Tube Rolling w/Crack

[jrihs]

Cool, How does it sound to you?

[Laudanum]

Cool, How does it sound to you?

It's a nice tube, sounds just like the 2 other 5998's I have.  There is some variation in the 5998's in terms of internal construction.  More specific, the getter.  Some are clear top, bottom getter.  Some are top getter.  I have each and they all sound the same to me.   Higher gain tube than 6AS7 and 6080.  There are descriptions within this thread, but basically it's just a bit cleaner and more detailed up top and possibly a little more extended.  Wonderful midrange and tight on the bottom end.  To my ear, the 6AS7 is a little warmer, maybe a little more bass impact.  But still not sure on the latter as the 5998 detail and extension up top may account for it.   I think it's a great tube and worth finding one if you can for a fair price.   You may end up seeking a spare or two, I did.   I could live very happily with the 6AS7 but think that the 5998 is a little bit nicer sounding tube.   That said, I wouldnt have one if I had to pay $100 for it.   I ended up paying a total of $115 for the 3 that I have.  They were all used but excellent.

[dwilli852]

The 5998's are good sounding tubes but hard to find. I picked up 3 for a hundred bucks plus shipping off Ebay.

The Western Electric 421a's are very hard to find and are selling for way to much IMO.

1950's RCA Black Plate 6AS7 or 6AS7G tubes are a good choice if you can't find any 5998s.

The 5998's have more gain than the 6AS7 tubes with a little cleaner sound, more detail and top end.

A good 6AS7 with a Bugle Boy, Mullard CV4003, Phillips Mini Watt or Siemens Silver Plate tube to drive it makes a great sounding setup.

Which ever way you go have fun with a great sounding amp and watch the prices for a good deal.

[Sh7eleven]

is the extra gain from the 5998 a substantial amount? With the stock tubes, I feel like I already don't have a lot of the volume control to play with. 

[dwilli852]

I'm not having that problem with mine running HD650 phones and Alps pot in my Crack.

My setup is PC with optical output to my DAC and RCA connections to the Crack.

Using Foobar with Wasapi (Windows Audio Session API) output for Flac files.

You could always pad the volume pot in the Crack with a resistor or I've used the volume control in Foobar to reduce the input to the DAC.

As there's no volume control on the DAC.

I've always heard it's better to control the volume on the analog side than the digital side.

Mine runs about 9 oclock on the Crack volume control with a 5998 tube and around 10 to 11 oclock with a 6AS7 RCA black plates.

Hope this helps.

[Laudanum]

is the extra gain from the 5998 a substantial amount? With the stock tubes, I feel like I already don't have a lot of the volume control to play with. 

It's enough that if you dont have much volume to play with now it will get even tighter.   But as suggested, sounds like it may help padding as it is now.  That would be the solution, if needed, with the 5998. 

[Sh7eleven]

I am using:

hd-600 - crack - marantz sa8001= not a lot of volume to play with, I suspect the marantz has a high output.
hd-600 - crack - dac - mac optical out = a little bit more volume play, but not much.

I have no ability to control volume from the marantz and don't really want to control the volume from the digital side. Padding sounds like the way to go.

Is it possible to tame the impact of the extra gain with a complimentary driver tube? In addition to the 5998, I have a mullard cv4003 on the way.

[dwilli852]

Tubes are amplification devices. Tube design and application control the gain. 12Au7's are medium MU (gain) devices along with the other compatible tubes for the Crack. So there's not much you can do with the tubes. I've noticed the 12BH7 and E80CC tubes have a little more gain than a ECC82/12AU7 but that's not going to help you. I haven't tried padding the volume pot and I'm not sure if there are any negative impacts. Hopefully someone will chime in with more or better recommendations.

[Sh7eleven]

Yes, I understand that a tube is designed for amplification, and thanks for the input on the 12bh7 and E80CC. Having the extra gain, I would stay away from those until I pad the pot. I get to full volume at about 830-9 o'clock with the stock 6080 and 12au7 - (but I'll take my questions on padding to another thread).

