Preamp Tubes? - Who, What, When, Where, Why, and How?

[BluesRocker]

Thanks Marty. Also I tried something different tonight. I put the BP in V1, the High Gain Philips in V2, the low gain Philips in V3 and a CP Tung-Sol high gain in the PI and that sounds pretty damn sweet. I might have to invest in a few more Philips and BP from ya

 

[MartyStrat54]

Well if you have a handful of good tubes, it makes rolling just that more enjoyable.

 

[MM54]

So Marty, What do you think about a side-getter 12AU7? There's one sitting on my bench, I've never seen a mini 9-pin with a side getter before. I believe it's relabeled Zenith, but the stamp designating "12AU7" looks very RCA-ish.

Also...

There's also a tube that all that remains of the label is a 7. I think there was an X before it, and it looks inside just like a 12AX7, so I'll have to test it as a 12AX7 and see how it goes . Stamped into the glass on the bottom in the middle is a backwards F. Mean anything?

 

[MartyStrat54]

Yeah, it's probably an RCA. Could have been made by Sonotone as well. It isn't worth sticking in your amp. The gain would go down the drain.

If you can post large, clear pictures. Alan or I could probably ID it.

 

[MM54]

I'll go take some.

In the mean time, does the backwards F on the other one mean anything (ie. manufacturer)?

 

[MartyStrat54]

It may be a clue, but it's not ringing a bell right now.

 

[MM54]

My camera sucks, so sorry for the wait Diregard the pink background, it's an old rag, the cleanest light-color one I could find down there to use as a backdrop

Here's a couple pictures of the side-getter 12AU7. It's interesting.
Side:

Side:

Top (no seams, or getter for that matter):

And here's the mystery one. I haven't been able to make sense of any of the labeling other than 'Made In Gt Britain'

Side:

Side:

Bottom (you can't really see the backwards F...):

Top (there is a seam, down the middle [not into quarters like some I've seen]):

So there ya go Sorry for the inconsistent pictures, like I said, my camera is junk. Half the time it doesn't flash when it should.

 

[RiverRatt]

Yeah, that top one is definitely an RCA side-getter 12AU7. I've got a few of those NOS-NIB. Not much use for them in guitar amps. There were a few RCA side-getter 12AX7s made sometime during the 1950's. I don't believe they made very many at all. Every one I've seen was relabeled "Sonotone" as Marty said, with the exception of one labeled "Fisher". They are actually my favorite RCA and sound great in V1 in a Marshall, but they are so rare I'm afraid to put much playing time on them. The side getter tends to be noisy in combo amps. Here's a shot from when I found my first couple of Sonotone (RCA) side getter 12AX7s. For some reason, only one made it into the picture. It's second from the left. The one on the right is a clear top 12AU7 like yours. This haul came out of one Hi-Fi set I bought for $10. I just wish they'd used two EL84/6BQ5's instead of the one ELL80.

I'm curious about that bottom tube. What if any marks are on the tube other than "Made in Gt. Britain"? If it's a Mullard, you should find two codes etched into the glass low on one side. The top one will be "I63" or something similar, and the bottom code will most likely be four digits and begin with a "B". If you can find that info, we can tell you exactly what you have. I've seen tubes with numbers and symbols molded into the bottom glass, but I don't know anything about them except that a diamond (square) means it's a Telefunken.

Here's a picture of an I63 (12AX7/ECC83) Mullard. Note the start of the "B" (Blackburn) code on the lower right side.

 

[MM54]

I'll take a look tomorrow after work, Alan, there may be some numbers like that, I don't remember though.

Do you still have those tubes? I see "BA6" in one - is it a 6BA6 or a 12BA6? The radio in my shop sounds like shit because one of the 12BA6s in it tests at like 40% and I don't have a replacement

 

[RiverRatt]

I've got two Raytheon 6BA6's. I've got a couple of old RCA and GE record players lying around and I'm not sure what they have in them. If I find anything, I'll let you know. You're welcome to the 6BA6's if you can use them.

 

[MM54]

Ah, I have a bunch of 6BA6 too, sadly they'll explode if I put them in for a 12BA6

I just got back from work so I'll go look for numbers, etc, on the mystery tube.

 

[MM54]

Alright, etched near the base of the tube (upside-down by my standards, to read it, the pins point up) is:

I61
32K2 (The 3 might be a B, I dunno, it's harder than hell to read)

 

[SpiritOfTheAge]

I'm curious about that bottom tube. What if any marks are on the tube other than "Made in Gt. Britain"? If it's a Mullard, you should find two codes etched into the glass low on one side. The top one will be "I63" or something similar, and the bottom code will most likely be four digits and begin with a "B". If you can find that info, we can tell you exactly what you have. I've seen tubes with numbers and symbols molded into the bottom glass, but I don't know anything about them except that a diamond (square) means it's a Telefunken.

That one with the clear top? Looks like a Brimar plate structure on that, ive got a mullard labelled as Brimar that has a B factory code and the standard phillips plate design. So it feesable that a Brimar plate design may have a blackburn factory code on it.

 

[RiverRatt]

Alright, etched near the base of the tube (upside-down by my standards, to read it, the pins point up) is:

I61
32K2 (The 3 might be a B, I dunno, it's harder than hell to read)

I'll almost guarantee that it's a B. Mullard was really good about marking tubes (unlike some Philips factories), and that is a stereotypical Mullard code. It was made in the Blackburn plant in the 2nd week of August, 1962. They switched over to the short plates around 1960, and the type code changed from I61 to I63 around 1964, so all that checks out. Great tube! How does it sound?

 

[MM54]

:eek2:

I haven't put it in my amp yet (don't know how it even tests) to know how it sounds - I have a handful of 12AX7's that need testing, I'll probably do that later.

I'll see if there are similar markings on any of them and let you know.

I need some boxes for these guys... I'll add that to my next order from Tube Depot haha

(Alan - I'll also test those 6L6s in a few minutes when I go to do the 12AX7s and let you know their %s)

 

[eljeffebrown]

here we go. Thrawn sent me. you know my head. I wanna go JJ free and I wanna go High Gain, Way High! Help me out my brothers! you can add power tubes in here also just so'z I don't have to post over there but if I have to I will! Thanx a bunch in advance!

 

[MM54]

Well eljeffe in a couple days when I finish rolling, I'll have a bunch of suggestions for preamp tubes

To others - The Mystery Mullard tested very good (and flashed at startup), and another one (Marked "IEC Mullard") tested even better. Hopefully tomorrow I won't be too tired after work (doubtful, we're still roofing) and will get a chance to move them around with the GEs and RCAs I have sitting around and see how they sound.

 

[eljeffebrown]

sounds good.

 

[MartyStrat54]

here we go. Thrawn sent me. you know my head. I wanna go JJ free and I wanna go High Gain, Way High! Help me out my brothers! you can add power tubes in here also just so'z I don't have to post over there but if I have to I will! Thanx a bunch in advance!

Okay I went back and read your previous posts. I could have swore that I left you an answer about 4500DR's.

Anyway, if someone sold you a high gain pack for a 4500, they should be shot. The only tube in the preamp circuit is V1. V2 and V3 are not in any gain stage and V4 in the phase inverter.

As I have said before, the best tube is a high gain Raytheon Black Plate. This tube seems to smooth out the amp and give it a tighter bottom end.

EDIT-V2 not in the preamp circuit and V3 is the PI.

 

[MM54]

(Pssst, Marty... v4 in a 900DR is a power tube - there's only 3 preamp tubes )