TUBE EXPERIMENTATIONS | by Mr. Miniwatt

[Mr.Miniwatt]

I am not at the level of building myself an amplifier, I play more with different tube types and experiment their effect. But I will document myself related to what you told me. I consider the amplifier I already have to be very good for what I need.

 

[Mr.Miniwatt]

I started this morning with some experimentation related to the ECC81/12AT7 family. I bought some bulk packs of tubes and I start progressively to dig into them, identify the tubes and use some of them on my amplifier. This is a part of a tour I plan to make with several ECC81 and also the british A2900, in order to check how I see these after many months of using almost exclusively Siemens E88CC in input stage.

So, I took the first one, made some measurements and checked if the tube works fine on the tester, then I put it on the amplifier to enjoy it.



Regardless of the branding, this is a Valvo E81CC gold pin, and the detailed photo shows us the date codes on the bottom.



As you can see, VG0/D9J4 follows the Philips standard and can be easily identified by the Philips code book, so this was an easy one (VG=E81CC). On the amplifier sounds quite nice, I think it is one of the best 12AT7 I was able to try. But more about this when I will listen to other 12AT7 because coming from E88CC, I still have a preference for those ones.

The next pick from the bulk pack was something which is still under investigation, something I assume it is a Siemens E81CC, this time branded Siemens and also produced by Siemens in their Munchen factory.



The date codes etched on glass will be the key for me to correctly identify it: Cϕ 5≠ 1D. In my view, according to what I was able to find until now, this is a Siemens E81CC triple mica. I do not have unfortunately a Siemens code book, to see if C means E81CC and to help me understand more from these Siemens date codes. I am still working to gather data and try to deduce some of them, but a code book like Philips would have been useful.

What I can say in addition is that I performed some measurements to these tubes, according to ECC81 standards:



While the Valvo E81CC was around 70%, the Siemens seems to be quite stronger. I doubt the tube is unused, so maybe I need to try it and see if the gain remains similar with the other, this being another clue about what is this tube. Pinout seems the same with 12AT7. Since the 12AX7 and 12AU7 measure completely different, I still think my assumption was correct.

Later edit:
It seems here they had another E81CC with similar codes, so yeap that's a Siemens E81CC.

 

[Mr.Miniwatt]

In the afternoon I have decided to continue to try a few of the tubes I was able to recover and measure from the bulk packs. This time I chose something totally different to both Valvo E81CC and Siemens E81CC, which both sounded nice and close to my preferences: an old D-getter Tung-Sol 12AT7.


This tube measured terrible (a little bit above 50%, so around 5mA for 250Va, -2Vg1) but since it is quite unique in my collection (I do not have other Tung Sol ECC81/82/83) I wanted to try it.



It has a small hum from the start, and the overall sound is more tubey, less detail and a more forgiving tubey sound. Not bad, from time to time, and a good contrast to what previous tries provided. I also have around a RCA one, rectangle getter, that one maybe in another day.

And since my previous investigation ended, I will start a new one:



This is another mistery tube, another ECC81, this one measuring quite good, above 80% on both sections. No date codes, just "RIO" and 2854 which might be the 28th week of 1954. In rest, rectangle getter fixed without rod, directly on mica. The mica from the bottom seems transparent. Searching for "RIO ECC81" brought me to an old radio which seems to be produced in Germany. What to say, seems a nice tube, black plates as many into audio like. In my case the color of the plate, shape of the getter or color of the base have no effect on audio quality but might be a mark of the age of the tube, and usually older tubes sound better to my ears, with a few exceptions.

I'll try to find out how the mistery "RIO" ECC81 sounds, and also try to decypher its origins.

Later edit: It seems the Tung-Sol 12AT7 started to raise a little bit the emission above 60% after some hours of usage, maybe the time I kept it on the tester was not enough, for such an old tube stored for decades. I'll measure this one again in my next measuring session. Unfortunately the hum remains, but it is low volume, barely hearable between tracks.

PS. My instinct tells me the mistery ECC81 is british made, those black plates, those round holes in mica remind me of GEC. But of course, I might be wrong.

 

[Mr.Miniwatt]

There was one more thing I wanted to do today, and this was more like a function check than a proper listening session. I wanted to see if 6Q7G can work in my input stage, set at 180V/4mA. Since this is a double diode high-mu triode, with "typical operation" around 1mA, I was expecting that at 2-3mA where I was planning to bias might be problematic. So I measured and paired 2 pieces of this tube:


This is Marconi Spain, which was something interesting for me. I never had any tube made in Spain, but according to the paper they sealed these:



Measuring I realized the negative control grid voltage goes towards 0, biasing quite similar to 12AX7 on my amp. But even in this case, I said why not, let's try it. 12AX7 works fine, but it's a 1W /section tube and I expect also these have lower plate dissipation. So 2-3mA should be a maximum I would dare to try.



