That looks OK to me and I would anticipate that it will work out fine. IF you could have the rectifier tube a little further away from the layout board and maybe lined up with the other 8pin sockets, you might consider that.
Regarding OT and impedence………….. Dumble purposely mismatched some of his Dumble amps using 8 ohm speakers with 6L6's. Kevin O'Connor of London Power states the following:
Q: I thought impedance matching was critical. Some designers say the output transformer must be changed if you want to use different output tubes. That seems awfully expensive.
A: It is awfully expensive, and also a ridiculous suggestion. There are two issues here, though; one is the notion of “impedance matching”, and the other is simple design preference.
As stated throughout our TUT book series, speaker load impedances and reflected loads to the output tubes are all “nominal”. An 8-ohm speaker may actually look like anything from 6-ohms to 100-ohms, depending on the frequency, since the reactive impedance changes with frequency. This means that the reflected load to the tubes is varying widely over the frequency range.
A nominal 8-ohm load may reflect 4k to the plates of the output tubes with a given transformer. The amp might be designed to produce its maximum power into this load, with a designed frequency response. This is the “power bandwidth”. If we change the load to 16-ohms, the reflected load doubles and the frequency response shifts upward. We lose bass but have a brighter sound, and also lose power. If we change to a 4-ohm load, the reflected impedance drops to 2k, into which the tubes produce less power, and the bandwidth is again narrowed.
The reason for the confusion, I believe, is that people think tubes will try to behave the same way transistors do. Into half the load impedance, a transistor will try to deliver twice as much current. The device may overheat and destroy itself in the process. Tubes, however, simply don’t behave like transistors.
The design issue for impedance matching comes into play when a designer takes the approach that “everything is critical”. In some circuits, this may be the case. Tubes don’t really care. There is no optimum load for a tube unless you are going for minimum THD, and this then depends upon the other operating conditions. For guitar, criticality is purely aesthetic. The designer says “this is good”, “this is bad” and in that decree believes it to be so. He is correct in his subjective impression, but should not confuse the subjective and objective.
Food for thought!
With respect, Tubenit
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