New Express build with pictures!

[Jackie Treehorn]

Ok, here's a few things I would try.

The two blue wires going to the plates of V1a and V1b, I would not run them parallel to each other.

The grid of V1b, I would try to move so it is perpendicular to the plate and cathode wires. I recommend shielding that wire, as it will give you more layout options without having to worry about losing top and transient response from capacitive coupling to the grid where the tubes miller capacitance will make the effect far more extreme. You've already got shielded wire on V1a, anyway.

Then I would move the wire on the cathode of v1b so it is not parallel with the plate of v2a. But, make it parallel with the plate of v1b (local negative feedback) and experiment with the distance to kill the oscillations. You could also try a bit on v2a, too, making the black and blue wires slightly more parallel.

Maybe try the wire to the cathode of the phase inverter down against the chassis, avoiding the grid.

I would try a bit of distance between the wires to the power tube grids while keeping them parallel. But, I wouldn't run the negative feedback wire parallel to those wires.

I was checking out the wires from the output transformer to the power tube plates. Is one brown and one striped coming from different sides of the transformer?

I like your parts choice! Polystyrene treble caps sound a lot better than mica. They give a nicer sound to the top end. So, those are oil caps of some sort you're using for coupling?

[gearhead]

Another tweak is to increase the separation distance between the blue and yellow wires that run from the bass pot.

[Cliff Schecht]

Ok, here's a few things I would try.

The two blue wires going to the plates of V1a and V1b, I would not run them parallel to each other.

The grid of V1b, I would try to move so it is perpendicular to the plate and cathode wires. I recommend shielding that wire, as it will give you more layout options without having to worry about losing top and transient response from capacitive coupling to the grid where the tubes miller capacitance will make the effect far more extreme. You've already got shielded wire on V1a, anyway.

Then I would move the wire on the cathode of v1b so it is not parallel with the plate of v2a. But, make it parallel with the plate of v1b (local negative feedback) and experiment with the distance to kill the oscillations. You could also try a bit on v2a, too, making the black and blue wires slightly more parallel.

Maybe try the wire to the cathode of the phase inverter down against the chassis, avoiding the grid.

I would try a bit of distance between the wires to the power tube grids while keeping them parallel. But, I wouldn't run the negative feedback wire parallel to those wires.

I was checking out the wires from the output transformer to the power tube plates. Is one brown and one striped coming from different sides of the transformer?

I like your parts choice! Polystyrene treble caps sound a lot better than mica. They give a nicer sound to the top end. So, those are oil caps of some sort you're using for coupling?

The wires coming from the OT are brown and blue, but the blue one was hacked too short by me so I used another piece of cloth covered wire from the same tranny (it had 250/500 windings that I clipped short), soldered it on and double heatshrinked it before routing it through the back of the chassis. So yeah, my V5 is getting the brown wire and V4 is getting the blue wire which is annoyingly backwards from what Ron's layout says. Perhaps the Stancor A3801 copiers were backwards from what the actual unit is (I have a real 3801 on here if you didn't see my mention of it before). So yeah, that was an annoying snag but an easy fix nonetheless.

The poly's are just what I have on hand but I agree that they sound much better in a lot of places than mica caps. I have a huge collection of NIB ones that I picked up for very cheap. If you're looking for any values let me know, I've got a lot of 'em! I got the Vitamin Q 0.22uF's and C-D 0.1uF's (yes all paper/oil caps) from David Root which I also sort of prefer over the "standard" Mallory PVC caps not just for their sound but their stability and physical strength.

I think a combination of shielding the V1b grid wire, adjusting the plate wires a bit, moving the PI wires apart and moving the FB wire away from these really did the trick. I also separated out the bass pot wires but didn't find out if this helped or hurt. I sort of did all of the tweaks and bends at once so I'm thinking it was just the combination of tweaks that contributed as a whole.

I ended up with an Amperex 7205 in the first preamp stage which also helped clean things up a lot (I only have one of these though!).The amp as of now seems about as stable as an Express gets. Not too much hiss but a LOT of treble which is not so good for the ash/maple 52 Tele RI I play.. I've seen Glen's trick of using a 250pF cap in the PI but what other tricks do people use to tame some of the highs without hacking on the circuit?

[Cliff Schecht]

I guess the other thing is that my wall voltage is 125V which shoves the heaters up to something like 6.95V.. Should I put a dropping resistor in there to get the voltages down or just live with it..?

[paulster]

Heater spec is usually +/-10% on tubes, which would be 6.93V tops, so you're right at the upper limit but it's debatable whether or not it's worth doing anything about.

I'll have a proper read of the thread and look at the photos tomorrow to see if I can see anything.

[redshark]

I think the biggest diference regardless of brightness is what speakers do you play and type of cabinet. What tweak did you do to the bass pot wires? can you post a new pic?

