Blackburn/Mullard EL34

[Ivan H]

These (matching date code) Valvo branded duet been have in my JMP50 for around two months, so haven't yet seen a lot of use.
I did have to clean a little dust etc off them before taking the pic. Date codes B2J3 (Blackburn, 1962, October, 3rd week).
By coincidence, of all the single halo getter xf2 duets I have, the only "matching date code" duet (Philips Miniwatt branded) has the same B2J3 date code. The "2" in this instance showing 1972 manufacture.

These have been serving in my black
flag JTM50 type build. Pic is an old one.
One question I'd like to ask is what % of max plate dissipation people bias these (Mullard) EL34's to? I find I like them down toward 60% in my 50 watters. Cheers

 

[StingRay85]

I typically aim for around 35 mA, sounds good on all amps I have. Nice sets. Valvo labels were intended for the German market I guess. I have a similar set of '63, but unfortunately they're not in such pristine condition anymore. I pulled them from a Dynacord Eminent amp, that also contained smooth plate telefunken.

 

[StingRay85]

Could be handy for people with a Maxi Matcher 2. My data set. The line is average of all the used tubes. Probably safe to say that tubes above the line are better than the ones below

 

[Pete Farrington]

I’m not sure that much should be read into the transconductance reading you’re getting. That will tend to vary with anode current, so the higher current valves (ie at those particular electrode voltages) will naturally tend to have higher transconductance.

I suppose that the Maximatcher is intended to match valves, rather than fully characterise them.

To get a fuller picture, I think that the transconductance at 2 or more anode current levels, which span the normal operational range, would be an improvement.

The importance that the chart seems to place on anode voltage is unwarranted, in regard of pentode operation. Anode voltage only really has relevance to the anode dissipation and hence valve life. Neither anode voltage or dissipation (per se) are significant with regard to how the stage operates.
The control grid and screen grid voltages / the ratio between them, is largely what determines anode current, and hence transconductance and stage gain.
Admittedly that’s moreso for beam pentodes than suppressor grid types such as the EL34.

 

[StingRay85]

Hi Pete, I think you misunderstood me. If you consider the average as drawn by the trend line, anything above it is better than what is below. So at 35 mA you would want to read out 5.4 or higher. At 40 you should be above 5.7. So my NIB tube that measures 22 mA and 4.7 mMhos is still fine. The one that measures 38 mA and only 5.2 is suspicious. This is just silly data collecting, I know, but some things noticed me, for example that my Xf4 surely measure stronger than Xf2. Also, when I compare this to my 20+ RFT power tubes, they are well below the Philips tubes

 

[Pete Farrington]

Perhaps so, I’ll ponder it a bit more.
Whatever, kudos on gathering and compiling the data set!

 

[mildew]

Thanks for this thread, very informative. I have a small treasured collection of NOS Mullards, some blackburns, mostly Mullard labels.
Im trying to get them to last the rest of my life, so its awesome to learn so much about their construction.
Personally for rock gain or higher i prefer JJ's to NOS, but for home stereo and clean poweramping a digital device you cant beat NOS for reproducing "feels"

 

[Pete Farrington]

Once you've used them, they're no longer NOS, they become vintage production or whatever

 

[playloud]

This is an excellent thread!

I had an unfortunate experience with double-getter XF2s a couple of weeks ago. A local seller - who had only done me well 'til then - offered me a used quad for ~US$300. As I suspected, it was too good to be true. When I put them in my Marshall, one arced internally, one red-plated, and and the other two had mismatched bias (at least the date codes matched!) The seller had tested them on an emissions tester, but they obviously weren't up to 490V DC. I also managed to electrocute myself with those DC volts when I stupidly checked if the HT fuse was blown too soon after turning off the amp - at least that was memorable!

So these pics of working XF2s are making me a little sad. But I don't think I will taking any chances with used EL34s from here on out.

For the sake of additional data points, here are the exhausted ones (note the bias/redplate annotations!):

IMG_1292

• playloud
• Apr 23, 2021

IMG_6231

• playloud
• Apr 23, 2021

 

[StingRay85]

Damn, those look really, really bad. Flash almost gone, burn marks, no guide pins anymore. Any chance of getting your money back? Feel sorry for you. I hope this thread will be helpful for people wanting to buy Philips/Mullard in the future, if a tube looks like that, walk away.

You do raise a valid point. My tester only goes to 400V. But one should actually test their functionality and matching on higher voltages too, to lets say 500V. The only thing with a little value left is the nice Mullard boxes.

 

[playloud]

Oh yes. The seller refunded me right away and was extremely apologetic.

I figured they were pretty used but decided to take the risk, given the price. Now I know that was a bad idea...

