The true sound of S.E. Class A not push pull etc. for guitar.

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9/27/2000 7:38 AM

Bill

The true sound of S.E. Class A not push pull etc. for guitar. I think alot of us want to know what a pure powerful true s.e. class A amp i.e. 20watts and up would sound like for guitar. I guess a parallel pentode design to save money on tubes would be a good place to start. Now what about those even order harmonics would they be better sounding for guitars?(maybe to thick sounding?) Would a pentode tube have as many even order harmonics as a DHT 300B in the same pure s.e. class A design? Has anyone used a Cary Audio amp for testing a high power pure class A amp for guitar?     Thanks,Bill

 

9/27/2000 7:53 AM

nuke

Well, the best bet is to build one and see what you think of it.     Maybe start with a set of One-Electron SE output and power xfrmrs and some chinese or russian trodes to use as stunt tubes. You could be cooking for a few hundred bucks. If you take care of them, you can always sell the xfrmrs if you don't like the results.     Triode strapped pentodes don't work exactly like triodes, so you'll probbably want to try out true triodes. Direct heated tubes are not real practical for guitar amps as they are more delicate than indirectly heated tubes, like the 6080.     Should be a fun experiment.

 

9/27/2000 12:27 PM

Ray Ivers

Bill,     I've put a push-pull/single-ended switch in my Marshall 4001 Studio 15 combo (6V6 output tubes), and I can tell you what a poorly-executed, extremely low-power SE stage sounds like to me. It's the mega-thick, edgy heavy-metal grind! SE stages will put out so much MORE distortion than P-P stages for the same amount of output tube overdrive, because of the absence of the even-order harmonic cancellation effect of the P-P stage. The odd-order (chord-interval) distortion is still very much there, and the addition of the even-order harmonics (octave-interval, at least till the 6th harmonic) just sounds like 'more' distortion to me, not 'better'. I don't own a distortion analyzer, but it sounds to me like an SE stage puts out more of everything harmonic-wise.     Ray Ivers

 

9/27/2000 3:02 PM

MSR

Ray,   I'd be very interested in seeing a schematic of your SE/PP switch. I gig ALOT with two Champ type SE rigs and your observations about the harmonic content are pretty much what I have experienced.   As well a few years back a company called Rocket put out an SE rig using an EL34 that was good for 20 watts. As far as I recall it received high marks from Guitar Player in their review       MSR

 

9/27/2000 4:23 PM

Stan Cotey

I have seen people add a switch that disconnects signal from the grid of one of the power tubes -- the idea being that with the tube idling, the currents in the OT will not become unbalanced as they would if one simply removed a tube.     I'm not sure how I feel about this although I have tried and it seemed to sound okay. I don't think I buy the thing about totally correcting transformer balance. I don't remember loving the sound of it enough to keep it around for any length of time.     My test subject was a Vox JMI era AC30, which I also tried a Pentode/Tetrode switch in. Ditto with the results.     It's easier to do on a cathode biased amp, btw, because at the simplest level, you can ground the grid (assuming a grid resistor is in place). On a fixed bias amp, you have to keep the grid at bias potential regardless of signal content.     E-mail me if you'd like a schematic although it comes without recommendation.

 

9/27/2000 5:20 PM

tommy

Just to throw this in, I have always been under the impression that when switching a push-pull to single ended as described above, the bias may need changing to get the now single-ended tube in its proper operational area. This is more so for push-pull amps biased for class AB, where the tubes are not set at mid-swing on the transfer curve.     This kind of ties in with the Class A discussion that is going on in another thread. If the push-pull amp is Class A, then the signal can just be removed from a grid with no change in operating point. If it is biased near cut-off in push-pull AB operation, removing the signal from one tube(side) will give a very distorted output, in effect, only half the waveform.     Just my thoughts.     Chris

 

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