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Having a spare moment in the shop, waiting for parts to arrive, I extracted a classic Oscillator from my pile of stuff in one corner of the shop. A Bruel & Kjaer 1022 Beat Frequency Oscillator. I'm about to set up another small test bench over at the Guitar Dept/Rental Depot down the street, and start going thru the large inventory of speaker cabinets, where I know there has to be a large pile set aside with one or more blown speakers.
In my shop at the main rehearsal studio complex, I have a smaller successor to the B & K 1022 (the B & K 1023), which, like it's predecessor, can drive speakers directly at low (but adequate) wattage (7W for the 1023, 2.5W for the 1022). This has always been adequate to use to drive the speakers in any of the combo amps I have up on the bench, when checking for blown, buzzing, and rattles without going thru the combo's amp to do that. For the larger bass cabinets....8-10's & such, I'll have one of my shop power amps to supplement for higher wattage.
It had been several years since I had this 1022 BFO powered up, and did know it needed a little work. I moved it to the bench, plugged in my IEC Male to Nema 5-15 Female adapter, it having a Nema 5-15P Male Pins on the recessed power connector, and powered it up. The Meter lamps and Frequency Scale lamps were all dead, so the only hint it woke up was the low current indication on the power analyzer feeding it, and, in switching it on and off, seeing the meter move from the power transient. Initially, I wasn't getting any output. I rotated the Automatic Scanning switch (used for local/external frequency scanning), and that woke it up. So, switch contacts on that need attention.
I moved a known working 12" woofer to the bench, and connected it to it's Matching Transformer output terminals, set it for 6 ohms.....the one normally used for driving speakers. I printed out the Frequency Calibration procedure from the operators' manual, and set the frequency dial to 60Hz, as this instrument uses Line Frequency as a scale reference using a Beat Frequency procedure to calibrate it. Set the Oscillator level to mid-scale, and pressing the momentary Power Frequency Beat button in, I first used the Fine Frequency control to try and find the beat frequency. No luck, so set that Fine Freq control back to mid-position, and used the recessed Coarse screwdriver control and adjusted it, finding the beat frequency, where the output level meter is now swinging considerably about the mid-point. Went back to the Fine Control, and finally achieved a steady reading between either direction where it would be swinging again. Checked the tuning by adjusting the Frequency to 120Hz, and all was fine.
What I've always loved about the Bruel & Kjaer generators is their frequency knob lets you sweep 10 octaves with one turn of the wrist. While the frequency range on this 1022 is 20Hz-20kHz, you can tune it lower than 20Hz. Setting the frequency dial to 20Hz, with the Frequency Increment set to 0Hz, you can then carefully detune to the left. If you go down 20Hz, you'll stop the oscillator, and if a speaker is connected via the output matching xfmr, it will object loudly. But, going that low, I can set the output to around 2V or so, and can take it down to a couple hz (detuning by 18Hz.
At these low frequencies, if there is any cone rubbing problems, you can both hear it and often see it......sometimes spot the cone separating from the surround or on the spider suspension below the cone. There's plenty of force being applied to the speaker. Plus, these oscillators have modulation provisions....warble tone. I tend to use warble tone from them when checking speakers as it's easier to listen to, and you can set both the rate and bandwidth of the modulation. Even use it for limited low frequency sweep, using 1Hz rate and 100Hz bandwidth, setting the Frequency dial to 120Hz....it will sweep from 20HZ to 220Hz, or even greater, setting the dial to a higher frequency. You wouldn't want to let it go below 0Hz though.
When I began restoring this, I placed the face of the instrument down on three short 2 x 4's, so I could remove the four special long metal shoulder washers that hold the housing to four long threaded shafts attached to the frame of the chassis, and lifted off the housing. Then, moved back to the bench, facing the rear of the unit. I didn't get any images inside this, but it's very similar to that of the 1024 Sine-Random Generator I restored a couple years ago.
The Meter and Frequency Scale lamps look like 3AG-style fuses (1/4" dia x 1-1/4" long), 6.3V/250mA. I had a small stash of them, and also checked to see just how common they were by googling 'fuse-type lamps', finding prices ranging from $1.10 thru $1.65 or more from a variety of sources. The meter lamps (two of them) were mounted in open-frame clips, only one installed, burned out. I didn't have my service manual here, so I wasn't sure if they're in series or parallel. Put two new lamps in, checked with the power applied, and now had the meter illuminated. The Frequency Scale lamps are harder to get at. I had to remove the smaller concentric Fine Tune knob, then remove the larger Frequency knob, then turn the instrument around to face the back, and using a long metal shaft, I was able to tap on the four plastic pegs from the large black scale housing, driving them forward in their tensioned holding clips, turned the instrument around to face the front, and finished carefully prying the large housing off the front panel. That left the frequency pointer still mounted to the tuning shaft, and access to the pair of meter lamps, one on each side of the shaft, underneath that large green disc behind the knobs. I replaced the two burned out lamps with new ones, then carefully returned the scale housing, seated it flush with the panel, and restored the two large tuning dials. Now the Frequency Dial lights up.
