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

[MartyStrat54]

Things are getting a little slow around here. I think it's time to launch a new theme here. It's October...how about something scary like Count Telefunken? Yeah, everybody is starting to really show some interest in these fine tubes.

Here is a picture of a Tele Smooth, Tele Ribbed and Tele/RFT Smooth. I was wrong when I stated earlier about the RFT's construction. It is for the most part identical in every way. The Smooth Tele on the left has a red tip. Telefunken would paint the tips blue or red to designate them as medical or test equipment approved.

The vast majority of hi fi users will claim that the smoothie is the better Tele. I have used all three and the differences are not worth mentioning. I will say that a stronger gain Tele has a different sound over a lower gain one. By this I mean a 21-22 versus a 25-24. Out of all the Tele's I have, only three measure in the upper twenties. I am getting 12 more in and some of them are going to be V2's as I have dealt with this seller before.

I am looking forward to using an Amperex 7025 in V1 and a 29-28 Tele in V2. That ought to sound awesome.

Well ghosts and goblins, it's time to let those Tele's wail in your high gain amp. Please don't overdo it.

I went back and looked at the RFT's and they all have a thicker, longer tip at the top of the bottle like the one in the picture. Also, notice the dark base on the RFT.

 

[solarburn]

I'm looking forward to giving one of these a spin in V1. Should be ghoulish for sure!

Well at least with my playing...

 

[RiverRatt]

Here's my triple threat. Left to right: 1966 Mullard (GE 6681), Raytheon black plate, and the Telefunken (Fisher) smooth plate.

 

[MartyStrat54]

Pay close attention to the year of that 6681. It's 1966. That is the year all of the crazy shit started to happen. Alan...I have never seen a "pinched top" 6681. You have got some spooky tubes.

Anyway, that's one hell of a power trio you have.

 

[solarburn]

Yep, that's a tri-fecta of tone. Just look how sexy that BP is.

 

[MartyStrat54]

Yep, that's a tri-fecta of tone. Just look how sexy that BP is.

Yes, they are a thing of beauty. They sound damn good as well.

 

[MartyStrat54]

You know it never ceases to amaze me. I won't mention who, but a forum member was asking for tube help. I always try to steer them here, but some folks get intimidated by the volume of pages in this thread.

So I give this guy the benefit of the doubt and give him four or so replies. I just read his latest post. He bought Groove Tubes and JJ preamps and if I remember, GT power tubes. Right across the board of what I told him not to get. Can't give out anymore or you'll know who he is.

Well Ha-Fucking-Ha...I hope you enjoy your new tone pony.

 

[wegman]

You know I was a run of the mill mild mannored Joe till I found this thread. Now I am looking for old tubes like a junkie looking to score. I have been asking everyone I know if they have any old tubes. It turns out a guy I work with used to repair TV's and old electronics. I told him what I was looking for and he knew right away what it was. He said he is going to look around and see if he has anything. If he does it is mine.

If I come across anything interesting I will post it.

Let's say this guy comes up with something. Any words of wisdom before I go popping a 40 year old tube in my Marshall?

I mean it sounds like crap right now but at least it works.

 

[MartyStrat54]

Putting a bad preamp tube is not going to hurt the amp and you will know right away that it's bad. Without a tester, all you can do is roll them. I wish you the very best and I hope the guy loads you down with some nice 12AX7's. What you will hope for is White Label RCA, 59-66 Raytheon Black Plates, any tube that says 5751, 12AT7, 6681 or 7025. Any thing with a black plate, GE, RCA or Sylvania.

If you score, try to get some clear pics up (I suck at it myself, but some of it is my digital camera) and then we can tell you what you have.

 

[RiverRatt]

Pay close attention to the year of that 6681. It's 1966. That is the year all of the crazy shit started to happen. Alan...I have never seen a "pinched top" 6681. You have got some spooky tubes.

Anyway, that's one hell of a power trio you have.

