The original circuit appears to use a 2R2 resistor in series with the PT HV secondary - so a CL-140 NTC would exhibit about the same resistance at 50% of 1.1Arms rated steady state current, and could be a direct swap-out if wanted.
PSUD2 can be used to indicate the NTC rms current (ie. the same as the secondary winding current). Although not having all the circuit details, NTC rms current looks to be around 0.55 - 0.6A, so that provides some detail as to why that particular NTC was recommended.
Raising the filter cap from 100 to 220uF is likely to halve the Vpp ripple on the OPT B+ supply, and have only quite a minor increase in peak winding current (which helps avoid increasing other forms of hum), but would have a noticeable increase for turn-on peak current - and hence the advantage of using a NTC (assuming it's cold at turn-on), as it would suppress turn-on peak current to less than the original design with 100uF.
The diode rms current appears to be below 0.3A, so the UF4007 is a good substitute (the UF4007 is not as robust as the 1N4007 so some caution is needed to check the use of UF4007 in doubler applications). The original diodes could be left in place if needed, and the UF4007 added in series, if authenticity and retaining existing parts was a concern.
PSUD2 can be used to indicate the NTC rms current (ie. the same as the secondary winding current). Although not having all the circuit details, NTC rms current looks to be around 0.55 - 0.6A, so that provides some detail as to why that particular NTC was recommended.
Raising the filter cap from 100 to 220uF is likely to halve the Vpp ripple on the OPT B+ supply, and have only quite a minor increase in peak winding current (which helps avoid increasing other forms of hum), but would have a noticeable increase for turn-on peak current - and hence the advantage of using a NTC (assuming it's cold at turn-on), as it would suppress turn-on peak current to less than the original design with 100uF.
The diode rms current appears to be below 0.3A, so the UF4007 is a good substitute (the UF4007 is not as robust as the 1N4007 so some caution is needed to check the use of UF4007 in doubler applications). The original diodes could be left in place if needed, and the UF4007 added in series, if authenticity and retaining existing parts was a concern.
Galu, not much to say about the Cadet integrated. I rescued it from an empty apartment in Leeds during the 1990s, and had it serviced. I replaced the screw speaker terminals with something better, and that is all she wrote. Has worked ever since. was in my main system for a few years, just lately replaced by Leak ST20
Cheers Steve
Cheers Steve
Thanks Steve, keep that Cadet safe, warm and dry!
I was out in my man cave today, in sweltering 15 degrees heat, cleaning the contacts of my HG88's pilot bulb which had been lighting erratically.
Gave the switches and pots a squirt of switch cleaner while I was in there. Am now ready for some more vintage valve action! Cheers!
I was out in my man cave today, in sweltering 15 degrees heat, cleaning the contacts of my HG88's pilot bulb which had been lighting erratically.
Gave the switches and pots a squirt of switch cleaner while I was in there. Am now ready for some more vintage valve action! Cheers!
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