The tube itself it quite beautiful.



But soundwise, these were a little bit disappointing. Sounded congested and sharp somehow. It might be a problem of burn in, but also a problem that my input stage is not properly designed to use tubes like these. I guess here bias around 1mA as they advise on the datasheet is desirable. So I'll put these in the category of "high-mu small current" where I also have some 6AV6/6AT6/DH77 and maybe focus on these on another amplifier. In the meantime I can try to see what experiences had others with these, but unfortunately not many describe at what operating point they used them.

Anyway, nice looking and interesting tubes.

 

[adrian cheng]

It's a Brimar 12at7

 

[Mr.Miniwatt]

It's a Brimar 12at7

So my instinct was not so far from the truth. Thank you for helping me identify it.

I think this one is similar.

 

[Mr.Miniwatt]

This morning I continued my tour of the 12AT7, trying an RCA 12AT7 rectangular getter from 1960.


Here everything went as expected, great bass. This is in fact the thing I like the most at RCA, the bass and relatively smooth presentation. This a tube for jazz in my view. Too bad I am not quite listening to that genre, for what I like I prefer a slimmer more dynamic presentation.



While I like in general the RCA tubes, I prefer to keep RCA in output stage (807 or 6L6 usually) and put in input stage something more transparent. But of course, this is a personal approach, everyone has its own way of combining these and this is in the end the beauty of tube rolling.

I have around also a GE, but I will not try it, I do not like GE, especially newer production.


This can sit in the box without problems. I haven't even checked or measured it, but has to be NOS, nobody is using GE. LOL

 

[Mr.Miniwatt]

And another mistery tube, which I will investigte its origins, this time a 12AU7.



This tube looks quite interesting to me, especially because the plate is fixed on the mica by some chrome feet. I haven't seen anything like this before. This is the only one in my collection which has such a construction. This kind of tube type printed inside an octagon is usually specific to american tubes but it is in a different shape on those. Here we have both american and european designations.

I think it's also a british tube, so might also be Brimar. I am unsure, but I will look to see for other clues to identify it, mostly because seems unique to me.

 

[adrian cheng]

And another mistery tube, which I will investigte its origins, this time a 12AU7.

View attachment 145540

This tube looks quite interesting to me, especially because the plate is fixed on the mica by some chrome feet. I haven't seen anything like this before. This is the only one in my collection which has such a construction. This kind of tube type printed inside an octagon is usually specific to american tubes but it is in a different shape on those. Here we have both american and european designations.

I think it's also a british tube, so might also be Brimar. I am unsure, but I will look to see for other clues to identify it, mostly because seems unique to me.

Made by RCA

 

[Mr.Miniwatt]

Made by RCA

While about the other I was not surprised was Brimar, about this one I am really surprised is RCA. Thank you again.

I started to look about "RCA 12AU7" and found this ATES licensed by RCA on Ebay which seems similar with mine. But this one has ring getter and seems produced in Italy. Incredibly interesting tube, even if I was not interested in listening now to 12AU7, this tube has to be tried by me.

Here Radio Antigua mentions this as "Fivre" production. I will have to document myself on ATES and these tubes produced under license in Italy. I have to admit I do not know much about it.

And it seems also Langrex is selling it here.

 

[adrian cheng]

While about the other I was not surprised was Brimar, about this one I am really surprised is RCA. Thank you again.

I started to look about "RCA 12AU7" and found this ATES licensed by RCA on Ebay which seems similar with mine. But this one has ring getter and seems produced in Italy. Incredibly interesting tube, even if I was not interested in listening now to 12AU7, this tube has to be tried by me.

Here Radio Antigua mentions this as "Fivre" production. I will have to document myself on ATES and these tubes produced under license in Italy. I have to admit I do not know much about it.

And it seems also Langrex is selling it here.

Also Marconi sticker as well

 

[Mr.Miniwatt]

Also Marconi sticker as well

The tube was cleaned by me, it had a rectangular horizontal sticker which was not present, only traces of glue which I have removed before making the photo. That one could be a Marconi logo maybe. Or those tax stamps they were putting on tubes in Italy.

I was reading now at Watford Valves about ATES here, I will borrow the excerpt since I already mentioned the source:

The company ATES was established in 1959 in Italy for the construction of electron tubes. The production started with the cooperation of RCA which was one of the Major shareholders of ATES. In 1963 the name “Aquila Tubi Elettronici e Semiconduttori†was changed in “Aziende Tecniche ed Elettroniche del Sudâ€, Hence the name ATES. The Audio valves were all made under licence and were the RCA designs. In 1972 ATES merged with SGS (Società Generale Semiconduttori) and the company name became SGS-ATES. ATES disappeared completely from the company denomination in 1985. The Ates valves were all made to very high standards and normally to very high standard. They offer RCA sound quality and construction.

