Can you tell what tubes these are? (Mullard)

Jeff West

Member
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1,028
V846- Yes, you're right that "rX" on Philips EL84 is analogous to "Xf" on their EL34s, it is the "two character" code for a particular type of valve, e.g., EL84, but was not specific to a particular factory, for example in late '50s you find these "rX2"s from Hamburg, Heerlen-made Dutch Amperex would have "rX3" and Blackburn-made Mullard "rX1". The "type number" included as the third character ("1", in this last case) adds additional meaning but does not nec go in chronological order and is not always exclusive to one particular Philips factory/time frame, unfortunately.

The way to tell the date and factory is in the second line of codes, like "D7H", where D=Hamburg, 7=1957, H=August (I miscounted the month code the first time, above!).

It is easy to get the different codes confused, like the "r" example mentioned (which does indicate Canadian manufacture like was said, if it begins the second line of code); also, contrary to what you read, these "etched" codes are not all etched and can rub off, so sometimes the top line is missing, etc. Also, they frequently screened the other labelling right over them!

You can find a list of Philips factory codes and the "two character" type codes (w/a couple of minor errors) reprinted various places on the net, like at Triode Electronics: http://www.triodeel.com/images/philipstubecodes.pdf The first page is the factory codes, all those later pages are "two character" codes (labelled "two digit" codes but they're not all digits, right?!) What that doesn't tell you though is when the used the different codes and which factories used which, that gets complicated.

Just to add to the obsessive dating fun, Philips valves often have one or even two additional date codes that will be a little or occasionally a lot later than the date of manufacture. For example, that "7-52" (or is it "7-50"?) that you can make out on the left EL84 means 52nd week of 1957, and refers to when the Bugle Boy logo ink was screened on. That ~4 month gap is typical or even on the short side, I've got an EL37 w/'59 factory code but it has 1963 Mullard logo date, although that's unusual. I mention this second date because it can help refine further when equipment was made, if that's of interest. For example, if those EL84s were original in your non-guitar amp, gururyan, then it couldn't have been made prior to 1958.

Knowledge of the factory/date codes is also handy for discerning those particular gems among dirty nondescript looking used tubes all in a box under the table at your local hamfest, so you can confirm that that Zenith 12AX7 is actually longplate Dutch mC6 12AX7!

Reeek- You sound like an enthusiastic tube scrounger all right, what are your favorites?

gururyan-If you feel inclined to send me an e-mail at Jawket@hotmail.com, I might be able to help you get access to some kind of tube tester.

Jeff W.
 

gururyan

Member
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4,853
Well, is there any reason to doubt the condition of the tubes? Do I really need to have them tested? What's the worst that could happen? I don't even have an EL84 amp right now (yet, anyway) so I wouldn't be using them for a long time as it is. I wouldn't mind selling them to an honest person that gave me a fair price for them, and in return I would refund them if they tubes turned out to be no good...which doesn't seem to be the case.

On the subject of tubes, I can see this being something I would fall into. I don't need another addiction or source of GAS...but I think I have been bit. So, this being the case...I have 3 12AX7 and 2 5881 Sovtek tubes in my Fender Blues Deluxe. I have never heard any other tube in this amp but to be perfectly honest, I really love the sound I get when it's warmed up. Should I mess with a good thing or is it a case of not knowing what I am missing? I mean, I'm going to have to change the tubes someday and I am not the original owner. Speaking of, the original owner said these were not the original tubes.

So, if that's the case...I have a lot to learn about tubes. I have no clue what to get. I love a warm, rich tone...not sure what tubes do what. I guess I will have to search the archives.
 

Reeek

Member
Messages
1,196
Jeff,

One of my favorite tubes is the Genelex KT66. I love the Mullard and RCA EL84s. I love Hytron 6V6GTYs But I love tubes in general. For preamp tubes, I have so many but of course Mullards are a benchmark. I have some original NIB Tesla ECC803s which are totally sweet tubes. I love using various 5751's in my 12AX7 amps too. I'm running one in one of two inputs on each of my Sano 160Rs. These are world class sounding amps.