It's just a plain ol' Mullard. It has a 163 code and the date code is B6K1. The GE code looks like UY with what looks like 183-5 under that. GE must have needed to fill an order or something. I tried it in V1 with the Tele in V2. It wasn't as good as either one with the Raytheon BP in V2.

I still think the Arcturus 12AZ7 is the coolest-looking tube I have. The logo is very intricate. It's clearly a Raytheon short black plate. Whether its a Ray 12AZ7 or a 12AT7 is anybody's guess, but the construction looks just like that relabeled Tung-Sol AT7 I sent you. Was it any good, BTW?

 

[RiverRatt]

You know I was a run of the mill mild mannored Joe till I found this thread. Now I am looking for old tubes like a junkie looking to score. I have been asking everyone I know if they have any old tubes. It turns out a guy I work with used to repair TV's and old electronics. I told him what I was looking for and he knew right away what it was. He said he is going to look around and see if he has anything. If he does it is mine.

If I come across anything interesting I will post it.

Let's say this guy comes up with something. Any words of wisdom before I go popping a 40 year old tube in my Marshall?

I mean it sounds like crap right now but at least it works.

Wegman, it's an addiction. I've driven 50 miles on a rumor that there might be some tubes around. Don't forget to raid old Hi-Fi sets from the mid-1950's to the mid-1960's. I bought one turntable/AM/FM stereo box that had a Mullard EZ81 recto, a couple of good 12AT7s and these two Sonotone ECC83 clear tops that nobody can identify but sound great. I'm thinking they are RCAs until I find conclusive evidence. Console sets are good, too. I've got a sweet 6BQ5 (EL84) that I pulled from an old TV chassis in a barn. You never know where goodies will turn up.

Good luck with the TV guy. TV sets use a lot of oddball tubes, but occasionally you'll find a gem. If you're going to be a successful hunter, you need to study ALL the different numbers that are basically the same tube. There are a lot more than you'd think. And don't believe every tube substitution chart you see on the internet. Some tubes will work, but have a different pinout and require some voodoo to use.

 

[wegman]

Marty, RiverRatt

Thanks for all the information. I really appreciate it. I didn't realize there were other tubes that would work. I asked him to look for 12AX7s/ECC83s. He knew right away they were pre-amp tubes. I was not schooled enough to tell him to look for others.

I will tell him to be on the look out for some of the others you guys mentioned.

I am like a little kid at Christmas. I can't wait to go to work tomorrow.

 

[RiverRatt]

Here's a list that has some substitutions. One thing to realize is that while, for example, all the substitutions they have listed for the 12AX7 tube type will work, but may have different gain characteristics. Also the power tubes they have listed would not substitute without some changes to the bias resistors at least, but any of the tubes you see listed here would be good to look for. The 6CA7 = EL34 = KT77. I don't know why they put all those others as subs.

Tube Substitution Table

Also, any 12A_7 will substitute for any other, but as above, they have different gain levels. 12BZ7s are an interesting 12AX7 substitution, too. In the second gain stage, they can really make a Marshall sound hot-rodded. A 12BH7 will behave about like a 12AT7.

 

[solarburn]

I'm just giving a quick blip here but I got the EH6CA7's in. PV was 475v and biased em' to 75% PD and spanked my plank!

I give them a on both gain and clean channels but I still need to open them up the rest of the way and that means I have to wait until the father-in-law goes out to breakfast. Its a bitch having to wait for this to happen. The rest of the family deals with me but I won't blow him out of the house. I'm not that mean. The kids they just go play outside. The wife lets it happen. I give her props for that. Doesn't mean I like her though...:eek2:

Anyways I won't give my seal of approval until I light the chubby bottles up for some high volume torture sessions...poor neighbors.



