Stoked that i have come accross your channel..I have the 2019, came from ch9 television station Sydney Australia, last calibration 16thJuly1999..I hope the electrolytics havnt shit themselves. .😊
Tank you so much for you excellent video. great detail and very helpful in allowing me to repair the unit i have. I really like the idea of using the spec ann to measure the gain of the amps. Super idea. I just bought a 2022 and it was working on some frequencies but not all. Thought it was the OM345s but turned out to be a 100ohm resistor feeding 12v to the VCOs running at 171c as the 220uf cap on the VCO side was a complete dead short. Someone had been in before me and added resistors to some of the OM345s an the others are working ok so far.
As has already been pointed out bridging pins 1 and 5 with a resistor (my choice would be 5.6K) will restore the bias to the BFR93 transistor used as a signal amplifier in the OM345 where the on board resistor has failed and the module will start working again. This procedure is very easy and quick to do and no messing about trying to build and fit a MMIC amp instead.
Excellent video; those hybrids tend to be the usual failures in these units. Yet I feel they are so good its worth going the extra mile, as it were. Really good instructional video!
Even though these units are getting on in age, they are still a really useful bit of kit. Back in the day Marconi and R&S used a lot of wideband RF OM amp modules in their instruments. The OM345 was origanally produced by Mullard which was of course closely connected to Phillips. Later the component side of Phillips turned into NXP which produced the OM2045 as an equivalent. I also have the small PCB's which use a Mini Circuits MICC device, however these are 50 Ohm amplifier as opposed to the 75 Ohms used by the original device. If I am honest, I am not sure what effect this has on the instrument. Interestingly, NXP still produce a close 12dB gain 75 Ohm 5MHz - 1GHz equivalent IC (BGA3012 SOT89) however; they are 8v devices, so I guess it would be possible to knock up a Hybrid PCB that includes a V reg as a direct replacement. Interesting video as always, keep up the good work. Best regards M0XFX
Measure the output pin (pin 5) with a DVM. If the internal resistor has gone OC (a common fault with these modules), then pin 5 will show 12v instead of 6-7v, as there will be no bias voltage to turn the transistor on. If this is the case, then bridge pins 1 & 5 with a 4k7 resistor. It may not be an ideal permanent repair (or perhaps it will), but it will get the module working again so you can check for any other faults.
Stoked that i have come accross your channel..I have the 2019, came from ch9 television station Sydney Australia, last calibration 16thJuly1999..I hope the electrolytics havnt shit themselves. .😊
Tank you so much for you excellent video. great detail and very helpful in allowing me to repair the unit i have. I really like the idea of using the spec ann to measure the gain of the amps. Super idea.
I just bought a 2022 and it was working on some frequencies but not all. Thought it was the OM345s but turned out to be a 100ohm resistor feeding 12v to the VCOs running at 171c as the 220uf cap on the VCO side was a complete dead short. Someone had been in before me and added resistors to some of the OM345s an the others are working ok so far.
Just for accuracy Marconi instruments was in Stevenage Herts. No mass produced test equipment was made in Chelmsford post 1975 or perhaps prior.
As has already been pointed out bridging pins 1 and 5 with a resistor (my choice would be 5.6K) will restore the bias to the BFR93 transistor used as a signal amplifier in the OM345 where the on board resistor has failed and the module will start working again. This procedure is very easy and quick to do and no messing about trying to build and fit a MMIC amp instead.
Excellent video; those hybrids tend to be the usual failures in these units. Yet I feel they are so good its worth going the extra mile, as it were. Really good instructional video!
Even though these units are getting on in age, they are still a really useful bit of kit. Back in the day Marconi and R&S used a lot of wideband RF OM amp modules in their instruments. The OM345 was origanally produced by Mullard which was of course closely connected to Phillips. Later the component side of Phillips turned into NXP which produced the OM2045 as an equivalent. I also have the small PCB's which use a Mini Circuits MICC device, however these are 50 Ohm amplifier as opposed to the 75 Ohms used by the original device. If I am honest, I am not sure what effect this has on the instrument. Interestingly, NXP still produce a close 12dB gain 75 Ohm 5MHz - 1GHz equivalent IC (BGA3012 SOT89) however; they are 8v devices, so I guess it would be possible to knock up a Hybrid PCB that includes a V reg as a direct replacement. Interesting video as always, keep up the good work. Best regards M0XFX
@13:33 The average weekly wage in the UK in 1986 was around £155 per week, not £20. Perhaps in 1966 it was nearer £20.
Measure the output pin (pin 5) with a DVM. If the internal resistor has gone OC (a common fault with these modules), then pin 5 will show 12v instead of 6-7v, as there will be no bias voltage to turn the transistor on. If this is the case, then bridge pins 1 & 5 with a 4k7 resistor. It may not be an ideal permanent repair (or perhaps it will), but it will get the module working again so you can check for any other faults.
💔 'Promosm'