My first all-valve project was an RIAA-correction amplifier for moving-magnet cartridges. As I wanted to make a circuit without semiconductor devices and as using a battery or a mercury vapour rectifier with smoothing for the heaters seemed unattractive, I used an AC heater supply. I took several precautions to reduce hum, such as using EF86 valves (with their low heater-to-grid capacitance) with decoupled cathodes for the input stages, using shielded twisted audio cable for the heater connections and using a voltage divider with two 100 ohm resistors as a "centre tap".
Much to my surprise, the hum was below the (quite low) noise floor as long as the transformer was far enough away from the circuit. The heater circuit didn't cause any hum issues at all, only the transformer's stray field did.
Much to my surprise, the hum was below the (quite low) noise floor as long as the transformer was far enough away from the circuit. The heater circuit didn't cause any hum issues at all, only the transformer's stray field did.
Back in 1930'Th rectification and filtering were too expensive for ordinary consumers. As well as regulation of screen grid voltages. Today it is cheap and easy, and there is no excuse not to do that making high end amplifiers.
I tell them, "Sorry, you are not my customer.
I tell them, "Sorry, you are not my customer.
For indirectly heated valves, it's also a complete waste of energy unless you make a switched-mode power supply, which much complicates matters.
Yikes! One must watch the dates on these posts. But this one is too good to let pass. Well said; often wondered myself!
Dc on heaters: Have become a 'why not' matter in the last decades, what with regulators and easy diodes freely available. Just a warning regarding those smacked-on rectifier + small capacitor jobbies: 'D.C.' poorly filtered with spikes like digs' hairs can cause more interference than properly laid-out a.c.. One does talk of a moderately well-filtered smooth d.c. if there is any ripple left.
But I come from the days when it was possible to have a hum-free RIAA circuit (possibly preceded by a stage of quiet amplification) with a.c. on heaters and often not clean mains a.c. at that.
Well; anything can be done wrong easily.
So, if you know how to get great results even from AC, from DC you can get even better results.
The most common mistake is, designers keep forgetting that wires have resistance and inductance, and mix rectifier and input currents through the same wire. Even if it is a thick bus, it has a resistance.
So, if you know how to get great results even from AC, from DC you can get even better results.
The most common mistake is, designers keep forgetting that wires have resistance and inductance, and mix rectifier and input currents through the same wire. Even if it is a thick bus, it has a resistance.
Now I know who's buying those tiny 3 digit meter boards on Ebay!
LOL
Powered from 8V filament DC, metering voltage drop on cathode bias resistors. Pretty convenient!
i will be evaluating this 24v dc suppy for use in 6c33 amps.....https://www.lazada.com.ph/products/...o4l.cart.0.0.78043e17ML1Trb&urlFlag=true&mp=1
Hi tony,
You might want to use one that has the metal shield installed. This will really help contain the RFI emitted by the switcher.
I just ordered two 24 volt power supplies, one for each project I'm working on. The supplies in the case cost more, but less switching interference is well worth the extra. There will be some 24 VDC to 12 VDC switchers and I might have to go linear, or find a box for them.
Best, Chris
You might want to use one that has the metal shield installed. This will really help contain the RFI emitted by the switcher.
I just ordered two 24 volt power supplies, one for each project I'm working on. The supplies in the case cost more, but less switching interference is well worth the extra. There will be some 24 VDC to 12 VDC switchers and I might have to go linear, or find a box for them.
Best, Chris
Chris, i just received a totally enclosed 24vdc 20A power supply, cost was around U$20..the one i linked was used to power our kampana amps and even if you located it close to the amplifier board, there was no interference whatsover that can be heard thru the speakers....that is why i am convinced that smps is the way to go forward...
I use four of these in the one and only amp I built that has built in metering... DC 0-1V Analog Voltmeter Analogue Voltage panel meter SO45 directly Connect 608307748306 | eBay
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