New Express build with pictures!

[bigbeck]

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?

Yes, I actually changed the switch to an ON-OFF. In my amp,C-8 is .0047uf with a .01uf on the switch. Even with that, The Tele is still very bright! For me the tone is perfect when playing an SG through it - without the .01 cap and bright switch.

In my opinion, the Stock Express and Tele is not a good combination, unless you want to use it to cut steel or etch glass.

[Cliff Schecht]

I was doing some playing earlier with this amp and ran into a strange problem. Well a few problems but the big one was that with my Tele (stock single coils) going through a 20 foot cord I made years ago, I was getting a strange crackle in the high end, not unlike popcorn popping. I swapped out tubes like crazy and played around a bit but the problem persisted. When I moved the amp to another room and switched to a Charvel with humbuckers and a different cord, the crackling completely went away. I went back to the Tele with the new cord and the crackling was again completely gone, everything sounded spot on. It may have just been the cord or the combo of that cord and that guitar, I'm not sure but more testing will inevitably reveal the problem.

The single coils are a problem themselves because of the amount of hum I get with them. None of my other builds hum this badly with single coils but then again, the ungodly amount of gain in this amp will of course pickup any noise that's getting interjected into the single coils. I might end up switching to a set of Joe Barden's (I'm a huge Danny Gatton fan) eventually to prevent problems at shows and practice but this guitar has not been any trouble until now.

Something else I noticed was that with the amp flipped over and the guitar dimed, tapping on all of the caps didn't give me the usual "thud" that I get most of the time. The amp was on and working fine so I'm not so sure why the microphonics went away, perhaps because I'm using a really nice set of tubes (Amperex 7025 in V1, Telefunken in V2 and V3, 1945 Sylvania 6V6's in the power amp). This tube combo sounds absolutely fantastic, I really dig the sound of 6V6's in the power amp. Doesn't clean up as well but the sound is killer nonetheless.

Also, my tube heaters are now running at slightly over 7V (like 7.05ish). My wall voltage measures quite high (125V so I'm thinking I need to add a set of antiparallel diodes to one of the heater wire connections. I don't want to carry around a variac to gigs..

The radio problem completely went away when I added a 10k Dale resistor to V1a, so thanks to Paulster for that suggestion! The amp is sounding fantastic now and aside from the high heater voltage, all is well in the amp it seems...at least for now .

[paulster]

Also, my tube heaters are now running at slightly over 7V (like 7.05ish). My wall voltage measures quite high (125V so I'm thinking I need to add a set of antiparallel diodes to one of the heater wire connections. I don't want to carry around a variac to gigs..

That's just outside the upper limit of the specification for tube heater voltage so I'd be inclined to bring it down a bit. At a 120V wall voltage you'd still be at 6.75V, so I'd try to bring it down to around 6.6V or below, so it won't end up being too long when you're out and working with a regular 120V supply.

If you've got the room I'd recommend a couple of aluminium clad power resistors (the type that can bolt to the chassis) rather than the diodes since you won't get any noise induced into the circuit from these, whereas there is that risk with the diodes.

You need to put a resistor (or the pair of diodes) in each leg of the heater supply though to ensure it's still balanced around the 0V reference point.

The radio problem completely went away when I added a 10k Dale resistor to V1a, so thanks to Paulster for that suggestion!

If you mean the 10K suggestion in the other thread from yesterday then it's FYL you want to thank for that! I've mentioned before using as low a grid stopper as you can get away with to not impact the tone, but FYL suggested the 10K value.

[Cliff Schecht]

FML, I meant FYL .

I have yet to do a build where I didn't include a dropping resistor to reduce my heater voltage. I calculate that at 7.05V, to get down to 6.3V I need about a .2 Ohm resistor. I'm thinking a .1 Ohm resistor on each leg will do the trick just fine, although when I'm using 6V6's the drop won't be as much (but still in a safe range).

[passfan]

I was doing some playing earlier with this amp and ran into a strange problem. Well a few problems but the big one was that with my Tele (stock single coils) going through a 20 foot cord I made years ago, I was getting a strange crackle in the high end, not unlike popcorn popping. I swapped out tubes like crazy and played around a bit but the problem persisted. When I moved the amp to another room and switched to a Charvel with humbuckers and a different cord, the crackling completely went away. I went back to the Tele with the new cord and the crackling was again completely gone, everything sounded spot on. It may have just been the cord or the combo of that cord and that guitar, I'm not sure but more testing will inevitably reveal the problem.

