Finally my DIY tube amp project gets kick-started

[mbhangui]

I am facing some challenges with the AC input voltage post the lockdown era. My power transformers were designed for a primary voltage of 230V AC. But off-late i am measuring higher than normal AC input voltage in my area. In the morning around 10AM its around 235V, in the evening around 240V and after 10PM as high as 249V AC are measured in the past one week interval. This high input voltage in transformer primary is causing a higher secondary AC voltage too. For instance when its 249V AC input, my secondary voltage is as high as 465V AC rather than the normal 425V AC thats required.

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I was going through your post and came across this. This is across entire Maharashtra and started exactly after lockdown last year. I had to install voltage stabilizers throughout the house. I lost few things before i installed the stabilizers - computer SMPS, fuse of allo shanti LPS. SMPS of RO water purifier and people I know have had their television sets, microwave owens fried. The side effect of the increase in voltage is also an increase in current consumption and definitely marginal increase in consumption. Don't know if this voltage increase has been done deliberately. I have voltmeters with bright red 7 segment displays installed in all rooms. All complaints regarding high voltage have been brushed aside by MSEDCL. The voltage is exactly what you describle. Normal in the morning and by late night it is atrocious.

 

[IndianEars]

India's Rated Voltage is 240 Volts ( +/- 10%) AC, 50 Hz

 

[raghupb]

@mbhangui
If your lighting line is on UPS, add a servo stabilizer at UPS output.
This way you are somewhat guaranteed a fixed voltage across the home.

Cheers,
Raghu

 

[mbhangui]

@mbhangui
If your lighting line is on UPS, add a servo stabilizer at UPS output.
This way you are somewhat guaranteed a fixed voltage across the home.

Cheers,
Raghu

I don't have a problem now. I have put stabilisers for almost everything. What I'm trying to understand is why is the MSEDCL pumping this voltage after the lockdown. Is it because the demand has fallen and the state has not yet reduced power generation? Is it being done to extract more money (more voltage, more current and higher electricity bill) from hapless consumers? Our society had multiple meetings with the MSEDCL folks and we showed our voltage readings throughout the day and cases of multiple equipments, tv sets, laptop and macbook charges, led tubelights, etc getting fried by high voltage after the lockdown and MSEDCL keeps saying that if the equipment gets fried it is the equipment fault. They should be able to handle upto 250v (but I have myself observed voltage going upto 254 volts in the night). Something ain't right after the lockdown.

 

[IndianEars]

India's Rated Voltage is 240 Volts ( +/- 10%) AC, 50 Hz

240 V + 1% = 264 Volts.

254 Volts should not cause distress to any BIS compliant ( ISI mark) equipment

Upto 264 Volts AC is within specification

 

[mbhangui]

You will not find imported equipment catering to ISI. Even apple mcbook pro charger is rated 100-240v. The only thing that apple does is to provide an indian plug for macbooks sold in India.

As per the (erstwhile) Indian Electricity Rules, 1956, vide Rule 2(av), the following were the limits:

-Low Voltage: Not exceeding 250 V.
-Medium Voltage: Not exceeding 650 V.
-High Voltage: Not exceeding 33000 V.
-Extra High Voltage: Exceeding 33000 V

However, it may be noted that the IE Rules have now been superseded by the Central Electricity Authority (Measures Relating to Safety and Electric Supply) Regulations, 2010 and the above definition is removed in the CEA Regulations, 2010
The National Electric Code (of India) 2011 (Reaffirmed in 2016): Part 1 – Section 2

-Low Voltage: The voltage which does not normally exceed 250 V (Cl. 3.3.37)
-Medium Voltage: The voltage which normally exceeds 250 V but does not exceed 650 V (Cl. 3.3.38)
-High Voltage: The voltage which normally exceeds 650 V (but less than 33 kV) (Cl. 3.3.39)
-Extra High Voltage: The voltage exceeding 33 kV under normal conditions (Cl. 3.3.40)

Note: The definitions given in 3.3.37 to 3.3.40 are based on the provisions of IE Rules. It may, however, be noted that voltage ranges as defined internationally are at variance with the above definitions.

