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 Post subject: Re: Collins R-390 solid state regulator
PostPosted: Nov Sat 04, 2017 2:02 pm 
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Decided to try just the reference tubes and as expected without the 200 volt zener they worked as they should.

At no load the B+ was quite stable at 180Vdc, but when I loaded the circuit and I increased B+ high enough so the tubes would reliably start the output voltage was almost 183Vdc with the reference tubes being kept under 3mA current so I see now why the reference tubes weren't used in a solid state regulator design like this simple one.

In fact I wonder if one could get better performance from the original regulator if the reference tubes were substituted with a 180 volt zener?


EDIT:

At a unregulated B+ of 250Vdc and a load of 126mA the heatsink is getting very warm. Isn't too hot to the touch and I can hold my hand on the heatsink for at least 10 seconds.

I may need to look into installing a small fan on the heatsink drawing air through the heatsink and I'll put something inside to divert the air from the fan out the holes in the side of the case.

Will know for sure when I get the 180 volt regulator installed and the series zeners as I can then use a lower B+ voltage which will equal less power being dissipated by the pass transistor.

Wonder if there's any harm in having the driver transistor mounted to the heatsink or will that serve as some sort of temperature compensation?

The variable voltage Ac supply I'm using to power the transformer has an air intake on the front panel so I placed the heatsink in front of the intake so that air would move over the heatsink.

Cooled the heatsink down quite nicely.

With a cool heatsink the 200 volt zener is reading 200.28 Vdc
With the heatsink as hot as it will get the 200 volt zener is reading 201.37 Vdc.

The ripple voltage is 24.6 Vrms, but I suppose that will drop once I get everything right using the zeners to drop the B+ as that adds another filter cap in the circuit.
This is something I want to have thoroughly tested before it sees any use with my R-390.


EDIT 2:

Was wondering how I could power a small 12 volt fan if needed and I thought why not put the fan across one of the 20 volt zeners with a suitable series resistor. The ideal would be to make the last zener a 12 volt one so there would be no resistor necessary, but I'd have to order one.

So here's what I came up with.

Attachment:
Regulator 7.jpg
Regulator 7.jpg [ 74.97 KiB | Viewed 447 times ]


Some measurements using the reference tubes and a 190 ohm resistor between the first and second 10uF filter caps.

Attachment:
Regulator measurements.jpg
Regulator measurements.jpg [ 22.37 KiB | Viewed 447 times ]


Further measurements.

Attachment:
Regulator measurements 2.jpg
Regulator measurements 2.jpg [ 27.32 KiB | Viewed 447 times ]


The initial tests prove that the basic circuit is viable and that the transistors chosen will work properly.

Once the parts are in and installed I will then have the final measurements.

When I am sure everything is ok I will leave the circuit running for the greater part of an 8 hour work day and see how well the circuit holds up along with taking another set of measurements to see if anything has changed to where it causes the regulated voltage to exceed the +/- 1Vdc spec of the original regulator circuitry. Will also use other series resistors with the load so that I can see what the effect of a varying dc load is on the supply to see that the output voltage remains within spec.

I will first test it without the fan just to see how hot the heatsink gets and its effect on the voltages.

If everything then looks good I will install the regulator on the audio chassis and install the audio chassis and power supply back in my R-390 and see how well it works in the receiver.


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 Post subject: Re: Collins R-390 solid state regulator
PostPosted: Nov Tue 07, 2017 1:53 pm 
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Ok I'm going to need some help here.

The spec is +/- 1Vdc which it does seem to meet at 180mA B+ current.

If I unload the circuit completely (not sure what the minimum B+ load of the R-390 is) the voltage is around 183 Vdc.

The zeners on the other hand I needed four not five and they run very hot. In fact they were hot enough at the leads to start melting the plastic of the clip leads I used to connect them.

Each is a 5 watt zener and according to the measurements I get which is 95.8 Vdc dropped across an 80 volt zener string with each zener having a tolerance of 5% which is +/- 1 volt and looking at the data the zeners are operating within their limits so I guess the zeners getting that hot is just normal. I may try to put them against the audio chassis just to see if that will reduce their temperature.



EDIT:

Pretty sure that a 5 watt zener should not get hot enough to melt solder so the zeners even though they seem to be running within their current limit will not work.

Also I noticed another problem.

