[Doc B.]

The 6AS7G is essentially equivalent. The 5998 is actually a little bit different spec, but for this circuit it can be considered equivalent and plugs right in. I happen to like the sound of the 5998s I've used a wee bit better than the 6080 or 6AS7, but YMMV.

 

[c540]

I am also a fan of the 5998! 
 
Doc, I remember reading that the 5998 lowers the output impedance to about 50 ohms, is this correct?
 
The 5998 sounds great paired with a tungsol black glass and a bugle boy 12au7a.

 

[Doc B.]

In the Crack it probably lowers the output impedance to more like 90 to 100 ohms.

 

[c540]

Thanks Doc!
 
 

 

[MrDavis]

I finally finished my Bottlehead Crack + Speedball + Upgrades.  Its painted with rustoleum hammered copper and the wood has a gloss finish on it.
 

Upgrades

Speedball
Neutrik locking jack
TKD 2CP2511 100kohm pot
Genuine Sylvania Pilot Light
2.2µF Axon film bypass cap on the last power supply cap (Probably don't need this with a choke installed?)
Triad C7X  choke replacing the last power supply resistor
Axon 91µF/250V output film caps
 
Tubes
 
Currently using a Tung-sol  5998 and JJ ECC82
 

 

 

 

[aroldan]

Whoa! beautiful!. What tubes are those?
 
Quote:

I finally finished my Bottlehead Crack + Speedball + Upgrades.  Its painted with rustoleum hammered copper and the wood has a gloss finish on it.
 

Upgrades

Speedball
Neutrik locking jack
TKD 2CP2511 100kohm pot
Genuine Sylvania Pilot Light
2.2µF Axon film bypass cap on the last power supply cap (Probably don't need this with a choke installed?)
Triad C7X  choke replacing the last power supply resistor
Axon 91µF/250V output film caps

 

 

[RingingEars]

Nice work MrDavis. I'll be installing my AXON 91µF caps and Alps blue velvet pot later this afternoon.
Have you had a chance to A/B the resistor/choke? Do you notice a substantial difference(or any difference) between the two configurations?

 

[MrDavis]

It was a subtle difference.  I'm still new at this hobby and really don't know how to describe it.  Anyway, it was an inexpensive upgrade. 

 
Quote:

Nice work MrDavis. I'll be installing my AXON 91µF caps and Alps blue velvet pot later this afternoon.
Have you had a chance to A/B the resistor/choke? Do you notice a substantial difference(or any difference) between the two configurations?

 

 

[RingingEars]

Quote:

It was a subtle difference.  I'm still new at this hobby and really don't know how to describe it.  Anyway, it was an inexpensive upgrade. 

 


 

That's what's so nice about the crack. It's an inexpensive amp to begin with and you can upgrade it pretty inexpensively also and it sounds flat out great with high impedance cans.
 
 

 

[BmWr75]

 

Any idea which of these mods had the greatest impact on improving the sonics?  My guess is the large caps.
​

Quote:

I finally finished my Bottlehead Crack + Speedball + Upgrades.  Its painted with rustoleum hammered copper and the wood has a gloss finish on it.
 

Upgrades

Speedball
Neutrik locking jack
TKD 2CP2511 100kohm pot
Genuine Sylvania Pilot Light
2.2µF Axon film bypass cap on the last power supply cap (Probably don't need this with a choke installed?)
Triad C7X  choke replacing the last power supply resistor
Axon 91µF/250V output film caps
 
Tubes
 
Currently using a Tung-sol  5998 and JJ ECC82

 

 

[MrDavis]

My ears liked the Tung-sol  5998 tube upgrade the most.  Followed by the large caps.
 
Quote:

 

Any idea which of these mods had the greatest impact on improving the sonics?  My guess is the large caps.
​

 

 

 

[RingingEars]

Quote:

My ears liked the Tung-sol  5998 tube upgrade the most.  Followed by the large caps.
 


 

Even more-so than the speedball upgrade or did that go in right away?

 

[MrDavis]

The speedball went in first and then a day or two later the caps went in.  I didn't spend much time comparing the difference. The tung-sol 5998 tube is the one that really stands out. Its gives the amp more clarity and tighter bass.  My ears really like it.  YMMV.
 
Quote:

Even more-so than the speedball upgrade or did that go in right away?

 

 

[RingingEars]

I've heard that from more than one person. The 5998 sounds like the way to go. I'm running an RCA 6AS7G at the moment. I love the ST shaped tubes, but didn't hear a big difference between it and the stock 6080. The new caps and pot are going in in the next couple hours. I'll report back.

 

[Beefy]

 
Quote:

Any idea which of these mods had the greatest impact on improving the sonics?  My guess is the large caps.
​

 

In my build, the Speedball was the first upgrade and made by far the biggest improvement.