The hidden gem among 12AX7/ECC83 NOS tubes, the RFT ECC83

[blr2]

Since many of us use tube amps or preamps, and like to do at least some tube rolling, I decided to post this here.


It is about a less known vintage tube(s) made by a company called RFT. These tubes were made from the beginning of the 60's till the end of the 70's in the ex Telefunken plant in Erfurt, that remained in the Soviet occupation zone. Presumably, some of the Telefunken tooling from the 40's was used and modified to make these tubes. They mostly made small tubes for radio and audio applications. Although, their EL34s are very highly regarded, I'll focus on their ECC83/12AX7 tube.


I call the RFT ECC83 the hidden gem among all NOS tubes. They used to be widely available in Europe, especially Germany and Eastern Europe until about 10 years ago when the stocks started to slowly dry out. They were dirt cheap, costing considerably less than new production tubes. Prices have gone up since then. The last couple of brand new tubes costed me close to $25 a pop including shipping. IMO, even at that price they are a steal. The tube is very short plate, which helps with microphonics.The gain is typical of 12 AX7/ECC83 tube, possibly slightly less than the hottest of the LPS.


RFT ECC83/12AX7 sound nothing like any new production tube. I'm not that kind of guy that will take about a night and day difference in instrument amps when changing a single tube, but this one definitely have a character on its own. It's warm and thick sounding, you'll immediately notice it. Put it in V1 position and you'll hear your amp getting thicker. The bass is rounded and the mids are thick and prominent. I know that some guitarists love this tube in newer Marshalls where it offsets the brightness of these amps. It is bass amps/preamps that the RFT ECC83 shines, IMO. I've used them in all my tube gear for close to 15 years now (3 amps and a preamp/DI box). It made all my tube gear sing. Again, I'm not a big tube rolling guy, and wouldn't spend a fortune on NOS tubes. I don't find much sound difference in most new production tubes I've tried,and even some old ones, but these ones are different. Lately, I put one in the V1 position of my newly acquired Ampeg PF20T. Immediately noticed the warm character. It brought this little head a step closer to a real B15.


Just a piece of advice. Ifyou find some of them at a decent price, do not hesitate.

 

[FugaziBomb]

After years of tube rolling, I'm still dubious of the impact it has. I've only found two applications where various 12ax7s have had audible differences in the circuit, and both of those were situations where I was using them for high gain preamp distortion. I really wanted to believe, but I'm more of a skeptic than ever now.

 

[Passinwind]

Since many of us use tube amps or preamps, and like to do at least some tube rolling, I decided to post this here.


It is about a less known vintage tube(s) made by a company called RFT. These tubes were made from the beginning of the 60's till the end of the 70's in the ex Telefunken plant in Erfurt, that remained in the Soviet occupation zone. Presumably, some of the Telefunken tooling from the 40's was used and modified to make these tubes. They mostly made small tubes for radio and audio applications. Although, their EL34s are very highly regarded, I'll focus on their ECC83/12AX7 tube.


I call the RFT ECC83 the hidden gem among all NOS tubes. They used to be widely available in Europe, especially Germany and Eastern Europe until about 10 years ago when the stocks started to slowly dry out. They were dirt cheap, costing considerably less than new production tubes. Prices have gone up since then. The last couple of brand new tubes costed me close to $25 a pop including shipping. IMO, even at that price they are a steal. The tube is very short plate, which helps with microphonics.The gain is typical of 12 AX7/ECC83 tube, possibly slightly less than the hottest of the LPS.


RFT ECC83/12AX7 sound nothing like any new production tube. I'm not that kind of guy that will take about a night and day difference in instrument amps when changing a single tube, but this one definitely have a character on its own. It's warm and thick sounding, you'll immediately notice it. Put it in V1 position and you'll hear your amp getting thicker. The bass is rounded and the mids are thick and prominent. I know that some guitarists love this tube in newer Marshalls where it offsets the brightness of these amps. It is bass amps/preamps that the RFT ECC83 shines, IMO. I've used them in all my tube gear for close to 15 years now (3 amps and a preamp/DI box). It made all my tube gear sing. Again, I'm not a big tube rolling guy, and wouldn't spend a fortune on NOS tubes. I don't find much sound difference in most new production tubes I've tried,and even some old ones, but these ones are different. Lately, I put one in the V1 position of my newly acquired Ampeg PF20T. Immediately noticed the warm character. It brought this little head a step closer to a real B15.


Just a piece of advice. Ifyou find some of them at a decent price, do not hesitate.

I have a couple, to me they exhibit unusually early breakup and/or high compression and are not my favorites for my particular bass applications (dead clean) at all. Great for high gain guitar amps (aka noise toys) though, IMO and IME, with very low micrphonics in the particular ones I own.

