[Isaacc7]

@Isaacc7 I'm using old Russian version 6П7С of the 6bg6ga. I'm very pleased with It and even more than with some 807 tube I have.
I'm a bit curious about the 13D1 tube, is it a 25V SN7 like https://frank.pocnet.net/sheets/155/1/13D1.pdf ? Have you ever compared with 12SN7GT (I'm only limited to 6.3 and 12.6 V for heater so 25V is not for me).
For bad recording or mp3 listening, i'm using RCA gray glass 6SNT7GT it make sound a bit smoother and makes recording default less hurting me than with 6SL7 or even sylvania 6SN7 or 7N7..

Yes, the 13d1 is a 25v tube. I have, and use, plenty of 12v tubes but I don’t have another Brimar in 6v or 12v to compare, sorry. Among 12sn7 I really like the 14n7 (best Sylvania in my opinion), GEC b36, and RCA 12sx7. I do a lot with single triodes as well. 12j5gt are cheap and many of them sound amazing. Glad to hear you’re getting good sounds from your tubes. I am going with the idea that the 6bg6 and 807 are essentially the same tube most of the time. That way I only have to buy each brand once lol. I have RCA, GE, and Sylvania 6bg6ga and a whole bunch of European 807 and equivalents. I love this tube family so much.

 

[OctavianH]

I have to admit @Isaacc7 that I read with a lot of interest your findings about triode vs ultra linear. But while doing that I also realized I did not really understood correctly what ultra linear meant. From time to time we need to go to Wikipedia.

A pentode or tetrode vacuum-tube (valve) configured as a common-cathode amplifier (where the output signal appears on the plate) may be operated as:

• a pentode or tetrode, in which the screen-grid is connected to a stable DC voltage so there are no signal variations on the screen-grid (i.e. the screen-grid has 0% of the plate's output signal impressed on it), or
• a triode, in which the screen-grid is connected to the plate (i.e. the screen-grid has 100% of the plate's output signal voltage impressed on it), or
• a blend of triode and pentode, in which the screen-grid has a percentage (between 0% and 100%) of the plate's output signal impressed on it. This is the basis of the distributed load circuit, and is usually achieved by incorporating a suitable "tap" on the primary winding of the output transformer that the vacuum-tube (valve) is connected to.

The impression of any portion of the output signal onto the screen-grid can be seen as a form of feedback, which alters the behaviour of the electron stream passing from cathode to anode.

And my confusion was related to pentode and ultra-linear, I was thinking these are the same thing. At least until you explained it here. Now that I started to understand what you do, let us know more about triode vs ultra-linear and how you get along with it. This is something I cannot do but I consider it a point of interest.

Regarding my own rolling activities: Saturday was a point in time which makes me think it does not make sense to try new tube types. When I first put A2293 on the amplifier I was very impressed, a nice triode sounding somewhere in EL84 style with some british sweet mids, what to say, good sound. On Saturday when I put it 1:1 with EL50 I could not listen to it anymore. So, it was unexpected for me to be disappointed about something I was praising a few days ago. In short: I'll stick to my side contact pentode era and try to see what we can do in that range of tubes, next stop EBC3 which is a double diode triode! Not many triodes on that family so I am really curious to see how it will perform.

Later edit: Interesting discussion here. Now honestly I know not much about load lines and so on, but does it make a difference to evaluate triode/pentode/ultralinear on a headphone system or on some speakers? I have no clue and it would be nice to know if the findings on the Odyssey will be relevant on my use case with a headphone.

The linearity of the frequency response is "better" with Ultralinear. However, that is usually achieved with more negative feedback derived from additional OPT windings, which squashes or compressed the sound. So your Pentode operation will yield better response and more of a "tactile" or SET sound*. The 5 elements of a Pentode tube can be considered more complication than say a 3 element triode, so many purists prefer Triode designs because of the simplicity (SET) and reduction of elements.

By that ideology a Triode would have an even more pure sound, but as you move away from the linearity of Ultra-linear, you pass Pentodes and move on to Triodes. So Triodes are typically even less linear in frequency response than Pentodes, with a commensurate reduction in damping factor to boot.