When I first turn the circuit on with everything at room temperature regulated B+ is 178.5 Vdc then slowly increases as things warm up.

I seemed to get much better regulation using the two zeners and the reference tubes. They don't reliably start on 200Vdc though, but I can put a 20 volt zener in series with the 200 volt zener which will give 220Vdc and that will ensure the reference tubes start.

What the article failed to mention is whether the tests were done when the receiver was first turned on soon as the tubes warmed up or if the test was done after the receiver was operating for awhile.

I am going to try the reference tubes again using the 20 volt zener in series with the 200 volt zener and see if the regulation is any better from cold startup to the temperature everything stabilizes at.

The problem there is the reference tubes when they come on get bright briefly which might be the 22uF cap discharging some so I may swap it with the 2.2uF cap.

What I need to do is use the 180 volt regulator and try it in my R-390 under actual operating conditions and see how it does.

So long as it meets spec under actual operating conditions then I'll be happy.

I don't see how the circuit could have ever met spec.

Don't know if my test setup is faulty or if the circuit really does vary over that wide a voltage range.

I'm sure the problem has to be where the zeners are mounted given they are where the heat is.

If I were to move them to a cooler spot such as mounting them under the chassis to the regulator tube socket terminals perhaps they would be more stable.

I do know the regulator heatsink will need a fan.

Unless anyone knows of a way to add feedback to this circuit I may just ditch it in favor of the original and hope my weak pass tubes never go completely bad and that when they do I can find a reasonably priced pair.


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 Post subject: Re: Collins R-390 solid state regulator
PostPosted: Nov Tue 07, 2017 4:58 pm 
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Ok I've tried the circuit and it isn't good enough for me.

What I would like to do is to do the circuit right as in properly substitute for the original regulation circuitry in the R-390 or if there's a way to just substitute for the pass tubes that will work as well.

The following is pertinent to just substituting the pass tubes if possible to do so.

The one difference mine has compared to the stock R-390 is the 18K power resistor as seen on the regulator schematic broke so I replaced it with a 25K power resistor with adjustable tap which I set for 18K.

If it is not possible then a whole new regulator circuit is what I need.


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 Post subject: Re: Collins R-390 solid state regulator
PostPosted: Nov Tue 07, 2017 5:44 pm 
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I would advise against any kind of hybrid approach.....It think you have 2 rational choices:
--design a new circuit
--buy a fan...;)

My recommendation for a new circuit: a differential pair which compares the output voltage to the zener reference. The zener, in turn, would be driven by a current source.

Here is a quick sketch of the concept:
Attachment:
collins_reg.jpg
collins_reg.jpg [ 19.96 KiB | Viewed 435 times ]

Q1 is a current source to drive the zener. Make the zener current at least 10X the base current of Q4
Q2 is the driver, and Q3 is the pass transistor.
Q4 and 5 are a differential pair. These are sometimes sold a matched pair in one package--for applications requiring high accuracy.

Operation:
the current source puts the zener at an known and constant voltage, subject only to temperature effects.
The differential pair compares the output voltage to the zener voltage, and develops an error signal which drives Q2. Q3 simply supplies the required current gain and low output impedance.
Except for Q3, all the transistors can be low-cost small-signal devices. (Q4 and 5 should be the same type and "reasonably" matched.)
Some caps will be needed for filtering and stability. (feedback amps make nifty oscillators...)

I can attempt to do the actual design if:
1. I get detailed requirements
2. I find the time
Feel free to guess which will happen first.......;)

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 Post subject: Re: Collins R-390 solid state regulator
PostPosted: Nov Tue 07, 2017 8:54 pm 
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The requirements are 180 +/- 1 volt at up to a maximum of 200mA with the input B+ jumping up to between 400-500Vdc completely unloaded.

I think the issue with the circuit I used is that I expected it to meet spec when I used different components different layout and different heatsink than what was found in the radio the regulator was in.

It could be that the circuit won't work with other parts than what was specified.



EDIT:

Tried the original regulator circuit and noticed my B+ was 174 Vdc which is way out of tolerance.

I adjusted the 18K resistor until I got 180 +/- 1Vdc from no load to 180mA load.

That would get me by until a proper solid state regulator is devised provided I do not need to go through the alignment procedure again given the lower B+ when I did the alignment a few weeks ago. Then again it seems to have ben working just fine on 174 Vdc.