So according to this information, the tube has to be produced after 1959 but looking at that rectangular getter, I do not know why but for me seems a tube from the 50s. I will try to find more info about this 12AU7.

 

[Mr.Miniwatt]

Returning from the 12AT7 bunch back to Siemens E88CC was for me similar to a veil being lifted between me and the music. And this is why the ECC8* families will never be able to touch the frame grid tubes. My results with double triodes (ECC88, E88CC/E188CC/E288CC) or single triodes (EC80/EC86/EC88) were better than with the ECC8* or half types like for example 6C4.

And while I consider the E88CC more balanced across the frequency range, more detailed it is also not fatiguing or harsh in any way. Some of the 12AT7 I have tried yesterday were very good, but still had some small harsh moments (even the Valvo E81CC) in specific passages. It can be that the tubes need more time on my amplfiier, but from my experience, in the end my evauation will be similar.



I have planned to try the mistery ECC82 which was later revealed to be an RCA ATES 12AU7 but I could not stop the listening session. So for a while the E88CC will be my partner in crime. What would follow later? I have no clue.

 

[DasguteOhr]

This morning I continued my tour of the 12AT7, trying an RCA 12AT7 rectangular getter from 1960.

View attachment 145536
Here everything went as expected, great bass. This is in fact the thing I like the most at RCA, the bass and relatively smooth presentation. This a tube for jazz in my view. Too bad I am not quite listening to that genre, for what I like I prefer a slimmer more dynamic presentation.

View attachment 145537

While I like in general the RCA tubes, I prefer to keep RCA in output stage (807 or 6L6 usually) and put in input stage something more transparent. But of course, this is a personal approach, everyone has its own way of combining these and this is in the end the beauty of tube rolling.

I have around also a GE, but I will not try it, I do not like GE, especially newer production.

View attachment 145538
This can sit in the box without problems. I haven't even checked or measured it, but has to be NOS, nobody is using GE. LOL

GL 6201/12at7 five stars is a really good tube from 1950-1960 mostly the highest grade series from General electric

 

[Mr.Miniwatt]

GL 6201/12at7 five stars is a really good tube from 1950-1960 mostly the highest grade series from General electric

I do not have any "5 stars" one around but I have one with simple green lettering from the 70s. I have posted it a few posts above. I never tried it but measures NOS and I might give it a chance. I do not like GE from 70s and 80s but earlier ones might be better sounding. I have some GE 6K6 from the 40s which sound quite good. 6K6 is a nice alternative for 6L6 in amplifiers like mine which do not need very high maximum ratings.

 

[Mr.Miniwatt]

The weekend is near, so this forces me to be more innovative. I want to change both stages and go towards more budget friendly tubes which are also sounding very nice. But I want to do this in 2 steps to let me understand better what is going on. I always prefer to keep a pair fixed in one of the stages and roll the other stage, this helping me understanding more about the qualities of the tube in the rolling stage. In order to help me, I usually keep a more neutral tube, towards what I consider "reference" in the fixed stage. I do not want to blend too many flavors and be distracted by some benefits brought by the other stage. So if until now I had Philips 4654 5-code, I will go towards more unknown but still close to reference in my view, the Telam EL86.



EL86 is not new to me, it is in fact one of my favourites output tube types I often used. Telam EL86 is one of the types which are going towards a more neutral, reference tuned sound and it is a perfect choice for me to allow me evaluate some tubes in the input stage. From all the types I own and tried, my favourite EL86 remains the Mullard D-getter (MI1 revision, B-code) earlier version, but that one is quite rare and it is more musical and warm than this one, it is the perfect blend between a warmer more emotional sound mixed with the technical qualities of EL86. Unfortunately, I cannot call it a reference, even if it is my favourite from them all. The reference will never be the most engaging one you will listen, but it will be the most correct sounding from a sound signature perspective.

I guess people are surprised that I am not choosing the famous EL84. For me that one is a more musical tuned tube, higher gain and more dynamic but not so "correct" sounding according to my standards. EL84 is the fun tube, EL86 is the reference and this can go on also towards 4654 metal base being my reference and not 4689 metal base which is also an idea more fun tuned. Compared one by one, for me EL86 is more linear than EL84, punchy bass and a wider soundstage, but not so musical as the EL84.