Which drags us kicking and screaming to the topic of speakers and their load characteristics when "viewed" by an amplifier's output circuit. If your speakers are a relatively benign load, Triodes might be the best compromise for overall performance, but if they're less benign speakers then Pentodes driving them might be better. If they're a really tough load (low impedance with inductance and capacitance swamping resistance), then Ultra linear might be the best performing topology.

So... if Pentode is better in your opinion and with your speaker load characteristics, then it's better! The speaker/amp interface in a system may be just as important as the arm/cartridge combination in an analog front end. Those two combinations seem to have the greatest determination on the sound of an audio system.

 

[Isaacc7]

I have to admit @Isaacc7 that I read with a lot of interest your findings about triode vs ultra linear. But while doing that I also realized I did not really understood correctly what ultra linear meant. From time to time we need to go to Wikipedia.



And my confusion was related to pentode and ultra-linear, I was thinking these are the same thing. At least until you explained it here. Now that I started to understand what you do, let us know more about triode vs ultra-linear and how you get along with it. This is something I cannot do but I consider it a point of interest.

Regarding my own rolling activities: Saturday was a point in time which makes me think it does not make sense to try new tube types. When I first put A2293 on the amplifier I was very impressed, a nice triode sounding somewhere in EL84 style with some british sweet mids, what to say, good sound. On Saturday when I put it 1:1 with EL50 I could not listen to it anymore. So, it was unexpected for me to be disappointed about something I was praising a few days ago. In short: I'll stick to my side contact pentode era and try to see what we can do in that range of tubes, next stop EBC3 which is a double diode triode! Not many triodes on that family so I am really curious to see how it will perform.

Later edit: Interesting discussion here. Now honestly I know not much about load lines and so on, but does it make a difference to evaluate triode/pentode/ultralinear on a headphone system or on some speakers? I have no clue and it would be nice to know if the findings on the Odyssey will be relevant on my use case with a headphone.

I dislike analysis like the one you linked to. It sounds technical but is actually just audiophile magic thinking dressed up with a sprinkling of tech terms. In particular the idea that a problem with pentodes is that they are more complex and triodes are simpler doesn’t make any sense from a sound quality perspective. Triodes and pentodes basically work the same way but the pentode, in pentode or ultralinear operation, has additional control grids for more efficient operation. The signal flow is the same in both. And if you wire a pentode as a triode, it is a triode electrically. Running pentode or ultralinear does mean that the amp design is a little more complicated. You have to supply the screen grids with power as well as the anode. In pentode mode you would ideally want a regulated screen supply. So yes, the amp is more complicated but that doesn’t magically make the sound worse.

The best part was when he talked about different speakers performing best with different kinds of amps. His mentioning of ultralinear feedback quashing dynamics doesn’t make any sense. Ultralinear is a kind of feedback but it is a different kind than is inevitably needed with pentode output. Pure pentode operation always requires global negative feedback, that is feed back from output to input incorporating the entire circuit as part of the feedback loop. This kind of feedback has the very well deserved reputation of messing up the sound IMO. It’s why I stay away from hifi amps with 12ax7 in them. The only reason to have that much gain is to give you plenty of room for lots of global negative feedback. High feedback amps are the go to designs for classic high power amps from the likes of McIntosh, Dynaco, Marantz, Quad, etc. They measure very well and are powerful. It should be noted that all of those companies switched to the even better measuring solid state devices when they became practical to do so.

Where was I? Oh right, feedback. Ultralinear feedback uses feedback from the output stage back in on itself through the transformer. It has the same effect of linearizing the signal but with a much shorter path and fewer of the issues that global feedback has. Apparently it is also easier to implement. If your circuit design is too complicated global feedback can lead to oscillations. You can think of pentode mode as having zero Local feedback and triode mode as having 100% local feedback with ultralinear being somewhere in between. Triode mode offers to lowest distortion (hence needing less global feedback) and lowest output impedance but lowest output power. What works best will depend on your speakers. Headphones are so sensitive and tend to have much simpler loads so power and output impedance typically isn’t as big an issue. The different output modes will sound different because the feedback changes the distortion profile so maybe ultralinear could still be desirable for headphone amps.

Sorry that got so long. I am hardly an expert in this stuff but I feel like I have a pretty good grasp on the basic trade offs of big questions of amp design. Because speakers require more power there are more tradeoffs to worry about. My belief is that high global feedback designs simply don’t sound as good. I suspect it is why I have never really liked solid state as much. Those amps inevitably have lots of it. But if you need the power, judicious global feedback is a great tool to have to modify the sound.

