Caevan O’Shite

Hey, Myles! I recently picked up a Radial Tonebone "Plexitube" pedal. It uses a 12AX7 in a low-voltage/"starvation" design... I'd like to know if trying different preamp tubes in it will give me different gain/overdrive responses, allowing for greater response to changes at the guitar's volume-knob for cleaning-up and vice-verse... Or, is the pedal's gain/overdrive/distortion more due to its SS circuits, and thus less likely to be affected by any tube-swapping? I want an idea of how worthwhile it would be to open it up to get at the internal tube-socket (not exactly as simple as it could be) and swap various tubes in and out... Thanks!

And thanks from me, too, Myles!

Say, Myles... If an output-transformer is suspected of being bad, you just disconnect it, throw a DMM across it for continuity and possibly for resistance to get an idea of how close to spec'ed impedance it is, right? What would you think if an amp repair-tech said he couldn't tell you wether an O/T was good or bad without a replacement on hand to compare it to or swap-out to see if the amp then worked with the replacement?

Can I butt-in and recommend a good book? (I do so because it would be plagiarism to copy or quote the source-book...) How To Service Your Own Tube Amp by Tom Mitchell has some excellent trouble-shooting flow-charts and tips addressing common problems. Step through the one that applies and you're much more likely to locate the cause; certainly with less frustration. It is clearly and logically written and organized. Stewart-MacDonald has 'em in stock; well worth the cost, you'll likely refer to it over and over again.

It will all boil down to personal taste but the Duncan amps can have reliability issues and the modules on the convertible are hard to find .... Westwood Music in West L.A. was the only place I ever saw any and that was years ago. Throwing my two-cents in here, of two people I've talked to in person over the years who had used those SD Convertible amps, both used them in gigging cover bands and BOTH cited reliability issues, and then some.

I have a tattoo, a serial-number in my ear from when I used to be a K-9 corps dog with the MPs in Alaska... I'm tellin' you all the zomby-troof; here I'm-is, the Zomby-Woof!

While you're on the topic of these Jensen Mod speakers... How do you think a Jensen Mod would sound in my Carvin 'Vintage 33' (a 1x12, with the GT "SAG" Hi-Gain tube-set & a Mullard-remake MPI in it)? And, how about a pair of 12" Jensen Mods in an open-back cab for a vintage Silvertone 1482 "head"? (An unknown previous owner converted the 1x12 combo to a "head" sometime in its distant past.) It's a 2x6V6 affair with tiny little anemic transformers... I do not have a speaker-cab for it yet, but I think I want a 2x12 and I like the description above concerning the Mod's having a Brit flavor on top.(And, yes, I do know that I'll want to use a pair of impedances wired accordingly to yeild the correct impedance for the output-transformer.) With both of these amps, I'll be wanting as much touch-sensitivity and clean-to-overdrive range with the guitar's volume-pot as possible; I play fingerstyle 100% of the time, and vary the cleanness to overdrivenness by my touch and rolling the guitar's vol'-knob up and down. I also prefer as much harmonic-swirl as I can get, as well. (Hehh-hehh- I've been using the Carvin's "Soak"-channel almost exclusively, for clean as well as overdriven tones, just by setting it louder than I intend to play and rolling the guitar's vol. up-and-down like that... Nice, fat, warm, full clean-tones, and I never hit a switch!)

Now, that'd be irrationality in action! Sorry to have hijacked this thread with such wise-@$$ posts, Myles!

Not used in rational guitar amps. Well, I want a very IRRATIONAL amp!! Maybe, maybe a cross between a Tone King Galaxy, a Perplexing Plexi, and a Deizel, with weird discontinued tubes and old eliptical-shaped Gretchsh speakers in it... maybe that would be an irrational amp, huh?

Hahh-hhaahh!

And thanks AGAIN for that sweet Mullard-style MPI, I am still enjoying the great benefit of it and often feel a tad guilty for not popping in here like this more often, Myles!

Pardon me for butting in here, but I might be able to shed a little light on your pickup question, Junior 1... Gibson's P-100 pickups are actually a humbucking dual-coil design (I believe that they're the "stacked", vertically-aligned type), whereas their look-alike predecessor and progenitor, the P-90, is a true single-coil design. The P-100 doesn't seem to have a very good reputation, the only comments I've ever heard or read about 'em have all been negative! If you want an authentic P-90 "soap-bar" or "dog-ear" sound, you probably want a Gibson, Seymour Duncan, or other authentic, single-coil P-90 type pickup. I HAVE read somewhere a while back about someone getting great results with coil-tapping a P-100- that is, installing a switch that cuts-out one or another of its two coils. If you had a triple-throw switch installed that selected among the bottom, both, & top coils, you could go from "vintage-y" single-coil to humbucking (stock, like you have now) to a bolder, more "modern" single-coil tones, respectively... I'm pretty sure that the P-100 has enough conductor wires to allow for this switching... Let me know how you make out here! (PM me.)

