Express clone variations....

[redshark]

Has anybody tried to build an express clone according to the Trudy schematic??

https://tubeamparchive.com/viewtopic.php?t=9493

you can find the schematic on that thread.

If someone did or someone has heard the Trudy amp....how does she sounds?

I'm curious, diferent power supply and voicing....

[redshark]

I'm surprised nobody has tried to use the Trudy schematic. I think it wouldn't be that dificult to make those little changes but using same Francesca pics for reference.

[Richie]

If you read through some of the old post along those threads. Brian Wallace posted the info, and seems it was getting overlooked. So i reposted it.
I was supprised to see, many people had never seen or heard of it,but the info had been there all this time.
I have built one like it, and it was a very nice sounding amp, and played great. Liked the sound of the Brown CDE caps too. I think Brian also sells some OTs for Wreck amps. Most of the Express amps are very much alike, but the layout may be a little different, or a small tweak here and there on some. Some may use different parts over the years too.

Probably many more pics of Dumble amp innards, that the wreck amps.

[rooster]

OK, correct me if I am missing something? The differences are:

#1) a 100K slope resistor vs. 150K
#2) a 500K vol pot vs 1M
#3) a .004 coupling cap (combined) vs. .002
#4) an 470 ohm resistor to ground off pin 2 on V4 (New one on me - what in the world?)

That's everything, right?

OK, plainly, looking at the 100K slope resistor vs. 150K, this thing is mid heavy. I say that because the 150K slope has PLENTY of mids already - egads, why offer more? And then the .004 cappage allows for even more bass at V2 - why? OK, so I have no idea why the 470 ohm resisitor exists unless it is bleeding off some extra filament voltage or something - anybody? I have never seen this before, new one like I said. As to the 500K Vol, I use this and some of the other builders here do too, I like it actually.....Which all seems to add up to a very early version Express for sure, and something Ken would later fine tune. (The CDE caps, BTW - Richie, do you know what they were made of? Were they PVC?)

Anyway, short of the 500K vol pot, I think I will stay with the 'improved' version. But I did enjoy seeing this because I hadn't seen it before, and, yes, thank you for digging it up, everyone. It's great to see some history of Ken's developing work!

[WhopperPlate]

Hmmm, the 470 ohm resistor off of pin2 v4 is to bleed off some heater voltage? My heaters are running at like 3.35, maybe I should try something similar to drop my heaters down to 3.15 it's supposed to be.

Charlie

[redshark]

Does the 500k volume pot makes it sound darker than with the 1M? Maybe it could help to remove oscillations since you cut the volume range...

[rooster]

Luis - In my case switching to the 500K vol pot just gave me a more adjustable range. And, yes, I threw away some gain when I did this. However, since the 1M pot gives the amp more gain than I can use, it seemed like a no brainer. Too, FWIW, now the bright caps make more sense to be of a lower value - 50 and 100pf - because the pot value is a smaller value and therefore not blocking as much high end. ??

Talking about this for a minute, if you take an amp like a Plexi, where there is not that much gain on tap from the preamp, the 1M pot makes total sense as you turn the knob. With the Plexi you need all the gain you can get then but not so for the Express. Well, IMO.

So doing the math and my PEC pots, at 12 o'clock, the 500k is seeing only a 50K-ish load to ground and the signal is passing thru 450K-ish resistance, the 1M is seeing a 100K load and passsing thru 900K ohms of resistance. The former has less gain than the latter, and that's what I looked at. Since I was running the 1M pot at less than 100K to ground for my gigs, I wanted to make this range more finely adjustable. (And its interesting to note that Glen's pots are probably a 30% taper - real deal audio pots from the day, or maybe possibly 20%. Which means his 12 o'clock is seeing either 300K to ground or 200K to ground. Wow, that's a lot more gain! For me to get there with my 500K pot I have to turn it to the 3/4s on or what I'm calling the 3 o'clock position. And this is insane volume and distortion for anything I am doing. Plus, let it be noted, I am hooked on a modified tubescreamer to get my tone at a gig using the Express.)

So, wrapping this up, here Glen has around 700K-800K ohms resistance to run his signal thru - and to help him get to his tone, he uses the 500pf cap to get the highs across that distance. With my 500K pot on that high, 3 o'clock, I sure don't need my 50pf bright switch on at all. In fact, I use the 50pf cap typically when I am in the 9 o'clock range, bridging the 470K distance. I think the more important thought here is, looking at Glen's rig, is just exactly how much bass is being shunted by the 700K-800K resistance? For example, if a 500pf cap rolls off anything below 200hz, this means the low E string (which I think is 180hz), is fairly diminished in Glen's amp except for what the 700K-800K resistance is passing. Of course this balancing act is pretty clever if you think about it and Glen makes good use of it. The problem with all of this for me is - with my amp, my speakers, my guitar, my playing skills - I don't like how the 500pf cap sounds when running a 1M pot and the 500pf cap engaged. Eh, but then I don't have the pots he is using. They might make a difference of course in the puzzle. Eh, but then I am back to the volume thing - I can't use all that volume.

Ok, more info than you wanted Luis. Also, you and I were talking recently, and I told you I preferred a smaller PI cap? You might look at all of this and see why that could be. Since the 500K pot is not blocking the signal (translation: bass freq) as much as the 1M pot with the 500pf cap engaged, I need to knock it off somewhere else, and the PI is where because my Express(s) have plenty of bass.

Hm: It has just now occurred to me that I could add resistance to the top side of the volume pot and still reap the benifits of the 500K pot adjustment. The wire that runs to the bright switch could be replaced with a 270K- 470K resistor pretty easily. Well, something to think about...

[redshark]

Yes Ross, as you said....one more thing to think about!! This express amps are so mentally challenging!! Seems to me that every little change needs to be heard and analyzed. I have no electronics background so for me all this is a learning experience....

I'm so ready to start a ROCKET!!!

I hope that one is not as temperamental as the express!!!