The RFT 12AX7

“…there is a time and place for that out-front spank, but if your mood shifts to slightly more mellow, there is a simple solution…” Those who plug into Fender amplifiers from the classi…

www.vintageguitar.com

 

[winston]

After years of tube rolling, I'm still dubious of the impact it has. I've only found two applications where various 12ax7s have had audible differences in the circuit, and both of those were situations where I was using them for high gain preamp distortion. I really wanted to believe, but I'm more of a skeptic than ever now.

In the '90s I did a fair amount of tube swapping, I will say for guitar amps I could hear a noticeable difference between some West German 12AX7s I pulled from an old Fisher stereo receiver (warm and detailed but some were microphonic), and Sovteks (sounded spitty & grainy in comparison). Didn't notice any difference when retubing a Mesa Bass 400 with Ruby Tubes replacing a mix of Mesa & Tung-Sol tubes...Same with swapping preamp tubes in my Eden WT-400.

TBH I don't miss messing with tube amps!

 

[beans-on-toast]

RFT ECC83 / 12AX7 Preamp Vacuum Tube | www.thetubestore.com

RFT ECC83 / 12AX7 preamp vacuum tubes in stock and ready to ship! Find reviews, data sheets and specs to upgrade your tube amplifier.

www.thetubestore.com

 

[Wasnex]

Nice review of the RFT.

I don't find much sound difference in most new production tubes I've tried,and even some old ones, but these ones are different.

It could be the amps and circuits you have previously rolled tube into. IME Some circuits respond and some don't.

I have rolled quite a few current production 12AX7s and definitely noticed different personality traits in some circuits. One of my favorite combinations for bass amps is a Mullard ECC83 in V1 and a JJ ECC803S pretty much everywhere else. I have chosen different tubes for some of my bass amps. Also sometimes I put the original tubes back in place, because I do not hear enough of a difference to justify the cost of a new tube.

A tube I frequently seem to dislike in bass amps is the JJ ECC83S. I have used some of the pulls to mellow out a couple of my guitar amps for basement playing. However, if I was really using these amps as they were intended, I would probably replace the JJs with a punchier tube; perhaps a Tung Sol 12AX7.

I think the last tube I rolled was a 12AT7. A few years back I bought a Mesa D180. It sounded fabulous except one of the 12AT7s was producing a really nasty mechanical rattle. The amp was loaded with a full compliment of Mesa preamp tubes including a second 12AT7. I swapped the 12AT7s and the rattle decreased slightly but stayed with the tube socket. I tried an EH12AT7. It sounded very similar to the Mesa tubes and also had a lot of rattle. Tried a NOS JAN 12AT7WC. This tube had less gain and added a soft syrupy quality that I have liked in other circuits. I did not think it was an improvement in the D180, but I would have kept it except it also had a small amount of rattle. Final tube was a NOS Mullard CV4024. Warm sound with plenty of gain. Would not have been my first choice in this amp other than...NO F'ing RATTLE!

 

[Passinwind]

Some interesting background from @ThisBass on the provenance of RFT labeled tubes: Ampeg used East German made tubes?

 

[CryingBass]

In the '90s I did a fair amount of tube swapping, I will say for guitar amps I could hear a noticeable difference between some West German 12AX7s I pulled from an old Fisher stereo receiver (warm and detailed but some were microphonic), and Sovteks (sounded spitty & grainy in comparison). Didn't notice any difference when retubing a Mesa Bass 400 with Ruby Tubes replacing a mix of Mesa & Tung-Sol tubes...Same with swapping preamp tubes in my Eden WT-400.

TBH I don't miss messing with tube amps!

Fisher. I can tell stories. But thats cause I am 109 years old.

 

[CryingBass]

And Zenith. Really

 

[Deleted member 271037]

RFT (Rundfunk- und Fernmelde-Technik) was a state owned company that didn't just have ONE tube factory. They had several tube factories around the DDR, as well as many factories that manufactured other broadcast and communications related products. I think you're right that one (or possibly two) of the RFT tube factories may have been used by Telefunken in the past, probably pre-WWII, but definitely not all of them.

The tubes from the different RFT factories have pretty much identical internal construction, but they are VERY different from any Telefunken tubes, and also from most other ECC83/12AX7 tubes. For this reason I very much doubt whether any Telefunken tooling was used in the making of these tubes. Besides, any pre-war Telefunken tooling would most likely have been bombed into scrap metal by the allies, and the 12AX7 (as well as any specific tooling needed to make them) didn't exist until after the war. It probably took a few more years than that before any 12AX7/ECC83 were manufactured in bombed out, post-war Germany, East or West. At that stage I don't think Telefunken would have existed anymore at all in the East, so I doubt very much if any ECC83 Telefunken tooling was ever set up in the East.