Just to jog people's memory on what they are like. From the Tubestore:

At last something to replace the hole left since the EI 6CA7 went out of stock. These tubes sound every bit as good as the old EI tubes and are probably my favorite tubes for Hiwatt guitar amplifiers. It’s like they were made for each other. These tubes are like EL34’s on steroids. They handle high voltage and current without problems. As mentioned, there is nothing like a Hiwatt head powered by 6CA7 tubes and driving a 4x12 cab loaded with Fane speakers. This is classic rock tone at its finest. It’s the sound of Pete Townsend and The Who. The 6CA7 has more headroom than an EL34 and by the time you get it really crunchy sounding your pants are flapping in the breeze. Just the right amount of compression for great thick rock tone. Biasing levels can be dialed in from warm to hot without causing significant tonal changes. The EH is well constructed and should not pose any noise problems. If using these tubes in more reasonable systems the EH 6CA7 is capable of some really nice clean tones thanks to that extra headroom. If you want early Van Halen, these are not the tubes for you. If you want something loud and proud, you want to put the EH 6CA7 in your amp.

 

[solarburn]

You know it never ceases to amaze me. I won't mention who, but a forum member was asking for tube help. I always try to steer them here, but some folks get intimidated by the volume of pages in this thread.

So I give this guy the benefit of the doubt and give him four or so replies. I just read his latest post. He bought Groove Tubes and JJ preamps and if I remember, GT power tubes. Right across the board of what I told him not to get. Can't give out anymore or you'll know who he is.

Well Ha-Fucking-Ha...I hope you enjoy your new tone pony.

JJ's and GT's freek'n rule Broham!!!!!!!!!!! I've got to have it now! No time to stop and think. JJ's and Gt's for me man. I ain't got no time for you old tube talk'n crappers!


BELCH!

 

[wegman]

Marty, RiverRatt

Thanks for all the information. I really appreciate it. I didn't realize there were other tubes that would work. I asked him to look for 12AX7s/ECC83s. He knew right away they were pre-amp tubes. I was not schooled enough to tell him to look for others.

I will tell him to be on the look out for some of the others you guys mentioned.

I am like a little kid at Christmas. I can't wait to go to work tomorrow.

Well I scored a couple tubes. One is a 12BH7A Sylvania and the other is a
12AU7 and I can't tell who the mafacturer is.

So I can just pop these in and try them out?

 

[solarburn]

Well I scored a couple tubes. One is a 12BH7A Sylvania and the other is a
12AU7 and I can't tell who the mafacturer is.

So I can just pop these in and try them out?

The 12AU7 will have a gain factor of 20 as opposed to a 12AX7 which is at 100. So you will notice a sizable difference between the 2. If I used that 12AU7 in V1 it would neuter my overall gain on my DSL just to give an example.

Don't know bout the 12BH7A.

Here is a table to look at:

http://thetubestore.com/gainfactor.html

 

[RiverRatt]

You won't hurt anything by giving them a try, but odds are you won't like them in your guitar amp. The 12BH7 has about the same gain as a 12AT7 and might could be used as a phase inverter, but the 12AU7 will neuter an amp in just about any spot.

Both of these tubes can be (and are) used in low-watt guitar amplifiers as a power tube. There's a 1-watt amp project at AX84.com called the Firefly that uses a 12AU7 output tube, and I've been reading that Blackstar makes a low-watt amp that uses the 12BH7.

 

[MartyStrat54]

Joe...

I'm glad you like you new CP Power Tubes. Hey...maybe they finally got it right. Now I won't put them on the same level as a dual getter, black plate, Fat Boy. These tubes can take more power than any other 6CA7's, EL34's and KT77's. There are even some that are more rare than a regular Fat Boy. However, if these tubes can handle the plate power of my 602's (500VDC+), I will have to look strongly at them.

My main thing is I want to hear your review with the tubes at volume.

 

[MartyStrat54]

Well I scored a couple tubes. One is a 12BH7A Sylvania and the other is a
12AU7 and I can't tell who the manufacturer is.

So I can just pop these in and try them out?

Yes you can, but these tubes are not going to help you out. Sort of like a 20 watt light bulb versus a 100 watt light bulb. The tubes you have are very common and as Alan (RATT) said, you can give them a try, it won't hurt. However, they are very low gain and it will take you backwards instead of forward on trying to get better sound out of your amp.