Vt120a pre amplifiers
Of the broad lineup of Vox amps — from large all-tube amps to mini transistor amps — the Valvetronix Series is acclaimed by the broadest range of musicians and is being used in the widest variety of musical scenarios today. Delivering the perfect fusion of great tube amp sound and cutting-edge modeling technology, the original Vox Valve Reactor circuitry made its sensational debut in as the guitar amp for the new century. Since then, it has undergone continual renewal in response to the latest developments in amps, and in order to flexibly meet today's needs. The Valvetronix Plus series is once again powerfully and dynamically reborn, offering a larger number of highly evolved amp models than ever before.
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Poor routing is often a cause. Adding a three-prong cord will help. Also could be the coupling caps or cathode bypass caps.
Or could be filter caps, if the signal is modulated with 60 hz noise. Sometimes failing coupling caps. A torn or worn speaker cone could be the culprit. In rare cases the output transformer may be failing.
This amp had the following problems: -- good tone for 5 minutes, then a nasty, harsh clipping distortion on louder notes yep, bad tubes were the cause. Parts and supplies --New tubes Tubes availability can be an issue. But many manufacturers continued making tubes long after they were considered obsolete. And Russian-made tubes are still produced today. Generally, N. Tacked to the inside of your amp, or online schematicheaven.
Before you buy a vintage amp, do your homework. Check for schematics here: schematicheaven. With any luck, you'll know loads about the amp before you even purchase it! I'd recommend hands-on--i. But there are so many vintage amps on ebay, etc. Also, read some user reviews here: Harmony-central Amp Reviews Things to look for in a vintage amp: --Does it work at all?
This could be a recipe for frustration--if the transformers are bad, you could be looking at a very expensive project of course, you might have a bargain, too. Are you prepared to tackle an amp with tremolo and reverb circuits, as well as a multi-stage amplifier circuit? If not, stay small.
Unlike a modern PCB, point-to-point is a rats-nest approach, where the components are simply tied together with lengths of wire. This is a good thing, and actually makes noise-related problems easier to fix. Things to avoid: --Unsafe design Look for at least two transformers--every tube amplifier has an output transformer hooked to the speaker.
But some old amps forgo input power transformers, and are wired directly indirectly, actually, through a single cap to the AC line voltage. This type of wiring lacks 'isolation' and is dangerous! If that one old cap fails, you're a conductor! Check online schematics if you can't inspect the amp personally. The Kay A is a bit of a hybrid. It has an isolation transformer--but only for the amplifier circuit, not the tube "heaters. With a bit of rewiring, it's not too bad.
A separate power supply for the heaters would be the best option, however. Or an external line isolation transformer replacing the AC heater circuit with an isolated DC supply will also reduce hum. DO NOT come back and haunt me if you die The 'filter' caps can store fatal amounts of electrical current.
The caps are connected near the rectifier and are part of the power supply, and aid in converting AC to DC. In fact, they are a standard component in any power supply.
But that doesn't make it safe THEN, --Take a screwdriver or a jumper and short the capacitors leads. A jumper with a built-in resistor 10K or so will help prevent sparks here Some, or all of these methods may result in a spark Obviously, your flesh can act as a jumper also.
And don't work on amps in bare feet, on a damp basement floor. ALL tube amps need a recapping job at some point. Old power supply 'filter' capacitors are the primary cause of hum. And used or not, the capacitors fail over time. Electrolytic tubular capacitors have an optimum life of 10 years. Of course, they may last much longer. They will often operate sub-optimally for much longer.
But tube gear is sensitive to cap failure. Tubes circuits operate at higher voltages, and many amps are quite simple. Older caps with outmoded technology 'paper electrolytic' are almost certain to fail over time. In one sense, tubes are less susceptible to cap failure--unlike solid-state amps, many will continue to operate, although poorly.
Cap types Most common replacement caps are: Non-polarized polypropylene, or mylar Rating: V minimum Most builders and rebuilders use high quality polypropylene 'orange drop' caps. But a quality mylar cap exceeds the characteristics of the original capacitors.
I wanted to retain the vintage sound, so I choose mylar. It's amateur builders, not pros, that insist a certain type of cap is a must. In any event, the difference is subtle, and the qualitative differences are a matter of personal taste. Is the difference between cap types real?
Here's an interesting cap bench test. Polarized electrolytic Rating: depends on the amp. I used V caps where the originals were V. Regular 'computer' type electrolytic capacitors work fine. Especially for the power supply filter caps. They come in two packages: radial , with the leads on the same end, and axial , with the leads on inline on both ends. Oh, Yeah Inserting one backwards--fireworks!
Note: The first set of filter caps installed were purchased at a local electronics store. This store is nerd heaven --or so I thought. Some of their components are in yellowing packaging; clearly getting old.
