Tube question..........

muncybob

Tubes are still a fairly new world to me and I have yet to roll any, but I'm working up to it. I just realized that I think I have 2 different type tubes in my pre phono section. A pair of 12AX7 and a pair of 6DJ8. Is this unusual....would I not be better off with all the same/matched tubes?

megasat16

himmmmm.....If there are two different type of tubes and it's working, it might be that your pre is designed to use that way. It's a little unusual design to use two different tubes for left and right channel but there are circuits that uses each half of the 12AX7 and 6DJ8 for each channel. Or it might be that it uses a single 6DJ8 (or 12AX7) for phono stage and the other tube for the preamp gain stage.

What pre is that?

doctor r

These are not interchangable. Your circuit probably has one 6dj8 and one 12ax7 per channel.
The tubes have different conditions in which they operate at their best audio performance and the circuit is designed for those conditions. Small 9 pin tubes may also have different electrical connections for the pins that in some cases can cause damage to your amp if you do not do a little research. Google "12ax7 equivalents" and "6dj8 equivalents" to investigate those possibilities. There are a lot of 12ax7 varieties as well as 6dj8 to try both new production and from the classic years. Have fun. Roll carefully and be prepared for some great experiences.
Rick

muncybob

The pre is a Dynaco Pas4, I think the good doctor is correct in that it's one of each for each channel. My question was prompted by a comment on another forum that all 12ax7's in the phono stage is the way to go.................

megasat16

I have Pas3 MKII and it uses all 12AX7 for all 6 tubes. The Pas3MKII and Pas4 looks very similar but totally different circuit. I believe Pas3MKII uses each half of the tube for the left and right channel. Pas 4 uses different tubes for the phono stage from the gain stage. Like the Dr. said, they are not interchangeable so you need to roll other AX7 in the current AX7 spots and other 6DJ8 in the 6DJ8 spots.

muncybob

The phono stage is very quiet and sounds pretty good except that at my age I seem to have developed some tinnitus and maybe related to that I find the higher frequencies a bit harsh while at the same time I love deep bass. Any tubes recommendations to make my ears happy? Currently the 12ax7's are Tungsol and the others are Sylvanias.

MrBuhl

I like the PSVanes that came with my MLP, but have also found that I also like Holland Amperex quite a bit as well. I've tried (in 12ax7) NOS Raytheons, Sylvanias, & PSvanes. The RCA black plates are famed to be really great in 12ax7 but I only just finished the quad I need to try them out. Mine are very reasonable two mica, and supposed to sound very nice. The three mica versions command top dollar but are legendary in my reading anyway.

machone

I am also new to tubes. My only experience is with a Yaqin CD3 tube buffer. With the original tubes the bass was not dynamic and loose. Also both tubes were noisy when tapped. I ordered a noise tested matched pair of NOS Sylvania 6SN7GTB tubes from Brent Jessee. The bass is back and tight. Highs float. Mids and vocals sound very natural. Huge soundstage with depth.

MrBuhl

For your 6Dj8's, I haven't found any I like better than the Holland Amperex so far. I have a set of orange globes I got from Voltz that are just amazing, and also some Bugle Boys that I like very much as well.

You can get a great deal by getting Holland made Amperex tubes labeled for other companies, (RCA, etc) same as a bugle boy without the BB on the tube. Look for the same plate and getter designs made in Herleen Holland plant. I haven't even found the legendary A frame versions (too expensive usually), but the ones I have still make my ears happy!

Check out Brent Jesse's site, he gives good tips and describes tube sounds to give you a general guideline on what to look for, I've found it helpful.

FWIW, I'm regurgitating what my ears have told me and what I've read - I'm pretty new to tubes too - there are many folks on here who have forgotten more than I even start to know!

heiney9

Try 5751's in the 12AX7 position. Raytheon black plates, Sylvania gray and black plates, RCA black plates and Tung Sol all make great 5751's

H9

megasat16

Amperex Holland made great tubes. They are my preferred daily preamp tubes.

I also like 7025 tubes for preamp spots.

Brimar (real Brimar CV4004, not rebranded mullard) and Mullard M8137 with box plates are also great for preamp tubes.

Faustin

heiney9 wrote: »

Try 5751's in the 12AX7 position. Raytheon black plates, Sylvania gray and black plates, RCA black plates and Tung Sol all make great 5751's

H9

Hey H9
What differences would be experienced using the 5751 in place of the 12ax7? I am pretty new to tubes as well and have done some reading etc to get some more education. IIRC the gain for the 5751 is less than the 12ax7. Besides less volume output, can you expect a different sound??

muncybob

Some great advice that I will be looking into...next question, what is a good/trusted source to obtain tubes from? Since I'm a newbie at this I don't trust the usual auction sites unless somebody can give me the name of a seller that can be trusted.

I'm also going to look at some updated caps. I got a good deal on this pre and even after updates I think I'm still ahead of the game.

Jim Shearer

Where you buy depends in part on what tubes you need. For my Dynakitparts.com amp I have bought from Jim McShane:
http://www.mcshanedesign.net/
may not be the cheapest place to buy, but he thoroughly tests the tubes, and has provided me solid advise.

Cheers, Jim

marvda1

i second Jim McShane.

muncybob

Wow....lotsa tubes!! Why would he not suggest the 5751 into the phono stage?

MrBuhl

^^ was wondering that too! ^^

megasat16

For phono stage, 5751 has less gain than 12AX7 so it may not be suitable as a sub. Using 5751 instead of the 12AX7 may reduce your phono stage gain even though it will lower some pops, hiss and crackles at the same time.