TUBE EXPERIMENTATIONS | by Mr. Miniwatt

[Mr.Miniwatt]

Purpose

This thread plans to be an open discussion related to tubes. I am a tube roller interested in their history, pinouts, internal construction and date codes. I also try to measure them using my basic tube tester. I am doing this for several years, started a thread more as a personal blog and free discussion on another forums but since they imposed a limitation on double posting they currently blocked my activities. I have a full time job and only several open slots where I can perform some tube rolling on mostly unknown tube types. I try to expand our knowledge on tubes, to increase my understanding in this area and also to provide a fun place for people interested in the same things as me to discuss and help each other.

My amplifier

The context of my tube rolling is a little bit different that what you will find on other amplifier centric based threads, where people gather to share their impressions based on a specific piece of equipment. I have a custom made Ultrasonic Studios amplifier called Eternity. There are only 2 built in the world and they are somehow unique. This amplifier was built at my request by a very nice and knowledgeable person who is deceased and a part of my work is also dedicated to him. I want to keep his memory alive and share to others a part of his work. Because nobody can describe better the amplifier than the builder himself I will quote him here:

Eternity is basically a low power version of Infinity. A SET, single ended triode, amp with open loop (no gNFB) and parafeed output. The input stage, using the 6AV6 tube, is grid (fixed) biased. Followed by CCS loaded source followers that drive the output tube grids. The grid drivers relieve the input tube of any drive duty. Tubes do only voltage amplification. Tubes do what they do best and FETs do what they do best, supply current. The output stage is also SE and grid biased, using the 6S19P tube. All tube anodes are gyrator loaded. Both B+ and B- supplies are regulated. Eternity, just like Infinity, will have more of the old tube sound than Oblivion and Citadel has. This is because it’s single ended. The balanced amps cancels a lot of distortion and are also constant current draw amps, while Eternity is not. It’s a matter of taste what sound signature you prefer. Eternity can drive efficient speakers as well as headphones. Power output is 3W into 8 ohms. 1W into 8ohms, 430mW into 20 ohms, 170mW into 50 ohms, 90mW into 100 ohms, 45mW into 200 ohms, 30mW into 300 ohms.

I will make some personal remarks about the amplifier. In order to provide more information, my amplifier uses fixed grid biasing, by providing a negative voltage to the tube control grid. My input stage is fixed at Va = 180V and Ik = 4mA with a range of safe operation range of 3-5mA. The output stage is fixed at Va = 200V and Ik = 20 mA with a safe operation range of 15-24mA. This means that every time I will use a tube I will have to measure and pair to keep both tubes from left and right channel in the specified range. I can use almost any tube in this amplifier, as long as I can bias it to keep it in the above mentioned ranges of current. I have 5 sockets, for output stage there are 2 wired for 6V6 and for input stage there are 2 wired for 6J5 where I use in general single triodes or triode strapped tetrodes or pentodes and 1 socket for double triodes wired for 6SN7. In fact, output stage is also triode strapped. Because I was a fan of 6N7 back in the day, I asked the builder to wire 6J5 to be able to natively use 6N7 with both triodes in parallel. The trimmers I have for negative voltage have a limit around -13V for input stage and -55V for output stage. So if a tube requires more I will not be able to bias is and therefore not be able to try it. But even with these limitations I was able to try a broad range of tubes and explored many families already.

Fixed grid biasing and this kind of gyrator loaded plates with source followers made from MOSFETs made my amplifier sound extremely controlled, neutral and clean. It is a low distorted design which does not necessarily sound tubey. So my remarks during tube rolling will be mostly made in this context. Last but not least, it is a headphone only build, without any output sockets. Besides this, I have a very bad taste on music, I am a Black Sabbath and Slayer fan. So unfortunately I will not be able to provide many useful information to elf eared audiophile people.

People interested in finding more can look here, they can see some nice photos and also a part of my past activities. Apologies in advance for the amount of spam, I also consider that some of the discussions were interesting. Looking back I think the magic of the thread was the bunch of people from different backgrounds and using different amplifier which provided common findings. Some listened to speakers, others to headphones, some were Lampi users but we all found common ground in our common love: tubes.

