Join me in welcoming a new piece of TE at home !
![Cool 8)](https://www.eevblog.com/forum/Smileys/default/cool.gif)
A Metrix type 920 ! Of course you don't know what a type 920 is.. neither would I if I didn't have it on my bench...
Remember that huge Metrix Wobuloscope boat anchor I bought recently ? .. Thinking it was a super duper luxury sig gen... when in fact it's a highly specialized bit of kit meant to test TV sets. Was mistaken, my bad, impulse buy, regrets... no business owning this thing... that's what happens when you are so young that you don't have a clue what a Wobuloscope is....
Well last week I finally found what I was really looking for... a more general purpose sig gen. Well according to the manual it's still not quite general purpose, meant to test radio receivers. So the frequency bands and output signal amplitude levels (very low...) reflect that.
But that's OK. Compared to the Wobuloscope, it's "general purpose enough" to my linking. I mean it has a broad frequency range, can go quite low, 50kHz, and can go quite high, 50MHz. It has also amplitude modulation which I wanted. The output attenuator is also versatile, wide dynamic range, with both a pot and a range switch to select levels from 1uV up to 10mV (up to 100mV for the modulation signal/tone, 400Hz).
Also has input for an external modulation signal.
And it's MUCH small and lighter than the wobuloscope !!!
A third of the weight at 6,5kg, a third narrower, a third of the depth, it's not even a boat anchor at all in fact !
![Confused :-//](https://www.eevblog.com/forum/Smileys/default/confused0024.gif)
And I love its front panel paint colour, much prefer that to the light grey of the Wobuloscope.
I also love how the front panel is slanted, makes it super easy / comfortable to operate !
![Cool 8)](https://www.eevblog.com/forum/Smileys/default/cool.gif)
Inside, it's a MUCH simpler instrument, so much easier to work on ! A lot less stuff, only 3 tubes in all, and everything is super easy to access, a dream.
Oh, and it also comes with the original paper work / file, containing only a handful of pages but enough to squeeze operation of the instrument, parts list and schematic, the latter of which fits on a single page !
![Cool 8)](https://www.eevblog.com/forum/Smileys/default/cool.gif)
Oh, and it comes even with its original warranty card ?!
![Shocked :o](https://www.eevblog.com/forum/Smileys/default/shocked.gif)
Oh, and it's in excellent nick inside out, and cost only 30 Euros ( 42 euros shipped) !
So... for all these reasons I just could not resist, this was the one for me !!!
![Cheesy :D](https://www.eevblog.com/forum/Smileys/default/cheesy.gif)
So now let's get rid of the Wobuloscope...
Seller said it was untested, of course... what do you expect for 30 Euros these days !
![Laughing :-DD](https://www.eevblog.com/forum/Smileys/default/smiley_laughing.gif)
Honestly I assumed when he said that, he was just trying to cover his ass because he probably stole the tubes in it !
So when I opened it up, I fully expected to find... no tubes. But go figure, they are still in there !
![Shocked :o](https://www.eevblog.com/forum/Smileys/default/shocked.gif)
Mind you, as I said only 3 tubes in this thing, and probably none that interest audiophools.
A 6X4 rectifier tube, and a couple 6J6 tube ( a double triode) for the oscillators.
I don't know this 6J6 tube, none of my Tek scopes have them.
Just had a quick look on Ebay, some of these 6J6 cost 50 USD but most of them are single digit money, phew.
I immediately noticed that someone worked on this thing before.... the power supply section has clearly been visited / reconstructed !
One of the two big smoothing caps has been replaced with a cheap modern radial. Also, the beefy resistor connecting the two caps has also been replaced it seems (looks too modern to me...), and I also notice a beefy diode soldered directly to the socket of the rectifier tube ! So I guess that tube is dead.
I looked at the output of the generator on my scope. I can see the modulation signal (alone), frequency about correct, looks like a clean sine wave, but amplitude is very low. Should be 100mV tops, but I get 2mVpp, I can just about see it on my scope (2mV sensitivity, signal is just one division peak to peak).
As for HF, when cranked to the max I am supposed to be able to get 10mV out of it (RMS or Peak or Peak to Peak I don't know...)... and I can just about distinguish some HF content, of a frequency that may make sense, and that I can get to vary when I move the main rotary dial. But signal amlpitude is so minuscule it's hard to figure out a signal in the noise floor of the scope...
So.... looks like I have life, but very, VERY weak life... so either the attenuator is kaput, which seems unlikely (it's just a few resistors / switch and a pot, and it behaves appropriately), or I just have two weak 6J6, and a dead 6X4 rectifier tube.
So probably need to replace the 3 tubes, well at least the two 6J6, and I should probably be back in business. Need to order them so will take some time for shipping sadly, I am so impatient...
This instrument is so simple and so easy to access, it's probably possible to fix it easily and quickly and cheaply... so will try to do so.
Obviously before I order new tubes, I will first check the power supply to make sure it's been fixed properly, then check the amplitude of the HF and LF signal BEFORE the attenuator, to be 100% sure it's a weak oscillator(s) and not a faulty attenuator.