PX4 vs 2A3

[Paul Barker]

Thank you Jaen and Nick.

Jaen your comment about the straight sided PX4 sounding toppy does line up with my experience, and since Nick brought the 300b into the mix, I would say the PX4 demonstrates the greatest lack of the 300b as we used to experience it 15 years ago, any amp around with it in at that time including the WE 300b lacked finesse at the top end. These days people do better with it. For me the PX4 outed the 300b. though they were different power classes so it wasn't a comparison anyone else would value it showed me the error of the common direction.

Shame I never managed to obtain balloon PX4's and also a great shame two of my balloon PX25's died. But I have some good ones of those left, just a few.

I think Nick has highlighted an error in my rationale, the curves don't tell the whole story.

Jaen the chances of me hearing a German AD1 are very slim, and never expect to purchase any unless I turn out to be one of those unusual lottery winners that gets double figures of millions.

But thanks for sharing the very useful experience.

It is shame on me I never even tried my single AD1 to date. But if measurements are anything to go by it shows lines more equally spaced over to the right than any of my PX4's and 2a3's are out of the game altogether if 2nd harmonic distortion is the measuring line..

Thinking about it, here it is, could this be German made? Writing is English.
Here it is actually having it's curves traced.



Further more, this valve, with a BR4 base strikes me it could be another AD1 and maybe it is German by the spelling. Steve maintains it is a version of the PX4. I am not convinced, because it's curves are exactly the same as the AD1 I have, the bottle is the same shape, just it's on a British base.

[Alex Kitic]

Just saying the modern manufacturer's are misguided by the USA economic dominance (which is not guaranteed to continue).

While I am not the least a fan of the US (I was even brought up not to be inclined to that country, just like I am currently bringing up my children with the idea that they must study and leave the country if they want to have half a decent life) - the economic domination of the USA will continue: they will see to it one way or the other.

Not to say the 2a3 and 300b are bad valves. Just that there is better!

Of course they are not, and while I would be more than happy to use PX4 and PX25 instead, those are virtually extinct.

As far as contemporary production goes, I tend to consider those tubes as a kind of their own, something new and maybe worthwhile: I do not believe in true replicas.

[JeanBeo]

Hi Paul,
Your AD1 could be French or Deutch made as the German Philips-Valvo made have a different shape. Is there a factory code on the tube?

Could your mystery tube be a Tungsram P15/250 (an AD1 with 4 pins socket) like the one on the picture?
Is there any marking? Looking at your picture, there is something written on top of the bulb.
Jean-Noel[/img]

[Alex Kitic]

...at that time including the WE 300b lacked finesse at the top end. These days people do better with it.

I think I already wrote about it, but I guess it is OK to point it out one more time:
The Chinese fake mesh 300B, in particular the globe shaped one (I have not heard the other ST shaped type, they are not identical in construction since the filament suspension is different - but I am going to find ou, sooner or later) - is particularly good in the mids and highs. Actually, the finesse is addictive and impressive, resembling the very best possible. The bass is less prominent, but in the RH300B that is not a problem since quantity (oomph) is traded for quality (fast and vibrant).

This characteristics is so impressive that when I think of 300B (like EH300B) I immediately separate mentally the globe shaped fake mesh as a highly desirable tube on its own. I should probably try other similar Chinese tubes to check whether it is the fake mesh or the suspension. My amp cabinets are not metallic and between medium density and wood and Plexiglas, I believe they aren't too resonant.

[Paul Barker]

Th anks both.

I'll have a look at both valves tomorrow for other marks but don't recall finding any. The traces reveal they are one and the same electrically and consequently different to px4 Electrically. Keep them for best I shall.

[steve s]

Hi Paul,
Your AD1 could be French or Deutch made as the German Philips-Valvo made have a different shape. Is there a factory code on the tube?

Could your mystery tube be a Tungsram P15/250 (an AD1 with 4 pins socket) like the one on the picture?
Is there any marking? Looking at your picture, there is something written on top of the bulb.
Jean-Noel[/img]

That tungsram i believe is a re badged mullard, i have both to compare somewhere i will check them out later
They are are different anode to the osram px4 so i would expect differences,

My own opinion of my px 4's is the the earlier versions retrieve another level of finer detail, the bass and the top end in my experence are very close.

But i would guess its all about opinion and very system dependant.

[steve s]

[quote="Alex Kitic"]
and while I would be more than happy to use PX4 and PX25 instead, those are virtually extinct.

As far as contemporary production goes, I tend to consider those tubes as a kind of their own, something new and maybe worthwhile: I do not believe in true replicas.[/quote

I think its good to think of the modern production as not true replicas
Thats really been been Pauls point, providing evidence to prove some of them are nothing like the originals
But in there own right many of them provide a very good sound

There are still plenty of PX4 and 25's around though.... There is a cost involved obtaining them though..

[Alex Kitic]

Yes, I guess Paul shares exactly that opinion - current production tubes cannot be considered true replicas (or clones), rather "imitations".

It is quite normal that those tubes should exhibit differences in respect to the NOS tubes, just like the NOS tubes are not all created equal.

