At the beginning of the year I hatched a plan to get my sv572 amp off it’s breadboard and into a box. This was mainly to keep it away from prying hands which were bodily pulling components off the board, no matter where I tried to hide it.
I changed the amp to choke input and dc heating using Rod Coleman’s regulators. I bought a Hammond 372FX (300-0-300 170ma) and decided to use an RS 2x9v 100va frame I had in the bit box for the heater supply. Rod didn’t have an example transformer for sv572 so I thought as the heaters were 6.3v @ 4 amps then 100va would be ok(that’s 2x9v@5+amps) . The B+ requirement is for 500v @ 100ma and 300v @ 12ma. The rebuild is documented here:
Vitalstates - SV572
Well the build went ahead….and bit me in the ****. The B+ transformer got really hot and the heater transformer buzzed like a pneumatic drill. I learned that a ct transformer is no good for full wave bridge(bit late but never mind)…so I sourced a 0-600 @ 150ma frame and a 2x9v 120va toroid for the heaters. Re drilled the chassis, moved everything around to accommodate and thought what a good plan.
Well the build went ahead…..and bit me in the ****. The B+ transformer got really hot, and the toroid got really hot. Rod Coleman explained that the transformer should have 3 times the capacity of the heater requirement(bit late, but never mind)….so I sourced a 2x9v frame at 200va which is 9v at 11-12Amps. I also sourced a 0-600v at 200ma frame(remember, I only need 500v @ 113ma). Also put the heater rectifier on a heatsink at the rear of the chassis. Re drilled the chassis, moved everything around and sat back thinking what a great plan.
Well the build went ahead…and bit me in the ****. The B+ transformer gets very hot and the heater transformer also gets very hot. I’ve measured both transformers and according to my dmm with temp measure they are both reaching 70 deg C after about 30-45 mins. Also, upside down on the bench, without the base screwed on, all is quiet. As soon as the base is brought anywhere near the chassis all hell breaks loose. By that I mean the base vibrates and makes the whole chassis shake and there is much noise. Steel chassis and steel base.
Amp sounds very nice but with the heat and vibrating when it’s got the base on it’s destined for the scrap.
The questions:
What is a realistic max temp for a transformer. Is 70degs reason for alarm. It’s way hotter than my Pass amps because I can’t apply the 5 second rule, more like 2 seconds. I didn’t expect a 200ma transformer to get hot when asked to deliver just over 100ma. Is that a reasonable expectation.
Is the loud buzzing the result of some interaction between all the transformers and chokes and the steel base. Would an aluminium base cure the problem?. The thing that confuses me is that the last incarnation didn’t buzz/vibrate and the only thing that’s changed is one choke that used to be on top is now inside and 1 transformer that used to be inside is now on top.
Ed
I changed the amp to choke input and dc heating using Rod Coleman’s regulators. I bought a Hammond 372FX (300-0-300 170ma) and decided to use an RS 2x9v 100va frame I had in the bit box for the heater supply. Rod didn’t have an example transformer for sv572 so I thought as the heaters were 6.3v @ 4 amps then 100va would be ok(that’s 2x9v@5+amps) . The B+ requirement is for 500v @ 100ma and 300v @ 12ma. The rebuild is documented here:
Vitalstates - SV572
Well the build went ahead….and bit me in the ****. The B+ transformer got really hot and the heater transformer buzzed like a pneumatic drill. I learned that a ct transformer is no good for full wave bridge(bit late but never mind)…so I sourced a 0-600 @ 150ma frame and a 2x9v 120va toroid for the heaters. Re drilled the chassis, moved everything around to accommodate and thought what a good plan.
Well the build went ahead…..and bit me in the ****. The B+ transformer got really hot, and the toroid got really hot. Rod Coleman explained that the transformer should have 3 times the capacity of the heater requirement(bit late, but never mind)….so I sourced a 2x9v frame at 200va which is 9v at 11-12Amps. I also sourced a 0-600v at 200ma frame(remember, I only need 500v @ 113ma). Also put the heater rectifier on a heatsink at the rear of the chassis. Re drilled the chassis, moved everything around and sat back thinking what a great plan.