The Output Level control was behaving raspy, as well as the meter when muting the generator wasn't going all the way down to zero, suggested I had some caps to change. I didn't find any date codes inside, but would guess this was built in the early 70's. I was able to replace the main power supply caps easily, though the output filters of the supply weren't really accessible without having to remove a lot of wires from the harness, so there, I did resort to clipping the old caps off right at the body, leaving long leads to which I was able to wrap my new caps around and quickly solder them into place with a small heat sink clip at the PCB end of the left-over wires, so I didn't damage the PCB solder joints.
The Level Control was the hardest part to restore. Wire Wound pot, and hard to extract. I had to remove a shielded wire and the source/ground wires to it, having to reach in with the soldering iron and grip the wires. Easier removing then putting back together, for sure. I opened the pot's cover, carefully wire-brushed the wiper surface at the two ends where it was raspy, then applied Caig contact lubricant, exercised the control, and put it back into place, successfully re-soldering the wires. Now the level control is well behaved without any of the discontinuities I was getting.
It also has a step attenuator, accessible in the ATT position of the Impedance Matching switch, which provides 10dB steps from 12V down to 120uV full scale, output thru the B & K shielded socket (I have one of their BNC adapters installed in that connector).
I see these instruments from time to time on ebay for not much money. There's an earlier version that's all tubes, with the meter assembly on the outside of the panel, rather than recessed like this is. The smaller B & K 1023 that sits atop a stack of instruments (top Grn box below the headphones in the last picture) on my bench usually fetches several hundred dollars. It took years to find one affordable. So, after the basic maintenance, I have another solid workhorse that I can park over at the rental depot and start digging into all the Marshall, Orange, Fender, Ampeg and loads of others to cobble cabinets back together. We're not set up for doing re-coning here. We had considered that when I came on board back in 2009, but, the inventorying of so many different cone kits, and the limited shelf life of adhesives........it was just cheaper to either send the salvageable speakers out to be re-coned, or replace them. Still costly, but, should be another interesting adventure.
In my shop at the main rehearsal studio complex, I have a smaller successor to the B & K 1022 (the B & K 1023), which, like it's predecessor, can drive speakers directly at low (but adequate) wattage (7W for the 1023, 2.5W for the 1022). This has always been adequate to use to drive the speakers in any of the combo amps I have up on the bench, when checking for blown, buzzing, and rattles without going thru the combo's amp to do that. For the larger bass cabinets....8-10's & such, I'll have one of my shop power amps to supplement for higher wattage.
It had been several years since I had this 1022 BFO powered up, and did know it needed a little work. I moved it to the bench, plugged in my IEC Male to Nema 5-15 Female adapter, it having a Nema 5-15P Male Pins on the recessed power connector, and powered it up. The Meter lamps and Frequency Scale lamps were all dead, so the only hint it woke up was the low current indication on the power analyzer feeding it, and, in switching it on and off, seeing the meter move from the power transient. Initially, I wasn't getting any output. I rotated the Automatic Scanning switch (used for local/external frequency scanning), and that woke it up. So, switch contacts on that need attention.
I moved a known working 12" woofer to the bench, and connected it to it's Matching Transformer output terminals, set it for 6 ohms.....the one normally used for driving speakers. I printed out the Frequency Calibration procedure from the operators' manual, and set the frequency dial to 60Hz, as this instrument uses Line Frequency as a scale reference using a Beat Frequency procedure to calibrate it. Set the Oscillator level to mid-scale, and pressing the momentary Power Frequency Beat button in, I first used the Fine Frequency control to try and find the beat frequency. No luck, so set that Fine Freq control back to mid-position, and used the recessed Coarse screwdriver control and adjusted it, finding the beat frequency, where the output level meter is now swinging considerably about the mid-point. Went back to the Fine Control, and finally achieved a steady reading between either direction where it would be swinging again. Checked the tuning by adjusting the Frequency to 120Hz, and all was fine.