I picked what looked like the newest of the bunch. The caps 40uF, V lasted for two weeks before failing --first a bit of crackling, then a lot of crackling and the amp began cutting out From now on, it's mail-order from a reputable firm digikey, jameco, etc. Many guitar amps have the larger electrolytic caps in sealed "cans. They usually are the power source filter caps.
These can be replaced, but-- -- Replacements are X as expensive as a handful of single caps -- Even if you can find an electrically-identical replacement, finding the same physical dimensions is difficult height, diameter, etc. If circuit changes are made, and not all the sections are used, it's just a waste. S' 'New Old Stock'--good for tubes, bad for caps.
So it's quite easy and common to replace with individual polarized capacitors. I removed all the wiring from the can, then rerouted to the new caps with a terminal strip. Terminal strip are cheap, simple to use, and very common in vintage gear.
The terminal strip was attached to the chassis with a steel pop rivet and steel rivet backing-plate. The hole was pre-existing cool! The old 'can' was left in place for looks, and for a reference to whoever 'recaps' this amp in the future.
The filter caps, originally rated at V, were replaced with V versions. Yes, you caught me --the 20 uF bypass cap is still only V, because that was the only one I had on hand This is part of Mod A--I've since replaced it with a 10uF V cap When replacing the filter caps, don't exceed the capacitance values by much I went from 40 uF spec to 47 uF. More capacitance sounds good, right?
Less hum, you say? Unfortunately, amps with tube rectifiers can't handle high capacitance values--they cause voltage spikes that wear out the rectifiers quickly. Other than the filter capacitors, the other caps in the amp will be one of these Step 8 will help you identify each of these types : 1 Coupling Caps -- connect the signal path between stages 2 Tone Caps -- roll off different frequencies to ground, for tonal effects 3 Cathode-Bypass Caps -- integral part of "cathode biased" circuits Most of these caps will be of the non-polarized variety.
The occasional cathode bypass cap could be a polarized, however. The coupling and tone caps should have voltage ratings comfortably higher than the max voltage the circuit might see--with cap and induction spikes, just assume these should be volts or greater.
The bias voltage for tubes rarely exceeds volts, however. A 50V capacitor will work fine for the cathode-bypass caps. Use a 30W soldering iron. Grasp the leads of the old caps with needle-nose pliers, if you are smart , and apply the iron. They may take some wrestling to remove.
Eg&G Ortec Vt120A Fast Timing Preamplifier
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Vox Valvetronix VT120+ 120-Watt 2x12 Modeling Guitar Combo
Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts. Wed Apr 26, am. Wed Apr 26, pm. The Dynaco Tube Audio Forum. Would you like to react to this message? Create an account in a few clicks or log in to continue. You are not connected.
Ortec Vt120A Fast Timing Preamplifier
Great 6 string guitar amp for any type of music terrific sound. Comes with three way foot switch an a owners manual. Amp is just sitting around need room, this amp can be played on 60 or watts. Great sounding and playing amp, Very punchy, Clean Highs and lots of Crunch. Ampeg VT Tri Ax series 1x12 tube guitar combo.
Ampeg vt120 tri-ax Tube amp - $345 (alexandria bay area)
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2BY2/2BY2-DD and 3BY3/3BY3-DD Integral NaI(Tl) Scintillation Radiation Detector
Hopefully by Friday or when I go to the shop, it'll still be there for me to test drive. They sound a LOT better cranked too, I mean, the attenuator on the back on 10 and the master volume on half or above, eg gig volume. I've had my VT combo for probably five years now. Neither of the two tubes have been changed. As already stated, they do best fairly cranked. No matter the power level the amp is set to, the master volume, volume and gain should be at least halfway up. Not only for tone but for feel too.
Based on the acclaimed VOX Valve Reactor circuit, which utilizes a genuine 12AX7 vacuum tube in the power stage, these advanced digital amplifiers retain the familiar warmth of a genuine tube amp. Specifications and features are subject to change without notice. X This site uses cookies. To see how cookies are used, please review our Cookie Policy , By clicking the "I Agree" button, or by continuing to use this site, you are indicating your agreement to our cookie policy.
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By continuing to use the site, you agree to our Privacy and Cookie Policy. Integral preamplifier and high voltage HV for convenience and safety. Low power consumption mW , ideal for portable applications. Single-cable connections for most applications. Incorporating the bias supply in the PMT base eliminates high voltage cable connections to bulky, external, HV supplies.
Looking for help with a Hybrid guitar amp, this is a modeling amp, solid state watt and a tube pre amp 1 watt, using a single 12AX7 tube. The amp is going on seven years old and have been considering replacing the tube, after reading about different tubes which one would be the best, I keep seeing the same comments "After break in, the tube sound great". Not being a EE a 1 watt pre amp input or output will the tube ever break in, or are the voltages supplied to the tube the same whether its 1 watt or 65 watts. Don't waste your time or money, the 12AX7 in there is barely doing anything break-in really?
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