My problem now is that I only have two 6V6 amp left in my collection but I have probably 40-50 vintage 6V6 tubes, many that are HIGHLY regarded and still in their original box. I often consider offing some but I never get around to it. Many of the best were bought from Mike at KCA.


gururyan,

You can always sell them on eBay under the caveat that they were pulled from a working amp (if it was working) and sell as is. The ppice will be reduced but you could quite possibly get something for them. I've bought used untested tubes before when they were a well regarded tube, knowing that it may be bogus. But if not, then I got a great tube for a low price.
 

Jeff West

Member
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1,028
Yeah, "plug 'n' play" is definitely part of the repertoire, especially w/preamp tubes. You already did that w/the AX7, right?

Main value of most common emission testers you might run into is to check for shorted elements within the tube, serious grid emission, and to give some general indication of the functioning of the tube, at unrealistically low voltages though.

The power tubes are generally the ones to be most cautious about checking out- internal shorts can damage your equipment or even other, good power tubes if you run them. It is possible for them to appear to work and even sound alright with partially shorted elements, too.

If you do just plug in unknown or questionable power tubes, at least keep the lights out and the room dark and watch them for awhile, including while you play. If the plates start to glow dull orange and/or you see any sparks or arcing inside, even once, don't continue. The former could just indicate the bias is off for that tube, but thermal runaway can also indicate problems in the tube.

If you develop a feel for signs of serious wear, prior overheating, etc. of power tubes, that's also reason to tread more cautiously. But not foolproof, a tube can look virginal and pristine and still be problematic.

Jeff
 

gururyan

Member
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4,853
hahha, well now you've scared me. :eek:

As far as the AX7, yeah...I tossed it in my Vox and really like the change. Would it be beneficial to toss it in one of my 3 AX7 spots on the Fender? Is it unwise to have 2 of one and 1 of another in the preamp? Would one of the preamp spots be yield the best position for the Amperex?

Are Sovtek tubes good/bad on the typical hierarchy of the tube pyramid? Are they known for any certain tones?
 

Jeff West

Member
Messages
1,028
guru- Part of the beauty of tube accumulatin' is that you can try whatever you want out, swap in and out, etc. to heart's content, especially 12AX7s in guitar preamp. Conventional wisdom is you may get the best initial feel for the sonic character of 12AX7 by tying it in V1, i.e., the earliest stage of amplification. But you can try it anywhere and everywhere you have other AX7s now.

Reeek- That's some good tube-taste, IMO, espcially telling that you started with KT66s. If you have some older ones, do you have any w/double letter date codes that start with "S" (1961)? If so, are they grey or clear? We were trying to pin down the change, I've seen multiple 2/61 ("SB Z") that are grey and have 1/62 ("TA") that are clear. Same w/the change from single getter cup at the bottom to double halo rings, which occurred somewherein '64 ("V") I think. Maybe can compare notes on Hytron 6V6 specimens too sometime . . .

Jeff
 

drbob1

Silver Supporting Member
Messages
26,836
No harm to try the 12AX7 in your other amp. Often works the best in the first tube (the one farthest away from teh power tubes and closest to the input jack) but it can also sound great (especially if you're cranking it) in the 3rd position.

Something to think about-those are very desirable EL84s, and they are drying up fast. Two years ago you could buy Mullard EL84s for 1/3-1/2 the cost of Mullard EL34s, now they cost the same. I'd keep them-they'll appreciate in value, and when you finally realize the sublimeness of the EL84 in a guitar amp-you'll have them right there! Sooner or later, when you get a real tube jones going, you can buy a tube tester off Ebay for $70, that'll allow you to make sure that they're at least working...
 

gururyan

Member
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4,853
I just went to a local pawn where I go for cool stuff...a hidden treasure basically. I started looking in the hundreds of ancient amps he had. I saw tubes galore with mountains of dust on them and names I recognized even being an beginner tube geek. I saw tons of old Tung-Sol tubes.

