There's plenty RS, farnell, digikey, mouser. If you get a CT 12v one. You can use 2 diodes rather than 4 and reduce the voltage drop there.
Great. That should be here tomorrow, along with a 15000uF capacitor and a bridge rectifier. But what are the 0.2Ω resistors in your circuit for? RS don't seem to stock any.
If you decided not to get a SMPS, I'd follow baudouin0's advice and get a 12Vac CT transformer. Due to two diodes' voltage drop in a bridge rectifier, acquiring 6.3 Vdc from a 6Vac winding is a rather tough job.
Best regards!
Best regards!
I was going to wire up the two 6v windings in parallel and use baudouin0's circuit from page 11. Would that not work?
I stand corrected - putting the windings in parallel and using a full wave schottky rectifier gives more voltage. So second schematic in #104 is the the one to go for. With the transformer you have and the DC resistance the minimum voltage on the reg is 7.2V - you could drop the output slightly to 6.2v.
LT1764AETPBF | Analog Devices LT1764AETPBF, LDO Regulator, 3A Adjustable, 1.21 → 20 V 5-Pin, TO-220 | RS Components
The dropout is 175mV @ 1A.
LT1764AETPBF | Analog Devices LT1764AETPBF, LDO Regulator, 3A Adjustable, 1.21 → 20 V 5-Pin, TO-220 | RS Components
The dropout is 175mV @ 1A.
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Thanks. Could you explain why I need the regulator? Can I not just dial in the voltage with a resistor? Once it’s right, the load isn’t going to change.
The unregulated supply is rich in 100Hz and higher harmonics and may get into your signal path in the same way the hum does.
Ah - understood. Thanks.
Do I need a trimmer pot to adjust the voltage then, or just the fixed resistors in your schematic?
And can you suggest a shottky that’s through hole fixing?
Do I need a trimmer pot to adjust the voltage then, or just the fixed resistors in your schematic?
And can you suggest a shottky that’s through hole fixing?
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Would these be all right?
SB5100-T | Diodes Inc 100V 5A, Schottky Diode, 2-Pin DO-201AD SB5100-T | RS Components
SB5100-T | Diodes Inc 100V 5A, Schottky Diode, 2-Pin DO-201AD SB5100-T | RS Components
There's no need for a regulated heater supply, I'd say. Just drop excessive voltage by a suitable resistor after the filter cap. If there should be any hum left, get a 2nd cap after the resistor.
After all, all these components most probably take much more space and are much more expensive than a stock SMPS.
Best regards!
After all, all these components most probably take much more space and are much more expensive than a stock SMPS.
Best regards!
Yep or a 1n5820. You don't need more than 30v reverse voltage and the Vf gets better with lower reverse voltage. I suggested a regulator only because the hum is loud in the first place. If 50Hz hum is audible so might be 300mV of sawtooth rectified 100Hz as the higher harmonics the ear will be more sensitive. The TO220 will need a small heatsink (~1W). If you replace the 4k3 with a 4k7 and a 47K in parallel that's more accurate. No you don't need a pot.
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I agree with Kay that normally a regulator would not be needed but in your case with the loud hum it brings the 300mV 100Hz or so down to virtually nothing - so you have a good DC source. Its not very big a TO220 standing vertical with a small heat sink.
Well RS used Parcelfarce to 'deliver' my parts and I'd nipped out. They're the only courier who won't leave parcels with a neighbour or in a safe place - so I don't get it till Monday.
I tried grounding one side of the heater voltage and running it to the EF86 in shielded cable but that didn't help. Then I found a BR2512 bridge rectifier in a drawer. So I fitted that, along with a 15kuF capacitor and Bob's your uncle - no hum. The heater voltage is too high at 6.9v but I can get that down - maybe a resistor or another capacitor. But other than that, job's a good 'un for the time being.
Thanks for all the help - it's been great.
I tried grounding one side of the heater voltage and running it to the EF86 in shielded cable but that didn't help. Then I found a BR2512 bridge rectifier in a drawer. So I fitted that, along with a 15kuF capacitor and Bob's your uncle - no hum. The heater voltage is too high at 6.9v but I can get that down - maybe a resistor or another capacitor. But other than that, job's a good 'un for the time being.
Thanks for all the help - it's been great.
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Do you feed the EF86 exclusively from that? Then connect a 3.3 ohms resistor in series with the heater. Or wait until the 2nd EF86 is also connected and measure again. I guess the voltage will sag sufficiently.
Best regards!
Best regards!