Express Issues

[gktamps]

I'm running a 2 x 12" open back cab with one Gold and one Greenback, and it's my go-to cab, though I have 4 others. Really love the warm, complex sound. Really sings, but has good tight response.
I use it with all my Rockets, 2 Express, and Liverpool, not to mention other heads.

[jkey04]

I've heard good things about the Gold/Green combination as well. Looking at picking up a Bogner Alchemist 2x12 with greenbacks from a local guy at a great price. Maybe i'll swap one of the greenbacks for a gold...

If nothing else, the two greenbacks will make another great test cabinet for builds to add another flavor besides the Z-best with V30/H30 combo.

[RJ Guitars]

If you don't mind going back to look into the electronics, I had a Liverpool that had harshness issues that I tamed a few years back. i used a combination of ideas from various sources and really turned the amp into a joy to play. I'll cut and paste what I think are the critical notes from that effort. It's on page 3 if you want to see the original post... otherwise the good stuff is copied below. https://tubeamparchive.com/viewtopic.php?t=11528

1) I went back to all the original component values from the Liverpool schematic with only a couple subtle exceptions. It helped but still sounded Harsh. I had tried all kinds of things including a bunch of trimmer pots. I just pulled them all out and put in simple components.

2) I tried an output transformer snubber that kills high frequency oscillations... something featured in Guitar Player magazine that I'd used effectively with poor quality EL34 tubes before. In this amp it killed a lot of tone and didn't fix the problem. I took it back out.

3) Installed lower gain preamp tubes including a 5051 for V1 and a 6072 for V2. Not as crazy but still lots of high frequency hash and ice pick in your ears tone.

4) I then found a few things mentioned inside TAG that transformed this amp into an entirely different animal (in a good way):

https://tubeamparchive.com/viewtopic.php?p=235160
https://tubeamparchive.com/viewtopic.php?p=219333

a. 250pF cap across the phase inverter anodes - really smoothed things out.

b. Installed .033uF PIO Russian caps in the phase inverter... I wasn't sure I could hear any effect but I was inclined to think it cut some of the harshness. I'd heard these were great sounding caps and added a lot of smoothness to an amp.

c) Added a 100pF bypass cap (I used Poly-Styrene caps) on the V1a plate load resistor... The impact of this was huge... I liked this so much I added them to all of the plate load resistors on the other gain stages. If I wanted to keep a little more of the wild child int his amp I would say that only the first stage was essential for this particular amp.

d) Finally I read a 47pf snubber from the anode to the cathode one the preamp tubes. The logic here was that the frequency of noise this kills is far above the audible but messes with the stability of your amp... not a huge effect but maybe audible.

e) I changed the bright caps to 50 and 100 pF Poly Styrene... the 250 and 500 pF from the original schematic were just way over the top. I can effectively use and actually enjoy the bright function now.

The cumulative impact of this created a great sounding amp with sparkling clean tones and a decent solid bottom end and still retained the clean to mean thing with a really rich overdrive tone. I can still sense some instability if I push everything and stand in the wrong position with my strat. I haven't been able to really turn it up and blast away for any long time periods yet but I like it so far.

This was an unusually unstable Wreck build - maybe in part because I broke the component layout from the original but I think it was because these little EL95 tubes were just getting hammered by a huge ugly signal and they couldn't handle it. I need to go back with the scope and look at the waveforms but without knowing otherwise, I think the tone is fantastic. I would say that for the average Wreck this might take too much edge off but I wanted to see how far I could go in taming the beast. The lower volume clean tones are just amazing and unlike anything I have ever heard from a Wreck.

[jkey04]

Great advice RJ! I'll continue to explore my Express build and report back...

[jkey04]

Lesson Learned: Do NOT use 716P caps in the tonestack.

That was the root of the issue. I swapped them for Mallory 150s and its a totally different amp! Usable now. I also lowered the slope resistor to 33k. I kinda like it so far...

The tweaking continues.

[Colossal]

Lesson Learned: Do NOT use 716P caps in the tonestack.

That was the root of the issue. I swapped them for Mallory 150s and its a totally different amp! Usable now. I also lowered the slope resistor to 33k. I kinda like it so far...

The tweaking continues.

Interesting. I built an Express prototype once using 716P throughout and it was very stable. Wonder if you had a bad cap?

[jkey04]

Colossal - That is a possibility. I need to measure capacitance of the 716P caps I pulled out to see if they are in spec...

I'll report back.

[jkey04]

Both 0.022uf 716P caps i pulled from the tone stack measure good. Spot on actually. Weird... The EQ definitely wasn't working properly with them in. The amp was shrill and lacked bottom end.

The Mallory 150s have made the difference! Amp is sounding great now. Just need to work out a better bright cap method to keep it from squealing when engaged at higher gain settings.

[Littlewyan]

I found changing the 715p caps I originally used to 6PS Caps made a big difference in tone. The tonestack wasn't unusable with the 715p caps though, just sounded different.

[andresound]

The H75 is in a cab by itself so I won't be replacing either speaker in the Z-best cab.

I'd love to try a 2x12 greenback and gold combo...

I have a 2x12 closed back (old vibroluxe cab) loaded with a early 70,s (T1281) 30w green back and a Gold Alnico. Best this express has ever sounded with the exception of a late 60's 4x12 Marshal cab loaded with 25w greenbacks that belongs to a friend!!! The greenback is less efficient and this helps with the Express.