HPG1 Low output and instability

Apologies - I am a newcomer and posted this incorrectly, so it came up on the admin page. Trust this is correct now and the moderator can delete the other post

I purchased a HPG1 signal generator three months ago new from a reputable source to use in the audio range from 10 - 20,000 Hz. When I connect it to my valve (tube) amplifier input, the output is low and the voltage is unstable, cycling through a set of voltages. The amplifier input impedance is probably about one megaohm. The performance is more satisfactory when connected directly to the oscilloscope 50 ohm input.

The build is 1134. I think from an earlier query that this build is several years old.

Please can you tell me:

The current build

Whether you can update the firmware

Whether this will solve the problem

Thank you.

The latest build is 1406.
Firmware upgrade can only be done by the manufacter, please contact your dealer.
We can also check the output signal.

Please note that the input impedance of an Oscilloscope is 1Mohm, not 50 Ohm
50 Ohm is the characteristic impedance of the cable/connector

Please check the generator on a normal amplifier, bofore returning