Well the build went ahead…and bit me in the ****. The B+ transformer gets very hot and the heater transformer also gets very hot. I’ve measured both transformers and according to my dmm with temp measure they are both reaching 70 deg C after about 30-45 mins. Also, upside down on the bench, without the base screwed on, all is quiet. As soon as the base is brought anywhere near the chassis all hell breaks loose. By that I mean the base vibrates and makes the whole chassis shake and there is much noise. Steel chassis and steel base.
Amp sounds very nice but with the heat and vibrating when it’s got the base on it’s destined for the scrap.
The questions:
What is a realistic max temp for a transformer. Is 70degs reason for alarm. It’s way hotter than my Pass amps because I can’t apply the 5 second rule, more like 2 seconds. I didn’t expect a 200ma transformer to get hot when asked to deliver just over 100ma. Is that a reasonable expectation.
Is the loud buzzing the result of some interaction between all the transformers and chokes and the steel base. Would an aluminium base cure the problem?. The thing that confuses me is that the last incarnation didn’t buzz/vibrate and the only thing that’s changed is one choke that used to be on top is now inside and 1 transformer that used to be inside is now on top.
Ed
Attachments
The B+ power supply is here:
http://www.vitalstates.org/diy/amplifiers/sv572-ps.jpg
On the last transformer(150ma rating) measuring across a 10R resistor between the rectifier and the first choke showed 1.16v(112ma). The power supply has not been touched other than to swap in the new transformer so I have no reason to believe the current draw has changed.
The heater power supply is here:
http://www.vitalstates.org/diy/amplifiers/sv572-hps-cct.jpg
The voltages all look valid:
9 vac on secondarys under load
10.43 vdc between rectifier and first cap
10.36 vdc between last cap and regulator.
Adjusting the current on the regulator easily produces the required 6.3vdc across the filament.
Ed
not just the wiring, if one of the diodes is gone its no longer a bridge and DC flows through the secondary ... may not even have a major impact on voltage/current readings ...
i ended up with a seperate ps for the 3 amp heaters on my gm70 amplifier as the alloy chassis got so hot. i use a 300va tx just for the heaters.
i built a pp sv811-10a amp years ago and still have low milage tubes so nice to see someone using these sv tubes, they look great on paper but are a bugger to use as i'm sure you know!
enzo
i built a pp sv811-10a amp years ago and still have low milage tubes so nice to see someone using these sv tubes, they look great on paper but are a bugger to use as i'm sure you know!
enzo
Built with SV811-3 years ago as well and still use it. The example of this amp shows pretty good how complex a single ended design can get. But in addition to nice music it can help to stay in shape - if you lift the 50+ pounds from ground to the desk from time to time.
Even though I use the 382X as B+ transformer, the 372FX should be sufficient. If just the 372 would get hot, I would check wiring, rectifier and the transformer itself. An input power supply choke will buzz or rattle if it has any loose parts, such as laminations, and it can also make your chassis sing... But since your ok dimensioned heater transfomer gets hot as well...? Maybe some charts showing both transformer load currents can help...
Marcus
Even though I use the 382X as B+ transformer, the 372FX should be sufficient. If just the 372 would get hot, I would check wiring, rectifier and the transformer itself. An input power supply choke will buzz or rattle if it has any loose parts, such as laminations, and it can also make your chassis sing... But since your ok dimensioned heater transfomer gets hot as well...? Maybe some charts showing both transformer load currents can help...
Marcus
thanks for the interest guys.
Current thinking puts the problem in 1 or more of 3 possibilities:
1. Both transformers(B+ and heater) have no insulating washers on the frame bolts...I am waiting for delivery of shoulder washers to see what effect these have.
2. I have 10 transformers in/on a steel chassis....many people have commented on the use of steel chassis and the perils therein.
3. The big mains transformers and one large choke are very close to each other which may give induction osmosis(my phrase, for humour).
I am starting with the transformer washers and will progress through the list if a solution is not found.
Ed
Current thinking puts the problem in 1 or more of 3 possibilities:
1. Both transformers(B+ and heater) have no insulating washers on the frame bolts...I am waiting for delivery of shoulder washers to see what effect these have.