As for the RFT ECC83 itself, I 100% agree with SOME of what you're saying. These tubes are generally very low on microphonics, have a VERY warm/fat tone, a rather unique midrange texture and they really shine in bright sounding, overdriven Marshalls. The RFT ECC83 is my absolute favorite tube in V1 in a Marshall Plexi. It does something that NO other tube will do in a Marshall. Pure magic! RFT + Plexi is THE sound of rock guitar as far as I'm concerned.

However, there's a negative side as well IMO. The fatness comes at a cost. The RFT ECC83 is rather lacking in detail/clarity compared to pretty much ANY other vintage 12AX7 (although not quite as bad as SOME current production 12AX7s). The midrange may be fat, but it also has a kinda "congested" texture. The highs are considerably rolled off (more than ANY other 12AX7 I've tested) and the low frequency extension is rather poor. The RFT ECC83 also breaks up faster than ANY other 12AX7 I can think of. Between the poor low extension, the poor clarity in the mids and the extremely early break-up, I personally don't like this tube in bass amps at all.

In my opinion the RFT ECC83 is at it's best in overdriven vintage Marshall amps, or in SOME high gain amps, or MAYBE if you want to roll off the highs in an overly bright clean amp. The RFT ECC83 is also a great tube for convincing anyone who doesn't think tubes make a different that tubes do in fact make a difference. It is THE most different sounding 12AX7/ECC83 tube out there. If you can't hear the difference between an RFT ECC83 and ANY other 12AX7 in V1 in a proper tube amp... you probably need a hearing test.

Apart from these applications there are better tubes out there for MY taste, like vintage Mullard, Philips Heerlen, RCA, Siemens, Tungsram etc. For a bass amp I would personally even prefer several current production tubes over the RFT.

The RFT ECC83 is certainly a unique tube though, both tonally and visually. It's perhaps the most easily recognisable 12AX7-type of all. If you like it, no other tubes will do the same.

Be aware that the glass, although rather thick, also tends to be rather brittle with these RFT tubes. Be VERY careful not to bend the pins, because the glass may crack and ruin the vacuum.

 

[Deleted member 271037]

To avoid any confusing (or perhaps add to it...) I will add to my post above that RFT tubes were in fact rebranded as Telefunken (as well as many other brands) after Telefunken (and other Western tube manufacturers) shut down their own tube factories.

This means that you can definitely find Telefunken branded ECC83 (as well as EL34) where the internal construction looks identical to RFT. However, this is NOT because they were made on old Telefunken tooling. They're simply rebranded RFT tubes. Genuine, Western German Telefunken-made tubes look VERY different.

 

[logdrum]

Simpler circuits is where this tube rolling matters, like tweed deluxe or tweed Bassman, True Class A amps , Vox AC family of amps and tube microphones. Not in bass amps. When I had the 400 as well as the CL, the best tubes were from Mesa nd what came with the SVT CL, The only time I saw improvement was to the non sexy Sovtek Mil Spec specially if you have some agro effect chain on the front

My conclusion was I wasted time and money tube rolling. Zero improvement and in some cases made things worse, Learning your amps topology and how the gain, EQ works with your instrument is more imprt6ant than the tube.

 

[blr2]

Simpler circuits is where this tube rolling matters, like tweed deluxe or tweed Bassman, True Class A amps , Vox AC family of amps and tube microphones. Not in bass amps.

Would you describe something like b15 or PF20/50 heads as being simple or complicated?

 

[coreyfyfe]

Nice review of the RFT.

It could be the amps and circuits you have previously rolled tube into. IME Some circuits respond and some don't.

I have rolled quite a few current production 12AX7s and definitely noticed different personality traits in some circuits. One of my favorite combinations for bass amps is a Mullard ECC83 in V1 and a JJ ECC803S pretty much everywhere else. I have chosen different tubes for some of my bass amps. Also sometimes I put the original tubes back in place, because I do not hear enough of a difference to justify the cost of a new tube.

A tube I frequently seem to dislike in bass amps is the JJ ECC83S. I have used some of the pulls to mellow out a couple of my guitar amps for basement playing. However, if I was really using these amps as they were intended, I would probably replace the JJs with a punchier tube; perhaps a Tung Sol 12AX7.

I think the last tube I rolled was a 12AT7. A few years back I bought a Mesa D180. It sounded fabulous except one of the 12AT7s was producing a really nasty mechanical rattle. The amp was loaded with a full compliment of Mesa preamp tubes including a second 12AT7. I swapped the 12AT7s and the rattle decreased slightly but stayed with the tube socket. I tried an EH12AT7. It sounded very similar to the Mesa tubes and also had a lot of rattle. Tried a NOS JAN 12AT7WC. This tube had less gain and added a soft syrupy quality that I have liked in other circuits. I did not think it was an improvement in the D180, but I would have kept it except it also had a small amount of rattle. Final tube was a NOS Mullard CV4024. Warm sound with plenty of gain. Would not have been my first choice in this amp other than...NO F'ing RATTLE!