In all frankness, I am more skeptical when it comes to the various current production tubes from boutique manufacturers from mittel-Europa. While I would like to consider those tubes really special, they are exorbitantly expensive, and it is disputable whether their sonic value holds water in the quality/price relationship. The Chinese tubes can be very good sounding and are rather cheap - in fact, it is possible that current Chinese production is slowing the rise of prices of NOS tubes.

What I mean is that some people really are so well endowed with funds that they can spend whichever amount in the search for perfection (or perceived perfection, or marketing induced perfection) and get to enjoy it without suffering. When a representative or dealer tells you that their extremely expensive tubes are anyway targeted to a rarified and particular clientele... what else is there to add? Frankly, I do not care - I can live happily without ever trying any of those boutique tubes, and if asked to choose a gift, I would always choose the NOS version, without hesitation and regardless of price.

[JeanBeo]

I just had an other look at the picture of your tube, Paul.
If you zoom in, you can clearly read TUNGSRAM written on the top of the bulb. If it measures the same as an AD1, it will be a P15/250 which is the same tube as AD1 but with a 4 pin socket instead of the "transco" type socket.
As Steve suggested, it could well be a Mullard rebadged as there has been a lot of tube swapping between manufacturers. I don't know Mullard references very well. Did they made AD1-equivalent valves?

There is a page on the Universal Vademecum on the AD1-PX4-p15/250 valves but as I am a new user I cannot yet post links.
You ca find it on Frank's Electron Tubes website.

Jean-Noel

[Paul Barker]

I have the book thanks.

[steve s]

I take my comments back paul, well sort of

My Mullard aco44 are different to my tungsram,the valve is similar but not the same, my tungram has nearly a black inner coating, the mullards are grey, the constuction is different too, i have another that looks identical in construction to the tungsram but slightly shorter its a radio record ac/ px4, which i've never heard of?
One of the mullards is labeled cosser xp4. Its nothing like the early cosser xp4

The radio record is on the left, tungsram next, then the mullards, i have a few more mullards they are all the same though. If you click on the pic they will be the right way..

[steve s]

I need a decent camera my ipad don't cut the mustard ..

[Greg]

I need a decent camera my ipad don't cut the mustard ..

Haha. iPad is fine for this type of shot. You need to get your light right and probably little more as long as your hand is steady.

[Alex Kitic]

Sometimes I get the impression that topics just die... and this one is actually interesting. Besides agreeing with Paul about the PX4 and the rest, Chinese tubes included (although I consider those as current production different tubes and rather enjoy them, not expecting the emulation of the sound or quality of the produces of yester-yore)...

There is one aspect of the PX4 which is "inferior" to the 2A3. It is the voltage rating of the filament, 4V vs. the 2.5V of the 2A3. This implies more hum with AC on the heaters - particularly in classic no-feedback amps. Of course, it is less hum than from a 300B in the same amps... but the 2A3 has an advantage here.

That said, I have managed to find my pair of 6B4G, used a long time ago with my SE no feedback amp. Well, there are a few things to stress here:

1) Hum: obviously higher than with 2A3, but actually it seems that the 6B4G is the "highest level" of hum on the "up to inaudibility" scale... after this level, it becomes rather easy to hear the hum if one sticks his ear in the woofer or midrange of an RH amp.

2) Hum take 2: I remember the same pair of tubes used to hum A LOT more in my no-feedback SE amp: with the same speakers and rest of the system I could hear hum between songs when listening at late night hours (i.e. when the outside noise is very low, when I can hear both battery operated clocks in the room clicking as the seconds go...). What does that mean? Well, it means that the RH type feedback does something to the AC filament hum of direct heated tubes... so who is willing to try it at least for academic sake, might try a quick mod on his 6B4G amp...

3) Tubes lifetime - my pair of 6B4G (NOS double anode type) was used for years, but during those years I probably did not do all that much listening. Thus a realistic estimate is between 1000 and 2000 hours. But they measure like new, i.e. bias voltages are just like they should be in a new pair. I cannot compare directly since they were used with a cathode resistor and the 300V/50mA rationale... but it seems like nothing has changed.

4) Sound: obviously, the 6B4G sound very much similar to the Chinese Octal 2A3 (as made for Audio Innovations amps). The construction is actually different enough - separated anodes and different filament suspension: the Shuguang tube suspends the filaments directly on the upper mica... But the sound is very similar, and it is frankly hard to say which one is better. Maybe the 6B4G NOS... but the Chinese 2A3 has a more pronounced midrange and more typical DHT sound signature... but great highs on both...

[Paul Barker]

On the hum, you can get rid of 6b4g hum in a normal SE amp (without feedback) with Stephie Bench's hum cancellation technique.

The schematic on the right

I tried it and it worked for me on these speakers which are I think 95db maybe a little less.

Regarding raw PX4 with just the 50hz component nulled on Lowther speakers sounds like the substation is on the plot of land beside the house.

I remember someone telling me how they had visited a certain character in the DIY community in London area who has a lot of presence on the net. (He shall not be named.) The visitor told me, that when he and his friend came away they turned to each other "didn't it hum?".

In those days it wasn't uncommon for a few of us, myself included to tolerate this 100hz hum in single ended amps. PP amps by simply ensuring same phase for the push as the pull came with their own natural cancellation. My last push pull dht amp didn't need any help, hum was a non issue with AC heating.