Service Data Rank Bush Murphy TV IF Sweep and Marker Generator 12050

Hi Chris, 

If you find anything let me know as well, mine works a treat but suspect it can do so much more. I saw that listed and was tempted as it has the original knobs too.

Posted by: @freya

if you find anything let me know as well

Hi Stephen, I certainly will. 👍 

The only other mention I've found of this is Mike Bennett having one with some failed diodes. I intend to fully document the device with detailed photos and anything I can find associated with it. What I find crazy in all the time vintage forums have been around (almost 20-years now), there is virtually nothing to be found for it. Hopefully I can address some of that shortfall now, however, I'm not holding out too much hope of finding service data, but never say never.

I guess you've mainly used it for 405 alignment then? How have you found it? Was connecting it up fairly straight forward? I guess you've never found a cct either.

Yes 405 only, it works great and is easy enough to connect. Like you i have never found anything whatsoever about it.

I look forward to seeing it being used on 625

Ah!  Here we go a wobbulating

On the TV screen.

That certainly looks like it has a lot of potential. I guess the main concern is how accurate it will remain after all these years, but, if the TV sets themselves don't drift massively out of true, as it were, then the test gear should at least be equally good?

@katie-bush 

Hopefully the markers are Xtal controlled and won’t be far off.

@nuvistor

A friend of mine has built a custom crystal-controlled marker generator, using individual crystals for every line-up point imaginable - which of course means he can have more than one on at any time.

Although it's been ages since I've had my hands in anything vintage, I would use one of those cheaply-available DDS boards to generate a marker now. 

@cathovisor 
Probably much more difficult to find suitable Xtals today and buying a number of different frequencies would be expensive.

Yes DDS would be easier and less expensive.

Still each to their own and if they are satisfied with the price/performance that’s all that matters.

@nuvistor 

Oh, there's plenty of companies out there who'll cut crystals to whatever frequency and spec you desire - but they won't be cheap...

Oh dear, it's been got at. When I opened it, a board fell out! I've reinstalled it and will fit a new mains lead, makes me worry about why it was in this state, maybe a fault, we shall see. I'll fit a new mains cable, and power up.

All cleaned up

Well it powered up without any drama, not knowing how to drive it. Not sure if the output corresponds to what the unit is allegedly set to. Good news there is output, It looks like it should be 34.65MHz, but the scope is only seeing a little under 19MHz.

It will be sweeping approx 30-40Mhz, the marker is at 34.65, the sweep is probably confusing the scope.

Feed the gen into the first IF stage and take the output of the detector to the Y amp of the scope, should be some sort of trigger or sweep output to drive the X plates. Assuming the video detector is a diode not a fancy I.C. 

There is a X output of some form on the back, could be trigger or a sweep to drive the X plates or X amp.

Missing is the Z output socket, that controls the brightness of the trace to highlight the markers if my memory serve my correctly.

Hi Frank, thanks for your input, its much appreciated. The "z" output socket is there, it had just come away from the panel and I'd not bothered to take a new photo. Here it is.

So this is mainly down to user error,  🤔 without a manual I've no idea how I should be hooking this up to do a test. I hoped I could see some output without having to hook up to a TV.

The September and October 1960 PT in the library have some details of using a sweep gen. Probably other issues as well but that was the first if found.

In the system in PT the x time base of the scope is controlling the sweep, in others it’s the opposite way, it doesn’t matter as long as the X sweep is in sync with the generator sweep.

At least there is a sign of life in works, and that can only lead to hope that this will be a fixer-upper! - Not bad for "first light"(?).

@crustytv - connecting these things up is as per what Frank said. 'Newer' sweep generators provide a drive waveform for the scope's X plates, older ones used to be driven from the scope when they had an X output.

The Z output will modulate the trace intensity - in some cases to 'bright up' the markers, but often to suppress the trace on the scope when the sweep waveform 'flies back'.

If you can get the X timebase and sweep in sync you may be able to use a diode probe to see the output which without tuned circuits should be a straight line DC voltage. 

Rather than trying it on a TV, I'm going to power a 3000 IF panel via a 30V supply, this setup worked when using the PM5334. However, I'm still not understanding how the RBM should be connected, apologies for the 'thick' moment. The PM5334 with the benefit of the manual was set up as shown on the left. The right is what I have for the RBM.

d

@crustytv 
I would check if the  X socket on the RBM is input or output, that way the sweep can be synced. Once you get the x axis sweeping in sync you can inject the output on the front panel to the input of the I.f amp, I presume the output is a sweep of frequencies from approx 30-40 MHz. The vision detector output to the Y amp. Not sure of the detector in that IF board, if in doubt use a diode probe to the last IF secondary.

All this is from when I last used a sweep gen in the 1970’s so it’s all a bit sparse for me.