 

[keith_correa]

India's Rated Voltage is 240 Volts ( +/- 10%) AC, 50 Hz

I think that's dated. I think it has been revised to 230 Volts with tolerance of ±10%. So, 207 Volts - 253 Volts is within the electrical code.

 

[IndianEars]

Keith, do you have a reference to back your claim ?

 

[IndianEars]

You will not find imported equipment catering to ISI. Even apple mcbook pro charger is rated 100-240v. The only thing that apple does is to provide an indian plug for macbooks sold in India.

As per the (erstwhile) Indian Electricity Rules, 1956, vide Rule 2(av), the following were the limits:

-Low Voltage: Not exceeding 250 V.
-Medium Voltage: Not exceeding 650 V.
-High Voltage: Not exceeding 33000 V.
-Extra High Voltage: Exceeding 33000 V

However, it may be noted that the IE Rules have now been superseded by the Central Electricity Authority (Measures Relating to Safety and Electric Supply) Regulations, 2010 and the above definition is removed in the CEA Regulations, 2010
The National Electric Code (of India) 2011 (Reaffirmed in 2016): Part 1 – Section 2

-Low Voltage: The voltage which does not normally exceed 250 V (Cl. 3.3.37)
-Medium Voltage: The voltage which normally exceeds 250 V but does not exceed 650 V (Cl. 3.3.38)
-High Voltage: The voltage which normally exceeds 650 V (but less than 33 kV) (Cl. 3.3.39)
-Extra High Voltage: The voltage exceeding 33 kV under normal conditions (Cl. 3.3.40)

Note: The definitions given in 3.3.37 to 3.3.40 are based on the provisions of IE Rules. It may, however, be noted that voltage ranges as defined internationally are at variance with the above definitions.

EXCELLENT.

Thank You

 

[keith_correa]

Keith, do you have a reference to back your claim ?

This, I think is the latest revision of the Indian Electrical Code.

https://law.resource.org/pub/in/bis/S05/is.sp.30.2011.pdf

 

[drlowmu]

Thank you for this discussion. When Hari first approached me in 2020 about designing his DC SE amp, an early question was to determine his home's line voltage. Even after applying ultra conservative designing, we managed to " fry" one 5 Watt rated Power Supply resistor. This was the first time I can recall this ever happening.

Hari also had to add resistance on some of the VACs of his tube's filament supplies to lower the filament operating voltages.. He very intelligently mastered that challenge.

The "positive" to all of this for Hari is that his Input / Driver's tube's Plate voltage ( Ea ) is now over 200 VDC. This VDC produces more swing and a better sense of "aliveness" than the 186.2 VDC it was designed it to have. 200 VDC, and over, on his Driver tube's plate is really nicer - sounding than 186 VDC. It is far far better than 150 VDC or even 160 VDC, we see in amps - on their plates in their front-end stages.

The high plate voltage allows the tube to SWING and " DO something" - respond better to the music signal on it's grid. It is special to hear !! No wonder Hari has been so pleased.

Since about 3 or 4 of 2021, I design-center all my Input / Driver tube's plate voltages ( and hence the direct couple ) to be 200 VDC to 210 VDC, as a matter of standard practice. We increase this VDC on the plate, and reduce the current through the tube if needed, to maintain a conservative operation.

Hari is now only dissipating 1.01 Watts through a 4.0 Watt rated 6FQ7. His Input / Driver tube will seemingly last "forever". We intend to increase the tube's current very soon, by 30%, in coming weeks. After upping the current, the tube will still be loafing - at 33 percent of it's rated maximum.

Hari, please report to us here on Forum, what you hear after doing this. Thanks.

Jeff

 

[Hari Iyer]

India's Rated Voltage is 240 Volts ( +/- 10%) AC, 50 Hz

That's a huge variation. +/- 10% can be 264volts which will short MOVs in devices. I have not measured over 254volts in my location.

