AVO HF-135 RF Signal Generator

AVO HF-135 RF Signal Generator

AVO HF-135 RF Signal Generator

A very good friend of mine decided to finally sell me some kit, and the prise of this small haul is this absolutely ‘Mint’ AVO HF-135 RF Signal Generator.

AVO HF-135 RF Signal Generator

The Sig Gen covers 100kHz to 240MHz in eight bands with a maximum output of l00mV into a 75 ohm load.

AVO HF-135 RF Signal Generator

The Sig Gen covers 100kHz to 240MHz in eight bands with a maximum output of l00mV into a 75 ohm load.

The unit has a builtin attenuation is provided by four 20 dB (from 0dB to -80dB) steps and a continuously variable control. 

AVO HF-135 RF Signal Generator

An R.F. level indicator monitors the r.f. voltage applied to the attenuator system. 

This is a little on the basic side as no markings are provided, just a mid point.

The output of the audio oscillator is available at the A.F. Output socket as an audio signal source of approximately l V r.m.s. Facilities are provided for external modulation between 50Hz and 5kHz to be applied at the Ext. Mod./A.F. Output socket.

AVO HF-135 RF Signal Generator

An un modulated R.F. output is available or alternatively, an internal audio oscillator provides 30% sine wave amplitude modulation at 1000Hz. 

The Internals.

The piece of equipment is in absolutely great condition for it’s age, I know that it is not brilliantly accurate and that there are much better units out there, but this is from a friend and it is in great condition, it was crying out for a good home to be looked after.

Radio Wrangler on the VMARS website gave it a rather good little writeup.


It's an OK sort of signal generator for fixing radios with.
It will make signals across the LF-VHF range, with AM on them if you want.

It isn't a piece of lab equipment.

The radio you test will usually be more accurately calibrated in frequency than this sort of generator.

You would use it for tracing faults in non-working radios.

You would use it for making a stable-enough signal for peaking the Rf tuning sections of a radio being aligned.

It doesn't do FM.

You could use it to peak-up a simple IF strip, but not to adjust an IF strip to a specific shaped response.

It's electronic components and valves are ordinary receiver types, so it's reliability is going to be reasonable and if anything goes wrong, it's easily fixable.

This model may have been inherited when AVO took out some of the competition by taking over Taylor Instruments, I don't know the date, but early to middle 60's is a guess.

It's unlikely you'll find many AVO sig gens on sale to give an idea of price.

The Marconi Instruments TF144H is a commonly traded item, but it's the next echelon up, a lab grade unit.

The HP equivalent is the HP606B which is a 1959 vintage and about the best of the simple VFO type sig gens.

Next echelon up, is the Marconi TF2008 which can do FM and align IF strips (They were use to do filters in RA17s!) and I bought one of these in the late 80s for £80.

For that price, you could have a choice of lab grade ex-military signal generators, or you may want the AVO as a classic bit of workshop gear for working on classic Long/Medium/Short wave broadcast receivers. If it's in spiffing condition, then its a classic in its own right.

Plenty of people will tell you that you don't need a Sig Gen for servicing classic broadcast receivers.

This is true.

What they may not tell you is that sig gens can still make things a lot easier.

This is also true.

Available Downloads

AVO HF-135 RF Signal Generator - Instruction Manual

AVO HF-135 RF Signal Generator - Schematic Diagram

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