I am finally started on my Express build. I am seriously considering a cathode bias. I tend to like amps with lots of compression & slow attack. A way to switch between cathode & fixed would be especially sweet. Have any of you seen a schematic for that. Have any of you cathode biased with any success or does it ruin the tone?
I have found a schematic for the Matchless Chieftan which uses a seperate 270 ohm bypassed with a 250 mf for each tube for the el34 bias. The plates are at 415v. Does this sound like it would still work for a 6v6?
Thanks guys. This is really feeling like a rewarding build.
Express build with cathode bias
Moderators: pompeiisneaks, Colossal
Express build with cathode bias
I've got blisters on my fingers!
Re: Express build with cathode bias
I'm interested in the cathode biased Express(or a Liverpool with two EL 34's or 6l6/5881 tubes) idea also...It doesn't seem like it should be too far fetched.
Re: Express build with cathode bias
My first TW was an Express done this way. I used vintage iron from an old Newman office PA amp, and that was cathode bias, so I stuck with it for the build. It was mostly an experiment (since the Newman cost me $40 for PT/OT). It was blow-your-hair-back loud--and mooger-fooger did it sing!!
It was too loud for me to use, but a friend played it and just had to have it, so now he uses it.
So, yeah, it works with EL34s in cathode bias. I think the EL34s crunch has a different character in fixed vs cathode bias, but it's just different--not necessarily better or worse.
It was too loud for me to use, but a friend played it and just had to have it, so now he uses it.
So, yeah, it works with EL34s in cathode bias. I think the EL34s crunch has a different character in fixed vs cathode bias, but it's just different--not necessarily better or worse.
Rich Gordon
www.myspace.com/bigboyamplifiers
"The takers get the honey, the givers get the blues." --Robin Trower
www.myspace.com/bigboyamplifiers
"The takers get the honey, the givers get the blues." --Robin Trower
Re: Express build with cathode bias
An idea I've been thinking about was to do it like Alessandro, he builds his amps, to work true class A, cathode biases them and runs the output tube in ultralinear operation, he explained in an interview that to get the most linear operation out of the tube, he used class A and that meant using low plate voltages and high current, I'm just not sure how to do all the calculations because I haven't looked into the tube charts yet...
But I'll probably end up doing something similar with the express preamp and a switch to be able to disengage the gain stage before the phase inverter, in case I need cleaner sounds.
But I'll probably end up doing something similar with the express preamp and a switch to be able to disengage the gain stage before the phase inverter, in case I need cleaner sounds.
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CaseyJones
- Posts: 856
- Joined: Fri Mar 17, 2006 1:29 pm
Re: Express build with cathode bias
One aspect of Trainwreck amps that Ken Fischer commented on while he was alive was that he was the only person who could voice a Trainwreck like a Trainwreck. Curiously enough I have a similar amp I designed back around 1980 that certainly IS NOT a Trainwreck! I shelved my design because my distortion tone was buzzy and harsh. Kudos to the late Mr. Fischer for having the technical chops and the ears to build what he built. We all owe Ken a debt of gratitude for leaving us his legacy.riscado wrote:An idea I've been thinking about was to do it like Alessandro, he builds his amps, to work true class A, cathode biases them and runs the output tube in ultralinear operation, he explained in an interview that to get the most linear operation out of the tube, he used class A and that meant using low plate voltages and high current, I'm just not sure how to do all the calculations because I haven't looked into the tube charts yet...
There is latitude in the design where it can be changed slightly and it's still nominally a Trainwreck. I don't understand it when builders mess with the design without a baseline build first. An Alesandro is a cool amp but it's substantially different in concept and execution when compared to a 'Wreck. Maybe they're two great tastes that taste great together... but probably not.
You mean more like a Dumble?!riscado wrote:But I'll probably end up doing something similar with the express preamp and a switch to be able to disengage the gain stage before the phase inverter, in case I need cleaner sounds.
May I humbly suggest that you build Kevin O' Conner's Standard? Don't mess with it just build it. If you MUST have a Trainwreck tone clone an Express preamp on one channel.
Re: Express build with cathode bias
sorry Casey I do not understand the point of your post, if I wanted to build the wreck I would do so... and hope to get as close as possible, this is not the case, it's not messing with anything, it's getting a couple of ideas and putting them all together, it's not a wreck and it's not an alessandro, it's a group of loose ideas, that like everything else need to first be put together and than optimized into what could be a nice little amp.
So your point was...??
So your point was...??
Re: Express build with cathode bias
I found a schematic
http://www.londonpower.com/GRAPHICS/pwr-fig1.gif
http://www.londonpower.com/GRAPHICS/pwr-fig1.gif
I've got blisters on my fingers!
Re: Express build with cathode bias
Yeah, that's it, I think there is a similar circuit in the Torres and TOT books for cathode to fixed bias switching.
I have that switching option in my Bogner XTC and I have also put it in my own amp design at the customers request. I find that personally I like the cathode bias on EL34 more than fixed in all my amps. The fixed is maybe harder, brighter sounding, more crunchy than the cathode bias. It's hard to tell really unless the bias point is the same for the two methods. I tended to bias more current in the cathode method and less current in the fixed method, just so that you could hear the difference when the switch is thrown. So that's really not a fair comparison. You could bias the tube for more current using either method. The Express is biased pretty hot so I'm not sure you'd hear much difference between the two methods in a Trainwreck.
