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#1
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AMI B
Bought my first ami b model juke. extremely nice cosmetically. when i
turn it on the turn table just spins. . changer is at rest. the turn table plugs into the junction box. ones ive worked on before plugged into the amp. does the amp have anything to do with the turntable. i did replace the fuse and heard the relay in the box on the mechanism chatter briefly. all halp appreciated thanks norm. |
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#2
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AMI B
On 4/10/2011 9:16 AM, em pinball wrote:
Bought my first ami b model juke. extremely nice cosmetically. when i turn it on the turn table just spins. . changer is at rest. the turn table plugs into the junction box. ones ive worked on before plugged into the amp. does the amp have anything to do with the turntable. i did replace the fuse and heard the relay in the box on the mechanism chatter briefly. all halp appreciated thanks norm. Yes the amp has to power up and energize a relay for the TT motor. |
#3
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AMI B
On Apr 10, 11:16*pm, em pinball wrote:
Bought my first ami b model juke. extremely nice cosmetically. when i turn it on the turn table *just spins. . changer is at rest. the turn table plugs into the junction box. ones ive worked on before plugged into the amp. does the amp have anything to do with the turntable. i did replace the fuse and heard the relay in the box on the mechanism chatter briefly. all halp appreciated thanks norm. If it has a selenium rectifier in the 28vdc, this may be giving low output due to age. This may result in the voltage collapsing under load, then coming up again, repeating over and over and leading to the chatter as the voltage rises and falls. The relay is likely to be powered from a 28vdc supply Measure the DC voltage at the power supply box, especially when the relay chatters. (Note that I have never seen a model B, am giving general advice based on the G here.) |
#4
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AMI B
On Apr 13, 1:26*pm, kreed wrote:
On Apr 10, 11:16*pm, em pinball wrote: Bought my first ami b model juke. extremely nice cosmetically. when i turn it on the turn table *just spins. . changer is at rest. the turn table plugs into the junction box. ones ive worked on before plugged into the amp. does the amp have anything to do with the turntable. i did replace the fuse and heard the relay in the box on the mechanism chatter briefly. all halp appreciated thanks norm. If it has a selenium rectifier in the 28vdc, this may be giving low output due to age. *This may result in the voltage collapsing under load, then coming up again, repeating over and over and leading to the chatter as the voltage rises and falls. The relay is likely to be powered from a 28vdc supply Measure the DC voltage at the power supply box, especially when the relay chatters. (Note that I have never seen a model B, am giving general advice based on the G here.) Scrub that, After seeing Tony's post, I found the schematic, http://www.verntisdale.com/schem/ami-b.jpg The relay is indeed in the amp, and relay coil seems to be driven by (in series with) the valve output stage, seems to turn on the relay when there is sufficient current passing through the output stage. Seems a very odd way to design it. As a starting point, I would plug the TT directly into the mains, so you can play a record and see if the amp has sound for starters. The capacitor across the relay is another trouble spot worth looking at. If this is leaky, it could result in the relay coil dropping in and out depending on the audio. If the sound is no good, this is probably the cause of the relay not closing and holding correctly. |
#5
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AMI B
On Apr 12, 11:08*pm, kreed wrote:
On Apr 13, 1:26*pm, kreed wrote: On Apr 10, 11:16*pm, em pinball wrote: Bought my first ami b model juke. extremely nice cosmetically. when i turn it on the turn table *just spins. . changer is at rest. the turn table plugs into the junction box. ones ive worked on before plugged into the amp. does the amp have anything to do with the turntable. i did replace the fuse and heard the relay in the box on the mechanism chatter briefly. all halp appreciated thanks norm. If it has a selenium rectifier in the 28vdc, this may be giving low output due to age. *This may result in the voltage collapsing under load, then coming up again, repeating over and over and leading to the chatter as the voltage rises and falls. The relay is likely to be powered from a 28vdc supply Measure the DC voltage at the power supply box, especially when the relay chatters. (Note that I have never seen a model B, am giving general advice based on the G here.) Scrub that, After seeing Tony's post, I found the schematic,http://www.verntisdale.com/schem/ami-b.jpg The relay is indeed in the amp, and relay coil seems to be driven by (in series with) the valve output stage, seems to turn on the relay That goofy relay/cathode setup was designed to keep the machine from playing before the output tubes had warmed up. There was no stay-warm. The obvious problem is that as the tubes age cathode current decreases, it is probably low now and causing that "chatter" also if the filter across it dries up (very likely now) audio will appear across that relay. Frankly, AMI and later Rowe never did a good stay warm in their tube amps. After the above setup, they went to a scheme that opened the B+ from the 5U4 not just in standby, but -between records-! This really pummeled both caps and transformer. Their later stereo amps atleast used a bleeder resistor to keep a slight charge on the filters but really..who designed this stuff. I modded the gray amps in my H-I-J by adding a relay connected to the scan control which in-turn controlled the input power (AC) to the amp and changed the mute connections so that it didn't open the B+. I did notice that on the units with AVC box AMI actually used the unmuting inrush to hasten the AVC un-squelch (compression release) so I had to modify that circuit too. I considered the late-50s AMIs to be the best constructed and have the best potential for true sound quality, but there were some really odd engineering choices made. Rob when there is sufficient current passing through the output stage. *Seems a very odd way to design it. As a starting point, I would plug the TT directly into the mains, so you can play a record and see if the amp has sound for starters. The capacitor across the relay is another trouble spot worth looking at. *If this is leaky, it could result in the relay coil dropping in and out depending on the audio. If the sound is no good, this is probably the cause of the relay not closing and holding correctly. |
#6
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AMI B
On Apr 14, 7:05*pm, Rob in NYC wrote:
