact.

I stick with the Shuguangs, NOS, and JJ's in the cathode follower spot.
Click to expand...

Good info.

To add to this, heater-cathode voltage is not the only danger to a tube in a cathode follower arrangement, if it's DC coupled, which is a common arrangement for driving tone stacks. The danger here lies in the grid getting pulled up to B+ before the cathode develops a voltage drop across it's resistor to elevate it from ground potential. This can happen upon a cold startup, and has been known to happen even despite standby being used to warm up the cathode. That high of a grid-cathode voltage can destroy a tube very quickly.
 
I've been using TS RI in V2 of my JMP's for a few years now no issues, i use NOS Blackburn Mullards & Amperex in the other slots.
 
baron55":i6fib5dr said:
I have heard rumors that the Sovtek 12AX7WC can handle the cathode follower position. But I don't know that as a fact.

I stick with the Shuguangs, NOS, and JJ's in the cathode follower spot.
Click to expand...

i have pretty extensive experience with the sovtek 12AX7WC's and the WA's or WB's would be much better suited for that position - the WC's have build quality issues from the factory and are very prominent to go microphonic on you.

id recommend a 12AU7 or 12AT7 for that stage - preferabbly JJ's for life expectancy.
 
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