Let's start!

I am new around, 2 days ago I searched for a forum where people are interested in tubes where I could continue my discussion. I was pleasantly impressed by the tube collection of mr. Adrian Cheng and thought here I might find some partners in crime which will help me explore the unknown world of tubes. Help me understand more, listen to more and why now, explore more unknown tube types. Unlike him, I am not a collector, I own many tubes but a big part of them are unkown types which are not valuable. As we know the tube value is dictated by fame and rarity. My war is not to own the rarest of ones, but to find the cheapest unknown types and to bring them back to glory in my small and unique amplifier.

I am Mr. Miniwatt and I welcome all of you here to discuss about tubes.

 

[Mr.Miniwatt]

Reserved.

 

[Mr.Miniwatt]

Reserved.

 

[Mr.Miniwatt]

I started my day with a small experiment related to EL5. EL5 is a tube type which raises a lot of interest to me because it is the predecessor of one of my all time favourite tubes, the 4654 and therefore, listening to it was planned by me for a few months already. Because I do not have a Philips version to try I had to use a pair of Tungsram EL5. A detailed photo of the tube here:


Since the purpose of my photos is the tube identification, I always try to show different sides of the tubes where a marking or some construction detail can be indentified. And I usually make photos before cleaning the tube or pins in order to preserve as much as possible the original markings. So you will see in some of the photos I will post oxidated pins or why not, dust on the glass. This does not necessarilly mean I use the tube in that condition.

Prior to my listening session I measured the tube just to see if all goes as expected, bias was similar with 4654/EL39. So in my case I had to set Vg1 = -15V on the amplifier to have both tubes as close as possible to 20mA. Since my amplifier needs to keep the output stage in a range of 15-24mA and I can set a common grid bias for both channels, I always have to pair and verify that both of my tubes will be in the same range when biased with the same value of negative voltage. So I set on my tester the Va = 200V and determined which value is the correct one for the control grid to keep both at the desired current.

After this preliminary step I was ready to go, EL5 for the first time on my small amplifier called Eternity.



Listening for a while to these Tungsram EL5, while keeping the Siemens E288CC in the input stage, let me realize that indeed, the sound is in the style of the famous Philips 4654, but the resolution and separation provided by the Philips versions is superior to Tungsram. This was a warm forgiving sound, a little bit blunt for my taste which goes usually to a more technical presentation. Not bad but not excellent either.

What really annoyed me was that the left channel developed in the first hours a small hum and the sound became muffled somehow. This means I will need to clean better those pins and hope for the best. I do hope that would be the solution, these old tubes using european side contact socket (P8A) are very prone to such behavior because of the way the pins attach to the socket, and sometimes but pressing the tube a little bit more on the adapter or cleaning the pins makes wonders. Of course, sometimes.

At the moment I plan to enjoy some music so I will let these maintenance activities for another time. EL5 went back into their boxes, keeping those adapters on because I avoid at maximum removing adapters from such old types of tubes, it is dangerous and the base might get loose or the tube even loose vacuum when doing this. It happened to me and I learned something from that.

Ok, this was the first episode of my tube experimentation, today I have learned something, how EL5 sounds. Moving forward, in my journey to experiment and understand more from the fabulous world of tubes.

 

[Mr.Miniwatt]

Since my experiment with EL5 ended brutally by one of my biggest enemies called hum I had to find a solution. In the end we are in the weekend when my schedule allows me to perform more experimentation. So I replaced the Tungsram EL5 from the output stage with Philips 4654 metal base. These tubes are for me a kind of reference for transparency and detail. While I do not own any of the famous Philips EL34 metal base, I consider these predecessors very nice sounding and I expect, in the same style. Here people experimenting with both can help me verify my assumption.



I have not changed anything on the input stage, Siemens E288CC is perfect from my point of view. But as usual, this tube combo has a problem. It sounds more sterile and dry than what I usually like to listen. Is this a technical presentation which lacks some enjoyment? I would say yes. For me this kind of sound goes more towards Violectric house sound and I sometimes ask myself if this is what we would like to achieve in a tube rolling thread. These very low distorted and technical tubes can compete, in my view, with any solid state amplifier, but because the sound lacks harshness and it is less fatiguing, is for me always better. I guess this was one of the reasons I started to enjoy tubes, besides the diversity you can obtain by tuning your amplifier.