[Cliff Schecht]

The speaker and cab I'm testing on is just that, a test rig. It's a 40's PA box (I seem to find these often either cheap or free) with a "repaired" Celestion Line 6 speaker (supposedly a 70/80). The speaker itself was stabbed by a jealous wife as I mentioned in another thread and that was given to a friend of my friend. The guy who gave me the speaker had repaired it with some black flexible glue of unknown nature and the speaker works but definitely sounds a bit ratty. I think that, combined with the open back of the shallow PA box didn't help in the brightness/brittleness area. All of that plus I'm using a maple neck Strat with a SD Little '59 in the bridge which is a bright guitar in its own right. Perhaps I should test it out with the ES335 tomorrow and see what kind of results I get.

I'm going to try this amp on my Vox cheapie 4x12, which sounds surprisingly good for the price, and the Bogner 1x12 cab that I usually use with my other Express. If it's still too bright then, I may end up messing with the amp a little bit then.

I guess I need to christen this amp as well.. Is the name Trudy taken?

Also, I'll post some pics of the new guts later tonight or tomorrow.

I may try adding some parallel diodes in series with the heaters to drop the voltage a bit. I don't want to hurt my only Amperex NOS 7025 and I really don't want to pay $100+ for a new one..

Has anybody tried NOS GE tubes in their amps? I don't know if it's just me or what but I've found that almost every GE tube I use sounds absolutely fantastic and quite consistent to boot. There's one that I use in my other Express that I really want to try in this one, it's just a normal 12AX7 but seems to be one of the magic ones that works better than others.

[JamesHealey]

Trudy was taken by Ken Fischer himself.. actually quite an interesting wreck we have a schematic of it that Brian Wallace from Marstran did around here somewhere..

[passfan]

I'm going to try this amp on my Vox cheapie 4x12, which sounds surprisingly good for the price, and the Bogner 1x12 cab that I usually use with my other Express. If it's still too bright then, I may end up messing with the amp a little bit then.



Has anybody tried NOS GE tubes in their amps?

I tried mine through a Marshall 4-12 slant 1960 and it was too dark sounding. Plugged into a 2-12 Bluesbreaker style open back combo that I put my Rocket in and it sounds great. I also have a GE jan 6072 (12ay7) from 72 I flip around from time to time that is the sweetest sounding thing. Spent 60 bucks to get it...well worth every penny.
Glad to hear your Express is presentable. I'd keep looking through the tubes though, I think it can get better. I left my V1b grid wire unshielded but laid a strip of foam under the turret board to give it separation from the chassis and dampen it. I can chopstick it now and you can't hear it.

[Allynmey]

Cliff, clean up the lead dress around V1. Lift the plates and grid wires in a hump over the heaters. Paper in Oil caps? PIO caps aren't a good way to avoid oscillation in this circuit. 15K grid stopper? wow! Must really be oscillating!

[Cliff Schecht]

It's not oscillating anymore. I got rid of the grid stopper and added shielded wire to V1b which, along with moving some of the other wires around as I mentioned before, killed any problems I was having. I can turn the knobs all to max and not have any oscillations but the hiss definitely becomes evident with the presence, mid and treble maxed out!

[bigbeck]

. I've seen Glen's trick of using a 250pF cap in the PI but what other tricks do people use to tame some of the highs without hacking on the circuit?

I play a Tele too. An easy fix is to get rid of the bright caps and put a .01 or .02uf cap on the bright switch. and hook it up in parallel with the .002 coupling cap. It's really a big improvement for playing at low to moderate volume. It's not needed for loud playing,though. Call it a Tele/Gibby switch. Otherwise you'll need a couple of miles of guitar cable to tame a Tele. After I did this simple mod,the amp was still bright enough for humbuckers. If you don't like it,you can always go back to the glass shattering bright switch.

[Cliff Schecht]

I will try this soon if my Bogner cab is still too bright. Or perhaps I'll try a ridiculous cable run first, but that's such a nightmare to carry around compared to just making a slight mod to the amp..

Do you leave off both the 100pF and 500pF caps on yours?

[geetarpicker]

I no longer run the 250pf PI cap in my clones, it helped to darken the EQ but was never quite as open sounding. It kind of helped at first but more recently I found some other reasons that my clones were just a tad brighter than my original and I did some more part swaps though still all at stock values. I always run the 500pf bright cap as it truly helps the clean tones. Try two Mogami gold cables in series, both 18' or 20'.

[JamesHealey]

trudy had 2 2n2 caps in parallel on the rc filter between 2nd and 3rd stage.. much more bottom this way. also try 250k treble pot some express's have been noted with this.. volume pot was 500k on trudy.. less gain.