Tube Rolling w/Crack

[dubiousmike]

Just buffing the pins with fine steel wool can work wonders. If you want to get hardcore you can chuck a Q tip in a Dremel and polish the pins with something like Simichrome.

Happy to report that after taking some fine grain sandpaper to the pins, and then inserting, removing and reinserting the tube a half dozen or so times, my 1959 rca blackplate (12bh7a) is now singing beautifully in my crack without the slightest hum. 

[williaty]

So I'm set for signal tubes for the near future (other than wanting to play with a 6SN7) but I'm having a devil of a time finding some alternative power tubes.

Specially, does anyone know where I could buy a 5998 (NOT 5998A)? Other than a pair on eBay, I can't find any to be bought at all.

[Laudanum]

I take it that you only want the ST shaped 5998 (Tungsol).  Not the straight glass which, I think are 5998A's (usually anyway).
There is one member here who may have one for sale but I'll have to let him speak for himself.  I'll PM him for you.  I picked one up from him.
Other than that, they will pop up on ebay fairly frequently.  You can also inquire in the tubes asylum at AA.  And check Audiogon.  But watch this thread or you Bottlehead PM, I may have a line on one for you.

[williaty]

Thanks Laudanum.

[Laudanum]

My pleasure.

[dubiousmike]

Im really liking the Tungsol 12bh7a the best right now and the RCA 5814A is just slightly behind it.

Thanks for recommending the TS 12bh7a!  I stumbled on a deal on one (nos from 1959) on ebay a week or so ago, and it arrived last night.  I am really enjoying what I'm hearing so far.  This may well be a new favorite for me. 

My early impression (via HD800's) is that the trebles have the same texture and timbre that I like so much from my 12au7 bugle boy but with the added fullness of sound (perhaps slightly elevated mids/mid-bass?) that seems typical of the difference between 12bh7a's and 12au7's.     

[castelletti]

thats what i was hearing too.  im not sure what the specs are on them...they could have more gain giving the illusion of that though.  whatever the case i really like them.  glad you are enjoying them too.  being relatively new to tube audio tube rolling is fun but i'd rather not throw good money after bad.                                                 

[TonyMc]

I just picked up a couple (RCA?) "JAN" 6AS7G. Yesterday. Hopefully they arrive sometime next week. I'm looking forward to doing a little rolling.
What seems to make the biggest difference in SQ with the Crack? Output tube or driver tube?

[Lee Hankins]

IMHO it is a waste of money to purchase any addition 6080 or 6AS7's for tube rolling over the stock tube, save your money and put it towards a 5998 or 2399, if one can not afford the 5998 then definitely try the 6AS7 over any 6080.  I have not heard the 421A, 5998A, or 7236, all variations in the 5998 family.

Tubes that I have rolled through my Crack (I had 17 6080/6AS7 tubes before purchasing the Crack, the 2399/5998 were the only tubes that I purchased):

6080WB: Raytheon, Sylvania, Tung-Sol, GE, and Chatham
6AS7G: RCA, Raytheon, and Tung-Sol
2399/5998: Chatham and Tung-Sol.  

Again IMHO in general the 6AS7 is better sounding than any 6080 tube.  The 6080 is an extremely rugged tube (really like the looks of this tubes internal structure), but just like the 5691/5692 tube in the 6SL7/6SN7 family, tubes build for long life and rugged uses are usually not the best sounding tube.

Driver Tube:  Way too many to list, but my preference is the 6SN7GT.  Tung-Sol round plate 6SN7GT, or RCA VT-231/6SN7GT, leaning towards the RCA in the Crack.

The 5998 is a large improvement over the 6080, not as big an improvement over the 6AS7 but still the better sounding tube.

I believe that the largest improvement in sound quality comes from the driver tube.  But, finding the best sounding driver tube for a 6080, does not mean that it would be the best sounding tube with the 6AS7 or 5998.  One must roll tubes for each individual Output tube to find the optimal sound.

Caution!!  The level of modification also greatly effects the quality of sound of any piece of equipment.  My Crack has the Speedball upgrade, 104 uf film OP Caps (parallel 52uf), last Power Supply cap is a 52uf film, and last PS resister replaced with a choke, and all PS and OP caps bypassed with .01 uf teflon caps.  If you have a stock Crack or have only the Speedball upgrade my recommendations may not apply, just a rough starting point.

[Beefy]

In my humble experience, switching the output tube to a 5998 yielded better gains than several different 12AU7's or a 12BH7 (although the 12BH7 is still very early listening).

*

On a semi-related note, one of the pins fell off one of the 12BH7's I bought. Huge shame, because it was a beautiful looking long-plate version

[williaty]

I'd agree that going from a 6080 to a 5998 was a much bigger change than messing around with different 12AU7s and 12BH7s. I have to wonder, though, if the primary reason for that is changing to the 5998 significantly lowers the output impedance. Even with high-impedance cans, that's still a good thing.

[Beefy]

I have to wonder, though, if the primary reason for that is changing to the 5998 significantly lowers the output impedance. Even with high-impedance cans, that's still a good thing.

As good an explanation as any!

[Laudanum]

Lee knows his tubes and has helped me with some 6SN7 info (thanks again, Lee).
I think it's worth picking up a socket adapter and trying some of the 6SN7's.  Outside of the more expensive top 5 6SN7's the Sylvania Chrome Top/Dome 6SN7's (GTA, GTB) are pretty nice sounding tubes and can be found for not much money, especially re-branded (Baldwin, Silvertone etc).  I was able to pick up a Sylvania Jan CHS 6SN7GT / VT231 (bottom getter) which I think is one of the top 5's on most lists.  This is a really nice tube.  So is the brown base sylvania 6SN7WGTA that I picked up in a lot of several 6SN7's.   But I could be very happy with the Chrome Domes and, atleast to my non-golden ears, they arent that far behind.  Of course, YMMV.  I plan on building a FPIII with octal sockets for 6SN7's.

I also have a Tungsol 5998 (and rebranded spare) that I picked up mainly to try with my AKG 601's.  The 5998 was reportedly of particular benefit with the 601's leaner bass because of the lowered output imp. of Crack when using this tube.  I cannot say that the bass is increased in quantity over the 6AS7 but it is tightened up and the added gain is of benefit for less efficient phones.  I agree that most will probably find it to be the better sounding tube overall, which is the most important thing.  I dont know if I would jump to buy a 5998 if money was tight and one was happy with the 6AS7 which really are nice sounding tubes.  But definitely worth a buy and try if the budget allows.  Again, YMMV.

[Beefy]

The 5998 was reportedly of particular benefit with the 601's leaner bass because of the lowered output imp. of Crack when using this tube.

I may be wrong here, but it is my understanding that a lower output impedance will actually reduce the bass. When calculating the cutoff frequency, the output impedance is in series with the load - and lower impedance increases the cutoff. The benefit from a lower output impedance is an increase in the damping factor - so whatever bass is there should be tighter.

Its a careful balancing act between these opposing effects, and really comes down to personal taste.

[Doc B.]

I did some listening last week to try to better distinguish the differences between the Crack and the Smack with headphones of various impedances and it was clear that Crack does have nice tight bass, even on lower impedance headphones, apparently due in part to the OTL design (as long as the cans aren't power hungry like LCD-2s or K1000s). When headphones are matched with the output impedance switch on the Smack its output transformers give a sense of better (more, deeper) bass balance with low impedance cans, but the notes are a bit less sharply defined. The Smack excels in the mid and treble regions where a transformer shows an advantage over a cathode follower in terms of smoothness and resolution.