Now I would not be opposed to making the regulator external and using an octal plug to plug it in provided the plug can fit through the holes in the side of the case by where the pass tubes would be. That way the circuit will not be limited by space constraints.

By going with a solid state regulator I'll be saving nearly 1.2A of heater current


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 Post subject: Re: Collins R-390 solid state regulator
PostPosted: Nov Wed 08, 2017 9:12 pm 
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Playing back and interpreting---plus some questions.

Requirements:
Supply voltage: 350 to 450? Volts steady-state
500 volts surge---regulation specs do not apply (survival only)

Output voltage adjustment range: 180 +/- 10 volts
Output voltage line and load regulation: +/- 1 volt for load from 100 to 200 mA, and supply from 350 to 450 volts.

Temperature stability?

Other?

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 Post subject: Re: Collins R-390 solid state regulator
PostPosted: Nov Wed 08, 2017 10:20 pm 
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Temperature stability.

As required to meet the +/- 1 Vdc spec.

Which if the regulator is external the only temp to worry about is that which the regulator produces.

I suppose it will be easier to design the reguator to be external to the receiver as there are then no space constraints plus I can use the 5" 120Vac fan I currently use to draw the heat of the pass tubes out to cool whatever heatsink is used.

What I'll then do is bypass whichever 47 ohm resistor connects to the terminal of the octal socket I use for the regulated output so that there is no voltage drop.


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 Post subject: Re: Collins R-390 solid state regulator
PostPosted: Nov Thu 09, 2017 9:48 pm 
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OK, how about this?
Attachment:
MOSFET 180v Collins Reg.jpg
MOSFET 180v Collins Reg.jpg [ 32.94 KiB | Viewed 394 times ]

The regulation from 150mA to 250mA load is 121mV or better than 0.07% with a fixed 300 volt supply. The power dissipations are listed as "PDxx". The 1N5371B Zeners are 5W devices, dissipating 0.7W each and the 1N752 Zener is a 500mW part dissipating 55mW. The MOSFET shown is a 500 volt part that costs about $1.90.

The output varies 0.34v over a 0 - 50°C range and it varies 2.74 volts over a DC input voltage of 250 to 400 volts.
John

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 Post subject: Re: Collins R-390 solid state regulator
PostPosted: Nov Thu 09, 2017 11:31 pm 
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The voltage variance with the input voltage is no good unfortunately for this application.

Thanks for the circuit though.

If there's a way to add a variable voltage adjust to it the circuit might work, but I prefer to use a feedback type circuit like the original was.


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 Post subject: Re: Collins R-390 solid state regulator
PostPosted: Nov Fri 10, 2017 12:40 am 
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For high accuracy and good regulation, you need gain....and also some kind of differential amplifier. That's what the Collins circuit does.

I will try to supply more details on my approach within the next few days.

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 Post subject: Re: Collins R-390 solid state regulator
PostPosted: Nov Fri 10, 2017 3:16 am 
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Ok thanks and I am wanting the circuit such that it is external to the receiver.

Figure that will make it easier to design and also will prevent the heat from the regulator from being in the receiver.


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 Post subject: Re: Collins R-390 solid state regulator
PostPosted: Nov Fri 10, 2017 10:07 pm 
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If you need regulation then try this circuit. It's adapted from the one published in the Linear Technology application note AN-2 Performance Enhancement Techniques for 3-Terminal Regulators by the late Jim Williams. It can be downloaded here: http://cds.linear.com/docs/en/application-note/an2f.pdf. For the prototype of this circuit and an explanation of how it works look on page 2-6.
Attachment:
Alt 180v Collins Reg with LM317.jpg
Alt 180v Collins Reg with LM317.jpg [ 33.74 KiB | Viewed 376 times ]

R3 represents a load of 200mA at 180 volts. By replacing it with a current source that varies from 100mA to 250mA, the output voltage varies only -13.3mV or 0.0074%. Replacing R3 and varying the input voltage, V1, from 250v to 400v, the output voltage varies at total of 1.9mV over that range.

R7 represents a 5K trim pot adjusted to set the output to exactly 180 volts.

John

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 Post subject: Re: Collins R-390 solid state regulator
PostPosted: Nov Sat 11, 2017 1:43 am 
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I like it a lot.

Does just what I need and the spec is way better than the original regulator.

I'll look at the info for it when I get home tonight.