 

[Isaacc7]

In other news, my amp is dead. The light comes on but I am not getting any power shown on the B+ meter or the bias meter. And of course no sound is coming out. I can only guess that I’ve done something to the power supply. It was working fine all night. Sigh.

Edit to add: Looking at the internal pictures Tomas sent me while he was building it, I can see several internal fuses. I will check those first before completely freaking out. It’s going to be a while though, I can’t actually lift this amp. And of course if it is a fuse the question of what caused it to blow is a worry as well.

 

[OctavianH]

In other news, my amp is dead.

These are bad news, well, let's hope for the best.

 

[Isaacc7]

These are bad news, well, let's hope for the best.

I have a working hypothesis. My current settings (pardon the pun) are as “wide open” as I’ve ever run the amp. I have in the past only gone up to 50ma per tube. I started with that setting with the 6bg6 tubes and then upping it to 60ma. When I switched to the vt60, I lowered the bias in case there was a weird mismatch and then upped it to 60ma. Since there is a fuse right by the regulator, I wonder if starting the amp with the bias set that high is what did it. That would be good and bad news. Good of course that there isn’t any actual damage to the amp. Bad in that I will have to fiddle with the bias every single time I turn on the amp with that family off tubes. Still, that’s what I’m hoping for.

 

[hpamdr]

I have the same issue with my new amp... I was really more than lucky to find the builder next to my Home !

The builder came home and did a quick diagnose this should be repaired when he have time.

I Also had an issue with fuse on Thomas amp at the very first. (like @OctavianH )

The story with new amp:
I first blow power fuse, next i replaced with a bigger value as my home voltage is a bit high and following builder advise. (from T1.6A to T2A)
It worked for two days and..... finally no sound in one side and other side crappy...

How the diagnose was done using a simple multi-meters:
First we removed all tube:
Turn on power and see if it light up.
Check heater voltage value on each tube socket (we got the 6.3) in your case you should verify probably all values to see if heating transformer is still ok.
Check rectifier tube socket to see power transformer voltage -> all was ok in my case
Put SS Rectifiers (To not destroy GZ34 and not have to check it) and check voltage on input/output tube Anodes. We got completely crazy results in output side. He suspected a capacitor blow !
Turn off power.
He did some other test checking resistor between grids, remaining voltages,.....
Finally we opened the amp and flipped it to check inside. One of the capacitor died (round top) and another one in not in good shape. During additional check we also found that protective resististor (like fuse) between tube and output transformer blow in order to protect transformer....
The amp will be repaired just replacing some caps, fuse resistors and a small update will be done (a new trick he was not doing in 2016)

 

[OctavianH]

I Also had an issue with fuse on Thomas amp at the very first. (like @OctavianH )

Indeed, Tomas delivered my Eternity with 1.6A slow blow fuse. At the moment after several tries I have a 3.15A one and no problem. I measured here 240VAC directly at the wall, so maybe this was the problem.

 

[OctavianH]

Finally some new developments related to the origin of the Philips PE06/40N. The guys from McChanson thread helped me tremendeously by showing me some other newer construction type of the same tube, that one made in France. And that helped me understand that my tube, which has the old Philips coding is not in fact a D-code tube. We have on mine KL/DUF and on the newer one with the new code DU8/E4F. So the TT = DU, C=F/8 depending on the version and then we have the FYM or FM. E4F is a french tube made around 1964? Looks so with ring getters right? Well, but mine are KL and K is not a factory in the code books I have here. Is missing. Why? Hell knows. But I went to the storage and made a photo of the box (or let's call it better packaging) I have for these:

Here we have a date, 6.11.1952 which leads us to the old Philips code (because they changed it around 55/56). And in this old code we have K as a factory code. But I tried to understand the language these words are written in.

So it's Swedish? Because the message on the paper is clear: guaranteed for 1000 hours, until 6.11.1952, so these are older. Excellent, while time goes into a direction, I moved in the other direction with the tubes. So who are you KAFT Control Agency Radio? Because you inspected this tube, most probably in Sweden, but this does not mean the K-factory is also in that country. Where are you, K-code factory?