The cathode method is less efficient because the cathode has positive voltage above reference ground by ~ 24 VDC (grid at 0 VDC). So you'd lose a bit of power (a good thing for an Express maybe) You also have the frequency step caused by the cap value. A 220mF cap won't cause much step, but you could play with that value as another "tuning" option.
270 ohm may be pretty hot at that voltage for an EL34. You may want to run a fan to keep things cool or bump to 330ohm depending on the plate dissapation your going for. It's definately too small for a 6V6, but you can put resistors in parallel and then have a switch for 6V6 or EL34 mode. Keep the bypass cap away from the resistor as those things get hot! I usually use two 10-watts in parallel or heat sink it to the chassis.
I have that switching option in my Bogner XTC and I have also put it in my own amp design at the customers request. I find that personally I like the cathode bias on EL34 more than fixed in all my amps. The fixed is maybe harder, brighter sounding, more crunchy than the cathode bias. It's hard to tell really unless the bias point is the same for the two methods. I tended to bias more current in the cathode method and less current in the fixed method, just so that you could hear the difference when the switch is thrown. So that's really not a fair comparison. You could bias the tube for more current using either method. The Express is biased pretty hot so I'm not sure you'd hear much difference between the two methods in a Trainwreck.
The cathode method is less efficient because the cathode has positive voltage above reference ground by ~ 24 VDC (grid at 0 VDC). So you'd lose a bit of power (a good thing for an Express maybe) You also have the frequency step caused by the cap value. A 220mF cap won't cause much step, but you could play with that value as another "tuning" option.
270 ohm may be pretty hot at that voltage for an EL34. You may want to run a fan to keep things cool or bump to 330ohm depending on the plate dissapation your going for. It's definately too small for a 6V6, but you can put resistors in parallel and then have a switch for 6V6 or EL34 mode. Keep the bypass cap away from the resistor as those things get hot! I usually use two 10-watts in parallel or heat sink it to the chassis.
Re: Express build with cathode bias
"One aspect of Trainwreck amps that Ken Fischer commented on while he was alive was that he was the only person who could voice a Trainwreck like a Trainwreck."
-actually he was quoted as saying that the only other ampbuilder who could build a TW and have it sound like a TW was Mr. HAD, but in the same statement he said that HAD would never build a TW circuit so he didn't have to worry about that.
With the amount of information on the TW circuits out there on the net, along with the larger quantity of people understanding the facets of these amps, I do believe that with attention paid to exactly which components are doing what that people on this board are making clones in the range of what TW circuits sounded like, with some of the more experienced builders coming into the ability to voice an amp to the degree of precision that KF himself had.
-actually he was quoted as saying that the only other ampbuilder who could build a TW and have it sound like a TW was Mr. HAD, but in the same statement he said that HAD would never build a TW circuit so he didn't have to worry about that.
With the amount of information on the TW circuits out there on the net, along with the larger quantity of people understanding the facets of these amps, I do believe that with attention paid to exactly which components are doing what that people on this board are making clones in the range of what TW circuits sounded like, with some of the more experienced builders coming into the ability to voice an amp to the degree of precision that KF himself had.
Re: Express build with cathode bias
Ken also taught a cople of people to do what he did with respects to "tuning" an amp. It is all in the tube selection. Ken would swap tubes until the correct sound was heard. One of the people he taught demonstrated it to me with his wreck in person. Pretty cool stuff.dr. who wrote:"One aspect of Trainwreck amps that Ken Fischer commented on while he was alive was that he was the only person who could voice a Trainwreck like a Trainwreck."
-actually he was quoted as saying that the only other ampbuilder who could build a TW and have it sound like a TW was Mr. HAD, but in the same statement he said that HAD would never build a TW circuit so he didn't have to worry about that.
With the amount of information on the TW circuits out there on the net, along with the larger quantity of people understanding the facets of these amps, I do believe that with attention paid to exactly which components are doing what that people on this board are making clones in the range of what TW circuits sounded like, with some of the more experienced builders coming into the ability to voice an amp to the degree of precision that KF himself had.
Re: Express build with cathode bias
I am looking forward to the tweaking. It is the first reason I got into this over a decade ago. I want to get as much of the real Express as possible with good components & layout. I am a builder but I am a player first. I want a very expressive (do you think that's where Express came from) amp. I love to play sustain & harmonic feedback. I am thinking that this will be too loud & bright for me just from the soundclips so I am thinking ahead for mods to build in. Cathode bias & triode switch seem like easy things that sould not ruin the tone when not activated. I was real torn between this & the Astroid & the Liverpool. Low voltage el34s won.
I've got blisters on my fingers!
Re: Express build with cathode bias
and for a little mor sustain- add a keeley compressor with the 4 knobs....the sustain will be sweet...add a tube screamer with it and you'll have officially made the sound known as budder....smooth creamy rich and textured.