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Given one 12AX7 how would you run it given the rest of the amp is SS?
Given one 12AX7 how would you run it given the rest of the amp is SS?
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Old 28th July 2018, 10:43 PM   #61
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by Printer2 View Post
To my ears I think the speaker might partly to be the cause of your opinion of the amp.
I agree that the stock speaker isn't great. I found the stock Frontman speaker overloaded easily if you turned up the bass or volume. I also had a Super Champ XD and a Princeton Reverb reissue at the time, and I remember connecting the Frontman electronics to the speakers in the other two cabs to see what difference that made. Neither of the other two speakers overloaded, and I believe the PRRI speaker sounded duller than the other two.

To my ears, both the Super Champ XD and the Frontman speaker have a wider and flatter frequency response than the typical guitar speaker. In the SCXD, this is probably a good thing, the DSP being responsible for the frequency responses and voicing of the various models, rather than having one speaker that has its own characteristic sound colouration permanently built-in.

But trying the Frontman electronics with other speakers produced only subtle differences, like twiddling the treble or bass control a little bit. To me, none of the speakers made the Frontman sound anything other than thin and cold. With a duller speaker, it just sounded dull, thin, and cold, all at the same time!

The trouble with the Frontman (for me) is the same one I heard with every home-brew guitar amp I'd made between 1985 and 2005 or so: it sounds like plugging your electric guitar into a Hi-Fi amp, with inaudibly low levels of THD. And that's a sound I really don't like. Thin, cold, and, as you said, with harsh pick-attack and transients.

It was only in late 2009, when I tried my first guitar amps that had actual valves in them, that I started to understand. For me, those few percent of low-order harmonic distortion that you get so easily and so automatically from a valve is crucial to good clean guitar tone. Maybe also a "squashing" of transients as the valves reach the nonlinear ends of their operating range.

At any rate, hearing a Vibro Champ XD (single-ended runt cousin of my Super Champ XD) for the first time was a revelation: it had a crappy-sounding tiny cab, a crappy-sounding tiny speaker, and it still had much more attractive timbre to the clean tone than my larger push-pull Super Champ XD! The nonlinearity of the single-ended 6V6 in the Vibro Champ XD was, literally, music to my ears. It came through even when listening to a lousy speaker in a lousy cab.

Since then, I've become convinced that we humans don't all hear the same way; just as one person might love the taste of fish, while another is revolted by it, and a third doesn't care either way, one person might loathe a Hi-Fi-clean guitar amp, another might be indifferent, a third might love it. (Les Paul himself loved Hi-Fi clean guitar pickups and guitar amps.)

As my ears continue to age, there will probably come a time when I can no longer hear a difference between a good valve guitar amp and a guitar amp built around semiconductor chips that were, in fact, designed for Hi-Fi (inaudibly low THD levels.) But for now, I can still hear a difference that is significant to me.

I note that in the last year or two, digital modelling amps and guitar amp emulation software is finally starting to reproduce that subtle valve distortion that occurs long before outright clipping ("crunch" and "drive" in guitarist-speak.) From online clips I've heard, products like the Atomic Amps AmpliFire and Boss Katana 50/100 sound quite convincingly "valvey", and in an A/B blind listening test, I might not be able to tell that they are in fact solid-state.

More importantly, whether they sound exactly like valves or not, they sound really good, at least in some clips. An example: YouTube

-Gnobuddy
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Old 1st August 2018, 10:03 PM   #62
Batboy88 is offline Batboy88
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Cutoff and or the Fireeee lol. run it wayyyy over and bring up the heaters too.
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Old 15th August 2018, 04:29 AM   #63
Printer2 is offline Printer2  Canada
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Got a 1962 Lowry organ for free last week. Anybody need any useless tubes? I got a bunch. 6X8A and 6FA7, the first a pentode triode with a shared cathode, the second a twin plate tetrode. The first tube maybe a front end of a two channel amp as in the Fender Deluxe but with a pesky pentode in one and a mild triode in the other. The twin plate tetrode?