On Apr 12, 11:08*pm, kreed wrote: On Apr 13, 1:26*pm, kreed wrote: On Apr 10, 11:16*pm, em pinball wrote: Bought my first ami b model juke. extremely nice cosmetically. when i turn it on the turn table *just spins. . changer is at rest. the turn table plugs into the junction box. ones ive worked on before plugged into the amp. does the amp have anything to do with the turntable. i did replace the fuse and heard the relay in the box on the mechanism chatter briefly. all halp appreciated thanks norm. If it has a selenium rectifier in the 28vdc, this may be giving low output due to age. *This may result in the voltage collapsing under load, then coming up again, repeating over and over and leading to the chatter as the voltage rises and falls. The relay is likely to be powered from a 28vdc supply Measure the DC voltage at the power supply box, especially when the relay chatters. (Note that I have never seen a model B, am giving general advice based on the G here.) Scrub that, After seeing Tony's post, I found the schematic,http://www.verntisdale.com/schem/ami-b.jpg The relay is indeed in the amp, and relay coil seems to be driven by (in series with) the valve output stage, seems to turn on the relay That goofy relay/cathode setup was designed to keep the machine from playing before the output tubes had warmed up. There was no stay-warm. The obvious problem is that as the tubes age cathode current decreases, it is probably low now and causing that "chatter" also if the filter across it dries up (very likely now) audio will appear across that relay. Is the whole amp turned off when the mech is at rest then ? Frankly, AMI and later Rowe never did a good stay warm in their tube amps. *After the above setup, they went to a scheme that opened the B+ from the 5U4 not just in standby, but -between records-! This really pummeled both caps and transformer. *Their later stereo amps atleast used a bleeder resistor to keep a slight charge on the filters but really..who designed this stuff. Oh dear, I see the problem now. I guess they learnt with experience over time I was quite happy with the sound of these too, and the JEL amps, when they were set up properly. The G-80 I had sounded brilliant with records from that era, but with modern (80-90's) records, it showed its limitations. IIRC that the top end was cut off, as records back then didn't have the high frequency range of those later on. I modded the gray amps in my H-I-J by adding a relay connected to the scan control which in-turn controlled the input power (AC) to the amp and changed the mute connections so that it didn't open the B+. *I did notice that on the units with AVC box AMI actually used the unmuting inrush to hasten the AVC un-squelch (compression release) so I had to modify that circuit too. *I considered the late-50s AMIs to be the best constructed and have the best potential for true sound quality, but there were some really odd engineering choices made. Rob when there is sufficient current passing through the output stage. *Seems a very odd way to design it. As a starting point, I would plug the TT directly into the mains, so you can play a record and see if the amp has sound for starters. The capacitor across the relay is another trouble spot worth looking at. *If this is leaky, it could result in the relay coil dropping in and out depending on the audio. If the sound is no good, this is probably the cause of the relay not closing and holding correctly. |
#7
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AMI B
On 4/14/2011 5:05 AM, Rob in NYC wrote:
Frankly, AMI and later Rowe never did a good stay warm in their tube amps. After the above setup, they went to a scheme that opened the B+ from the 5U4 not just in standby, but -between records-! This really pummeled both caps and transformer. Their later stereo amps atleast used a bleeder resistor to keep a slight charge on the filters but really..who designed this stuff. AMI was always "different". Even in the later solid state amps they went the opposite way and leave the amp powered up as long as the juke is plugged in, even if it's turned off! Never quite understood that one. Tony |
#8
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AMI B
On Apr 15, 1:24*am, Tony Miklos wrote:
On 4/14/2011 5:05 AM, Rob in NYC wrote: Frankly, AMI and later Rowe never did a good stay warm in their tube amps. *After the above setup, they went to a scheme that opened the B+ from the 5U4 not just in standby, but -between records-! This really pummeled both caps and transformer. *Their later stereo amps atleast used a bleeder resistor to keep a slight charge on the filters but really..who designed this stuff. AMI was always "different". *Even in the later solid state amps they went the opposite way and leave the amp powered up as long as the juke is plugged in, even if it's turned off! *Never quite understood that one. Tony And to make it even more confusing, this is done in only the 120v models. 240v ones - all turns off, including the amp. (this is also documented in the shop service manual) I think in the manual it was to allow paging, and a "remote power on" device behind the bar. Still doesn't explain why the 240v models missed out on this. I only ever had one location where they wanted a power switch behind the bar, and in this case we just ran mains cable from out of the juke to a standard household 10a light switch behind the bar next to the volume controls. |
#9
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AMI B
On Apr 14, 10:24*am, Tony Miklos wrote:
On 4/14/2011 5:05 AM, Rob in NYC wrote: The biggest probelm I had with Rowe SS amp was MM1 (I still have two MM1 hideaways in service in retro diners) . Again, they had the amp mains switched -between records- and to make matters worse, the muting relay actually shorts the output of the amp rather than just the pre- in. This combination is deadly to output transistors as the switching transient thump hits a dead short! The biasing diode setup was primitive but workable. I added a relay to the scan control that turned them amp and TT motor on at the beginning of a session (that also eliminated a micro sw) and reworked the whole mute and AVC system as well as improving high response in the preamp and driver sections. There is still very slight crossover distortion but the amps is not used at low enough levels for this to matter. The physical build quality of the Rowe amp/machines was very good but again, didn't anyone review these designs? Frankly, AMI and later Rowe never did a good stay warm in their tube amps. *After the above setup, they went to a scheme that opened the B+ from the 5U4 not just in standby, but -between records-! This really pummeled both caps and transformer. *Their later stereo amps atleast used a bleeder resistor to keep a slight charge on the filters but really..who designed this stuff. AMI was always "different". *Even in the later solid state amps they went the opposite way and leave the amp powered up as long as the juke is plugged in, even if it's turned off! *Never quite understood that one. Tony |
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