 

[Hari Iyer]

Thank you for this discussion. When Hari first approached me in 2020 about designing his DC SE amp, an early question was to determine his home's line voltage. Even after applying ultra conservative designing, we managed to " fry" one 5 Watt rated Power Supply resistor. This was the first time I can recall this ever happening.

Hari also had to add resistance on some of the VACs of his tube's filament supplies to lower the filament operating voltages.. He very intelligently mastered that challenge.

The "positive" to all of this for Hari is that his Input / Driver's tube's Plate voltage ( Ea ) is now over 200 VDC. This VDC produces more swing and a better sense of "aliveness" than the 186.2 VDC it was designed it to have. 200 VDC, and over, on his Driver tube's plate is really nicer - sounding than 186 VDC. It is far far better than 150 VDC or even 160 VDC, we see in amps - on their plates in their front-end stages.

The high plate voltage allows the tube to SWING and " DO something" - respond better to the music signal on it's grid. It is special to hear !! No wonder Hari has been so pleased.

Since about 3 or 4 of 2021, I design-center all my Input / Driver tube's plate voltages ( and hence the direct couple ) to be 200 VDC to 210 VDC, as a matter of standard practice. We increase this VDC on the plate, and reduce the current through the tube if needed, to maintain a conservative operation.

Hari is now only dissipating 1.01 Watts through a 4.0 Watt rated 6FQ7. His Input / Driver tube will seemingly last "forever". We intend to increase the tube's current very soon, by 30%, in coming weeks. After upping the current, the tube will still be loafing - at 33 percent of it's rated maximum.

Hari, please report to us here on Forum, what you hear after doing this. Thanks.

Jeff

Off late in the morning the line voltage hovers around 235vac to around 240vac. I have measured a driver plate voltage around 193vdc. TBH I have not taken notes on how the setup sounds with 192vdc vs 204vdc and hence everything I write will be a guess which I want to avoid. Moreover, I am doing many other minor changes with respect to grid to ground input resistor type change, preamplifier volume control changes and am not able to pinpoint what exactly improves the SQ. I have ordered a Wirewound Potentiometer recently to replace my Allo step attenuator which predominantly use a metal film resistance. I have replaced my input resistance from metal film to carbon composite. I am planning a precision thin film resistance in that place as per your suggested values next month. I am already quite happy with the carbon composite preset but that's with the Allo stepped attenuator. Once I modify that with the Wirewound Potentiometer things will again change.

 

[IndianEars]

This, I think is the latest revision of the Indian Electrical Code.

https://law.resource.org/pub/in/bis/S05/is.sp.30.2011.pdf

Thanks Keith. This is excellent and a document I have been seeking for a long time.

For Years, I have wondered if India was still at 250 VAC (Highest In the World) or had dropped to 240 Volts AC Single Phase.

Interestingly, Both, You & mbhangui have pointed to 2011 Documents ... One that says 250 VAC and another at 240 VAC ... leaving me as confused as ever.

I have checked the rated Voltage on Commercially available Incandescent Bulbs and they indicate 240 VAC.

Any definitive pointer by you or mbhangui would be Great

 

[Hiten]

When I was planning to make tube amp (now abandoned) I took non scientific and probably compromised performance approach. As long life of tubes/components and fun build was my goal. I measured mains voltages every half hour for two days (daytime) and noted down lowest and highest voltages. Than after one week again for half a day measured voltages. I discarded one off high voltages (I measured max. 248v), noted most common voltage I was getting. My average common figure was 235 V. My (all crude calculations) figures to give transformer winder was at 245V Primary, 6.5V for heater at that input. This way for occasional high voltages the secondary voltages would be within tolerance Besides at 235v input heater filament would have long life as it will be getting around 6v. Was calculating B+ voltages in various combination of CRC and CLC in PSUD designer, but then things were not working out on getting output transformer and the project was abandoned.

edit : corrected

 

[IndianEars]

That's a huge variation. +/- 10% can be 264volts which will short MOVs in devices. I have not measured over 254volts in my location.

