What is the typical conversion for solid state watts vs tube watts? I know it may vary with factors, but generally what is it?

Any tube amp is required to add higher volume (for tubes to get warmed up) and that's how tube amp sounds really loud. If you take solid state and tube one with power of 50 watts, then they will be pretty same in loudness (and in power). The bigger speakers, the more loudness and power they'll deliver

My lead guitarists 15W tube seems to be comparable to my solid state 100W, FWIW. Unless you are going to play a big auditorium (2000 people), 100W tube might be overkill.

I misspoke. It's a switchable 5 to 3 watt tube amp. I guess based on my very limited data set I will venture a ratio of 20:1...

Typically, Tube seems to be a 3:1 in my experience. The speakers can make a huge difference however. Also, the largest problem with solid state is not the volume, but it's ability to hold it's own in the mix.

I've heard (this may or may not be true) that the wattage doesn't mean much eitherway - the efficiency of different amp/speaker combos is what's important. Although, obviously, in general higher wattage means higher volume, there are no hard set rules. Having said that, I've only ever come across REALLY loud 50w tube amps. I've never come across a really loud 50w transistor amp. So I'd say probably tubes are much louder. Not sure why. However I use a pair of 100w HH studio power baby transistor amps and they are LOUD. But I think they use MOSFET, which is not often used now..

I'd go along with the 3:1 ratio if they're run through the same speaker cabinets. Some tube amps are just incredibly loud. I have a 100w Fender Twin which can run at 33w - even at the low power setting it's extremely loud. I've rarely used it at 100W; it's just too loud for anything but an outdoor festival. Vox AC30's are very loud as well. . It's a disadvantage though in many cases. Tube amps sound best when they're turned up. If you have to run them at a low volume setting, they don't sound anywhere near as good.

Watts are watts -- no difference. Amps are generally rated for a given amount of distortion, and that's the real difference between tube and solid state amps. All amps can produce MORE than their rated power, but distortion increases. Guitarists think that distortion of a tube-based power amp is more pleasant than that of a solid state amp ( that was true back in the '60's, at least, and most guitar players are well and truly stuck there gear-wise), so they will routinely drive a tube amp into double the rated power without a thought and be happy with it. As it turns out, most higher-end solid state amps designed for guitar these days actually do NOT get nasty and gritty (a tube emulation circuit designed and never patented by an engineer from Carvin back in the early '70's or late '60's does a good job of mitigating that). But as with the "breathing" nitrocellulose lacquer and "old-growth" stories, the mythology persists. And the cheapo beginner amps are generally unwonderful, so they support that myth. At about 100W for tube amps, transformer weight and hearing loss come together to generally limit things. A typical head only can weigh between 40 and 70 lbs. My solid state bass amp weighs in at around 10 lbs. And it has 1500W.

doesn't matter to me either way all I know is I have a vintage Peavey VTM120 (120Watt) and matching celestion equipped 412ms overkill for my needs for sure since it is nothing more than a practice amp but considering i cant seem to sell it for enough to replace it with another smaller tube amp and it is vintage and still has the dipswitch plate cover and celestion G12k-85 speakers i will just have to find a way to be content with it

There can be a perceived difference in loudness because of the way different amplifiers clip or distort. Tube clipping is slower/softer and power supply sag can add to this effect (set the old Marshall on 11). Whereas, the Solid State (SS) amp will tend to clip abruptly when the design limits are reached. Therefore the “apparent” loudness can be different, although the effective power dissipation, or watts, is essentially equivalent. There is no real difference between Tube amps and SS amps maximum "loudness", there is no "ratio" or any such thing. As someone else said, “Watts is Watts”. The speaker(s) can make a difference due to variance in efficiency, but the output of amplifiers are (should be) rated in Watts into a specified load. Watts are the same wherever you go, they are not different in London, New York, or Istanbul nor between Fender, Ampeg or Marshall nor between Tube and Solid State amplifiers. However, there are different ways of measuring volts and amps; typically peak, RMS, peak-to-peak, or Average. Such nomenclature simply describes different, but consistent, mathematical ways of defining the same AC waveform or music signal. In electronics, the derivation of Watts is basic algebra “Watts = Volts x Amps” based upon Ohm’s law where “Volts = Amps x Resistance”. The term “Watts” defines the amount of heat that is generated in a component or circuit. (In engineering the Watt is often referred to as “I squared R” -- such as “lower efficiency due to I squared R losses” -- because Watts = Amps x Amps x Resistance, where I is the reference for Amps.) So when you see a spec on an amp of 100W RMS into 8 ohms you can determine other info by applying the Ohm’s Law formula, such as the volts and amps that the amplifier is rated to provide. The trick some manufacturers play is that they don’t tell you if the “Wattage” is based upon RMS, Peak, or Peak Music Power and therefore play “number” games. Or, they may not specify the load impedance (2/4/8/16 ohms??). Another issue is speaker/cabinet quality where the frequency response is not necessarily the same impedance (AC resistance) across frequency, for example the speaker can be 8 ohms at 20 Hz, but 16 ohms at 1 KHz; this can obviously affect perceived loudness. When amplifiers are properly spec’d, then you can compare output ratings as apples-to-apples (or Ampegs to Fenders). You know that 100W RMS @ 8 ohms is going to be louder than 25W RMS @ 8 ohms. But, if another amp is rated at 100W RMS @ 2 ohms, then both 100W RMS amps still dissipate the same amount of heat into the load and are of equal loudness (at least in the theoretical). But, if you plug the amp rated 100W RMS @ 2 ohms into an 8 ohms speaker, it will not be as loud at max settings and will sound more like the 25W version. By definition, the 25W RMS tube amp will supply the same power as the 25W RMS SS amp into the same rated speaker load, and be essentially the same loudness (see first paragraph). But a 100W Peak (8 ohms) amp is not going to be as loud as a 100W RMS (8 ohms) amp due to the very definitions of Peak and RMS. Some cheesy manufacturers (especially automotive market) will advertise something like 1,000W into 4 ohms, when they are referring to instantaneous peak power which is typically considered as 8-10 times the actual peak value. The RMS rating is equal to 0.707 times the peak value, so 100W Peak is mathematically equivalent to 71W RMS – same loudness, different type of rating – all other aspects being equal. Using the term “Music Power” is another way of creating larger sounding numbers as compared to RMS ratings, but there is some rationalization behind this type of rating. So, just do your best to understand the different ratings and variances in a rig or system and do your best to compare apple-to-apple ratings. If advertised ratings are incomplete, then move on to another brand.

The old rules no longer apply. These questions are moot in the current solid state market. Quilter is the only game in town for solid state amps. Whether you prefer it to a tube amp or not is the only question, and it comes down to personal preference. But tone isn't the only factor anymore. Now that the sound of these amps has gotten so good, weight and reliability are now more important factors to take into account.