I will remain here for a while, but I will try to document myself a little bit about EL5 and also E288CC. I would like to know more about them and also what experiences had others.

 

[Argonaut]

Welcome to the forum , I would anticipate Stephan @DasguteOhr , Brad @morricab plus a few others Valve aficionados might well join in presently .

 

[Mr.Miniwatt]

During the evening a new idea came into my mind and it was not easy to remove it. The idea was to see how far I can go into this direction of a more technical and "sterile" sound. Because the Philips 4654 was not the most technical output tube I can pair the Siemens E288CC with. That one is the Telefunken EL156.



Because adapters are hard to be removed and you have to drag them from the tight teflon sockets of Eternity, I put some socket savers between. For sure not the nicest option but it gets the job done. And now came the moment when I was surprised about the result. I was expecting this to sound different but in my view, this pairing sounds more real and has a better synergy than the previous one. Surprisingly, E288CC sounds very good with the Telefunken EL156, and the extra sparkle in the highs brought by Telefunken helps. But of course, excellent dynamics at the cost of less bass quantity. Tight, precise, extreme detail retrieval but might be an idea bright. Excellent soundstage. This combination surprised me and exceeded my expectations. A way to end the day in style. Nothing tubey here, but also no digital glare or fatiguing sound.

I will show you the Telefunken EL156 in detail, because the tube looks impressive:

 

[Designsfx]

@Mr.Miniwatt
Hey! Good to see you hear- I’ll check in on this from time to time to fill in the gaps

 

[Mr.Miniwatt]

Ah, here you are, didn't knew you are also on these forums. I had to move from that one because of double post being banned. It killed my way of telling my story. But I'll be on both and post wherever I can. LOL

 

[Designsfx]

Yes- I occasionally drop in here for updating the Lampizator TRP thread and of course the Progressive Rock thread. There are a few of us that bounce back and forth depending on the conversation.
I still have yet to go back to those humming EL5’s! Every time I think about loading them up I just say no because I don’t want to deal with it. Not looking for anymore at the moment as I’m going to start experimenting with an external filament heater setup. Hopefully this will lead me towards some rewarding ignored tubes!

 

[Mr.Miniwatt]

Absolutely. In the 12.6V land you can find cheaper and very nice tubes. I might also need to do that, because I bought recently a FDD20 tube with 13V heaters, that one works fine on 12.6V heaters but my amp has only 6.3V. Of course, no urgency, I have plenty to sample before that.

Speaking of progressive rock reminded me that I listen for 2 days already to the latest Dream Theater album. Quite good I would say.

 

[DasguteOhr]

Since my experiment with EL5 ended brutally by one of my biggest enemies called hum I had to find a solution. In the end we are in the weekend when my schedule allows me to perform more experimentation. So I replaced the Tungsram EL5 from the output stage with Philips 4654 metal base. These tubes are for me a kind of reference for transparency and detail. While I do not own any of the famous Philips EL34 metal base, I consider these predecessors very nice sounding and I expect, in the same style. Here people experimenting with both can help me verify my assumption.

View attachment 145232

I have not changed anything on the input stage, Siemens E288CC is perfect from my point of view. But as usual, this tube combo has a problem. It sounds more sterile and dry than what I usually like to listen. Is this a technical presentation which lacks some enjoyment? I would say yes. For me this kind of sound goes more towards Violectric house sound and I sometimes ask myself if this is what we would like to achieve in a tube rolling thread. These very low distorted and technical tubes can compete, in my view, with any solid state amplifier, but because the sound lacks harshness and it is less fatiguing, is for me always better. I guess this was one of the reasons I started to enjoy tubes, besides the diversity you can obtain by tuning your amplifier.

I will remain here for a while, but I will try to document myself a little bit about EL5 and also E288CC. I would like to know more about them and also what experiences had others.

a little bit about the history and origins of the EL 34. Who produces this tube for which company. If you ever get your hands on an EL 60 with a metal loctal socket, the beautifully crafted tube also sound very good.
was only produced for a short time with B9G socket was not a best seller and was then converted to octal as el34.


