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I've just finished a prototype guitar amplifier using a pair of 7591s. I also tried 6V6s and 6L6GCs in this particular design, but they didn't provide as much output power as the 7591s with the power supply I've built for the project. My question is whether 7591s are considered odd by guitar players, and if that might devalue the amp if I decide to sell it later. I frequently build a project, use it awhile, then sell it to fund something else. The difference in cost to me to build this with 6V6s, EL84s, 6L6GCs or 7591s is negligible, and I can make any of them produce good tone.My second question has to do with aftermarket tubes. I've used mostly triodes and old stock American tubes in my designs in the past. However, tubes like those listed above are more easily available new from aftermarket sources like Sovtek, JJ, EH etc. I had a bad experience with "no-name" Russian 6V6s a couple years ago, and I'm wondering if aftermarket versions of 6L6s and 7591s are OK. Mostly, I'm wondering how they compare with the originals in terms of specifications like gain and plate dissipation. That's where the 6V6s failed to deliver (the plates glow red at much less than rated dissipation), and I don't want to repeat the experience. I also don't want to build an amplifier that requires NOS tubes in order to perform correctly. I would really like to hear from anyone with experience in this area.
Follow Ups:
TK,Who'se your market? If you're trying to make a mass produced amplifier you probably will need to stick to the the more mass produced components so that you can cut every penny in production to satisfy the backers/bankers that you'll need to get into and keep production. And the musicians are going to care less cuz you're selling price more than absolute build.
Now if you're heading quickly for the big time you probably already know the answers. Those professional musicians with the cash pick up a $5K amp "cuz they like it" - while usually savvy about specific components, and often with some tech skill, are also aware that your can still find 6973s and 7355s and such if you really look so they don't give a "rodent's rectum" about the particulars as long as they amp sounds good and the particulars make sense (they will wonder why you're using chinese 6l6s in a 5K amp though but not an "exotic" nos tube). Unless you're already working in G'nashvegas and know the pros or unless you're a dentist working in a group of dentists who all like to play guitar and have $$$ it's hard to make money crafting guitar amps. Too much cheap stuff on the common consumer end and too much hogging of vintage equipment on the more money/less skill professional sector. Only a few ways to plug in and be successful.
I would like to encourage use of the 7591, for guitar amplifier applications. Gibson had used the tube in their line-up of guitar amplifiers (GA30, GA35); Harmony used it in the H-311 and H-322; and Ampeg got plenty of mileage from the 7591 (AC12, J12A, J-12D Jet, J-12R Reverbojet, R-12, M-12A, R-15, etc.).I would be less concerned with resale value than making it sound right to your own ears. While I may be a big fan of the 6V6/6L6 families, it doesn't stop me from enjoying less common or more esoteric types. I happen to think the 7591 is quite musical, and deserves broader recognition.
The 7591 mmight be a tough one to get the point across on a sale.. El-84 & 6v6 w/ Pentode/Triode switch is a good selling point & just damn nice to have on a guitar amp, I have 3 that have this feature. Matchless clones & a Vox Pathfinder clone from 1967 I think, There is a strong market with guitar players for small wattage amps, so many of the dual triode's would be a strong seller & tonally very good IMO, 6sn7 comes to mind. as a tube to use.. If my building skills were better with tube gear. I would sell a grip of tube amps for guitar players, they & I are fanatical about them..even more so than audiophiles..I think the 6v6 SE w/ pentode/triode switch & dual rect..SS/Tube would be a goodin.. My Kt 66 amp has external bias adjustments, dual rect..SS/tube, pentode/triode switch/-modern/classic switch & vari-slope 22k/33k/47k/56k There is a lack of good fairlly afforable low powered top flight tone machines out there.. . A small SE in 1 watt or less would be excellent for practice, then one would not have to use any of the tone sucking attenuators out on the market. I have tried most all of them & dislike them all for REAL tone & allways takes to much away. Also if you build tube gear for guitar players, please build a good front end boost..this is something the market needs desperatley.. the boutique chip things are raping everyone of there money...It is insane what they want for them,, all op-amp based most of them & only a few good ones.. One you could do interchangeable tubes for differant gains & such. I would buy such a thing in a split second.
If you're concerned about the resale aspect of the amp I would suggest not to use the 7591's, I've never heard of this tube being used in a guitar amp. Why not design the amp to able to use both 6v6's and 6l6's? The 6v6's would output around 20-22 watts while the 6l6's should get you 35-40 watts, I believe all that is needed would be to swap out rectifer tubes and then reset the bias. Allen amps offers this on several of his models.As far as new production tubes I can tell you that the TAD 6L6WGC is a great sounding tube, although I haven't used them long enough to know how the longevity will be, they came perfectly matched and I'm now running them in both a 64 Bassman head and a 64 Super Reverb. They don't have quite the midrange of the Slyvanias that I use as a reference but they're very close.
guitar players are very finicky about the tube type, so it would make a difference on sales to one. I have two guitar amps, a Fender Champ and a Marshall Studio 15, I picked both of them by sound, but both use the 6V6. 6V6, 6L6, EL34 and EL84's will be the big draws. Most guitarists know nothing about circuits, but know what tubes they like. As far as modern tubes go, you have to experiment to find a model that works at your operating points. There's a guy in town who makes amps with EL84's driven hard, and he's found one particular new brand that will last a reasonable time; others just don't hack it.
I have a Hilgen Basso Grande that uses 7591 and I like the sound quite a bit. Ampegs and Gibson also used to have 7591s. The tubes are still in production, but NOS 7591s, even used, are considerably more expensive than new production. (I prefer to buy used tubes, and I like it when they are even cheaper than new production. 6v6s, for example.)THat said, 7591 is a fine tube. Go for it if it sounds good to you.
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