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 Post subject: Rockola 1468 help
PostPosted: Sep Sun 10, 2017 12:23 am 
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I have a Rockola 1468 amplifier and power supply. Nothing else.
I recapped the mp section and on the power supply I replaced the selenium rectifier with a bridge rectifier.

What I have found is that there is a coil in the power supply I can push it and power goes to the plates of the tube when I let go it cuts it off.

Is there a way I can bypass this now by engaging the relay(which I'm not quite sure how to do. I believe adding voltage to the coil would engage it but I'm not sure.)

Thanks,
Jason
Schematic included I have 2 . The second one shows the jones plug connections.
http://arcarc.xmission.com/PDF_Jukebox/Rockola/Schematics/1468-75.pdf
https://drive.google.com/open?id=0B6x_Y11FgnCHc3VlU2ZHT185eEU


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 Post subject: Re: Rockola 1468 help
PostPosted: Sep Sun 10, 2017 7:46 pm 
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My guess is if you connect pin 2 ( yellow-green wire) to pin 3 (black-white wire) of the square four pin connector it will energize the relay. You could install a switch inline with this connection. The relay not only controls the B+ Supply but also increases the filament voltage to full rated. When the relay isn't energize the input line voltage is applied to the primary winding in such a way that the filaments only receive a lower (standby) voltage. This allows the amplifier to come up faster when it is used normally.

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 Post subject: Re: Rockola 1468 help
PostPosted: Sep Sun 10, 2017 11:25 pm 
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Thanks that worked like a charm.
It also has the cement round resistors that say A8KS 940ohm 140833. It has 3 connections
One is the 3k off the voltage doubler the other is the 1.5k going to the plate pin1 of the 6cy7.
My voltages were wrong, but the resistor seemed to ohm out fine( all leads disconnected)
I subbed a 1.5k and a 3k resistor in and the voltages are in line with what I should be seeing.

Will a resistor short out (it appeared like it was doing no resisting) Voltage drop just under a volt. They are replaced but I normally see resistors open or higher in value.

Thanks,
Jason


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 Post subject: Re: Rockola 1468 help
PostPosted: Sep Mon 11, 2017 3:55 am 
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I'm not sure exactly how that resistor is constructed, its probably a wirewound type. I suppose anything is possible. Glad it is working for you.

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"Excellent!" I cried. "Elementary," said he. - Sherlock Holmes


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 Post subject: Re: Rockola 1468 help
PostPosted: Sep Tue 12, 2017 1:45 am 
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940 ohm Standee power resistor has a 3k and a 1.5k resistor in the same body. It has 3 terminals and looks like attached photo.

Also there is a mute plug on this amp. Do you think it be the reason I cannot pass signal through the amp? I can input at the Phase Invertor and get audio but nothing before that.

Thanks,
Jason


Attachments:
standee.jpg
standee.jpg [ 30.86 KiB | Viewed 893 times ]
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 Post subject: Re: Rockola 1468 help
PostPosted: Sep Tue 12, 2017 4:56 pm 
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Sorry, I guess I thought you had everything working. I've seen wire wound resistors go open, sometimes increase in value, but most of those would of had a linear construction, since this resistor has terminals on the end perhaps it could short. I don't know why it would be called 940 ohm though maybe that is more of a part number. It isn't a standard part.
Do you have anything connected at the volume control socket?
I don't think it would help to activate the mute relay.

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 Post subject: Re: Rockola 1468 help
PostPosted: Sep Tue 12, 2017 11:12 pm 
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Location: Santa Clara, CA
Jukebox amplifiers have a mute relay that cuts off the audio when the changer mechanism is operating so that mechanical noise is not heard through the speakers when the mechanism is scanning or loading/unloading a record. If you do not need that feature, it would be best to wire some bypass jumpers so that the relay is not needed...there is no sense in wiring the relay so it is on all the time, you don't need that coil cooking away, or the switch contacts in circuit.

Also, some juke manufacturers used the same idea of a relay that would switch the tube power to a lower, "idle" state that would be fired back up to full voltage just before the needle touches down. Again, bypass this relay if you don't need that function, rather than attempt to keep a relay permanently energized.


Last edited by Bob E. on Sep Tue 12, 2017 11:14 pm, edited 1 time in total.

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 Post subject: Re: Rockola 1468 help
PostPosted: Sep Tue 12, 2017 11:13 pm 
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I have wired in a 25k pot. I'm gonna print out a schematic and take it to the shop and start scoping the stages to see where it starts and stops.