 

[Isaacc7]

Indeed, Tomas delivered my Eternity with 1.6A slow blow fuse. At the moment after several tries I have a 3.15A one and no problem. I measured here 240VAC directly at the wall, so maybe this was the problem.

I dunno, I am wary of substituting a higher rated fuse. The whole idea is that it should blow before anything gets damaged. If it has a higher rating and doesn’t blow then there is a higher chance of things after it getting damaged. Replacing fuses is annoying but they are a lot cheaper than repairing the amp!

 

[triod750]

Finally some new developments related to the origin of the Philips PE06/40N. The guys from McChanson thread helped me tremendeously by showing me some other newer construction type of the same tube, that one made in France. And that helped me understand that my tube, which has the old Philips coding is not in fact a D-code tube. We have on mine KL/DUF and on the newer one with the new code DU8/E4F. So the TT = DU, C=F/8 depending on the version and then we have the FYM or FM. E4F is a french tube made around 1964? Looks so with ring getters right? Well, but mine are KL and K is not a factory in the code books I have here. Is missing. Why? Hell knows. But I went to the storage and made a photo of the box (or let's call it better packaging) I have for these:



Here we have a date, 6.11.1952 which leads us to the old Philips code (because they changed it around 55/56). And in this old code we have K as a factory code. But I tried to understand the language these words are written in.



So it's Swedish? Because the message on the paper is clear: guaranteed for 1000 hours, until 6.11.1952, so these are older. Excellent, while time goes into a direction, I moved in the other direction with the tubes. So who are you KAFT Control Agency Radio? Because you inspected this tube, most probably in Sweden, but this does not mean the K-factory is also in that country. Where are you, K-code factory?

KAFT Kontrollbyrån Radiobesiktningen has to be the Swedish version of Signal Corps inspectors. And 'bränntid' is 'burning time', probably length of life within some parameters of use.

 

[triod750]

KAFT is probably short for Kungliga ArméFörvaltningen Tygavdelningen, seems to have been active between 1944 and 1954, then reorganised. So it must be a military test and control function (Kontrollbyrån Radiobesiktningen). But I have yet to find out more. Not easy to find any information.

 

[triod750]

Kungliga Armeförvaltningen Tygavdelningen can be translated into Royal Army Administration Equipment Department and Kontrollbyrån Radiobesiktningen into Control Bureau Radio Inspection.

 

[OctavianH]

Since we are speaking about Philips PE06/40N, I have put it to work, this time with Philips ECC40 Sittard. The combination is not accidental, I consider both as followers of the "old era", one because of the construction and the other because of the tone. And Sittard is for me somehow sharper but rich, so I said it will be a good pair with this one and I was not wrong.

I still think this tube is somehow the opposite of the sound of the red series. It's sharp somehow, fast and aggressive. I have no idea where they built it but it has nothing in common with those and sounds also an idea narrower. But the bass is punchy and with all these dynamics sounds quite unique. The glass is not coated but not clear either, it is somehow darker. And the construction itself is special, like somehow a combination of the old red series and newer tube. I'll show:

Similarities in construction can be seen below, and even if I cannot show the plate shape, believe me it's close or identical with this one but under the grey coating and not possible to photo and show better.

Definitely a very interesting tube and I hope that one day I will find out what KL/DUF means. Even if it is pinwise compatible with 807 this is a different animal, bias being different. One day we will know more about it.

 

[OctavianH]

I made yesterday some bold statements but I was not able to provide enough arguments, for example that Philips PE06/40N has common construction elements with "old" Philips red series which make me think it is one of the earlies pentodes they released with octal socket and might be in between old and new. Of course, pure assumptions. I also said that internal construction and plate shape in the 4654 and PE06/40N is similar, but soundwise they are quite the opposite. Now I made my homework and can also provide some arguments. To be able to see more inside I used a dead (lost vacuum) Tesla 4654 and a Philips 4654 where the red coating fell off, it's working perfectly fine but it is stored and used only to investigate construction. Please see below a photo of a Philips EL50 from top:

You see the plate? Mesh but the shape reminds you of the PE06/40N we have nicely presented in previous posts? Let's look at the bottom:

Now let's look as some Tesla 4654 produced in the 60s:

And the bottom photo of the same tube:

In the end, just for comparison, PE06/40N, same photo from yesterday:

I let you guys decide if there are similarities in construction or not. At least now I came to you with some arguments. One day we will know more.