> 1K/25W "HR2" resistor on HT output does not make sense
Very hard to keep track when the image is (for NO good reason) three times bigger than my screen.
However it *looks* like that 1K is relay-switched from the 12V supply. The 1K is only "live" when the power is OFF. It won't cook day and night. It will cook about 3 seconds after the 12V fades away (decaying exponentially).
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> The secondary windings shorting rectifiers as shown will draw infinite current
Oh, cool! I like things which start with a BANG! I totally missed that.
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> the slow-blow preamp and actually built one...
The SB uses about 6 or 7 ma per stage, 13mA per channel.
The power supply I found in the same ZIP seems to be 200mA. It could feed *sixteen* of these preamps.
It isn't critical about power supply voltage. 350V won't melt it, 250V won't seriously reduce maximum output, and it would run on 150V though increasingly "colored" at high studio levels.
Let's start with a 230V AC winding, fairly readily available. This can rectify-out to 230*1.4= 322V DC.
Assuming two channels, 25mA total, we might start with 25uFd. Actually on a small job needing clean power, I'd buy a 10-bag of 47uFd and start with one 47uFd.
I have some rules of thumb for preamp filtering but I'll assume you can do busy-work and pick a five cap design (leaving a half-bag of caps for another project). If you were making a million units you'd want to do a sharp study of cap count and cost.
Since we picked the first cap bigger than 1uFd/mA, the ripple should be under 5%, or under 15V.
We need to clean some more.
Five caps and a C-R-C-R-C-R-C-R-C filter needs four resistors.
Let's assume these resistors will drop from 320V to 250V, or 70 volt drop. At 25mA this is 70V/25mA= 2.8K Ohms. We need this in four chunks, so four 700 Ohm resistors.
The reactance of 47uFd at 100Hz is 35 Ohms.
One R-C section of 700 ohm resistor and 35 ohm cap reactance will reduce 100Hz ripple 35/735 or 1/20th.
Three such filters will reduce 100hz ripple by 1/(20*20*20) or 1/8,000.
15V ripple at first cap, reduced by 8000, is 2mV ripple output.
This may be clean enough; or we may need 100uFd caps (double the cost will give 8X the filtering).
The OVER-KILL design uses three $20 caps and a $30 choke.... over $100.
The more appropriate design uses five $4 caps and some cheap resistors... more like $30.
(In fairness, the KILL design will support 16 channels, the right-size was scaled for one or two channels.)