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mtheory

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mtheory last won the day on October 26 2010

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About mtheory

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  • Birthday 07/12/1961

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  1. The TP18 would be what you'd want. Turretboards.com has the Heyboer direct-fit replacement on sale ($75). You might also consider just buying a used Vjr head, considering what a replacement PT costs. I don't recall offhand what the specs are, but they should be printed on the label of the transformer.
  2. Fwiw, it's not altogether practical these days to measure gain by part number. Any given 100 lot of any given tubes can have a profoundly wide variance of measured gain. So much so, in fact, that it's not at all unlikely to find 12ax7s within the same 100 lot that measure no more gain than an at7 or less. Virtually none of today's built 12ax7's match gain on a level that was common in yesteryear's tubes. So, right off the bat, the highest gain 12ax7 in a given 100 lot sample is almost certain to be considerably less than what you'd have seen 30-40 years ago. Couple that with the fact that
  3. I must say that the descriptives don't match any stock Vjr I've ever heard. I find them to be mushy, dark, almost devoid of headroom at all, and pretty uninspiring, in stock form. Modified, that's a totally different story. My El34 conversion is one of my favorite amps, even if only pushing 7 watts. Before it became a turret board build, I went through every Marsally mod I could, including an OT upgrade. Everything I did dramatically improved the amp, but the rebuild to SE EL34 was spectacular. But, whatever works for the individual is what matters. If someone can get inspired by t
  4. I've not seen a schematic, nor have I tried one of these, but I have read mixed comments about it. The reverb is apparently pretty weak, based upon what I've read, tho I really have no use for amp reverb, personally. Truth be told, I think there are better amps available for about the same money these days.
  5. Almost certainly a bad cable on the board. Might be a good time to consider upgrading all pedal patch cables. George L makes a very reasonably priced cable that's very low in capacitance, although beware that the screw-on plugs DO come loose and cause problems from time to time. They may well be simple to repair, but it still sucks when it happens during a performance, and who's got the time to re-cut and repair ANY cable while on stage? Far better to eliminate the possibility of this type of flaky cable failure altogether, imo. If you use George L cable, you should either consider b
  6. I have to disagree with this a bit. Many amps will quite easily tolerate 100% mismatches, and some might actually even prefer it. It's something that requires a scope and signal generator to be absolutely certain of, but there's really no hard fast rule that mandates never, ever straying from manufacturer recommendations. If that were the case, we'd have to assume that every amp every made was made to utter perfection, and we all know that's not the case. Oftentimes, in fact, engineers make some rather boneheaded blunders in designing amps. I can think of many, many amps that were very po
  7. Any delay will do reverb-ish sounds, to a degree. Most digital reverbs tend to be a bit on the grainy side, if that matters. As far as reverb goes, it's pretty hard to beat tube driven springs, although they can be a bit noisy. Most digital pedal reverbs tend to be "grainy" sounding, although that's something that seems to be a subjective issue that some can't tolerate, while others don't even notice. That said, Boss, Behringer, TC, and Digitech are among probably a large number of major manufacturers that offer pedals with both reverb and delay.
  8. I can't recall offhand what that OE jack and daughter board looks like, nor can I recall what the purpose of there being a PCB there at all, but it's likely just something to solder the crap jack to. Regardless, there is a two conductor wire running to it from the main board. Just snip the the wires near the crap jack, strip them back, and solder to the new one. The shielded conductor is ground, so that goes to the sleeve terminal on the new jack. The other conductor goes to the tip. If you're unfamiliar with basic soldering technique, practice on something else first. Remember
  9. The stock jacks are crapola anyway. Replace with switchcraft, and you're light years ahead. Bummer if Epiphone stopped making the Vjr head, although there are about a billion of them floating around by now.
  10. Warranty on such a cheap amp wouldn't be a valid justification for me keeping it a medicore amp, imo, but I can see where if you're nervous about digging into it yourself, it can make sense to let them warranty replace it. Sounds as though you've got that, so that's cool. The JC20 is a far different beast. It's significantly louder, more articulate, and punchy than the Vjr, for sure. In stock form, it's actually quite usable, although it can tend to be a tad harsh, with mucho mids and highs. It takes some effort to dial it in, and what you find acceptable at one volume will have a te
  11. Good luck with that, Bruce. Do you mind if I asked you why you chose to go to all this trouble to have this repaired to original form under warranty, rather than look at some of the rather impressive mods that are widely utilized? It would be very simple to replace that OE PCB with a rock solid turretboard, as well as a beefier output transformer, and you'd not only resolve your problems, but you'd end up with a far better sounding, far better-built amp as a result. Not only that, but if you trained yourself on the skills required to do the job yourself, you'd inevitably learn a whole
  12. The PI should be very strong, high gain, and balanced. On a fixed bias amp (not sure whether or not this amp is), swapping this tube will change your output tube bias, which is probably why you're hearing it sound different with different PI tubes. If you swap this tube, the output tubes should be re-biased (assuming the amp is fixed, rather than cathode biased).
  13. Eminance isn't the only speaker maker with a 12" 4 ohm speaker. Try Weber and Jensen, for instance.
  14. That's correct. However, that specific load that makes the amp most happy isn't necessarily always what the manufacturer SAYS it is. Nor is that magic load necessarily the only load that the amp will run safely at. Many tube amps can safely run 100% mismatches without any detriment whatsoever. The problem is, you would never know that for certain without putting the amp on a scope to see what makes it the most happy, and monitoring the output transformer for excess heat. Heat kills amps, as you said. The question is, how do you KNOW FOR CERTAIN what sort of load is either too high
  15. Bear in mind that it MIGHT be that the reason the 8 ohm speaker sounded better was because the map was happier with an 8 ohm load than the stock 16. In that case, adding a resistor to create a 16 ohm load might be counter-productive. Generally, an amp will be happiest with whatever load the manufacturer says it likes to see, but that's not always necessarily the case. Sometimes, mismatches work better. The only way to know for certain, however, is to throw the amp on a scope and try different loads to see which it likes best. Otherwise, you could just guess, and run 8, since it's not all
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