But the 15W OT and pair of 6V6's made up for it. Cheap 9-pin sockets, the 8-pin are decent. Thinking of wintertime and throwing them in a Frontman 25R sized cabinet with a Frontman 10" speaker. A little grab and go amp with a laptop power supply and booster for the high voltage. Rather than a BF tone stack that would not leave much gain to drive it into clipping a Mosfet and tonestack that mimics the Tweed Bassman and gives back 10-12dB in gain over the BF in the midrange.



Click the image to open in full size.


Threw together the top cabinet for the project, the bottom a Bassman cabinet to try out the 10" speakers I got from the Hammond tone cabinet.


Click the image to open in full size.

Last edited by Printer2; 15th August 2018 at 04:32 AM. Reason: forgot the picture
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Old 16th August 2018, 05:19 AM   #64
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by Printer2 View Post
Got a 1962 Lowry organ for free last week
Another great score! Amazing!

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Originally Posted by Printer2 View Post
The twin plate tetrode?
I found a datasheet here: http://www.tubebooks.org/tubedata/hb...art_2/6FA7.PDF

Looks like the twin-plate tetrode was intended for "frequency divider and complex waveform generator" use, though I have no idea how.

That doesn't sound very useful in a guitar amp, and the drastic "tetrode kink" in the curves makes it useless for audio amplification.

But what leaped out at me was the triode-mode curves for the tetrode. It looks like the weird tetrode makes a perfectly well-behaved triode if you just strap the two plates and screen grid together (see attached image.) And that triode could very well be used as a gain stage in a guitar amp...though I didn't bother to work out gm, mu, and rp from the graph.

-Gnobuddy
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File Type: png 6AF7_tetrode_in_triode_mode.png (465.9 KB, 74 views)
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Old 3rd February 2020, 07:16 PM   #65
Printer2 is offline Printer2  Canada
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The one 12AX7 design might be pushed up the food chain in terms of my projects. Got bumped back down a little last night when my niece's husband emailed me about a Harmony acoustic guitar that is for sale in the area. It was sat on and the sides cracked all the way around. Yes I could probably fix it, the seller wants too much money for a guitar with multiple problems as far as I am concerned. Which brings up the fact that I was building a guitar for him but it was on hold. But I was thinking about it, I have the maple I want to use as a neck in my makeshift humidity chamber for some time. I added the body of the guitar last night, I'll spend more time on this one earlier than I thought.

I could not find the cigar box that I was going to use for this tube/SS hybrid. I looked all over, where did I put it? Finally gave up it will show up. Like the mold for bending sides I was looking for. I found other sizes, not the one I was looking for. I found the template I used for it, darn it I'll just make another. And this time I made it a cutaway. Still don't know where the original mold is.

So now that the maple guitar moved up on the list, I need to find the jig I got for preparing the scarf joint. Looked in a little cubbyhole of shelves I have. There on floor is the original 17" guitar mold. OK, it made sense me putting it there, not while I was looking fore it though. Pull it out, 'let's compare it to the new mold which I have on my bench'. Put the old mold on the floor, pick up the new mold to place it on the old one, there on the bench is the cigar box. It was against the wall tucked in behind the mold. the only thing I did not move when looking for the box.

Yes folks, this is what my day is like. Every day. I still have to find the second part of the scarf joint jig. Or I will have to make another one. I'm going to have a cup of coffee first. I deserve it.

Click the image to open in full size.

So, need to breadboard it first but the idea is the Class D amp in the left bottom corner. Above it the output jack, a SMPS to bring the incoming dc to 6.3V, the little board is a switcher that produces a +/- 24V, so 48V. The 6AK6 or Chinese equivalent does a reasonable job at this low voltage. Will throw a fet in front of it and before the amp module. A volume, bass, treble, and master volume. Simple and to the point. Subject to change.

Last edited by Printer2; 3rd February 2020 at 07:25 PM.
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Old 14th February 2020, 05:28 PM   #66
Printer2 is offline Printer2  Canada
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Did a little soldering, should be able to breadboard something.



Click the image to open in full size.