Hari,
During the past few years, the stability of the power has improved a lot.

Still Voltages in India do tend to fluctuate even beyond their rated value.

Your equipment seems to be on the brink with even the rated variation in the Mains Supply Voltage.

A regulated supply will probably not be acceptable from an audiophile point of view.... then maybe it would be prudent for you to build in an Over voltage Power cut out with a relay ?

Just a thought.....

 

[mbhangui]

Interestingly, Both, You & mbhangui have pointed to 2011 Documents ... One that says 250 VAC and another at 240 VAC ... leaving me as confused as ever.

I have checked the rated Voltage on Commercially available Incandescent Bulbs and they indicate 240 VAC.

Any definitive pointer by you or mbhangui would be Great

I did find one document of 2019 which said the tolerance has been increased to 240v +-10%. The reason for increasing this is mentioned as 'economic reasons' without explaining how this wide fluctuation will improve the economy. I can understand choosing 230v instead of 110v (thinner wire required to supply the same wattage). But increasing the base voltage from 230v to 240v and also increasing the tolerance to a whopping 20%, the only economy I see is for the Ambani Adani Tata plants to lower quality of distribution and get away with mischief. I do smell a rat here. The normal voltage used to be hovering around 230 v before the lockdown last year. When we fought with the MSEDCL guys last year to do something, the guy from our substation clearly said that in Maharashtra the voltage will not exceed 250v. When I showed him my excel sheet which clearly showed voltage going upto 254 volts in the night, he said I don't have an accurate voltmeter. In reality I have measured the voltage with 3 voltmeter (one of them is my calibrated fluke meter).

I will try to locate the document which says now the nominal voltage is 240v +- 10%. I really don't agree with this standard. The entire world (except probably China) is not going to exclaim about our wonderous ISI standard and start designing SMPS that will tolerate additional 20v.

 

[IndianEars]

I did find one document of 2019 which said the tolerance has been increased to 240v +-10%. The reason for increasing this is mentioned as 'economic reasons' without explaining how this wide fluctuation will improve the economy. I can understand choosing 230v instead of 110v (thinner wire required to supply the same wattage). But increasing the base voltage from 230v to 240v and also increasing the tolerance to a whopping 20%, the only economy I see is for the Ambani Adani Tata plants to lower quality of distribution and get away with mischief. I do smell a rat here. The normal voltage used to be hovering around 230 v before the lockdown last year. When we fought with the MSEDCL guys last year to do something, the guy from our substation clearly said that in Maharashtra the voltage will not exceed 250v. When I showed him my excel sheet which clearly showed voltage going upto 254 volts in the night, he said I don't have an accurate voltmeter. In reality I have measured the voltage with 3 voltmeter (one of them is my calibrated fluke meter).

I will try to locate the document which says now the nominal voltage is 240v +- 10%. I really don't agree with this standard. The entire world (except probably China) is not going to exclaim about our wonderous ISI standard and start designing SMPS that will tolerate additional 20v.

Would really appreciate it if you could share the 2019 document that gives the rated voltage as 240 VAC +/- 10%.

Many Thanks

 

[mbhangui]

Would really appreciate it if you could share the 2019 document that gives the rated voltage as 240 VAC +/- 10%.

Many Thanks

I managed to locate the article. It is not an official document from IEC. The standard voltage ( in India ) for low and medium line distribution was 230 V for single phase and 230 / 400 V for three phase system but due to economic advantage IEC recommended 240 V for single phase and 240 / 415 V for three phase system voltage with ± 6% voltage variation.

Standard Alternating Voltage in India

The IEC decided ± 10% voltage variation allowed for 240 V for single phase and 240 / 415 V for three phase system voltage in the year 2009.

www.myelectrical2015.com

 

[Hari Iyer]

Given the voltage situation (increased) it's very risky to import tube gear from Europe that are designed for 220vac. It's a clear 40 volts difference. That could drastically reduce tube filament life unless you reduce the filament voltage by other means. Diy triumphs here.