Fender Bassman10 - Seeking Clean Tone but distorted output

[digi001]

I would think the 'recording out' is just some 10K-1M Resistor in Series with the Output load. So if the Output Load Resistance (no speaker present) is very High then there will be a Voltage Divider present, thus the low signal

The amp has a shorting speaker jack, so that with nothing plugged in, the output is shorted.
The recording out is just a ~1/10 potential divider from the speaker output.
With a proper 8 ohm load (rather than a short eg a fraction of an ohm), the signal from the recording output will be way bigger, might be too much for your system, way over 2Vrms, when 0dBU is 0.775Vrms https://www.montagar.com/~patj/db_db.htm

That box looks to be just an Lpad nicely packaged up.
The amp will likely put out over 50 watts so I suggest something with a bigger rating, as it will sound better the higher you turn the master volume.
If you want an lpad, consider something of at least 100 watts, like http://www.parts-express.com/parts-expr ... m--260-262
My experience is that a 10 watt amp can make a 15 watt lpad overheat to the point of emitting smoke.
Weber sell dummy loads, but the resistors may need heatsinking https://taweber.powweb.com/amptechtools/truload.htm
But a proper reactive load would sound better, as a tube power amp (even UL) has an output impedance that is significant in comparison to its rated load impedance. This means that the output voltage / power will tend to track the variation in speaker impedance with frequency, resulting in a treble and bass boost.
The net result being that a purely resistive load can sound flat and middy in comparison to a load that mimics a speaker's impedance - frequency characteristics.

Yes a master volume controls output wattage, but there's no correlation between the MV setting and output power, other than very trivially, such that it may well be able to put out full power at halfway or less.

Awesome thanks.

Yes it looks like I can just use a striaght 8 Ohm load as the amp already has a Recording Output.

Whats the difference between the big WEBER power resistor and the 50W 'Motor'? The Motor has some inductance? People think it makes a big difference in sound? I honestly thought the tone sounded great with NO LOAD attached to my Amp (despite the volume), so maybe a simple Power Resistor will be just fine?

[pdf64]

Yes, Weber's motor type load is a speaker voice coil, so will be inductive, and the amp will react to that.
But if you're happy with the sound of the existing shorted output, then a straight resistor may be ok.
Bear the power rating of the resistor in mind; if you can't be sure it will be adequately heatsinked (if it's that type of resistor, ie with holes for mounting bolts) then the rated power handling will need to be increased still further, eg 200 watts.