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 Post subject: Re: NO audio but proven osc coil function
PostPosted: Feb Mon 11, 2019 1:57 pm 
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Joined: Jan Wed 07, 2015 10:39 pm
Posts: 202
Location: Jamison PA
Yes, I am going to keep the set. I have two of them and the next one will be easier I hope. One cabinet is done and the other is getting a grill made for it.

This is the 3rd Crosley with the Synchonode vibrator that I have. The other is a United Motors(Delco) 4049 that is made by Crosley and is also a 32v set. They all feature the seperate 5 pound rectangular power chassis box mounted upside down at the top of the cabinet. It features a crosley made vibrator wrapped in a felt and sealed in a rectangular coffin suspended by rubber anchors, a power transformer, two chokes, plus the electrolytics and related caps. I was forced to buy a solid state DC to DC converter for the 4049 as the vibrator box and transformer were sent out in the mail and never returned. It works well, just no buzzing.....

I've only seen one question on this board in the search for a Crosley 159. I may be the only person with 2, but who knows??

Would a Simpson 260 meter have the impedance needed to measure the voltages?. If not any recommendations??

I use a digital one, as the needle on the others is always hard to read......older eyes you know....

Thank you

Mike


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 Post subject: Re: NO audio but proven osc coil function
PostPosted: Feb Mon 11, 2019 3:00 pm 
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Location: Victoria, Australia
One must be careful with solid state Vibrators. Conventional Mechanical vibrators (not synchronous where there is no rectifier) are in the main not fussy about polarity. The solid state one nearly always is. There is normally a very HV cap on the vibrator, those had a massive attrition rate. I would other than it, recommend wax paper caps there, be replaced with 630V types.

The only issue with digital will be that where there are high value resistors a digital will read higher, but they can get into serious strife with dirty fluctuating DC and mechanical vibrators create dirty DC with spikes.

Marc


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 Post subject: Re: NO audio but proven osc coil function
PostPosted: Feb Mon 11, 2019 3:11 pm 
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delco32 wrote:

Would a Simpson 260 meter have the impedance needed to measure the voltages?. If not any recommendations??

I use a digital one, as the needle on the others is always hard to read......older eyes you know....

Thank you

Mike

A VOM such as the 260 is closer to what was used in "the old days". BUT: I find it better to just use a modern high-impedance meter** and make the appropriate adjustments. If nothing else, just look up the tube in question to see "typical" voltages. With most tubes, if you are within 25% or so of the typical values, the set is going to play.


**All things equal, you are better off with the accuracy of the high-impedance meter, with no need to make corrections every time you measure something. Also, if you use 2 different kinds of meters, you will need to remind yourself when a correction is needed.

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"It's always something". --Gilda Radner (1946 - 1989)


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 Post subject: Re: NO audio but proven osc coil function
PostPosted: Feb Mon 11, 2019 4:59 pm 
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Joined: Jan Tue 16, 2007 7:02 am
Posts: 2854
Location: Lexington, KY USA
Many of the old schematics specified a 1000 ohms per volt meter for the listed voltages. The meter's resistance depends on the 1000 ohms per volt number and the full scale voltage of the range chosen for use. Unfortunately it was unusual to mention the voltage range setting used, so you cannot actually determine how much load their meter imposed on the circuit.

A 1000 ohms per volt meter generally uses a 1mA meter movement with a series resistor to measure voltage. This meter would have a resistance of 10,000 ohms for a 10 volt range, and 500,000 ohms for a 500 volt range.

A Simpson 260 has a 50uA movement, for 20,000 ohms per volt. So it imposes a much smaller load on the circuit, but one that can still be significant. A 500 volt DC range would have 10,000,000 ohms impedance.

Many modern DMMs have a constant 10,000,000 ohm input impedance for all DC ranges. The ohms per volt value is different for each range, but generally much higher than what the old analog meters had. The classic VTVMs ran a constant 11,000,000 ohms for the DC ranges.

There are exceptions. Some analog meters did not have 1mA or 50uA movements. Some switched different resistors across the movement to provide more ranges, so the meter might have two or more ohms per volt sensitivity values, depending on the settings. Some DMMs have different input resistances. Meters for electricians may have lower input resistances to provide a small intentional load. The "free" meters from H-F tend to have only 1,000,000 ohms impedance on their DC ranges. Some lab-type meters offer higher impedances, sometimes only on particular ranges.

If you want to recreate the loading of the old service meter, you don't have to actually use such a meter, an external load resistor can get you the same reading. I guess it would be possible to assemble a range switch and a few resistors in a box then use a modern meter as a readout.

The suggestion to analyze the circuit to see what the correct voltages should be is a good one. You can ask here on the ARF, and someone will help with this, until you are confident doing it by yourself.

Ted


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 Post subject: Re: NO audio but proven osc coil function
PostPosted: Feb Mon 11, 2019 7:42 pm 
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Usually Lurking wrote:

The suggestion to analyze the circuit to see what the correct voltages should be is a good one. You can ask here on the ARF, and someone will help with this, until you are confident doing it by yourself.

Ted

It is very often useful to make a "DC map" of the set. This shows all of the major DC paths, starting and ending at the supply. It also allows you to calculate an internally consistent set of values for the voltages and currents. For tubes, these can be compared to the data sheets.

Basically, just draw the major paths and enter anything that is known---eg the voltage out of the rectifier, or one or more tube plate voltages. Then, make educated guesses at the other values and "do the math"---repeat as required. ((fancy way of saying "trial and error"))

I have tried to automate this process with limited success.....

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"It's always something". --Gilda Radner (1946 - 1989)


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 Post subject: Re: NO audio but proven osc coil function
PostPosted: Feb Mon 11, 2019 11:43 pm 
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I do have a simplified circuit of just the voltmeter part of an AVO here in a book. if one would find this more understandable in pictures? They were (on DC) 1000 opv on one low range & 500 opv thereafter.

Marc


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 Post subject: Re: NO audio but proven osc coil function
PostPosted: Feb Thu 21, 2019 1:55 pm 
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Joined: Jan Wed 07, 2015 10:39 pm
Posts: 202
Location: Jamison PA
Gentlemen,

The finished product. I am making the rubber mounts for the power chassis, but it is working outside of the cabinet at the moment. This is one of two 159's that I am doing....

Thank you

Mike


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 Post subject: Re: NO audio but proven osc coil function
PostPosted: Feb Thu 21, 2019 11:00 pm 
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Location: Victoria, Australia
In cases where there are no quoted voltages, no meter type listed, or I have reverse engineered the thing, I do like to jot down things, measured like coil resistances and voltages on elements, plus what type of meter was used: Once its going. That then provides a reference, should it dare to fail again, or (common) I get another. The latter reflected with one popular model, where I have refurbished around twelve of them.

In respect of test instruments, from basic to complex. One has to understand how they work and their limitations in order to fully understand what information they are presenting to you. As I have written many times; Used inappropriately, both analogue & digital meters can lie and much modern stuff cannot handle the RF & voltages found in tube radio.

Cabinet looks really good.

Marc


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