New Express build; first time post

[M Fowler]

It has the three way switching because I believe an original TW Express is darker sounding then the ones some people have built. There is a big difference in my three Express amps. The dark one is with Pacific transformers and allows me to use the bright switch. I have not found any Stancors yet to try.

I also changed mine to the switching colossal posted for stability. Not original to TW style but neither is my build.

Mark

[WhopperPlate]

So the dpdt is more stable than stock?

Mine is actually pretty smooth sounding. Bright switch isn't overbearing.

I'm swapping a lot of tubes right now; I'm finding it is making a huge difference in stability. I'm getting less and less of that weird distortion the more tubes I try. I've tried several brands of preamp, but the Tungsol are just unbeatable right now for harmonic content and note bloom. Feel the best as well.

I put in the 1.5k grid stopper on v1b and it did help, but the feel of the amp changed a lot and I felt and took away alot of magic.

I think I'm going to have to order some select tubes before I can do any more tampering with the circuit. The oscillations have been removed for the most part, but it's hard to tell what's what when I have it on ten.

I'm going to go swap more tubes.

Charlie

[redshark]

About the oscillations on 10......

I would love to hear at least 5-10 real express amps, also test them and dime all the knobs...I'm sure you would be surprised...

Mine still has those oscillations when I unplug the cable and dime all the controls....I feel that is an extreme test because there is no way you will be able to use those settings. Volume at 1pm, all at noon and bright switch on is the "normal" playing settings for most people around here.
If you experience oscillations with those settings when playing a guitar then fight the thing but if is quiet, sounds great, doesn't sound piercing and blooms fine without sounding congested I wouldn't worry about it that much.
I would love Glen to tell us what does it means to unplug a cable, dime all treble and prescense and volume and hear oscillations....is it a symptom the amp is no good?

Please enlight me....

[WhopperPlate]

I think whistles with no guitar and amp dimed is just microphonic tubes, no? I'm only having a little trouble in this department depending on the tubes.

The real issue right now is the weird distortion, oscillations and microphonics with the guitar plugged in on ten. I know I'm never going to play those settings, but the more I can supress them the better it will sound.

I think Glen said somewhere that he can dime his amp with his guitar and not have much problems. I'll let him confirm.

Charlie

[redshark]

Well, my oscillations ONLY happen with the knobs on 10 with NO guitar plugged in....

I ordered a couple of tested prewar Ei's for V1 and V2 and still my amp does have the oscillations so it's not only the tubes as people say.

I would love Glen to come and tell us the nature of the "bad oscillations", what is considered "normal" and what is not.

His opinion here is important because:
He is the only known owner of a real express that has been through the issue of building a clone of his own amp.
Another guy whose opinion on this thing is important is Allyn because he has been in a few real wrecks and I don't think he wouldn't mind to share the expected signs of the amp being stable.
Also Alan plexi_67 has been in a couple real expresses and his opinion could help us.

[redshark]

Actually ONLY when treble and presence are dimed and volume gets to let's say 3 oclock and NO guitar plugged in......to be more specific about my oscillation problem.....

So no worries cause in order to enjoy the AMP you need a guitar plugged in....

[paulster]

They shouldn't oscillate with all the controls dimed.

Actually a more acid test is to have all the controls dimed except the volume which you have on about 1-2 o'clock to present the highest source impedance, and the presence on about 5 to have a moderate amount of NFB which presents the worst case for oscillation.

Glen has confirmed that his original and clones are stable under these conditions, which is about the worst combination you'll face.

The grid wire to the second triode is the particularly tricky one, as I discovered recently when I added some damping material to a couple of chassis to help deal with trickier tubes and lifted the wire just a millimetre too much to cause rampant power supply modulation under these conditions.

These are tricky builds!

[geetarpicker]

They shouldn't oscillate with all the controls dimed.

Actually a more acid test is to have all the controls dimed except the volume which you have on about 1-2 o'clock to present the highest source impedance, and the presence on about 5 to have a moderate amount of NFB which presents the worst case for oscillation.

Glen has confirmed that his original and clones are stable under these conditions, which is about the worst combination you'll face.

The grid wire to the second triode is the particularly tricky one, as I discovered recently when I added some damping material to a couple of chassis to help deal with trickier tubes and lifted the wire just a millimetre too much to cause rampant power supply modulation under these conditions.

These are tricky builds!

I totally agree with this post! Since it's so hard to compare the actual tones and response of the amp when simply talking about it "online" my comments on oscillation issues or lack there of is just a point of reference.