Thanks,
jason


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 Post subject: Re: Rockola 1468 help
PostPosted: Sep Tue 12, 2017 11:17 pm 
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Bob E. wrote:
Jukebox amplifiers have a mute relay that cuts off the audio when the changer mechanism is operating so that mechanical noise is not heard through the speakers when the mechanism is scanning or loading/unloading a record. If you do not need that feature, it would be best to wire some bypass jumpers so that the relay is not needed...there is no sense in wiring the relay so it is on all the time, you don't need that coil cooking away, or the swirl contacts in circuit.

Also, some juke manufacturers used the same idea of a relay that would switch the tube power to a lower, "idle" state that would be fired back up to full voltage just before the needle touches down. Again, bypass this relay if you don't need that function, rather than attempt to keep a relay permanently energized.

I was given just the amp and power supply to try and get running for a guy a I know.
Engaging the relay is just while I have it on the bench. Once I give it back it's going in the jukebox. So given that I have just the amp and power supply do you think the Mute function is in play at all in this scenario. My plan is to start scoping the circuit to find where signal stops and starts.
Right now I get signal from the 1st grid of the Phase inverter but nothing before.

Thanks,
Jason


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 Post subject: Re: Rockola 1468 help
PostPosted: Sep Tue 12, 2017 11:45 pm 
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Ah, OK, if it's going back into a juke, you definitely want to retain those relays. Still, rather than futz around trying to energize the relay on the bench (unless you are troubleshooting the relay), you could bypass with alligator leads temporarily. I'm not sure what kind of mute relay scheme Rockola used.


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 Post subject: Re: Rockola 1468 help
PostPosted: Sep Wed 13, 2017 12:27 am 
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Location: Dallas, TX
From the schematics you posted, it looks to me that activating the relay would cause it to mute.
You already have the power relay taken care of.
I didn't realize either this was going back in the jukebox. No harm done though.
Is this amplifier the mono or the stereo version?
You posted the schematic for both (or most of them).

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 Post subject: Re: Rockola 1468 help
PostPosted: Sep Wed 13, 2017 12:40 am 
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It is the mono version. I included the Stereo schematic because the power supply is the same for both.


Thanks,
jason


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 Post subject: Re: Rockola 1468 help
PostPosted: Sep Fri 22, 2017 1:07 am 
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Well after a bout of sickness I'm getting back to this. I loose vol between the vol connector and the PI. I think it comes down to the Vol pot looking at the attached schematic I'm seeing 4 connections to the pot I only have a standard 25k pot to test with.

Any ideas?
attached a schematic that refers to what I'm questioning.
Thanks,

jason


Attachments:
scanm0011.pdf [125.65 KiB]
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 Post subject: Re: Rockola 1468 help
PostPosted: Sep Fri 22, 2017 1:26 am 
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Looks like five connections to me, two of them have to do with producing a 'loudness' curve on the volume control, not essential. Pin 2 would connect to one end of the volume control, pin 1 to the center wiper of the volume control and pin 4, the ground, to the other end of the control.

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 Post subject: Re: Rockola 1468 help
PostPosted: Sep Sat 23, 2017 10:29 pm 
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Ok I jumpered pin1 and pin2 to make vol full blast for testing. Somewhere's somethings still off. If you can help.

Thanks,
Jason

.01v 1k signal vol,treble, bass max Speaker switch in Phono only, AVC off and 8ohm load

voltages all VDC
Concerns I think are pin5 voltage on EL34's, On the PI Pin7 the 30v is 40v low( most of the voltages being a little higher than the schematic I'm going with cause I believe its ok. The low voltages not so much.)
The driver tube 6cy7 Pin7 the -1vdc( a cap with slight leakage)
The 12ax7 Pin2 -.03 leaky cap? Pin7 -31vdc big leaky cap or touching wire. Pin9 54vdc( appears AC and DC on the heaters is that ok?

Thanks,
nosaj
12ax7
pin1 160
pin2 -.03
pin3 1.81
Pin6 132
Pin7 -31
Pin8 1.81
Pin9 54vdc

V2
pin1 271
Pin3 124
Pin7 -1
Pin8 1.2
Pin9 159

V3
Pin1 228
Pin2 96
Pin3 104
Pin7 30.26
Pin8 -2.89
Pin9 1.06

EL34
Both tubes

Pin1 41.28 / 52vdc
Pin2 52 both same
Pin3 304 / 300
Pin4 307 / 305
Pin5 -7 / -13
Pin7 52v


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 Post subject: Re: Rockola 1468 help
PostPosted: Sep Sun 24, 2017 6:03 am 
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Location: Dallas, TX
reeves03 wrote:
Ok I jumpered pin1 and pin2 to make vol full blast for testing. Somewhere's somethings still off. If you can help.

