master volume amps

[dashizzler]

I'm amp experimenting, shopping and just looking for tone and have a couple questions. As for as heads with no master volume, like the 1959 plexi, as you increase the voulme, the gain is increased, so with that said you would want to put in "early break up" power tubes to get more gain, correct? But putting early break up tubes in a JCM 900 or a Bugera 1990 like I have wouldn't make a difference because they have high gain voicing in the pre amp and you could increase he volume according to your needs with the master volume? Correct? So would putting late break up tubes, like the 8-10 groove tubes or something like that in a higher gain amp give more headroom, or take away some of the high end sizzle? I like the Bugera but I also like the idea of pure analog tone tube gain that I'm guessing you could get from a plexi 1959 head with early break up tubes with the volume cranked. Am I in the ballpark here? If I'm not, please set me straight. Thanks for your time.

 

[chuckharmonjr]

In Master Volume amps...your sound comes primarily from the pre-amp section, so you want great pre-amp tubes. In a non-Master Volume amp you want great power tubes and a really good set of ear plugs along with tolerant neighbors.

 

[Purgasound]

The "early or late breakup" designation on the tubes is simply a ploy of marketing hype set up by Groove Tubes. The rating itself is not as accurate as you would think but it definitely doesn't have anything to do with breakup.

It's hard to explain if you're new to the tube world but you'll get the hang of it once you float around here for a while. Generally tubes are rated by the distributor so they can be matched. Most rating systems are much more accurate on a scale of 1-60 or 1-30 as opposed to GT's 1-10. Tubes would either be on the hot (low numbers) or cold side. (remember these are all layman terms). So think of it like this, all tubes need to be biased the same in any amp. The bias puts the tube within it's working spec. If a tube of let's say, rated at 20 was put in an amp and biased perfectly and then someone put in a pair of tubes rated at 50, you would need to adjust the bias to get those new tubes in the same parameters as the old ones. If you put in tubes rated at 20 you would need no adjustment (but it is always wise to check).

Hopefully this will kind of help ya get the idea of how it works. I will probably be flamed for not using any correct terminology... so of course I wouldn't take any of this as a perfect guide. I'm just trying to help you get the basic idea down.

Abandon the Groove Tubes!

 

[Jonathan Wilder]

Basically valves of a different rating will require a different negative control grid reference voltage to arrive at the same idle plate current draw. The higher the required negative voltage it will require, the greater the headroom the valve will have as it will require more signal swing at its grids to swing the grid to 0V (i.e. the point at which the valve hits saturation). They typically refer to these as a "cold" set, even though the idle plate current draw will be the same it will require a greater amount of negative voltage at the control grid to arrive at that idle plate current than a "hot" set would.

With a hot set, you need less negative voltage at the grid, hence it will take less of a signal swing to raise the grid to 0V and will be easier to overdrive them.

Example: You have a set that requires -45V at the grid to bias them to 35mA plate current. Now you need +45V of peak swing to swing the grid to 0V.

Now let's say you have a set that only requires -40V at the grid to bias them to 35mA plate current. Now you only need +40V peak swing to swing the grid to 0V.

As to whether this difference would be audible or detectable by dynamic feel of the amp is up to the player to decide.

 

[dashizzler]

Thanks guys. I'll keep on reading and posting. I've had jj's installed in my Bugera as recommended by the guy who does my amps. I was just using the groove tube rating as an example. I really like the Marshall style head. The sound of driven tubes is amazing and it blows me away how many different awesome tones you can get from 1 style of amp.