Crack+Speedball circuit change for 5998's?

[charnich]

HI. I know that you can run a TS 5998 on the crack+speedball without doing any circuit mods, however are there any simple mods (resistor value changes etc) that would OPTIMIZE the amp for the 5998's? Thanks!

[larcenasb]

In practice, a 5998 gives noticeable gains in power, clarity, and dynamics. Even though it allows you to use medium-impedance cans with the Crack a bit more optimally, it doesn't sound any worse or mismatched with high-impedance cans. Both get a lively supercharged sound. So, I don't think a circuit mod is at all necessary IMO.

But if you want to do this circuit mod anyway, maybe others with the expertise can advise you. All the best. Cheers.

[Paul Birkeland]

Both the 6080 and the 5998 could run more current, but the power supply would need some redesigning for that to decrease dissipated heat.  There is no additional power available with the 5998, and the output impedance decrease is certainly real but not enormous (somewhere around 90 ohms IIRC).

[charnich]

Got it. Thank you for the replies!

[larcenasb]

Just to clarify, I meant the 5998 gives a more powerful sound IMO compared to a 6080 or 6AS7G.

[Doc B.]

I think the effect most people hear is simply due to the lower "negative gain" of the 5998 cathode follower. In other words, it plays a little louder for a given volume knob setting. The slightly lower output impedance might make the bass seem a little tighter.

[larcenasb]

Ah, nice to know the reason for it. Thanks, Doc! Hope all's well.

[theGopher]

I don't want to put words into charnich's mouth, but wasn't his original question whether the parameters for the stock 6AS7 and 6080 tubes are optimum for the 5998? Does the operating point need to be tweaked for the 5998 or is it ultimately limited by the power transformer's current capability?

[Doc B.]

Not really. The optimal parameters for the tubes are pretty subjective in this case. If you look at specifications the 6080, 6AS7 and 5998 are not optimal audio tubes on paper. But the real world performance in the Crack amp suggests otherwise. So right off the bat it's difficult to say that optimizing to some published specs for these tubes is going to be the right direction. The general consensus is that the 5998 sounds better than the 6080 in a Crack (YMMV). Ipso facto the circuit is already better optimized for the 5998 than the 6080. And it's pretty clear after all these years that people really like the Crack with a 6080 in it. And so we really just come full circle to this being about tube rolling more than circuit optimization. If you want a circuit better optimized for the 5998 AND the 6080 you can build a Crackatwoa. It doesn't have to do with altering operating points but rather with optimizing the power supply regulation and the attenuator quality.

[theGopher]

Thanks Doc. If it ain't broke don't fix it I guess. I'm happy with my Svetlana Winged C 6N13S in my second hand crack. At £12 it's a bargain and sounds good to me paired with the right front end tube.

[Doc B.]

There you go. Whether you like it or not is all that matters.