[Isaacc7]

So that's how Deyan's adapters for 5b/254m looks. He's making a pair for me.

I will say that they hold onto the heat longer than the plastics adapters. Had to use a glove the other night to swap tubes. Usually I can just grab by the adapter within a few minutes.

 

[UntilThen]

I will say that they hold onto the heat longer than the plastics adapters. Had to use a glove the other night to swap tubes. Usually I can just grab by the adapter within a few minutes.

You just have to be patient and let the tubes and adapters cool off after powering off the amp. On days when I am really into tube rolling (which is most days), I have 2 amps powered on. While waiting for the tubes to cool down, I will use the other amp.

 

[UntilThen]

There are many cheap tubes which sound very good. For example this Philips 6BQ7A:

6bq7a are quite nice with an amplification factor between a 12au7 and 12at7 - 38. I have RCA and Philips Miniwatt ones.

 

[triod750]

6bq7a are quite nice with an amplification factor between a 12au7 and 12at7 - 38. I have RCA and Philips Miniwatt ones.

I have one Philips branded 6BQ7A here that is 'Made in U.S.A.'. Are there any internal differences in your versions?

 

[UntilThen]

I have one Philips branded 6BQ7A here that is 'Made in U.S.A.'. Are there any internal differences in your versions?

They are different. RCA ones have this [ structure on the side.

 

[triod750]

They are different. RCA ones have this [ structure on the side.

The one I have here looks like your RCA but is branded Philips in yellow and the text on the box is in French.

 

[Isaacc7]

Sigh. The fuses seem to be fine which means that there is something else going on. I didn’t see anything burnt nor did I smell anything so I’m not sure what’s going on. I guess the power transformer could have gone out but I always figured I would have heard or smelled something before it gave out.

The good news is that I have a torrid for the PT and those tend to not be too expensive. I also wonder if it would be even less expensive if I get one without a secondary winding for heaters since I can use external supplies. Anyway, I’m hoping for something simple and not too expensive.

 

[OctavianH]

I'll post some detailed photo of my 6BQ7A:

This has a sound towards solid state, nothing euphonic or holographic, but pairs well with the Philips 4654 metal base providing a kind of more neutral/technical sound. Of course, it is surpassed by many, like for example my all time favourite ITT Lorenz E88CC, but at the price I paid for it has a very good value. I expect it was manufactured in France by Mazda (Belvu) looking at those date codes. Those vertical points make me thing about Mazda/Belvu and that sort of tubes.

 

[OctavianH]

I guess it's time for me to continue on the path of the small red series tubes I plan to use in Eternity in input. I started this with EBC3 and ECH3, but there is a long road ahead. Let's continue, what he have here?

Well, a small invasion. But those more important are:

These are types I never tried before. Well, except ECH3 but that one was the Mullard straight bottle and here we have some french (I assume RT) made ST shaped one. Of course, my curiosity led me to try first ECF1.

Because I had no clue how to bias these I had to measure and those measurements led me to bias these around -11.3V. This is a medium value, one needed -10.2V and other -12.4V to reach 180V/4mA so well, I had to choose a medium value for both to be around that operating point. Gain is low for these, as expected from some pentodes. So I had to go above what I normally like on this amplifier, 1-2 o'clock was providing me the same volume level I am normally listening. So gain is below 20 for sure, hard to say exactly how much. In the datasheet they mention only the triode section with a mu = 20. Soundwise, dark and relaxed. This is the sound I am usually associating with RT. I was not very impressed about this, I prefer dark relaxed on output and sharper higher gain tubes on input.

Next I wanted to hear the EBF2.

Here I had to determine again the bias, and these bias around -11.6V as a medium value, so very close or the same as the ECF1. These had the same low gain but I was surprised to find a sound more transparent and less dark than the others. This was a surprise for me, I was expecting these to sound similar. Well, this remains a point of investigation for me because I like more what I hear on EBF2 than on ECF1.

It will take months for me to evaluate all, it's not even my prio 1. I want to listen more to EBC3 and EBF2 and try to see why I like these more than the others. The rest can sit in a box until I will have more ideas with them. A secondary purpose of mine is to obtain more clues about date codes and construction elements to be able to understand more about EL50 origins.

In the end, some nice detailed photos of what we discussed:

 

[OctavianH]

I was intrigued by the difference I claimed I heard when switching from ECF1 to EBF2. So I had to try ECH3, the ST shaped version.

The ECH3 ST shaped version, most probably also RT, sounded to me not very different than the ECF1. So this was again as expected, because my theory is that all these 3 types of tubes are sounding more or less the same, with RT dark relaxed flavour. In short, what I think is that the pentodes/hexodes insides these envelopes are biasing close and also sound close when strapped as triodes, and the different of type between ECF/EBF/ECH is related more to what is inside of the envelope. Of course, a theory. Since I never found anyone to listen to these I can consider it valid until a later point when someone or myself will invalidate it.

Because RT ECH3 and RT ECF1 sounded more or less close, I wanted again to check if the difference with EBF2 is the same. At a second try I felt they are not so different. So, it is clear that this was only a technical test, time will tell more about them. ECH3 biased around -8.2V, lower than the Mullard straight glass which was around -9.6V. Tubes are new, so here we see again how generic si the term of NOS. I will not go too much into the same direction trying many types of these, I got an idea about them and I honestly prefer the EBC3 made in Holland which has higher gain and sounds more transparent to me. All these pentodes are veiled, with the difference that the french ones are more romantic than the british ones. RT house sound vs Mullard house sound, which one you prefer, it should be present if you choose carefully one of these.

And as usual a detailed one with ECH3 ST shaped: