Certainly for the other equipment in the station there must be 120 volt circuits where a neutral can be tied into

In some localities the code requires that if the 220 (or 240) volt pair is used, that a neutral be included, in addition to the green wire frame ground.

These statements about availability of 120V power and neutral wires would be true on a 120/240V split-phase power system like we have in North America, but very few places outside of North America use this system.

The OP specifically mentioned 230V power, which is usually part of a 230/400V 3-phase power system, the most common standard outside of North America. Most likely, the 230V power being supplied to the unit is from a 230V line and the neutral, and there is no other wire available from which to derive 120V. In this case, you'd need an additional transformer as @vu2nan pointed out, or perhaps a series capacitor as you suggested earlier.

@Howard Walker can you confirm for us? Are you familiar with your mains power distribution? Can you tell us if you've got split-phase power or not? If you're not sure, just tell us where are you located.

 

Hi Howard,

Here's the modified schematic of the Heathkit SB-1000 HF Amplifier, to keep the fan running for three more minutes after the 'mains on' rocker switch is turned off.

View attachment 272412

In the absence of the neutral, the addition of a small 240V / 120V transformer is a must.

Also required is a 240 V ~ operated, 'true off-delay' timer that is to be set for a 3' delay.

With the rocker switch turned on and the timer energised, its contact closure is immediate and the fan motor starts.

With the rocker switch turned off and the timer de-energised, the delay in its contact opening keeps the fan running for 3 more minutes.

Nandu.

Am I right in thinking that the only difference between a "true off delay" timer and an "off delay" timer is that the first one has a small internal power source and is self powered during the timing phase after the supply drops out, where the second requires a constant power source in order to keep its output active?

If so, am I right in thinking that the OP could use either one, since they have un-switched 230V available at all times within the circuit, so they could wire the un-switched 230V to power the timer while using the switched 230V as the control signal?

I'm certainly not arguing against the "true off delay" as a viable option, but just wondering if the regular "off delay" is also viable, since it seems like they're a little more widely available.

 

OK, yes I did presume that the TS was in the USA, or some area with 120 volt power available. The connectors shown on the drawings agreed with that assumption. And Heathkit products are most common in the U.S. so the guess was reasonable.
We will need to hear from the TS to see what the reality is.
Exactly the same scheme, including using a second pole of the Operate/Standby switch to assure starting the fan, could be used with an external transformer.

 

@Howard Walker You state 230v, N.A. is 240v now, are you in UK by any chance?
This would make sense if the 120v is derived from a primary tap on the TFMR.

 

Am I right in thinking that the only difference between a "true off delay" timer and an "off delay" timer is that the first one has a small internal power source and is self powered during the timing phase after the supply drops out, where the second requires a constant power source in order to keep its output active?

If so, am I right in thinking that the OP could use either one, since they have un-switched 230V available at all times within the circuit, so they could wire the un-switched 230V to power the timer while using the switched 230V as the control signal?

I'm certainly not arguing against the "true off delay" as a viable option, but just wondering if the regular "off delay" is also viable, since it seems like they're a little more widely available.

Hi ebeowulf17,

Yes, you're right, either of them could be used.

I chose the 'true off-delay' timer as it simplifies the MOD!

Nandu.

 

Hi ebeowulf17,

Yes, you're right, either of them could be used.

I chose the 'true off-delay' timer as it simplifies the MOD!

Nandu.

A thermostat in the air stream is simpler because it does not need any power. Change the Operate/standby switch to double pole and then the fan runs when the tube starts making heat and keeps running until the tube is cool. The challenge will be in matching the switches. OR chamge the power switch to a double pole switch and then the fan will come on eith the poer, just like present, but only switch off when the air stream is cool enough. That might be better. The thermostat needs to be set for just a bit warmer than the ambient, probably around 100 degrees F.
and we still do not know what part of the world the TS is located in..

 

A thermostat in the air stream is simpler because it does not need any power. Change the Operate/standby switch to double pole and then the fan runs when the tube starts making heat and keeps running until the tube is cool. The challenge will be in matching the switches. OR chamge the power switch to a double pole switch and then the fan will come on eith the poer, just like present, but only switch off when the air stream is cool enough. That might be better. The thermostat needs to be set for just a bit warmer than the ambient, probably around 100 degrees F.
and we still do not know what part of the world the TS is located in..

Yes, Bill, most of the radio transceivers have 2 cooling fan options:

1. Cooling fan 'on / off ' control based on power amplifier heatsink temperature.

2. Cooling fan 'on' when the PTT is pressed and 'off with a delay' when it is released.

Nandu.

 

Yes, Bill, most of the radio transceivers have 2 cooling fan options:

1. Cooling fan 'on / off ' control based on power amplifier heatsink temperature.

2. Cooling fan 'on' when the PTT is pressed and 'off with a delay' when it is released.

Nandu.

Certainly that is true for many of the current transistorized transceivers. Which this item is not. It is a TUBE type power amplifier, that has neither a heat sink nor any power transistors., but rather a power tube, and it does not include a receiver at all.
Power tubes generate heat as long as they are powered, more heat while amplifying, but also while in standby. THUS THE COOLING REQUIREMENTS ARE RATHER DIFFERENT. This amplifier does not contain a heat sink for the amplifying tube,, so heat sink temperature is not a consideration.
AND, we still do not have any information as to what part of the world it is in, nor the availability of 120 volt power . Which, given that the internal source of 120 volts is unavailable with power off, matters a bit.

Based on a later comment we now know that the TS is based inside the USA, in amateur call area "4", and so the "230 volts" IS part of that local USA split power system,with a soild neutral in the center. In that case my initial suggestion will work. It will not be Orthodox, but it will function as described.

 

Certainly that is true for many of the current transistorized transceivers. Which this item is not. Jt is a TUBE type power amplifier, that has neither a heat sink nor any power transistors., but rather a power tube, and it does not include a receiver at all.
Power tubes generate heat as long as they are powered, more heat while amplifying, but also while in standby. THUS THE COOLING REQUIREMENTS ARE RATHER DIFFERENT. This amplifier does not contain a heat sink for the amplifying tube,, so heatsink temperature is not a consideration.

AND, we still do not have any information as to what part of the world it is in, nor the availability of 120 volt power . Which, given that the internal source of 120 volts is unavailable with power off, matters a bit.

Got it, Bill! Thank you.

Nandu.

 

Big questions that need answers before any really good solutions are given. Next question: does that DPST switch cut off the line power before it gets to anything else, including the transformer? If so, powering the fan will not be a small challenge. You will need either another transformer or some sort of voltage control device, possibly a resistor or a capacitor. I have seen both used for fans.
OR, and here is another question: Does the (whatever it is) also have a neutral connection? That would allow the fan and timer to have a 120 volt supply with as much capacity as you could need. And not require a transformer.Then a simple 120 volt delayed off timer would be easy. So let us know if a neutral connection is available. You might be able to get away with using the green wire safety connection, if one is present. Some folks will freak out at that suggestion, I am quite aware.

No, it does not. The switch controls the input power to the transformer and the 120 VAC output tap from the transformer to the 120VAC fan

 

Certainly that is true for many of the current transistorized transceivers. Which this item is not. It is a TUBE type power amplifier, that has neither a heat sink nor any power transistors., but rather a power tube, and it does not include a receiver at all.
Power tubes generate heat as long as they are powered, more heat while amplifying, but also while in standby. THUS THE COOLING REQUIREMENTS ARE RATHER DIFFERENT. This amplifier does not contain a heat sink for the amplifying tube,, so heatsink temperature is not a consideration.

AND, we still do not have any information as to what part of the world it is in, nor the availability of 120 volt power . Which, given that the internal source of 120 volts is unavailable with power off, matters a bit.

This is not a transceiver. It is a Heathkit SB-1000 amplifier, which uses a 3-500ZG tube. It covers 160 M thru 10 meters. I am a licensed Amateur Radio Operator (KI4VEO). It was necessary to provide this information to Heathkit, when I purchased the amplifier, so could do the modification, which would allow me to allow to use the 10 Meter portion of the amplifier band switch.

The 3-500ZG tube has an aftermarket heat sink, made from a machined aluminum block. The original heatsink, was too small, and nearly worthless. In addition, I added 17 feet, of twisted pair Teflon wire, to provided the necessary voltage drop for the filament of the tube. The filament voltage was measured at 4.95 volts, at the tube, at a pair of test points, that I installed on the back panel, of the amplifier..

 

OK, I had not been aware of heat sinks for glass tubes, that is new to me. I am also a radio amateur (Ham) N8QVS. so far I have not used an external power amplifier, except for boosting an HT up to 30 watts for mobile operation. I am aware that excess filament voltage shortens tube life quite a bit, and that adjusting it is often a big deal task. With that amplifier having a sinle transformer for al the voltages adjusting heater voltage has few options.
And with a US call you are in the land of 120 volt power availability. so the thermostat scheme could work with a mminimum of effort.

 

These statements about availability of 120V power and neutral wires would be true on a 120/240V split-phase power system like we have in North America, but very few places outside of North America use this system.