Difference only socket

 

[Designsfx]

a little bit about the history and origins of the EL 34. Who produces this tube for which company. If you ever get your hands on an EL 60 with a metal loctal socket, the beautifully crafted tube also sound very good.
was only produced for a short time with B9G socket was not a best seller and was then converted to octal as el34.
View attachment 145256

Difference only socket

That’s a great chart! I wish there were more examples of this out there.

 

[Mr.Miniwatt]

a little bit about the history and origins of the EL 34. Who produces this tube for which company. If you ever get your hands on an EL 60 with a metal loctal socket, the beautifully crafted tube also sound very good.
was only produced for a short time with B9G socket was not a best seller and was then converted to octal as el34.

Your diagram is very interesting and it confirms some of my findings, that the 4689 is in fact in the same style of sound as the EL34, being more musical and with sweetened mids. 4654 metal base is more linear, more close to the source and it is for me a reference in terms of neutral sound. The variation of getters for these was quite big, I have here disc getter, 2/3 disc, half disk, flat ring and double D-getters. And I guess this was also the order in the timeline. I will show a few tubes from my collection:

Philips Miniwatt 4689 (date code 52/FE5, flat ring getter):




Philips Miniwatt 4654 (date code E42/58K, 2/3 disc getter):



And the octal version Philips Miniwatt 4654K (date code P73/LIH, double D-getter):



From what I know, these were produced only in Eindhoven (5-code) and Bruxelles (L-code) and there is a slight difference in sound of the ones made by Philips in Holland compared to the ones made by MBLE in Belgium. In my case, I definitely prefer the Holland made versions.

It is interesting to see that from rounded plate, they transitioned to rectangular plate in the EL60 era. Some very old Philips EL34 metal base have this kind of black base instead of the flat one we see in your photos, but as I said I do not own any of them, I have however a few pairs of EL34, non metal base which I am not currently using because I prefer 4654 or 4689. But if you would ask me to choose between 4654 and 4689 I will still choose 4654. The tubes which are more musical (4689, EL34, EL41, EL51, EL84) tend to be warmer and more fuzzy in the lower registers, so you get a more "fun" tuning and renounce a little bit on the technicalities. These more musical tubes are also usually higher transconductance versions.

Regarding the chart, my remark is that Siemens/SEL Lorenz never produced EL34 and only rebranded. Siemens in general rebranded a lot of tubes, but in Germany some very rare EL34 metal base were produced by Telefunken. I also haven't seen any EL34 manufactured by Valvo in Hamburg. I am in general looking at manufacturers codes on the tubes and ignore the branding because it can be anything. For example I have a few Valvo EL34 branded tubes, with Valvo branded boxes which are in fact Mullard EL34 Xf2 double ring getters. Here is an example:


The Valvo logo, almost deleted, can be observed in the left side, date codes on the glass on the right side, Xf2 / B2J5, manufactured by Mullard in Blackburn.

And regarding tube boxes, I will show some original boxes for 4654K and 4689 manufactured by Philips.



Or these:



If people are interested we can continue to discuss about EL34 and I can come with some more photos of newer EL34 production, even some 6CA7 (american versions).

PS. I did not knew about EL61. Interesting.

 

[Mr.Miniwatt]

Speaking about metal base tubes and loctal socket reminded me of some more unknown tubes which have an internal construction closer to the old Philips metal base tubes we already discussed. So let me present you the Philips EBL21. This is a double diode pentode, successor of EBL1 where the pentode is an EL3 equivalent. I have not tried this in output stage, even if they should work, by triode strapping the pentode inside, but I tried these in input stage with not very nice results. In short, sounded veiled and did not reach the standards to remain in my usual suspects list.



There are also some Tungsram versions, one example here:




As you can see, this is a rebrand, the original yellow print is specific to Tungsram, and that "3" on a metal plate inside the glass is something I have seen at Telam tubes (for example Polam/Telam EL84, very nice EL84 tubes produced in Poland).