I'm going to see if it is something that can fit inside the R-390 properly.

If not no big deal as I'll just make it external.


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 Post subject: Re: Collins R-390 solid state regulator
PostPosted: Nov Mon 13, 2017 7:13 pm 
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Here's the regulator circuit.

Attachment:
R-390 regulator.jpg
R-390 regulator.jpg [ 91.86 KiB | Viewed 340 times ]


What size and type of heatsink do I need?

I do have the heatsink that I used with the TO-3 transistor for the other regulator circuit.

Will it be large enough or do I need something bigger?

Will the 47 ohm resistors cause any issues with regulation?

Lastly. If this circuit is small enough to be built inside the R-390 how would I go about adding a small DC fan if it is even necessary?

Perhaps a series string of diodes between the first filter cap and regulator circuit with the fan across them. The diodes would serve to limit the voltage to the fan to a certain voltage. The fan's speed would then vary with the power supply load. Or perhaps I could use a zener instead of the diode string or I could rectify the heater string and see if there's a small enough 40 volt fan.

Now if the circuit has to be built external then I could use the 5" 120Vac fan for cooling purposes.


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 Post subject: Re: Collins R-390 solid state regulator
PostPosted: Nov Thu 16, 2017 12:59 pm 
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I'm looking at two of these heatsinks (one for the MOSFET one for the LM-317) https://www.mouser.com/ProductDetail/Oh ... 7kRQ5UU%3d

http://www.mouser.com/ds/2/303/sink_c60-310628.pdf

The configuration I will use is the one where one fan can be mounted to both heatsinks.

Is that a good heatsink choice or will the TO-3 heatsink I used for the transistor earlier be ok for both devices?

If the TO-3 heatsink will work for both devices it will fit in the R-390.

If that is possible then I'll use the pass tube socket terminals as tie points for components and it will all be self contained.

I would then remove the hum balance adjust pot and install the 5K voltage adjust pot in its place.

The problem comes with how to power a fan if it is even needed.

EDIT:

Decided to try the heatsink I already have.

Parts are on order.


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 Post subject: Re: Collins R-390 solid state regulator
PostPosted: Nov Tue 21, 2017 2:30 am 
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Parts came in today. I will try to assemble the regulator tomorrow and test it.

If it passes the test and there is room and the TO-3 heatsink I used for the original solid state regulator can dissipate the heat enough I will install everything in the audio chassis and call it done.

If I need a fan I know a 60mm just is too large for placing on the heatsink so I will have to work something out. Perhaps a small blower type of fan would work that would exhaust the heat out of one of the side holes.


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 Post subject: Re: Collins R-390 solid state regulator (problem)
PostPosted: Nov Tue 21, 2017 7:38 pm 
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I built the circuit as specified and am fairly certain I built it right, but I have a problem.

The circuit will regulate until the input B+ goes above 280Vdc then it unregulates.

Also if I put a 180mA load on it the circuit never regulates at all.

Any idea what could cause that?

EDIT:

I found the problem. Noticed that whenever I would touch the heatsink the voltage would change slightly.

So I decided to ground the heatsink and the voltage is now stable only slightly varying as the heatsink heats up.

Don't yet know the voltage variance from cold to hot as the heatsink will get. Will check that tomorrow.

EDIT 2:

The regulator is vwery temperature stable only changing under 100mV from room temperature to fully hot.

Here's what concerns me.

The unloaded regulated B+ is 235Vdc and I can only assume that there is no B+ current drawn when the rceiver is first turned on.

From a load of 100 to 180 mA there is a B+ variation of only 100mV which is good.

The regulated output is stable for a line voltage variation of 110-120Vac.

Now I am using a 10uF cap on the regulator output to better simulate actual operating conditions.

Next step is to wire in the circuit to the audio chassis and see how hot the heatsink gets then.

If it gets too hot I'll figure out some sort of fan to cool the heatsink down some. Now I do have a few fans that only have a couple mounting tabs and no shroud around the blade and they run on 12Vac so I could maybe series two of those or use one and a resistor and figure a way to mount them.

Here's a picture of the regulator circuit. Still have two leads to put some insulating sleeving on so there's no chance of them touching anything and I'd really like to add another terminal for the input to the regulator, but there's no real room on the heatsink for another terminal.

