Amplifier input

[rsumperl]

Greetings,
I am in process of designing a tube amplifier. I have two solid state tuners (AM/FM & SIRIUS) that will be used. One tuner puts out 650mv into 5K and the other puts out 1.35v into 5K. How would you design the amplifier stage after these tuners?

Thanks,
Ray

[Arnulf]

Originally Posted by rsumperl

How would you design the amplifier stage after these tuners?

Quickly.

Determine the laod and desired power, decide on topology of the output stage, determine drive (current and swing) capability of the input stage based on input info and put everything together.

[azazello]

1 v input sensitivity.

[rsumperl]

I guess I goofed, I already have the push-pull stage designed and tested. I was concerned about the stages before the push-pull stage. I was concerned about the 5K load needed and the high level from the tuners.

Thanks,
Ray

[wakibaki]

The output impedance of the tuners is irrelevant, since the input impedance of most valve amps >> 5k. Thus only the voltage swing is of importance.

You want your amplifier to be fully driven by the lower output tuner.

The voltage drive requirement of a tube is normally determined by inspection of the load line drawn on the anode characteristic taken from the datasheet. This will also tell you the gain that the stage is achieving. As Arnulf says, work backwards from the output stage, determining the drive required by each previous stage until you reach a situation where the 0.65v input adequately drives the next stage after amplification.

If you already have sufficent gain (sensitivity) to operate from the existing inputs, well and good. If you have excess, throw some of the input voltage swing away with a voltage divider, which is what you will do in the case of the higher output tuner by judicious use of the input volume pot, although you can build 2 inputs or switch in a fixed divider if you so choose.

w

[Arnulf]

Originally Posted by rsumperl

I guess I goofed, I already have the push-pull stage designed and tested. I was concerned about the stages before the push-pull stage. I was concerned about the 5K load needed and the high level from the tuners.

You don't need 5K input impedance to get whatever output from tuners. That bit of information just says that your tuners are capable of driving such (very low Z) loads. Your amplifier's input Z will be in the range of 47K and upwards.

Since you already have a PP stage, all you need now is to figure out how much gain you need to drive it to full signal swing.