I thought about the voltage, still too low for adequate operation for a 12AX7 but a lower gain tube like a 12AY7 might work. I'll have to wire up a socket and give it a try. While I was rummaging around I did a , 'What is this?' Have no idea where it came from, I do not seem to have a picture of it which is odd. A 6V6 P-P radio with a 5U4 rectifier. I can't find any schematic or information on it with the model number. It has octal tube but a 12AX7 dropped in it.

Click the image to open in full size.
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Old 15th February 2020, 03:38 AM   #67
PRR is offline PRR  United States
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> I did a , 'What is this?'

It is probably a superior AM radio, will pull distant cities. Note RF stage.

It is a DeLuxe-class guitar amp project. Re-rig the IF stage as audio preamp.

Canadian Westinghouse, Hamilton from A43 to W552-A, 143 pict

8CHF-1 Radio Canadian Westinghouse, Hamilton, build 1956 ?
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File Type: gif 8CHF-1-42.gif (54.1 KB, 16 views)

Last edited by PRR; 15th February 2020 at 03:48 AM.
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Old 15th February 2020, 08:50 PM   #68
Printer2 is offline Printer2  Canada
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Originally Posted by PRR View Post
> I did a , 'What is this?'

It is probably a superior AM radio, will pull distant cities. Note RF stage.

It is a DeLuxe-class guitar amp project. Re-rig the IF stage as audio preamp.

Canadian Westinghouse, Hamilton from A43 to W552-A, 143 pict

8CHF-1 Radio Canadian Westinghouse, Hamilton, build 1956 ?

Thank you sir, I could not find the schematic. I probably would be stripping it and putting it in a different chassis, I bent up a few before I retired. I am starting to think I may end up with an excess of amps.



I looked up the 12AX7 and the 12AY7, they seem to have the same dynamic range given normal 12AX7 voltages and my desire to run the 12AY7 in the 50V range. Not sure about it in the cigar box though, about 2W of heater rather than 1W for the 6AK5. In a enclosed box the heat may add up. But of course breadboarding it first.
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Old 17th February 2020, 07:10 AM   #69
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by Printer2 View Post
In a enclosed box the heat may add up.
Takamine has a 12AX7 preamp design they call "Cool Tube", which is used in several of their more expensive guitars.

I believe it's run on 6V (no step-up that I'm aware of, though I haven't been able to locate a schematic), and also the tube heater is run at low power to keep them from getting hot enough to damage the wood in an expensive guitar (and, presumably, to prolong battery life.)

Gimmick or the real deal? I don't know, but I have one guitar that came stock with a Takamine piezo pickup and one of these Cool Tube preamps, and it sounds better plugged-in than just about any other piezo-equipped guitar I've played.

I can't swear that the better sound is due to the tube, though. For all I know, it could be better piezo pickup design (it uses one ceramic element per string), or the solid-state part of the onboard preamp may be the key.


-Gnobuddy
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Old 20th February 2020, 03:38 AM   #70
Printer2 is offline Printer2  Canada
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In response to another forum and something I have been thinking about for a while, I am building another building board. A 12" deep piece of shelving, some aluminum foil over it as a ground plane, a press-board back from an organ. A hole drilled into the press-board and a tinned wire running the length of it, sandwiched together with some screws. The wire will go to a ground point and the foil will act as a shield reducing noise.



Click the image to open in full size.


An assortment of switching power supplies at the back mainly 12V although I have other voltages and will discuss them at a later date. Will have a pair of octal sockets, pair of seven pin and four nine pin sockets. Along the left I will have some terminal blocks to make it easier to hook up the power to, not necessarily the ones shown, I think I have some others kicking around here, just depends if I will find them in time. In the front, a plate for input and pots. To the right of it is a stepdown converter hooked to a 6V pentode, will rewire it. Then the tiny board, a single voltage to +/- 24V converter, then a high voltage switcher to put out up to 400V if you can believe the ad.


Click the image to open in full size.


Done enough today, will do some soldering tomorrow and probably screw things down. Then the first experiment, see if the +/- 24V will be enough voltage to put across a tube or two. If so, build a preamp to go into a class D amp. I thought up this project to get a tube to run in a lower voltage circuit for the pedal crowd.
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