Question about impedence selector and different tubes

[daz]

I have a 3.2k marshall style 50 watt OT. I was told i can use 6v6 if i turn the impedence to 4 ohms with an 8 ohm speaker. I've been doing so with no problems. But what i want to know is can i also use a 16 ohm load if i set the selector to 8 ohms?

I'm using 6V6 at 420V and biasing to 22 Ma but using JJ's so it should be fine as voltage and current go.

[Old Tele man]

...different vacuum tubes/valves have different dynamic plate impedance (rp) characteristics, which the OT must work with.

...the idea is to have the "reflected" load impedance from the speaker(s) thru the OT 'appear' to the tubes as a plate-to-plate impedance (Zpp) that's somewhere between 1/4th and 1/10th of the output tubes' rp-value...with 1/6th value typically "optimum" with PENTODE push-pull operation.

...for example, consider the 6L6-series of tubes, which have rp=22.5K ohms and a "typical" OT Zpp range of between 5.6K, 3.8K and 2.25K, with the following examples:

RCA 55W 2x6L6GC: Zpp = 5.6K (1.8% distortion)
Fender 50W, 2x6L6GC: Zpp = 4.0K (5% distortion)

[daz]

I'm not a tech and i don't understand that. Can anyone just give me a yes or no answer?

[DirtyGeorge]

Yes, 16 ohm load on 8 ohm tap will give you the same reflected impedance
(6.4K) as 8 ohm load on 4 ohm tap.

[daz]

Thanks !