 

[DasguteOhr]

Your diagram is very interesting and it confirms some of my findings, that the 4689 is in fact in the same style of sound as the EL34, being more musical and with sweetened mids. 4654 metal base is more linear, more close to the source and it is for me a reference in terms of neutral sound. The variation of getters for these was quite big, I have here disc getter, 2/3 disc, half disk, flat ring and double D-getters. And I guess this was also the order in the timeline. I will show a few tubes from my collection:

Philips Miniwatt 4689 (date code 52/FE5, flat ring getter):


View attachment 145267

Philips Miniwatt 4654 (date code E42/58K, 2/3 disc getter):

View attachment 145268

And the octal version Philips Miniwatt 4654K (date code P73/LIH, double D-getter):

View attachment 145269

From what I know, these were produced only in Eindhoven (5-code) and Bruxelles (L-code) and there is a slight difference in sound of the ones made by Philips in Holland compared to the ones made by MBLE in Belgium. In my case, I definitely prefer the Holland made versions.

It is interesting to see that from rounded plate, they transitioned to rectangular plate in the EL60 era. Some very old Philips EL34 metal base have this kind of black base instead of the flat one we see in your photos, but as I said I do not own any of them, I have however a few pairs of EL34, non metal base which I am not currently using because I prefer 4654 or 4689. But if you would ask me to choose between 4654 and 4689 I will still choose 4654. The tubes which are more musical (4689, EL34, EL41, EL51, EL84) tend to be warmer and more fuzzy in the lower registers, so you get a more "fun" tuning and renounce a little bit on the technicalities. These more musical tubes are also usually higher transconductance versions.

Regarding the chart, my remark is that Siemens/SEL Lorenz never produced EL34 and only rebranded. Siemens in general rebranded a lot of tubes, but in Germany some very rare EL34 metal base were produced by Telefunken. I also haven't seen any EL34 manufactured by Valvo in Hamburg. I am in general looking at manufacturers codes on the tubes and ignore the branding because it can be anything. For example I have a few Valvo EL34 branded tubes, with Valvo branded boxes which are in fact Mullard EL34 Xf2 double ring getters. Here is an example:

View attachment 145270
The Valvo logo, almost deleted, can be observed in the left side, date codes on the glass on the right side, Xf2 / B2J5, manufactured by Mullard in Blackburn.

And regarding tube boxes, I will show some original boxes for 4654K and 4689 manufactured by Philips.

View attachment 145271

Or these:

View attachment 145272

If people are interested we can continue to discuss about EL34 and I can come with some more photos of newer EL34 production, even some 6CA7 (american versions).

PS. I did not knew about EL61. Interesting.

Nice tubes you have
Mullard el 37/38 tubes can be nice alternative too, be careful B+ not higher 400volt dc

As the tube looks from the shape, the bass sounds rather neutral at the base, in the midrange fuller (thicker) and at the top a little reserved smooth

 

[Mr.Miniwatt]

Nice tubes you have
Mullard el 37/38 tubes can be nice alternative too, be careful B+ not higher 400volt dc
As the tube looks from the shape, the bass sounds rather neutral at the base, in the midrange fuller (thicker) and at the top a little reserved smooth

I do not have any Mullard EL37 but I have some EL38. This one is branded Philips "Made in Holland" but it is in fact manufactured by Mullard in Blackburn as the codes etched on glass are telling us.



These EL38 have an interesting construction. These are black base, Hm1/B2D2, but I had in the past brown base, double ring getter and also double rectangular getters. All sounded the same to me but I am unsure how close are these to the grey coated EL37. In my view, these grey coated tubes sound an idea warmer, the most obvious differences could be seen at KT66, clear glass vs grey glass. For me these EL38 are fairly neutral, but feel somehow tasteless, I will chose at any day or hour EL156 instead of them.

It is also true that I am not quite listening to british made tubes for some time already, I always prefer the ones made in Holland or Germany.

 

[DasguteOhr]

I do not have any Mullard EL37 but I have some EL38. This one is branded Philips "Made in Holland" but it is in fact manufactured by Mullard in Blackburn as the codes etched on glass are telling us.