What I've always loved about the Bruel & Kjaer generators is their frequency knob lets you sweep 10 octaves with one turn of the wrist. While the frequency range on this 1022 is 20Hz-20kHz, you can tune it lower than 20Hz. Setting the frequency dial to 20Hz, with the Frequency Increment set to 0Hz, you can then carefully detune to the left. If you go down 20Hz, you'll stop the oscillator, and if a speaker is connected via the output matching xfmr, it will object loudly. But, going that low, I can set the output to around 2V or so, and can take it down to a couple hz (detuning by 18Hz.
At these low frequencies, if there is any cone rubbing problems, you can both hear it and often see it......sometimes spot the cone separating from the surround or on the spider suspension below the cone. There's plenty of force being applied to the speaker. Plus, these oscillators have modulation provisions....warble tone. I tend to use warble tone from them when checking speakers as it's easier to listen to, and you can set both the rate and bandwidth of the modulation. Even use it for limited low frequency sweep, using 1Hz rate and 100Hz bandwidth, setting the Frequency dial to 120Hz....it will sweep from 20HZ to 220Hz, or even greater, setting the dial to a higher frequency. You wouldn't want to let it go below 0Hz though.
When I began restoring this, I placed the face of the instrument down on three short 2 x 4's, so I could remove the four special long metal shoulder washers that hold the housing to four long threaded shafts attached to the frame of the chassis, and lifted off the housing. Then, moved back to the bench, facing the rear of the unit. I didn't get any images inside this, but it's very similar to that of the 1024 Sine-Random Generator I restored a couple years ago.
The Meter and Frequency Scale lamps look like 3AG-style fuses (1/4" dia x 1-1/4" long), 6.3V/250mA. I had a small stash of them, and also checked to see just how common they were by googling 'fuse-type lamps', finding prices ranging from $1.10 thru $1.65 or more from a variety of sources. The meter lamps (two of them) were mounted in open-frame clips, only one installed, burned out. I didn't have my service manual here, so I wasn't sure if they're in series or parallel. Put two new lamps in, checked with the power applied, and now had the meter illuminated. The Frequency Scale lamps are harder to get at. I had to remove the smaller concentric Fine Tune knob, then remove the larger Frequency knob, then turn the instrument around to face the back, and using a long metal shaft, I was able to tap on the four plastic pegs from the large black scale housing, driving them forward in their tensioned holding clips, turned the instrument around to face the front, and finished carefully prying the large housing off the front panel. That left the frequency pointer still mounted to the tuning shaft, and access to the pair of meter lamps, one on each side of the shaft, underneath that large green disc behind the knobs. I replaced the two burned out lamps with new ones, then carefully returned the scale housing, seated it flush with the panel, and restored the two large tuning dials. Now the Frequency Dial lights up.
The Output Level control was behaving raspy, as well as the meter when muting the generator wasn't going all the way down to zero, suggested I had some caps to change. I didn't find any date codes inside, but would guess this was built in the early 70's. I was able to replace the main power supply caps easily, though the output filters of the supply weren't really accessible without having to remove a lot of wires from the harness, so there, I did resort to clipping the old caps off right at the body, leaving long leads to which I was able to wrap my new caps around and quickly solder them into place with a small heat sink clip at the PCB end of the left-over wires, so I didn't damage the PCB solder joints.
The Level Control was the hardest part to restore. Wire Wound pot, and hard to extract. I had to remove a shielded wire and the source/ground wires to it, having to reach in with the soldering iron and grip the wires. Easier removing then putting back together, for sure. I opened the pot's cover, carefully wire-brushed the wiper surface at the two ends where it was raspy, then applied Caig contact lubricant, exercised the control, and put it back into place, successfully re-soldering the wires. Now the level control is well behaved without any of the discontinuities I was getting.
It also has a step attenuator, accessible in the ATT position of the Impedance Matching switch, which provides 10dB steps from 12V down to 120uV full scale, output thru the B & K shielded socket (I have one of their BNC adapters installed in that connector).
I see these instruments from time to time on ebay for not much money. There's an earlier version that's all tubes, with the meter assembly on the outside of the panel, rather than recessed like this is. The smaller B & K 1023 that sits atop a stack of instruments (top Grn box below the headphones in the last picture) on my bench usually fetches several hundred dollars. It took years to find one affordable. So, after the basic maintenance, I have another solid workhorse that I can park over at the rental depot and start digging into all the Marshall, Orange, Fender, Ampeg and loads of others to cobble cabinets back together. We're not set up for doing re-coning here. We had considered that when I came on board back in 2009, but, the inventorying of so many different cone kits, and the limited shelf life of adhesives........it was just cheaper to either send the salvageable speakers out to be re-coned, or replace them. Still costly, but, should be another interesting adventure.
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