2. I have 10 transformers in/on a steel chassis....many people have commented on the use of steel chassis and the perils therein.
3. The big mains transformers and one large choke are very close to each other which may give induction osmosis(my phrase, for humour).
I am starting with the transformer washers and will progress through the list if a solution is not found.
Ed
I've bumped this up because I'm still scratching my head over this one....
I have taken both transformers off the chassis and run them on the bench with their secondaries in a screew block with nothing attached. i.e absolutely no load. I have a maplin wall meter which measures, among other things, current taken from the wall.
both transformers(ht: 0-600v 200ma spec & heater: 2x9v 12amp spec) consume 250ma at the wall and both get hot after 1 hour running no load. The ht transformer gets very hot.
I have very limited experience with transformers, to date all my Hammonds have worked as per spec, so I really don't know if this is acceptable or not. Certainly I don't feel happy running an amp with transformers that get this hot.
I'd be grateful for any further input. I'm still waiting for delivery of the shoulder washers to see if they have any effect.
Ed
I have taken both transformers off the chassis and run them on the bench with their secondaries in a screew block with nothing attached. i.e absolutely no load. I have a maplin wall meter which measures, among other things, current taken from the wall.
both transformers(ht: 0-600v 200ma spec & heater: 2x9v 12amp spec) consume 250ma at the wall and both get hot after 1 hour running no load. The ht transformer gets very hot.
I have very limited experience with transformers, to date all my Hammonds have worked as per spec, so I really don't know if this is acceptable or not. Certainly I don't feel happy running an amp with transformers that get this hot.
I'd be grateful for any further input. I'm still waiting for delivery of the shoulder washers to see if they have any effect.
Ed
Hi Ed,
Some transformers do get hot regardless of load. It depends on the specified core-losses, and the rated primary voltage.
For instance, many transformers sold in the UK are rated 230V, (as per the UK supply spec), but the actual street hardware is still the old 240V supply we have had for decades. 240V into a 230V primary is usually OK, but a cheap or badly designed item, that already has high core losses at 230V, may get unpleasantly hot at 240V. Check your supply too - you my have 245V at your location.
My personal solution is to buy trafos from JMS, and specify 240V primaries. If you ask, they will specify the core losses and winding resistance for a given design, so that you can compare. With a 200VA (240V primary) and a 240V supply connected, you can expect core losses below 10W. Why not ask your trafo vendor for the rated losses for your parts, and we can then compare.
example JMS trafo, highly recommended 200VA split-bobbin design:
200 VA
These trafos work very well, despite low cost, but the appearance is somewhat industrial.
I am always willing to recommend a trafo for use with my Filament regulators, please ask at any time.
Some transformers do get hot regardless of load. It depends on the specified core-losses, and the rated primary voltage.
For instance, many transformers sold in the UK are rated 230V, (as per the UK supply spec), but the actual street hardware is still the old 240V supply we have had for decades. 240V into a 230V primary is usually OK, but a cheap or badly designed item, that already has high core losses at 230V, may get unpleasantly hot at 240V. Check your supply too - you my have 245V at your location.
My personal solution is to buy trafos from JMS, and specify 240V primaries. If you ask, they will specify the core losses and winding resistance for a given design, so that you can compare. With a 200VA (240V primary) and a 240V supply connected, you can expect core losses below 10W. Why not ask your trafo vendor for the rated losses for your parts, and we can then compare.
example JMS trafo, highly recommended 200VA split-bobbin design:
200 VA
These trafos work very well, despite low cost, but the appearance is somewhat industrial.
I am always willing to recommend a trafo for use with my Filament regulators, please ask at any time.
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i never used steel chassis for this reason....aluminum is easy to work with and does not interact with your traffos....
commercial traffos operate at higher flux densities, they have lesser primary turns and so can really run hot, especially when run at near their maximum ratings.....
that is the reason i design and build my own traffos, i run my traffos at less than 1T, some at even 0.6T, i have no heat issues as a result, i make them bigger than commercial offerings....
you can try to seat your traffos using acrylic....
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