New Express build; first time post

[WhopperPlate]

Yeh, could be the Spragues too. I think I'll just can them all and fire it up fresh with a new batch and resistor to safely form. For some reason my brain decided to forgo the process, probably because they were brand new. Shouldn't have underestimated the Express.

Redshark, I saw that thread you referenced and it was really encouraging to hear all the expresses started out wild and untamed. Now I need to find the Gerald Weber book! Throw in another twenty!

The thing is I put in an extraneous amount of time and effort on the wiring and getting as close to the pictures as possible, but that didn't really pan out the way I thought it would. If it ain't the caps then I'll start questioning my solder technique.

Charlie

[M Fowler]

You just need to walk away from the amp for a few days and regroup by going over the entire amp with a meter, a chop stick or whatever it takes to tame the bitch.

Don't think the rest of haven't had our share of stubborn amps.

The only TW that gave me fits was allynmey's 80w Express type of build that was a down right long ordeal.

Mark

[WhopperPlate]

Oh, I have been on a 4 day hiatus from this thing, and when I get back I'm ripping those stupid capacitors out.

Charlie

[WhopperPlate]

Hey guys,

I've got an NOS LCR 40/20/20/20 cap that I was thinking of using; does anyone have any experience with multi section can caps in the xpress? I'm curious how it will effect noise and such.

I'm just using parts that are lying around, and was thinking I could use 4 80uf sprague and run them parallel series for 80uf on the mains and then use the one LCR for the rest.

Charlie

[ampgeek]

I built mine with JJ cap cans and VVR as described/shown here:

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

Hmmmm.....hope that link gets you there. If not, search for "Express with Variable Voltage Regulator" thread started by UR12 in this Trainwreck Discussion section.

Mine is very quiet and stable (once I got through a boneheaded bias pot issue!). I do not recall ever seeing any posts describing problems with cap cans. So...I have to believe that there are no endemic issues associated with using cap cans in Express type builds.

Good luck!
Dave O.

[WhopperPlate]

Cool, I was just going to throw the can in next to the spragues, I think I have enough room, we'll see.

Charlie

[PlinytheWelder]

Here's mine with JJ can caps and a VVR3...
[img750]http://verosurfcam.com/TW14.jpg[/img]

[WhopperPlate]

NICE!

[RevD]

I know this might be a bone head question, but since your looking at everything.... You don't have any fluorescent lights or fans in your shop do you? Long shot, but I remember a post on another forum where it was finally discovered. Hope you get things right, I've built quite a few amps and was considering a Express but man I don't know if I could a) afford volumes or tubes to get it right b) trace down any problems with a high gain amp, highest gain I've built so far was my 18 watt TMB and that one even took a bit of tweeking wires to get it right.

Regards,

RD

[RJ Guitars]

... I've built quite a few amps and was considering a Express but man I don't know if I could a) afford volumes or tubes to get it right b) trace down any problems with a high gain amp, highest gain I've built so far was my 18 watt TMB and that one even took a bit of tweeking wires to get it right.

Regards,

RD

The Express build presents a very interesting dilemna. Do you want to build it over the line of instability and then bring it back or just hope to build it barely shy of that point? Then how do you consistently do either?

It is an amp that is by it's very design intended to be right on the ragged edge of instability. Apparently this is where the great tones and response characteristics of this amp originate. However, as near as I know there isn't really a single definition of instability so it is a little hard to quantify what that means, as applied to the Express design.

We have heard the tales of squealing and motorboating and such that are often tagged as the evidence of instabiity but I am not convinced yet that living on the ragged edge of every form of instability applies to the ideal design intentions...

I would think that technically there is some optimum level of gain and interaction between the stages that would help us understand what was intended in the design, and how to approach the ragged edge of instability or overcome it as needed.

Does anybody know the Ken Fischer (or other) definition of what "instability" means, considering the Express design?

rj

[redshark]

RJ, check the thread that I started about the "edge of instability". It's a very complicated topic because We haven't test every real trainwreck express build to know if they are 100% stable or not.
All that we have as reference so far is the Francesca pics which exhibit a couple of errors and the undocumented express which was a reject at some point.
By the comments of owners and people that has seen real ones the little variations are little 'fixes' to stop oscillations that can easily get inside a circuit with no grid resistors and lots of gain.
So there's no real source of information that can testify how stable they are or not and what is "approved" or not.

[M Fowler]

The areas I concentrate on are the brite caps and the NFB those two areas can cause trouble.

Shouldn't need 15k grid blockers on the entrance of V1, might need shielded wire to volume pot and use good preamp tubes. Your going to need to use a cover plate on the chassis as well. I didn't on my last one and have not had any trouble but I may pull that and put one in anyway.

Mark

[redshark]

Mark the 15k input grid resistor might not be needed as you said but at night you can easy pick a radio station if you have nothing there. A 10 or 15k won't make a big diference and it will solve the problem...my own experience....

[M Fowler]

Yes it solves a problem but is the guitar or guitar cord acting as the antenna and do other cords and guitars act the same?

I don't have any problem if the resistor is used. Everyone has to get their amp working the best they can with whatever works.

[PlinytheWelder]

You could also try ferrite beads instead of grid stopper resistors. IMO, they'll do less in the audio range and still do the job on RF.