Thanks,
Jason

.01v 1k signal vol,treble, bass max Speaker switch in Phono only, AVC off and 8ohm load

voltages all VDC
Concerns I think are pin5 voltage on EL34's, On the PI Pin7 the 30v is 40v low( most of the voltages being a little higher than the schematic I'm going with cause I believe its ok. The low voltages not so much.)

That screen voltage (pin 7) is low, so that might cut the signal off. Look at the 4.7M and the 330K that form a voltage divider that provides that voltage.

The driver tube 6cy7 Pin7 the -1vdc( a cap with slight leakage)
The 12ax7 Pin2 -.03 leaky cap? Pin7 -31vdc big leaky cap or touching wire. Pin9 54vdc( appears AC and DC on the heaters is that ok?

The 52-54V is coming through the hum control from the cathode bias of one of the EL34s, and I it seems high, should be near 29V. That would be a sign that the output tubes are pulling too much current. the plate voltage being low also points to this. Careful it doesn't burn out the output transformer.
I would replace any cap that isn't ceramic or mica. Go through the resistors and measure them, replace any that are out of tolerance,

Thanks,
nosaj
12ax7
pin1 160
pin2 -.03
pin3 1.81
Pin6 132
Pin7 -31
Pin8 1.81
Pin9 54vdc

V2
pin1 271
Pin3 124
Pin7 -1
Pin8 1.2
Pin9 159

V3
Pin1 228
Pin2 96
Pin3 104
Pin7 30.26
Pin8 -2.89
Pin9 1.06

EL34
Both tubes

Pin1 41.28 / 52vdc
Pin2 52 both same
Pin3 304 / 300
Pin4 307 / 305
Pin5 -7 / -13
Pin7 52v

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"Excellent!" I cried. "Elementary," said he. - Sherlock Holmes


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 Post subject: Re: Rockola 1468 help
PostPosted: Sep Sun 24, 2017 6:31 pm 
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So to figure out of tolerance you would take what it's supposed to be and multiply by 10%?

Thanks,
Jason and Elizabeth


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 Post subject: Re: Rockola 1468 help
PostPosted: Sep Sun 24, 2017 8:24 pm 
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Location: Dallas, TX
reeves03 wrote:
So to figure out of tolerance you would take what it's supposed to be and multiply by 10%?

Thanks,
Jason and Elizabeth


Well, it kind of depends. Some should to within 10% or 5%. I'm not sure how old you machine is but very old electronics were 20%. You can only buy 10%, 5% and less today. Many just go with the 5%, they don't really cost more. There are more different values available in the 5% series, because they cover the 'gaps' in the 10% series values.
Do you have the parts list table? It usually gives the tolerance of the individual resistors. Sometimes the schematic says " All resistors are 10% unless otherwise indicated." or such. Another way to know is the fourth color band on the resistors, unless the color has changed with time and heat. No fourth band is 20%, silver is 10% and gold is 5%. The % means plus and minus so a 100 ohm resistor could be anywhere between 90 ohms and 110 ohms and be OK, a 220 ohm 5% could be 209 to 231 ohm. You have to be careful measuring the resistor while they are still connected because sometimes other resistors and components can effect the reading because they provide another path around the resistor you want to measure. If the capacitors are good they will block the paths, tube elements except the heater will also block the side paths. Sometimes you have to un-solder one end of the resistor, but once you do that you may as well un-solder the other and just replace it.
The other thing used to define a resistor is the wattage, most are 1/2 watt, some are 1 watt. The bigger they are the higher the wattage.

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"Excellent!" I cried. "Elementary," said he. - Sherlock Holmes


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 Post subject: Re: Rockola 1468 help
PostPosted: Sep Mon 25, 2017 12:49 am 
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i just been unsoldering one side quite a few were high. the 4.7 m measured about 5.7 meg. don't have one of those so will have to order one. Made my way from the output tubes and the phase inverter, Have the driver and the preamp to still go through.

Thanks,
Jason


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 Post subject: Re: Rockola 1468 help
PostPosted: Nov Wed 22, 2017 3:57 am 
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Just about got it working. When i was working on it tonight I thought I saw some of the diodes in the bridge rectifier flashing. Never having used these kind before. IN1083. Sure enough turning off the light you can see intermittant flashing inside the ceramic and then the voltages will fluctate. Considering using a newer bridge rectifier package that just bolts to chassis.

Jason


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