The existing terminals consist of two of the insulating inserts usually used when mounting TO-3 transistors without a socket and a washer under one insert to make the heatsink thick enough and a terminal lug. The ground terminal uses one of the original mounting holes for the socket that was on the heatsink and one of its screws along with a terminal lug.

Attachment:
Heatsink A.jpg
Heatsink A.jpg [ 173.29 KiB | Viewed 234 times ]


Attachment:
Heatsink B.jpg
Heatsink B.jpg [ 162.88 KiB | Viewed 234 times ]


EDIT 3:

Was hoping to get away without a fan, but it doesn't look like I will be able to.

It isn't a voltage stability issue as the voltage is stable within a few seconds after applying B+.

It's heat.

The heatsink gets hot enough to where I can't touch it but a second or two and I'vbe not let it run much longer after that without some sort of fan on the heatsink. While that may be ok I personally don't like hot heatsinks as it can shorten component life.

What I may do is use the same 120Vac fan I used with the pass tubes which should hopefully draw enough air to keep the heatsink cooler.

I also removed the other three plate connections on the pass tube sockets so that the voltage amp tube would see no B+ whatsoever given that without the pass tubes and without the hum balance pot connected (removed to mount the 5K voltage adjust pot) the grid connected to pin 6 of the tube will then have B+ on it. I also removed the connection to the 18K resistor for the same reason. Might wind up just pulling the tube and using a resistor for the heater.

Now once this circuit has been in operation for awhile and thouruoghly vetted I will post a topic in the communicationd forum about this mod since that will get it exposure to people who have the R-390. They will then have a permanent solution to the increasingly rare pass tubes plus the regulation will be far better than the R-390's original regulator could ever achieve.


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 Post subject: Re: Collins R-390 solid state regulator (problem)
PostPosted: Nov Fri 24, 2017 1:02 am 
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That circuit isn't going to work without some sort of protections added to it.

What protections it needs I don't know.

I fired it up in the receiver and everything was working fine until I switched it to standby then back to AGC. Voltage shot up to full unregulated B+.

Don't know what fried in the regulator. Probably the LM-317 unless the 1N4007 shorted.

If so that may have saved the regulator.

I'm measuring 165 ohms from input to output and I swapped the leads around with the same reading.

So if the 1N4007 went bad it didn't fully short unless bot the 12N50E and LM-317 went mostly short.

Looking at the receiver schematic I think I see what happened.

There is a 4H choke after the contacts on the main function switch that apply B+ to the receiver so when the switch opened there was probably a HV arc. Now if it did damage the 1N4007 I don't know why unless the pulse was a negative pulse above 1KV.

If it is just the diode I might have one and if so can I put a cap and resistor (or snubber if I have one) across the choke to stop the arc when the receiver is switched to standby?

I'm fighting the urge to say screw it and go back to the pass tubes. I just need to press on and get it figured out.

It had never occurred to me that the choke is after the switch and that it might cause a problem.

Some good news is that with the regulator operating in the receiver even when the tubes are cold there's enough load from somewhere to keep the voltage at 180Vdc.

EDIT:

Disconnected the diode from output to input and got the same low ohms reading.

Tells me both the regulator and MOSFET went bad.

The only thing I'm sure survived is the 1N4148 only because it is in parallel with a 240 ohm resistor.

The rest of the semiconductors I may as well replace once a solution is found to better protect the regulator.

EDIT 2:

I just thought of something.

Relays often use a reverse biased diode across the coil to protect the driver circuitry. Would that work with the choke?

If so would a 1N4007 diode be ok or do I need one rated higher?


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 Post subject: Re: Collins R-390 solid state regulator (problem)
PostPosted: Dec Thu 07, 2017 6:46 pm 
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Concerning the regulator how can I protect it from being damaged when I set the function switch to standby then set it to one of the other functions?

I'm pretty sure it has to do with the choke in one part of the power supply right after the switch.

A reverse biased diode across the choke like what is done with some relays might help, but I am not sure the voltage and current rating I'd need.

When I do fix the regulator I'll just replace all the parts.

Would a reverse biased diode from the regulator output to ground work as well?

Just looking for the best way to protect the regulator should the receiver ever be set to standby then back to one of the functions. Not an issue with mine as I use a power strip to turn mine on and off given I have an amplifier connected to it along with the 120Vac fan, but if someone else were to build the circuit it would be an issue.


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