I assume you are allowing for transformer loading to ensure you deliver 6.3V? From your experience what is the headroom you allow? By padding down, I assume you mean trimming excess voltage with suitable resistor.
In my case, I aim to reduce 7.5V to 6.3V and 356V to 310V. Is there a simple rule of thumb or more complex.
First you need to decide whether you will handle this on the primary side or the secondary. The majority of recommendations so far have been for the former, as this way the equipment is kept original, or relatively close to. This means you may avoid adding unexpected problems to the operation of the amp/supply.
Or you make the second choice and trim the B+ and heater Voltages.
Or you make the second choice and trim the B+ and heater Voltages.
If only my son was an apprentice sparky, oh wait..
Good tip. Lets see if he comes through and give it a go.
If 250Vac rms is allowable and still an in-spec amount according to the utility, then use of a bucking transformer is a possible solution.
Probably the most expensive solution: I know that pv inverters support the feed-in of reactive current to lower the AC voltage, like a Q(U) function. Combine that with a battery storage and you should have pretty good control over your household voltage.
I would go for bucking transformer in this case. A custom replacement transformer will cost alot of money.
Using a dropping resistor may waste power and you would only want it in the case where power draw is constant.
If you are dropping 5% of your line voltage then you only need a bucking transformer roughly 5% of the size of your power transformer. Fairly low cost.
Using a dropping resistor may waste power and you would only want it in the case where power draw is constant.
If you are dropping 5% of your line voltage then you only need a bucking transformer roughly 5% of the size of your power transformer. Fairly low cost.
You could cut down on the power required, and have a wider range of adjustment if you run a bucking transformer from a motorized variac. In that way you can vary the amplitude the primary voltage is bucked by in continuously variable steps.
The % voltage levels you measure are +19% and +15%. Given your 220V rated Yaqin MC5881A, that would indicate a mains level at the amp of 253V to 262V.
Your smartmeter was reading up to 253V at the switchboard, and that would be quite accurate as it is a tariff meter. You generate PV, which would likely connect at the switchboard, so its unlikely you are connecting downstream of the PV inverter, so your amp is likely seeing up to 253V. Amps are likely to generate heater and B+ levels on the slightly higher side if you had mains voltage exactly at the equipment rating voltage (ie. 220V).
Given you should be aiming to get down towards 220V incoming mains voltage to match your amp, that does mean you may want to aim for a bucking transformer that subtracts about 30V. The easiest and simplest transformer to find is likely a 24VAC secondary with perhaps at least a 2A 24VAC secondary rating. Dick Smith sold thousands of that type with tappings, and even 2x 12V vintage Q-hal transformers would do the same job - its just packaging so that the transformers are safely untouchable, as the secondary winding now as AC mains on it, and the core may not be formally rated for connection to protective earth due to the secondary now sitting at AC mains.
A good project for an apprentice sparky.
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Some off-topic posts have been deleted.Thanks - interesting discussion and helpful insight. 😎
Mindful of safety when dealing with potentially lethal electricity, unless I find an exact match for a transplant the exisiting power transformer, a Bucking transformer also seems like a good option. I'm hoping to obtain a halogen transformer from my source as it's just become apparent scouring through my garage how scarce transformers are these days! I'll post results later on....
Mindful of safety when dealing with potentially lethal electricity, unless I find an exact match for a transplant the exisiting power transformer, a Bucking transformer also seems like a good option. I'm hoping to obtain a halogen transformer from my source as it's just become apparent scouring through my garage how scarce transformers are these days! I'll post results later on....
Thing is, if the electric company is supplying power that far out of spec, they need to be called on it, for safety reasons if nothing else.
Unfortunately it's not actually out of spec. The nominal supply voltage is 230V +10/-6% or 216V to 253V as per Australia Standard 60038. During maintenance/fault conditions it can range from 207V to 262V.
Why this is the is the case is whole over discussion and avtech23 posted a link above ... LV Voltage Report | Energy Council
It's a common issue here so, whilst I am happy to contact the supplier I am doubtful of it resulting in any benefit to my amp.
I wonder if it would be possible to incorporate the HV regulator from Jan Didden into the amp as an alternative to changing transformers?
T-reg HV regulator | Linear Audio NL
Boards are available from the Diya store:
Linear Audio T-reg V5 – diyAudio Store
T-reg HV regulator | Linear Audio NL
Boards are available from the Diya store:
Linear Audio T-reg V5 – diyAudio Store
I’ll take a look however I’m averse to modification of the original design especially transistorising else where might that end
None the less it’s a worthy solution.
Ah, ok. Good point although I'm certain there are plenty of smarter alternatives to regulating the heater voltage other than burning it off through a series resistor and turning up the a/c. 😱
It's all about this and that. Series resistance (a small amount) could be said to soft start the heaters, and won't add anything negative to the signal but is inefficient. I've also used series inductors to reduce heater voltage and filter the signal.
I agree for small amounts but in this case resistors are going to create heat issues given heater supply 7.56VAC, main secondary output is 376VAC and B+ is 474VDC. There is an entire thread on Yaqin MC5881A improvements including trimming voltages and adding inductive filters. It's a totally valid suggestion but I don't believe it solve the issue at hand.
Likely that power transformer is running pretty near its design limits, a little higher voltage for any reason could lead to core saturation and a fried transformer.
In any event not reducing the input voltage on the primary means the transformer will run hotter due to increased losses in the transformer and the higher load current resulting from the higher supply voltage.
Long term operation under these conditions will shorten tube life and likely the life of that power transformer.
A bucking transformer is a really good idea.
In any event not reducing the input voltage on the primary means the transformer will run hotter due to increased losses in the transformer and the higher load current resulting from the higher supply voltage.
Long term operation under these conditions will shorten tube life and likely the life of that power transformer.
A bucking transformer is a really good idea.
i have several of my amps sent to Australia, brought by Filipino balikbayans there,
i designed my power traffos at 240v primaries and 50 hz and should work fine there..
they run cool here in Manila.......
i designed my power traffos at 240v primaries and 50 hz and should work fine there..
they run cool here in Manila.......