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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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Join Date: Mar 2016
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

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Old 1st August 2018, 10:03 PM   #62
Batboy88 is offline Batboy88
Join Date: Aug 2018
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
diyAudio Member
Join Date: Apr 2010
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
diyAudio Member
Join Date: Mar 2016
Originally Posted by Printer2 View Post
Got a 1962 Lowry organ for free last week
Another great score! Amazing!

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.

Attached Images
File Type: png 6AF7_tetrode_in_triode_mode.png (465.9 KB, 14 views)
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