Just now I plugged in my original Express and you just can't make it oscillate even if you wanted to. I have used my amp on 10 during recording sessions and live, but typically not with the treble much passed 2pm and the presence passed about 1/2. Usually with the amp dimed I have to back the bass down to about 11pm to keep the bass from getting too loose. Still when folks talk about odd distortion on high notes and such it makes be believe that's an artifact of an amp with ultrasonic oscillations going on that in turn modulate the audio range. I think Ken called them "parasitic oscillations". Anyway diming the controls is just a way to get things more to the surface so that you can try to track them down. Even if you don't ever need to play the amp with everything dimed, I think that getting the amp stable will help the tones overall both dirty and clean.

[WhopperPlate]

Agreed Glen, if I can't dime everything and have no problems then I'm not done.

Yeh, PO: parasitic oscillation my arch enemy . Mine sounds like an crackly intermittent guitar cord connection, or a flickering light bulb is going on in the back ground of every note. At the same time it has a ghost note type harmonic that very apparently modulates the signal, so I'm also worried if my one of my caps was subject to infancy failure because the modulation seems kind of bad.

I think I'm going to go through and resolder any iffy connections and see if I can remedy anything. Tomorrow I'll have some time to throw it on the scope so maybe I'll be able to gleam something from that experience.

I'm also ordering some NOS preamp tubes from the TubeTramp so I can knock another thing off this list. I'm finding the ones I have are inducing alot of hum and buzz.

I also finally plugged in the bias probe and I was reading 12 to 14ma on every Tungsol and JJ I had. I threw some new GT 6V6HD's in the amp and it's drawing 35ma at max bias now, but they want to see like -42v to -50v, not -35v, so they aren't really helping either as far as judging amp performance. For the record the amp still has the same symptoms with these tubes as well.

So in general, I need some decent power tubes before I make any more changes. What's everyone's favorite? Are there any modern tubes that hold up, or am destined for NOS?

Thanks Again Everyone!

Charlie

[redshark]

Ok whopperplate, here is my take on tubes. When I tested my express the very first time I didn't have siemens EL34's but I had a pair of very old tungsol 6V6's which by the way biased a lot more in specs than what you are talking about. Of course you cannot compare new production 6V6 to the old one, not even close.
About the oscillations when dimed with Glen settings volume on 10 eq and presence in normal settings mine doesn't get any weird stuff, just A LOT more gain and bloom, by the way Glen I don't know how you can control that LOL
Still my express is not what you can call perfect but with normal settings is there.
Paulster I did your acid test with settings you mentioned and amp has no problems with guitar plugged in but what caught my attention was that when treble, mid and bass are dimed seems it cancel all the eq...weird.

I agree, this amps are a beast.....still I haven't figured out the noise with guitar unplugged and all dimed!! maybe is a sign that this amp should be played and not tested just to see when it fails....

[Structo]

If you used a shorting jack for the input jack, be sure that the switch is working.
If it doesn't short out the input when no cable is plugged in, that can cause a lot of what you describe.

[WhopperPlate]

To clarify, the GT 6V6HD is a higher voltage version of the normal 6V6 and requires more negative bias voltage to operate happily.

Any modern power tubes worth a damn in this thing or should I look for NOS?

Charlie

[paulster]

Personally I'd spring for a set of NOS Siemens EL34s since they're comparatively inexpensive and are the original EL34 that Ken used. They work fantastically well with the Express, unsurprisingly.

If your local Mesa Dealer stocks Mesa tubes, then see if they have any of the Mesa/Boogie branded NOS EL34 tubes in stock as these are Siemens too, and used to be pretty cheap until Roe ordered so many that they realised they were valuable! Siemens EL34s are a narrow bottle and have a dimple in the top, so they're easy to spot.

[WhopperPlate]

Really, Mesa Boogie huh? You can order those direct? Any other notable quality sources? Also what's the price generally on a pair of those?

I'm waiting for a reply on power tubes from the TubeTramp, so I'll see where that leads.

Paulster, thanks for the help.

Charlie

[paulster]

Really, Mesa Boogie huh? You can order those direct? Any other notable quality sources? Also what's the price generally on a pair of those?

Mesa (online): http://mesa.stores.yahoo.net/elsiemst.html
They used to be half this price so see if you find any left in stores at the old price and grab them if they do!
Angela Instruments: http://angela.com/el34germannostube.aspx
Steve is a quirky/cranky guy but he delivers the goods when it comes to tubes. Not cheap though unless he's having a bit of a blow-out on eBay (it happens occasionally).
Brian Sanborn on eBay often has sets for sale at reasonable prices, and his are usually well matched. I've bought loads from him without any problems whatsoever.

I'm waiting for a reply on power tubes from the TubeTramp, so I'll see where that leads.

I'm sure Terry will be able to come up with some great power tubes too. I buy loads from him and he is a straight-shooter. Erratic, but honest!

He used to have a big stash of the Trainwreck favourite Tungsram preamp tube too, so you might want to explore that avenue if your pockets are feeling deep!