The single coils are a problem themselves because of the amount of hum I get with them. None of my other builds hum this badly with single coils but then again, the ungodly amount of gain in this amp will of course pickup any noise that's getting interjected into the single coils. I might end up switching to a set of Joe Barden's (I'm a huge Danny Gatton fan) eventually to prevent problems at shows and practice but this guitar has not been any trouble until now.

Something else I noticed was that with the amp flipped over and the guitar dimed, tapping on all of the caps didn't give me the usual "thud" that I get most of the time. The amp was on and working fine so I'm not so sure why the microphonics went away, perhaps because I'm using a really nice set of tubes (Amperex 7025 in V1, Telefunken in V2 and V3, 1945 Sylvania 6V6's in the power amp). This tube combo sounds absolutely fantastic, I really dig the sound of 6V6's in the power amp. Doesn't clean up as well but the sound is killer nonetheless.

Also, my tube heaters are now running at slightly over 7V (like 7.05ish). My wall voltage measures quite high (125V so I'm thinking I need to add a set of antiparallel diodes to one of the heater wire connections. I don't want to carry around a variac to gigs..

The radio problem completely went away when I added a 10k Dale resistor to V1a, so thanks to Paulster for that suggestion! The amp is sounding fantastic now and aside from the high heater voltage, all is well in the amp it seems...at least for now .

Here is a link to an article that helped me out immensely. I used this technique on my custom V and it doesn't hum at all. I swear I can stand there with my express (or any amp) guitar plugged in and volume wide open and take my hands off the string and hear nothing until she starts feeding back. At lower volumes I take my hands off and forget it's still on until I bump a string. You might check it out as it was developed for the single coils in a strat.

http://www.guitarnuts.com/wiring/shielding/shield3.php

[Cliff Schecht]

Installed 0.1 Ohm resistors on each leg of the heaters. They are smaller power resistors (3 Watts) but have some FAT leads and I believe can handle the power (each one only sees 1.95A, so 1.95^2*0.1=.36W). With EL34's, this drops the heater voltage down to right below 6.1V, 6V6's should sit right at 6.3V. The hum in the amp went down slightly too, which isn't to say that it was overwhelming before but nothing wrong with getting a slight bonus with a safety modification like this.

My only concern now is that I will run the amp at a place that has a lower wall voltage and my heaters will sit too low. Better than being too high for sure but if I do run into this situation, I can always swap out 6V6's for some more safety margin (less current draw so slightly higher heater voltages). Do clubs and bars usually have a higher wall voltage as well? I'm not too experienced with playing bars/clubs so I'm interested in what others thoughts are. I'm under the impression that wall voltages in America have raised slightly from the 120V standard, but I guess it really just depends on where you live and what you are plugging into..

[passfan]

Installed 0.1 Ohm resistors on each leg of the heaters. They are smaller power resistors (3 Watts) but have some FAT leads and I believe can handle the power (each one only sees 1.95A, so 1.95^2*0.1=.36W). With EL34's, this drops the heater voltage down to right below 6.1V, 6V6's should sit right at 6.3V. The hum in the amp went down slightly too, which isn't to say that it was overwhelming before but nothing wrong with getting a slight bonus with a safety modification like this.

My only concern now is that I will run the amp at a place that has a lower wall voltage and my heaters will sit too low. Better than being too high for sure but if I do run into this situation, I can always swap out 6V6's for some more safety margin (less current draw so slightly higher heater voltages). Do clubs and bars usually have a higher wall voltage as well? I'm not too experienced with playing bars/clubs so I'm interested in what others thoughts are. I'm under the impression that wall voltages in America have raised slightly from the 120V standard, but I guess it really just depends on where you live and what you are plugging into..

Voltage in clubs will always be a problem unless you install a power conditioner in your rack. You may make your resistors switchable perhaps ? Then you could check and preset whatever the case.