I wonder if I should buy a tube tester, take it to the pawn, test tubes in those amps...buy the amp, sell the tubes.
 

gururyan

Member
Messages
4,853
Ok, lets say you know squat about testing tubes, what to look for , etc. Let's say you are beyond frustrated about the lack of tube testers and testing services in your area. Now let's say you are so fed up you play with the idea of buying a tester, learning how to test and putting an ad in the yellow pages...not expecting a big profit from the business, but at least providing a service to fellow tube users. Maybe even make some income on the side finding and selling old tubes.

What do you buy?
Is it easy to learn?
Am I just frustrated?
 

BPlexico

Silver Supporting Member
Messages
757
Well, if you are going to start a journey into the land of tubes and tube testing, this site is as good as any to start:

http://www.guitaramplifierblueprinting.com/


And you can visit here to learn about the Dual Triode Vacuum Tube Characterizer, a device for testing pre amp tubes...

Best of luck.

-- Barr
 

Reeek

Member
Messages
1,196
Jeff,

There are no etchings on my Genelex KT66's. Thay have the typical Genelex KT66 bottle with the bulge in the middle. The base is black and sloping as standard. The only print on the tube is the ink white square with the words KT 66 then some worn off words just under that then Made in England. The bottom mica spacer is square with rounded corners. The top spacer has two flat sides with two rounded serrated ends sort of like the 1960's RCA 12AX7's. The plate is a box shape about an inch and a quarter tall, maybe a bit more. It sits at a 45 degree turn on top of the lower mica spacer. There are two oval slots/holes in two sides of the box shaped plate. The bottle has a gray coating inside from about a half inch from the bottm and stops about a half inch from the top. There is a flashing on one side going about half way around the bottle at the bottom of the tube from the base and up about a half inch. This flashing material is similar to the flashing you see on an RCA blackplate 6L6GC but down near the base of the tube. IZt seems there is a getter behind the flashing but it's hard to make out its design. It looks big though. They have two L shaped fins on top and a reverse S single wire getter type wire that weaves between the two L shaped fins on top. It looks more like a jumper wire than a getter though. No etchings on the bottle anywhere. The original boxes are off white with two shades of gray on them. They say Genalex Tube, Made in England, Made for the General Electric Co. LTD. of England by its associated company the M-O Valve CO. LTD
 

Jeff West

Member
Messages
1,028
Thanks for describing in detail, Reeek.

The date code would be the pair of capital letters like "JK", etc. on the left at the bottom of the white rectangle, and there would be a one or two digit number toward the bottom right corner, but maybe some or all of those have rubbed off.

I think the black bases with later (non ST) shape tend to be very early '50s but may vary.

Yes, the gettering is at the bottom and just on one side, the getter support thang is cup shaped and upside down. Easier to see on the clear ones where it continued into the early '60s, then they went to dual halos, one on each side, in around '64. Doesn't really matter, it's just a dating thing.

KT66 is possibly my favorite too, for sound, history and overall tube coolness!

Jeff W.
 

gururyan

Member
Messages
4,853
Well, I dug this up because I am ready to get deeper into tubes. I love my Amperex 12AX7 Bugle Boys so much I want to expand. I need to find out exactly what this tube looks like with different labels. I want more but I don't want to pay for a nice logo bugle...it's the inside I like so much.
 

John Phillips

Member
Messages
13,040
Here's another interesting one. I pulled two of these out of a late-1970s Triumph amp a couple of days ago...



Just goes to show you have to be careful when buying tubes if you don't know what you're looking for. This one is an East German-made RFT. It's not a 'fake', the labeling is totally genuine, but it certainly isn't what you might expect it to be. I've seen RFTs with all sorts of labels on, but not one of these before.

It's a good tube - just not a Mullard.
 




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