So I am prepared for the weekend of "going cheap". Now I have to see what I will use in input stage to remain in my virtual budget of let's say 50 EUR. I will consider EL86 as 30 EUR/pair even if you can find them cheaper with some research, this allowing me to have a lot of fun in the input stage in the range of 20 EUR/piece tubes. Of course, I am not forced to avoid trying more expensive ones, but my purpose is to enjoy some bugdet oriented quality sound. We will see how this goes, it will be fun for sure.



After a few hours with the Siemens E88CC Aϕ I'll go towards more unknown tubes, which are selling cheaper. Because the price of the tube is always dictated by rarity and fame, not necessarilly by the sound quality it produces.

 

[Mr.Miniwatt]

What to do, what to do? We said we will focus on budget this time and also want to roll some good sounding tubes in input stage. It is clear for me that the E88CC and double triodes with frame grids do not have a chance to fit here, only maybe at the limit the single triodes like EC86. But I had enough of these lately and I will go towards a more "classic" path. So one of the choices which comes into my mind is the 6J6. I see on the extremely nice website of RadioMuseum that 6J6 has a predecessor the 6SN7 and the successor the 12AT7, gain being somewhere in the middle of these. A 7-pin almost unknown tube which sounds quite good, and if I want to add some drama to the table near the mostly neutral Telam EL86, the RCA square getter 6J6 is a good starting point.


This one fits without problems in the budget and looks quite nice also on the amplifier. Nice glow.



Now, I will not lie that some of these can be a little bit microphonic, this one crackled a little bit at start-up in the first minutes until it heated enough. But this is not a big problem to me, it sounds good, has nice bass and a decent level o clarity. In my view it is a good choice for a budget friendly amplifier.



The markings got almost deleted because of the usage, but the tube sounds fine. Luckily I made the inventory photo when I got it, and I can still see on it the date code, this tube being from 1959. In general, 6J6 are older than 12AT7 and you can easily find D-getters or older versions at a very correct price, thing which is not valid anymore for 12AU/T/X7.

Ok, I will continue thinking what I can use in the input stage and fit in my self-imposed budget.

 

[Mr.Miniwatt]

I have to admit, EL86 with 6J6 were very pleasant sounding, an excellent mid-fi combination which can be enough to live with, at least if you haven't heard the others. But I had another idea to try, and this is a premiere also for me. Whenever I think about cheap tubes I always think about full metal body ones. I had a good experience with many, mostly all I tried were RCA, like for example 6L6, 6C5 but from time to time I choose another double triode with common cathode like 6J6, named 6N7. Gain is between 6SN7 and 6SL7 and in general this tube is cheaper than both others, and if you choose a metal body one, prices go even lower. I had all kind of problems with glass versions of tubes, like loose base, noise and so on, but with metal body ones 0 problems. Of course, these will never be appreciated by many because they never glow.

So, my choice for today was Arcturus 6N7:



Here is a photo of several metal body 6N7:




On the amp, same style of sound, more tubey, as from the RCA 6J6 but the 6N7 metal body tube souds an idea more relaxed and with bigger soundstage. I always wondered why I have the feeling that the soundstage is proportional with the size of the tube. I know it makes no sense but well, experimenting somehow I correlated these. Another thing I have no explanation is the quantity of bass which seems to be proportional with the current of the heaters. 2 mysteries for me.

 

[Mr.Miniwatt]

I did not want to end the evening without listening to some british tubes which in my view will complement nicely the Telam EL86. I do not know if I am still in my self-imposed budget, but for sure I am not far from it. This time Mullard EF94 (or 6AU6 if you prefer). The 6AU6 is a pentode which sounds very good in input stage strapped as triode, and the gain remains quite similar with my previous tries, so around 35. But 6AU6 is very lively and musical, bringing some fun to the "reference" EL86. It is also an idea brighter than the previous ones.



I do not have a detailed photo of these Mullards, they have slightly different labels on them, but the construction is identical. I bought these bulk and paired them myself, mostly on internal construction and date codes than on what is written on the tube. The Mullard EF94 is one of my favourite budget input choices, this time in some 6AU6 -> 6J5 adapters. The sound is very nice, I knew this and left these for the late evening.

EF93/EF94/6AU6 are in my focus for the long term and while I have not listened to many, I have understood their potential. These will come more often in my rolling choices. 6AU6 is a very special tube.

 

[Mr.Miniwatt]

Being a little bit intrigued by the good sound I was obtaining from the Mullard EF94, I wanted to hear again my RCA 6AU6.



These are square getters, again very nice sound but more in RCA style. So a tube type will sound good regardless of the "house sound" of its manufacturer. I knew this and this is another proof to that. In the meantime I was able to make a photo of my Mullard EF94 I was previously praising.



The markings are not the same but the tubes are the same. I checked them in detail, when having several tubes in a box and made some pairs from them.

One thing is for sure, I need more 6AU6 in my collection.