captain chaos- Myles is right (of course, and as usual). I figured I'd post some ideas here that I've also posted on your other threads about this. (Myles, please correct me if I'm wrong with any of this.) All of those are very good tubes for that amp, really! If you can, get a full quartet. Much better than mixing and not matching a bunch of very different tubes. If you can get any of them in a matched quartet, that'd be best. Have the amp biased for the new output-tubes by a competant, experienced tech, it's kinda like setting their collective "idle". They'll sound their best and last longest. Easily worth the money, if they run too hot they can wear out extremely soon and then your original outlay is wasted, right? It'd also be a very good idea to get a new "phase-inverter" (the single little preamp-type, 12AT7 or 12AX7, etc., tube closest to the big output-tubes, that drives them) to go with the new output-tubes, they work and wear-out together as a team; better yet, get a "Matched Phase Inverter", aka "MPI" (one that's been tested for close uniformity between its inner triodes), it''l get the absolute most out of those matched output-tubes, and also the longest life. The combined difference and improvement can be dramatic, like night-and-day! If you can only get a pair of new output-tubes, a quick-&-dirty way to get by for now would be to only run with the two new ones (discard the other old ones), while simultaneously wiring-up only one of the two twelve-inch speakers inside the cab (leaving the other one disconnected) so as to be running into 8 ohms, effectively halving the output-impedance (a 4-ohm out going into an 8 ohm speaker, as opposed to the normal '4 ohm out/ two 8 ohm speakers wired in parallel for a 4 ohm load'). "Half the tubes, half the impedance". A good 50 watt Twin with one 12" speaker beats a not-so-good 100 watt Twin with two 12s! The difference in volume and headroom shouldn't be very noticable here.

Forgive my buttin' in, but- rockitsauce- you might want to be sure not to void your warranty. Myles is right (of course!), but I just wanted to throw that in. Be sure that you have it worked on by an AUTHORIZED, competant tech so that it doesn't void your warranty. (It's FREE, too.)

Acknowledged. I will replace the fuse today and make attempt #2. The meter was set to DC volts. If it makes ya feel any better, I did that once, too, Paul...

I've done all of the above wiring schemes before, and I've also owned a Fender Hot Rod DeVille 2x12, too!

If I may butt in- Lancer- The simplest and best solution is to simply use a 4 ohm 15" speaker, connected to the amp's extension speaker jack; you could put it in the same 15" cab, and hold on to the original 8 ohm speaker. You could wire one of the 12" speakers and the 15" speaker in parallel, both connected to the main speaker-output of the amp, to yeild a total combined impedance of 4 ohms. Of course, this would leave one of the two 12" speakers in the Hot Rod DeVille 2x12 unused. -or- you could connect a safe, reliable, suitable 8 ohm "dummy" load (like that in a Groove Tubes Speaker Emulator, THD Hot Plate, Dr. Z Airbrake, etc.) in parallel with the 8 ohm 15" speaker (both to the same extension speaker jack, in parallel, yeilding 4 ohms). This would allow for use of both twelves and the fifteen; think of the "dummy load" as a "silent partner". But... The simplest and best solution is still to simply use a 4 ohm 15" speaker, connected to the amp's extension speaker jack...

Hehhehh, that little black box of Aspen's... !! I've got an ooold, late 70's/early '80s GT Electronics Speaker Emulator unit (the original one, no attenuation for external speakers, no 'loop, and the "pole-filter" EQ, instead of the "amp-style EQ"). It's fantastic for providing a line-out direct send from a tube-amp's speaker-out, with or without other "real" speakers connected. I see that Harry Kolbe offers a separate, stand-alone attenuator that will either work along with his own "Silent Speaker" load-box/speaker emulator, *or* another one of the user's choosing. Myles, what do you think of using the GTE Sp Emu in tandem with the Harry Kolbe attenuator? Since I already know that I LOVE the reactive-loading characteristics of the GTE Sp Emu, I'm guessing that this would be a superior option to most attenuators out there?

Myles, would there be a feasable way for a competent, qualified tech to modify the effects-loop in a THD BiValve- perhaps tweaking some component values- to better suit a given, particular effects-unit? -OR- Vice-verse, mod the I/O of said effects-unit to better suit the 'loop of the BiValve? Thanks for any ideas you might have!

surgevw- what is the amp you're using with those 6V6's? Just curious! And, yeah, those "MPI's" can make a huge difference in most amps; great, aren't they?

Cool, thanks! So, for a bf Pro Reverb, what about the output transformer? Would you go with the popular bf Bassman-O/T, or the same or similar to the original Pro Reverb O/T? Or something else? -And- what would be your choice of speakers?

Saaaaaay, Myles- If you had a "blackface" Fender Pro Reverb 2x12 that was all-original stock (except for necesary things like filter-caps)- -but needed tubes, an output-transformer, and speakers- -what tubes, O/T and speakers would you put in there for yourself, and why?

Hey, Myles, wouldn't you know it- -the latest issue of Guitar Player magazine (ever hear of 'em?) has a "Relics" article reviewing an old Jim Kelly amp with four 6V6's and a 30 watt/60 watt High/Low power switch. Turns out, "F.A.C.S." stood for, "Foot Actuated Channel Switching". An external, piggy-back L-pad attenuator was automatically switched in whenever the "lead/overdrive" channel-1 was selected.

Saaaaaay, Myles... Remember those Jim Kelly amps, with four 6V6's and that "FACS" circuit? I haven't been able to scare up anything other than one schematic on them; got any further general information on 'em, or a source for such?

Saaaaaay, Myles... Remember those Jim Kelly amps, with four 6V6's and that "FACS" circuit? I haven't been able to scare up anything other than one schematic on them; got any further general information on 'em, or a source for such?