View attachment 145277

These EL38 have an interesting construction. These are black base, Hm1/B2D2, but I had in the past brown base, double ring getter and also double rectangular getters. All sounded the same to me but I am unsure how close are these to the grey coated EL37. In my view, these grey coated tubes sound an idea warmer, the most obvious differences could be seen at KT66, clear glass vs grey glass. For me these EL38 are fairly neutral, but feel somehow tasteless, I will chose at any day or hour EL156 instead of them.

It is also true that I am not quite listening to british made tubes for some time already, I always prefer the ones made in Holland or Germany.

Interesting that you describe British tubes in a more neutral way. Mullard is actually known for having a richer timbre in the midrange and for giving voices more body, for example. Mullard will never have the same dynamics and detail resolution as Telefunken tubes. That's what I hear when I compare both manufacturers. If you like a 156 pentode, you'll definitely like the RS 1003 tube from the F2a family. In terms of performance, both are on a similar level.

You can see from my little avatar what kind of tubes I prefer. The manufacturing quality of the Ulm factory, Germany is outstanding.
My sweet little rs1003 amp runs in my cousins system in the moment.love that tube
She needs 2.3 amps heating

 

[Mr.Miniwatt]

Interesting that you describe British tubes in a more neutral way.

Not all of them, only EL38.

If you like a 156 pentode, you'll definitely like the RS 1003 tube from the F2a family. In terms of performance, both are on a similar level.

I have to admit I did not knew about the RS 1003. I searched for the datasheet but it had no triode graphs to understand if I can bias these. Luckily I found here a triode connection measurement. I will borrow the graph, it seems for 20mA/200V I'll need around Vg1 =-8V.


This tube is very powerful, high mu and transconductance, seems dynamic. A power horse, nice one, thank you for letting me know about it.

I saw the ECC808 high-mu double triodes in your avatar, also read your signature where you speak about E88CC. I am also a big fan of the frame grids and E88CC. Tried also some nice Amperex ECC88 on my amplifier in input stage, very nice sounding. ECC88 has maximum Va = 130V but I put it at Va = 180V and 4mA here and worked without problems. In the end it has Wa = 1.8W / each section. Before trying it I read a lot about from where comes this limitation and why ECC88 is only 130V while the "pro" versions E88CC are 220V. Looking at ECC88/E88CC/E1888CC you see that constructionwise they are close. The explanation I was able to find is that the limitation comes because these were intended initially to be operated in cascode mode and in audio in the way we use them this is not needed anymore. Since the prices of E88CC are quite high, solutions like ECC88 or PCC88 are welcomed as substitutes.

 

[DasguteOhr]

Not all of them, only EL38.

I have to admit I did not knew about the RS 1003. I searched for the datasheet but it had no triode graphs to understand if I can bias these. Luckily I found here a triode connection measurement. I will borrow the graph, it seems for 20mA/200V I'll need around Vg1 =-8V.

Too small you need min. 200volt/ 100mA ua=ug2, ug3=0V vg -4V opt 2.5 k
If you like ecc88 as driver here a nice working amp if want build it.
Pout ~ 9.5 watt 3% thd

View attachment 145320
This tube is very powerful, high mu and transconductance, seems dynamic. A power horse, nice one, thank you for letting me know about it.

I saw the ECC808 high-mu double triodes in your avatar

If build a phono amp with the ecc808(ecc83) this tube have low miller cappacity real good for work with sut.

, also read your signature where you speak about E88CC. I am also a big fan of the frame grids and E88CC. Tried also some nice Amperex ECC88 on my amplifier in input stage, very nice sounding. ECC88 has maximum Va = 130V but I put it at Va = 180V and 4mA here and worked without problems. In the end it has Wa = 1.8W / each section. Before trying it I read a lot about from where comes this limitation and why ECC88 is only 130V while the "pro" versions E88CC are 220V. Looking at ECC88/E88CC/E1888CC you see that constructionwise they are close. The explanation I was able to find is that the limitation comes because these were intended initially to be operated in cascode mode and in audio in the way we use them this is not needed anymore. Since the prices of E88CC are quite high, solutions like ECC88 or PCC88 are welcomed as substitutes.

My linestage runs with e88cc or 6h30 tubes voltage ~100volt 9mA/ or 35mA 6h30 sounds both pretty good.