 

[AndyD]

Excellent thread. Thank you very much for taking the time to write it. I have learned a tremendous amount about this iconic valve.

 

[stickyfinger]

View attachment 87899 View attachment 87900

So you can see left to right an Xf2 double ring getter, Xf2 single ring, Xf3 and Xf4. Notice the getter flash, and this dark thin transparent band below the shiny part. This is in my opinion the one and only true indication of a NOS/NIB tube. Maybe in the future I'll conduct a test and see how many hours it takes to disappear

Do you notice any internal noise when shacking them in you hand?

I ask as I've bought 3 pairs of clean NOS NIB Xf2 for my amps and 2 pairs have noticeable noise. One pair sounds like the cathode coil is loose (springy sound) and the other pair sounds like something metal is just not tightly fitted. 3rd pair is the quietist but still my modern JJ and Mustard EL34s are dead silent when shaken in the hand.

I haven't tried them in the amp yet as I've just recieved them today. Figured you would know as you are the expert in this department. Hopefully this is normal and wont decrease tube life or increase microphonics.

 

[Matthews Guitars]

The difference in the appearance of the silvering of the getter flash is likely due to a difference in the material used for the getter flash.

Today, Barium (Ba) is the standard material used. It is both efficient in its task and non-toxic.

But all alkali metals can be used as a getter, in one application or another.

During the years around WWII, the Germans used Thorium in a lot of tubes. Which is why you may nave heard that some old tubes are radioactive.

Beryllium has sometimes been used. That's toxic.

Strontium is sometimes used, too.

The difference in the getter flash material is likely what accounts for the difference in the appearance of the edge area of the getter silvering. The "rainbow" visible in the edge of older tubes probably indicates a different getter chemistry than is currently used.

Here's a paper on getters that may or may not interest you.

https://psec.uchicago.edu/getters/wilder_getter.pdf


Although I don't recommend doing this due to possible chemical hazards, if you were to break an old tube that has the rainbow edged silvering and smell it, as the getter reacts and turns to white powder you'll get a distinctive odor. Break a newer tube with a getter silvering patch that doesn't have that rainbow edge, and you will probably pick up a different odor. Thus giving you evidence that different elements are used in the getter patch.

But sniffing Beryllium oxide is not something you WANT to do!

Still, if you've handled enough old tubes, you've probably experienced the smells that accompany a freshly broken tube.

 

[junk notes]

But sniffing Beryllium oxide is not something you WANT to do!

Does it turn blue. yeah? We know that's the high-grade stuff.

 

[StingRay85]

Do you notice any internal noise when shacking them in you hand?

I ask as I've bought 3 pairs of clean NOS NIB Xf2 for my amps and 2 pairs have noticeable noise. One pair sounds like the cathode coil is loose (springy sound) and the other pair sounds like something metal is just not tightly fitted. 3rd pair is the quietist but still my modern JJ and Mustard EL34s are dead silent when shaken in the hand.

I haven't tried them in the amp yet as I've just recieved them today. Figured you would know as you are the expert in this department. Hopefully this is normal and wont decrease tube life or increase microphonics.

Indeed a lot of my tubes make this springy sound. Its nothing to worry about. Its not amplified even when sitting on a bass cab

 

[StingRay85]

Worth noting is that another classic EL34 used in Marshall amps is the RFT tube, with the dimple top and narrow glass, has a lower transconductance/current ratio compared to Philips. Where current for a RFT needs to be around 35-37 to reach 5 mA/V transconductance, for a Philips this would already corresponds with around 5.5 mA/V. I base this on 25+ RFT tubes including 3 new in box tubes. A good audio comparison between the two tube types with a 2204 type amp is on my to do list.

 

[yladrd61]

Do you notice any internal noise when shacking them in you hand?

I ask as I've bought 3 pairs of clean NOS NIB Xf2 for my amps and 2 pairs have noticeable noise. One pair sounds like the cathode coil is loose (springy sound) and the other pair sounds like something metal is just not tightly fitted. 3rd pair is the quietist but still my modern JJ and Mustard EL34s are dead silent when shaken in the hand.

I haven't tried them in the amp yet as I've just recieved them today. Figured you would know as you are the expert in this department. Hopefully this is normal and wont decrease tube life or increase microphonics.

Should not be a problem in a head may cause issues in a combo.

 

[stickyfinger]

Should not be a problem in a head may cause issues in a combo.

Ya I tried them and they all work fine.
I was just surprised to find a bunch of the "holy grail" tubes from the golden age to not be structurally sound.

 

[playloud]

Just saw this quad on ebay: https://www.ebay.co.uk/itm/234104511734

Am I right to assume these don't have a lot of time left on them, judging from the remaining flash?