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 Post subject: Re: Rockola 1468 help
PostPosted: Jan Mon 29, 2018 7:02 am 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 755
Location: Dallas, TX
Yep. that's way too much ripple on pin 1. Also the DC voltage is too high.
Since pin 9 and 8 DC voltages are also high, the tube is drawing more current from the supply and that means the high pin 1 voltage isn't because there isn't enough voltage drop through the 1500 ohm resistor feeding the plates. Seems something is not right about the power supply. Doubler supplies do tend to have more ripple, so they usually have larger capacitors. Another possible problem is maybe the output stages are not doing there part to draw enough current to drop the supply voltage.
Measure the voltage coming from the power supply, that is the center tap on the output transformer primary.
EDIT: I didn't notice before that you said earlier that the voltage at the center tap was 470V instead of 420V. Also the supply voltage after the 3K was over 400V when it is supposed to be a little over 300V. The 470 might be because the silicon rectifiers have less drop that the selenium, but you should be seeing more than 100V drop across the 3K. I think you should recheck that resistor and its wiring. If too much current is drawn from a power supply the ripple will go up.

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 Post subject: Re: Rockola 1468 help
PostPosted: Feb Fri 23, 2018 3:12 am 
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Joined: Jun Sat 18, 2011 3:36 am
Posts: 1897
Location: Milton, FL 32570
Ok I tore out the power supply section and started over because when I started I was replacing a little her and a little there. and it was getting horrible looking. So I put in a tag strip so caps would be secured instead of floating. I'm not sure if I'm reading the schematic differently now but on the 220uf caps in the schematic I'm thinking I can just put the 100ohm from positive to negative on the cap.
I think I'm just tired and should wait till this weekend to look at it fresh.

jason


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 Post subject: Re: Rockola 1468 help
PostPosted: Feb Fri 23, 2018 8:38 pm 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 755
Location: Dallas, TX
reeves03 wrote:
Ok I tore out the power supply section and started over because when I started I was replacing a little her and a little there. and it was getting horrible looking. So I put in a tag strip so caps would be secured instead of floating. I'm not sure if I'm reading the schematic differently now but on the 220uf caps in the schematic I'm thinking I can just put the 100ohm from positive to negative on the cap.
I think I'm just tired and should wait till this weekend to look at it fresh.

jason

They should be 100K ohm, but yes that will work. Those caps are probably what is called bleeder resistors, they equalized the charging and will discharge the 200 uf caps when the power is off.
Looking back in the posts I see that you measured the voltages as being too high some time ago, but I didn't notice. You might have been working on another problem then.
The various drop in supply voltages as you move along the stages from the amplifier output section to the input section, depend on the current drawn in each section. The current drawn in each section depends on the voltage bias of the tubes in that section. I guess I am saying that things can get complicated. Hang in there.

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 Post subject: Re: Rockola 1468 help
PostPosted: Feb Sat 24, 2018 4:23 pm 
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Joined: Jun Sat 18, 2011 3:36 am
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Location: Milton, FL 32570
Well I'm not really sure how I even had it possibly working before. because When I soldered up the 5pin plug I reversed pins 2 and 4. Which when I tore the power supply out and started over Hooking up the caps in the voltage doubler would make the dim bulb go bright and the relay chatter. What I'm seeing is that the negative of one of the caps and the reversal of 2 and 4 was making a nasty short with the dim bulb saving the day.

Jason


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 Post subject: Re: Rockola 1468 help
PostPosted: Feb Sun 25, 2018 2:48 am 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 755
Location: Dallas, TX
reeves03 wrote:
Well I'm not really sure how I even had it possibly working before. because When I soldered up the 5pin plug I reversed pins 2 and 4. Which when I tore the power supply out and started over Hooking up the caps in the voltage doubler would make the dim bulb go bright and the relay chatter. What I'm seeing is that the negative of one of the caps and the reversal of 2 and 4 was making a nasty short with the dim bulb saving the day.

Jason

That's odd. Looks to me that reversing those wouldn't effect the operation. Pins 2 and 4 are the AC secondary of the power transformer. Also the 1 amp fuse should blow if there is too much current flowing. Try starting with the point marked 420VDC disconnected from the audio output transformer and the 3K ohm resistor. Maybe a rectifier is shorted. What bulb wattage are you using? It could be that when the circuit pulls enough current the bulb drops the voltage that the transformer gets and this isn't enough to power the relay. When the relay opens it cuts the power and thus the current the voltage across the bulb decreases and the cycle repeats. If you get the chattering relay to stop with a larger bulb and the 420V disconnected, connect the power without the dim bulb and measure the voltage on the 200 uf caps.
EDIT: In fact if you get to that point measure the AC voltage across pins 2 and 4 on that 5 pin connector.

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