[Laudanum]

Im running a 12BH7 and I thought they were actually lower "gain" than 12AU7 (around 17 versus 20, from memory) although I cant recall noticing a whole lot of difference.   Maybe it's the way the drivers are used in the circuit.  One of my sources is a Tjoeb 99 CDP which supposedly has an output in the 3.5 volt range.  Im not so sure it's that high but it's definitely higher than my 2 volt digital source.   My main phones are Beyers though which have a lower sensitivity than the Senns.   My AKG 601's are lower still.  My Quarts are higher than the Beyers and dont get a ton of use but I have enough play in the pot with those as well.  I think most of the volume control range issues discussed on the forum have been with Senn phones.  I assume that's because their higher sensitivity but it could just be their popularity, or a combination of the two.  Then again, listening level has a major impact as well as, not just the source, but the source material.  My CD's and LP's can be all over the place.  But I tend to listen louder than I probably should at times 

Anyway, below is a link to a pre-attenuation method on the Goldpoint site.  It is only 2 resistors and signal passes directly through only one of them.  I would have no problem with using it if needed.  Wouldnt cost an arm and a leg to implement using quality resistors.  Of course, you need 4 resistors, 2 per channel.  Anyway, resistor values listed are based on the value of the pot and desired amount of pre-attenuation/padding.  You could experiment with cheap resistors to find out how much you need and then swap in some better resistors.   Vishay RN's would probably be a good, budget concious choice but the sky is the limit just like anything audio 

http://www.goldpt.com/mods.html

[Paul Joppa]

The output tube is used as a cathode follower, so the gain of that stage is always a bit less than 1.0. Into a high impedance, the 6AS7 might have a fain of 0.65, vs. 0.8 or so for a 5998. For lower impedance phones, it's a little more complicated but in all cases the difference in gain between tubes will be small, maybe 1 or 2 dB.

[Sh7eleven]

Thanks for the helpful link.  I was able to put in a 6as7g and I actually find it more tolerable at the same volume levels than the 6080.  We'll see about the 5998, I'm definitely interested in putting the pad as suggested. Since I read electric schematics at a first grade level (the lines are wires right?), I'll give it a shot, but will post to make sure my implementation is proper.

[Laudanum]

Thanks for the helpful link.  I was able to put in a 6as7g and I actually find it more tolerable at the same volume levels than the 6080.  We'll see about the 5998, I'm definitely interested in putting the pad as suggested. Since I read electric schematics at a first grade level (the lines are wires right?), I'll give it a shot, but will post to make sure my implementation is proper.

Me too, in terms of schematic reading skills.  This ones easy though.  Resitor 1 (RP1) just goes inline between the signal wire from the RCA input jack and the pots input.   Resistor 2 (RP2) would solder from the input of the pot to the pots ground (you can just twist one lead of each resistor together and that connects to the pot input ... it's the same, electrically, as connected those 2 leads seperately).  

For testing, you can actually just clip some inexpensive resistors in temporarily with some small alligator clips (Radio Shack) to determine the correct amount of attenuation.   You can twist one of the leads of resistor 1 to one lead of resistor 2 (maybe apply a small amount of solder to keep them together).  Clip the signal input wire on the free lead of resistor one.  Clip the two resistors twisted/soldered leads to input of the pot.  Then clip the free lead of resistor 2 to the pots ground.   Just do this for each channels input, left and right.    
  
This is what I did when I was experimenting with the attenuation just in case I needed it.   I did it with an unmounted pot and took measurments just to get an idea of how it worked.   You are attenuating the input signal some so you do lose some overall, maximum  "volume" compared to no attenuation.  But if you arent using anywhere near the full range of the pot, you will never miss it.   Also, you dont need to find the exact resistor values.  Just for a rough example, if you needed a 46.6 K resistor and could only find a 47K, that would be plenty close enough.

[Sh7eleven]

excellent, I hope to get to this in a day or two. The 5998 arrived and, as predicted, it did reduce the amount of volume i have to play with.

[Laudanum]

excellent, I hope to get to this in a day or two. The 5998 arrived and, as predicted, it did reduce the amount of volume i have to play with.

Yep, figured as much.   What are your initial impressions of the 5998?  Like it?