Express with bigger bottom?

[sliberty]

Has anyone found a great mod to give the Express a bigger bottom?

The Rocket uses the same value cathode bypass cap on V1a as the Express, but has much bigger bottom. This is most likely at least partly because of the cathode cap on the output stage. But the Express is fixed bias...

I have been hesitant to boost the cathode cap on V1a because of the higher gain of the Express. But on the other hand, a JTM45 has a giant first stage cathode cap, adn it's bottom end is enormous.

Any thoughts on the best approach here?

[dave g]

A really quick and easy tweak would be to raise the .002uF coupling cap to .0047uF, .0068uF, or .01uF. Try it and see if you like it.

[redshark]

Do the 3 little changes found on "Ingrid" that I did to mine....

https://tubeamparchive.com/viewtopic.php?t=18142

[Reeltarded]

Add a .0022 cap in series with the NFB resistor and the output tap if all you want is some thump.

[marcoloco961]

Comparing the "taylor" rocket schematic to the "kelly" express the biggest things that stand out are the 50p treble cap in the tone stack of the rocket compared to the 500p cap in the express. This doesn't really add bass, but more scoops the mids and highs out some.

The rocket goes even further with a cut knob to help cut even more highs.

On the Rocket, the 33k grid stopper at the input might cut some highs, but I doubt it is audible. The 220k going into the PI of the rocket could cut some more highs yet.

As Dave mentioned, a larger coupling cap will let more lows through as long as you do not get oscillations or blocking distortion from too much low end. The Ingrid mod used a ceramic .0022 in parallel with the .0022 poly making it a .0044. This coupling cap and the 500p treble cap of the tone stack would be the quickest and easiest ones to experiment with to see if they get you where you want to go.

Try anywhere between the 50p of the rocket tone stack and the 500p of the express tone stack to see what you like, and possibly anywhere between .0022 and .022 for the coupling cap. I would suggest either changing one or the other first as opposed to both at once. I might further suggest that you go in smaller increments so you do not pass the sweet spot you might be looking for.

[Roe]

you could try a bigger poweramp or even adding a big choke before the OT as well as increasing filtering a little or decreasing negative feedback somewhat. try not introducing to much bass early in the circuit - its better to add bass later so that the bass is cleaner than the top end. I like reducing the cathode cap on the second gainstage to .68uf

[marcoloco961]

Just curious if you tried any of these mods, and if so, what were your findings, likes or dislikes?

[sliberty]

https://tubeamparchive.com/viewtopic.ph ... sc&start=0

[leadfootdriver]

I used 716p OD's for all tone and coupling caps. They have a bit more lowend compared to the Malory types.

[RevD]

Use 4 - KT88's?

[garlin]

delete

[garlin]

delete