12-01-2013, 07:17 PM
Gary's offer of the 1240R dropper sound just the ticket.
Failing that, what about this – a 30W Watt 1K Ohm 'Wire Wound Variable Resistor Ceramic Rheostat', just £2.93 post free (on a slow boat from China!), which - if not on this occasion - may be worth thinking about in other applications:
http://www.ebay.co.uk/itm/30W-Watt-1K-Ohm-Wire-Wound-Variable-Resistor-Ceramic-Rheostat-/350663047272?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item51a5257868
What’s not to like about that?
The dropper on the DAC90A is 950 + 150 +150 = 1250R total. If run on the 250V setting, (kindest to the valves), the HT tapping point is at 300R, so if this 1,000R dropper was used, and the tapping set at 300R for the HT, the HT would be fine, but there would be a shortfall of 250R for the heater chain, so an additional series resistor would be needed. The heater chain draws 0.1Amp, so if the nearest preferred value resistor to 250R was selected – 270R, then 27 Volts would be dropped across that resistor, and with 0.1 Amp flowing, the wattage would be 27 x 0.1 = 2.7 Watts. Hence, a ceramic wirewound 5 Watt 270R resistor, which is only 10mm square x 23mm long, should do the trick. Or to be on the safe side, a 10Watt one is 48mm x 10mm square. EG:
http://www.esr.co.uk/components/products...istors.htm
Just a thought.
Failing that, what about this – a 30W Watt 1K Ohm 'Wire Wound Variable Resistor Ceramic Rheostat', just £2.93 post free (on a slow boat from China!), which - if not on this occasion - may be worth thinking about in other applications:
http://www.ebay.co.uk/itm/30W-Watt-1K-Ohm-Wire-Wound-Variable-Resistor-Ceramic-Rheostat-/350663047272?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item51a5257868
What’s not to like about that?
The dropper on the DAC90A is 950 + 150 +150 = 1250R total. If run on the 250V setting, (kindest to the valves), the HT tapping point is at 300R, so if this 1,000R dropper was used, and the tapping set at 300R for the HT, the HT would be fine, but there would be a shortfall of 250R for the heater chain, so an additional series resistor would be needed. The heater chain draws 0.1Amp, so if the nearest preferred value resistor to 250R was selected – 270R, then 27 Volts would be dropped across that resistor, and with 0.1 Amp flowing, the wattage would be 27 x 0.1 = 2.7 Watts. Hence, a ceramic wirewound 5 Watt 270R resistor, which is only 10mm square x 23mm long, should do the trick. Or to be on the safe side, a 10Watt one is 48mm x 10mm square. EG:
http://www.esr.co.uk/components/products...istors.htm
Just a thought.
Regards, David.
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