The OP specifically mentioned 230V power, which is usually part of a 230/400V 3-phase power system, the most common standard outside of North America. Most likely, the 230V power being supplied to the unit is from a 230V line and the neutral, and there is no other wire available from which to derive 120V. In this case, you'd need an additional transformer as @vu2nan pointed out, or perhaps a series capacitor as you suggested earlier.

@Howard Walker can you confirm for us? Are you familiar with your mains power distribution? Can you tell us if you've got split-phase power or not? If you're not sure, just tell us where are you located.

Yes I am.

I don't want to use any external 120 VAC wiring to supply the fan voltage

You people are SMART. You can figure it out

 

You people are SMART. You can figure it out

Such flattery.

So if you want to operate the fan off of 230V I see three choices:

1. Buy a 230V fan
2. Add a 240V to 120V transformer
3. Try adding a capacitor or power resistor in series to drop the voltage to the fan

Your choice---

 

Such flattery.

So if you want to operate the fan off of 230V I see three choices:

1. Buy a 230V fan
2. Add a 240V to 120V transformer
3. Try adding a capacitor or power resistor in series to drop the voltage to the fan

Your choice---

I'm probably the least qualified person in this conversation, but I'll offer an opinion anyway.

My gut feeling is that the order you listed those options in is also a fair ranking of best to worst solution for the voltage drop part of the problem.

And I'd say the rest is pretty well figured out. @vu2nan offered a clear description and detailed schematic for the timer based solution, and @MisterBill2 offered an alternative using a thermostat instead of a timer (no schematic there, but the solution is pretty straightforward once you read the description.) Both approaches sound valid to me, so now it's just up to @Howard Walker to decide which solution to implement.

 

I have seen capacitors used to drop the voltage for a fan, so that may be a possible option. so it could be worth investigating.
As for "smart" , that appearance is also based on many years of experience and not forgetting what was seen. The label on the fan motor should state either the wattage or the current, which will allow calculating the value of a series capacitor to allow the motor to be powered by the 230 volts without overheating.
In the other direction, using the neutral connection will allow running the fan without any extra outside wiring.

 

In the other direction, using the neutral connection will allow running the fan without any extra outside wiring.

Since the TS stated the "neutral" was connected to chassis in post #9, I believe that it's a safety ground, not neutral, and should no be used for the fan connection.

 

Since the TS stated the "neutral" was connected to chassis in post #9, I believe that it's a safety ground, not neutral, and should no be used for the fan connection.

I am aware of that, and also aware that in most Ham Radio setups a very good neutral/ground connection is made. Thus the hazard is minimum. AND, if the outlet is done to code (as required in some areas of the USA), then there is already a neutral brought to the outlet box. In that case it would be simple to change the 230 volt outlet to one that included a neutral connection, and change the plug to one including neutral, and change the cord to one with Black, red, green, and white.

 

I am aware of that, and also aware that in most Ham Radio setups a very good neutral/ground connection is made. Thus the hazard is minimum.

I don't think we should be advising anyone to take chances mixing neutral and ground connections. While the odds of failure may be low, it still allows the creation of a very dangerous situation with a single point of failure. Following proper neutral and grounding practices will keep the setup safe until/unless there are two separate failures at the same time. I know people do what you described all the time and mostly get away with it, but I still think we shouldn't be advising others on a public forum to make potentially dangerous choices, especially when many of the people reading this forum won't understand the risks and potential failure modes as well as the more experienced users. I may be pushing the limits of my experience with regard to industrial timers or radio equipment, but I've been working with and designing high voltage (in my case, I just mean 120/240 or 230V, not any of the higher industrial voltages) equipment for over twenty years, so I'm not just blowing smoke or insisting we follow rules for the sake of rule following. There really are good reasons for maintaining good safety grounding practices and keeping the neutral path separate.

AND, if the outlet is done to code (as required in some areas of the USA), then there is already a neutral brought to the outlet box. In that case it would be simple to change the 230 volt outlet to one that included a neutral connection, and change the plug to one including neutral, and change the cord to one with Black, red, green, and white.

I do agree that, as long as there is a separate neutral available at the outlet box, then replacing the power cord and plug with appropriate four-conductor versions to bring a neutral into the amplifier sounds like a great idea.

 

I am aware of that, and also aware that in most Ham Radio setups a very good neutral/ground connection is made. Thus the hazard is minimum. AND, if the outlet is done to code (as required in some areas of the USA), then there is already a neutral brought to the outlet box. In that case it would be simple to change the 230 volt outlet to one that included a neutral connection, and change the plug to one including neutral, and change the cord to one with Black, red, green, and white.

That's fine, but you didn't make that clear in your post #36.
Neutral and safety ground are two different wires, and their functions should never be interchanged, even though they are both at ground potential
.