I've had a similar experience with the basic JJ 12AX7/ECC83S. I've had them in several amps with different circuits, usually they sounded a bit darker/duller than other tubes. I'd often swap for a mullard or tung sol branded new sensor, or in some cases a rebranded Chinese tube if it needed to go in a tighter socket, as a way to brighten up those amps. The new sensor made gold lion 12AX7s I've tried have been very bright but also prone to be microphonic. They had great gain in a Marshall jcm800 but it took five tubes before finding one which wasn't a ringing mess.

Would you describe something like b15 or PF20/50 heads as being simple or complicated?

I'd consider a B15 pretty simple but I did a test of 6SL7s in one of mine and I'd call differences subtle at most, negligible in most cases. I screened a handful of old glass as well as some modern new sensor products. All sounded good, so not a negative thing. But that's also a tube type where the cost of new production isn't much different than NOS.

 

[logdrum]

Would you describe something like b15 or PF20/50 heads as being simple or complicated?

The old B15's were more simplistic I believe but weren't the OG ones using a different preamp tube.

So for comparison I had both the Mesa 400 non plus with 6550 tubes no GEQ as well as the Prodigy 4:88 , The 400 behaved like a Fender Showman and had a cascading gain. But it won't go creamy like the older D180 which I felt was more in line with the Marshall Major. The 400 would respond some to a V1 and V2 tube change but you have to be playing very loud and pushing it. You definitely should not mess wit the Phase Inverter of this amp - you need something balanced

The Prodigy was definitely complicated, had voicing controls - Active and Passive EQ., boost and half power. Did not matter what went into V1 and V2 as long as they are within spec and not microphonic.

All these old tubes probably make a difference in tube microphones - for the better,?? it depends on the listener. There is a big cottage industry of new production specialized preamp and power tubes,


My opinion is that these are old electronic components sold at crazy prices and who knows how much use they have had.

I have an old Princeton and a post CBS Showman. I use new production tubes on them . Sounds just fine compared to the ones in my small old tube collection that is not microphonic or weak,

 

[blr2]

My opinion is that these are old electronic components sold at crazy prices and who knows how much use they have had.

I completely agree with this one, and I stated it clearly in my original post.

 

[NKBassman]

Based on what I've read here, I think I want one for the OD channel on my Verellen Meatsmoke. I already keep the treble rolled down all the way on that amp and still find it on the bright side.

 

[JimmyM]

I've had a similar experience with the basic JJ 12AX7/ECC83S. I've had them in several amps with different circuits, usually they sounded a bit darker/duller than other tubes. I'd often swap for a mullard or tung sol branded new sensor, or in some cases a rebranded Chinese tube if it needed to go in a tighter socket, as a way to brighten up those amps. The new sensor made gold lion 12AX7s I've tried have been very bright but also prone to be microphonic. They had great gain in a Marshall jcm800 but it took five tubes before finding one which wasn't a ringing mess.



I'd consider a B15 pretty simple but I did a test of 6SL7s in one of mine and I'd call differences subtle at most, negligible in most cases. I screened a handful of old glass as well as some modern new sensor products. All sounded good, so not a negative thing. But that's also a tube type where the cost of new production isn't much different than NOS.

The guy who I bought 6sl7's from told me he thought there was for all practical purposes no difference between them. That would follow my experience with them except for those New Sensor tubes! I got my B15n restored in 2008 and it was bangin', like a whole new amp. But V1 went ka-flooey so I replaced it with a Sovtek, and that glassy sound it used to have came right back. It was OK, but compared to the Sylvanias and RCAs I had, it was yuck. Worked fine in V2, though, which I believe was for the Eq.

So RFT is a name I never heard before, and I thought I knew everything .

 

[Al Kraft]

The guy who I bought 6sl7's from told me he thought there was for all practical purposes no difference between them. That would follow my experience with them except for those New Sensor tubes! I got my B15n restored in 2008 and it was bangin', like a whole new amp. But V1 went ka-flooey so I replaced it with a Sovtek, and that glassy sound it used to have came right back. It was OK, but compared to the Sylvanias and RCAs I had, it was yuck. Worked fine in V2, though, which I believe was for the Eq.

So RFT is a name I never heard before, and I thought I knew everything .

Just about the time I think I've got a good bead on something, someone really smart helps me know how much more I have to learn that I wasn't even aware of.

If you're not learning something new every day, the best you've got at your disposal is yesterday's news and history (depending on how good your memory is of course).

 

[CryingBass]

I saw the Tubes once. Right before Todd R.

Telefunken fun me says.