[Cliff Schecht]

I don't think making the resistors switchable is an option, that's too much wiring that I would be adding to the design and switches always add their own set of problems. In this case it would be physical size, a switch that has to carry 4 Amps of current will not be small and I don't want to cram more into this already "compacted" design (well, not compact by my standards but still a tight squeeze). Maybe I can figure out a switch that shorts the resistors when "ON" but again, I'd rather the heaters be too low than too high.

I don't want to lug around my variac so perhaps a power conditioner would be an option, except I don't use a rack at all! I don't know of any affordable floor-based voltage regulators either. Now I'm thinking I should take out those resistors or at least somehow make them shortable (e.g. a switch ) but this is a hassle to add on a finished amp..

[passfan]

I don't think making the resistors switchable is an option, that's too much wiring that I would be adding to the design and switches always add their own set of problems. In this case it would be physical size, a switch that has to carry 4 Amps of current will not be small and I don't want to cram more into this already "compacted" design (well, not compact by my standards but still a tight squeeze). Maybe I can figure out a switch that shorts the resistors when "ON" but again, I'd rather the heaters be too low than too high.

I don't want to lug around my variac so perhaps a power conditioner would be an option, except I don't use a rack at all! I don't know of any affordable floor-based voltage regulators either. Now I'm thinking I should take out those resistors or at least somehow make them shortable (e.g. a switch ) but this is a hassle to add on a finished amp..

I thought about adding it in the top plate right above the heater wiring where the resistors are. You wouldn't have to add any wire and if you leave the back open it would be easy enough to reach.

[martin manning]

Cliff, if you have to deal with high line voltage regularly why not build yourself a small box with a 6.3 or 12.6VAC filament transformer inside, wired in "bucking" configuration? Simplest would be a 6.3VAC unit hardwired to knock 125 down to 119 or so, but you could get fancy with a 12.6VAC CT and a switch to get line -6.3 or line -12.6 (for those old Tweeds), power indicator LED, ground check LED... Include a fuse to match the transformer rating either way. Still another thing to carry with you if you go out, but much smaller and lighter than a Variac!

MPM

[Cliff Schecht]

Martin, that's a fantastic idea! I may look into something like that eventually. For now, I've swapped out the .1 Ohm resistors on each leg for .05 Ohm 3% 5W resistors to get a much more reasonable drop. As of now, fully loaded with EL34's, I get 3.9*.1 or about .39 V dropped across the resistors bringing down my heater voltage to 6.48 V. 6V6's will sit a little bit higher at about 6.7V but this is still an acceptable range and not so dangerous when I do encounter normal wall sockets. Dropping almost 0.8V with my old configuration was just too much, I think what I have now is about perfect for any situations I might encounter.

[Cliff Schecht]

Played this amp at a gig last night with just the chassis sitting on stage behind the drummer. I had to run the attenuator pretty low to not drown out everyone but through that Egnator 1x12 cab, everything sounded great! I was playing my stock '52 Tele RI and didn't have ANY problems with hum or other noise. I'm quite happy that everything worked so well so quickly, I would have hated to be the guy holding up the band!

[Colossal]

I was playing my stock '52 Tele RI and didn't have ANY problems with hum or other noise.

Cliff, 52 Tele RI eh? That is a seriously sweet guitar and I've been really thinking about getting/building one as of late. How do you find the distortion characteristic driving your Express with a Tele? Do you hear the spank/jangle/twang of the Tele underneath? What style of music do you play?

Inquiring minds want to know...

[Cliff Schecht]

I love this guitar/amp combo! The Tele really shines with it's relatively low output pickups driving a high gain amp and IMO the sound of the guitar still comes through quite well. Even at full-on distortion, the neck pickup sounds very Strat-lilke while the bridge pickup has all of the bite that one expects from a Tele. With the clean sounds, the neck pickup sounds very full and is great for chording and the bridge has all of the twang and snap that you'd ever want from a Tele.

I play mostly blues, country blues, bluegrass, and blues rock stuff but in the past I've played it ALL. With just this guitar and amp combo I can pretty much nail any sound I'm after, it's especially nice not having to muck with any pedals to get that singing high gain sound - even with single coils!

[Colossal]

Wow, great description man! That says it all. Sounds like it is an awesome setup.