Tube choice and impedance

[Jeph]

Sorry if this is basic, but I'm interested in learning about tube choices and impedance. i.e. with an EL34 in this amp, the 4/8/16 ohm taps are what they are, while with a 6V6 the 4=8, 8=16, 16=32. Do I have this right? I'm planning on playing with both tubes in my build and would rather have a good understanding of this prior to making any potentially costly mistakes.

[UR12]

Sorry if this is basic, but I'm interested in learning about tube choices and impedance. i.e. with an EL34 in this amp, the 4/8/16 ohm taps are what they are, while with a 6V6 the 4=8, 8=16, 16=32. Do I have this right? I'm planning on playing with both tubes in my build and would rather have a good understanding of this prior to making any potentially costly mistakes.

Jeff

I will give you my 2 cents. I guess these are just observations on my part. I am not going to talk so much about tubes as I am about OT primary imp. Usually Marshall uses about 3500 ohms for its EL34 amps using 2 tubes. Ken used either a 5200 or 6600 ohm imp on his EL34/6V6 outputs. Two 6v6s in an AB1 Push-pull configuration run around 8000 ohms. Of course there are a lot of things that determine the best OT primary imp or plate load, such as Plate voltage , grid current, etc,etc. So if we take 3500 and subtract it form 8000 you get 4500 this is the range between the two. 1/2 of the 4500 will give you 2250 or the midpoint or middle of the the range. So if we add 3500 and 2250 we get 5750. If we were trying to find the impedance in the middle of the range 3500 to 8000 it would be 5750 ohms. This is close to the 5200 or 6600 Ken used. Based on this both the 5200 and 6600 are kind of in the middle between the EL34 and 6V6 output imp and there is probably nothing you need to do extra regarding the Imp switch. In other words You shouldn't have to worry about the 4=8,8=16,16=32 thing. Just swap out the EL34s put in your 6v6s (Check bias) and if you are running a 8 ohm cab just set it on 8 ohms and go. Just my Humble Opinion!

[Jeph]

Thanks Dana. One of the reasons I asked is due to the following from another post:

One thing to remember, though, if you're running 6V6 at double load (8 ohms on the 4 ohm tap) you're at about 10K with the 5200 tap. Excellent range for 6v6 (most Deluxes are in the 8K primary range). That's the main reason I'd consider 5200 on the primary.

I think my knowledge of circuts etc... is still too basic to follow how/why using an 8ohm load on the 4ohm tap with 6v6s would result in 10k resistance. Can I assume the same numbers would apply to EL34s, but that wouldn't be a good idea since 34's run about 6500 ohms in this configuration?
Since I will be "playing" with different tubes and the 5200/6600 taps I'd like to make sure I don't get into trouble.

[Funkalicousgroove]

Keep in mind that Primary Impedance isn't an exact science, 2 6V6's will run just fine at a 6K6-5K2 Primary. To really determine prime opeating points you'll need the actual Manufacturer's Test Data with Loadlines plotted for Plate to Plate Impedance, and what you'll find is that the tubes will run fine over a good range of Plate to Plate Impedances.