Hello,
Thank you in advance for any advice. Please forgive me if I missed an existing discussion and re-direct. I am hoping to learn more and continue making my shopping cart.
For SSE build, the full 500V B+ at bleeder resistor R2 exceeds the data sheet 350V working voltage with a similar situation at R4, etc. All metal oxides this size that I am finding are 350V.
Is metal oxide specified for cost and performance (noise) tradeoff? Or is the surge capacity of metal oxide necessary?
The parts list specifies:
Metal oxide in the power supply R2, R3, R4. Also R14/R24, R18/R28.
Wirewound R1, R17/R27.
Metal film everywhere else.
I had considered a few options, but am not sure how to proceed.
Option 1:
Two 75k 2W metal oxides in series to step down.
Fitting two 75k metal oxide 2W (MOS2CT52R753J) in a series zigzag in the R2 space would each see 250V and dissipate 0.8W each. They are rated to 350V and could step down the B+ without exceeding rating and benefitting metal oxide if this is needed.
Option 2:
Single 150k 3W metal oxide with a 500V rating, such as NTE 3W415 (it is bit larger).
Royal Ohm, SR Passives, and NTE have some metal oxides with list 500V working voltage. Problem is they either require minimum orders or become physically larger. For reference, the holes are 25.4 mm apart. The parts list R2 is metal oxide 283-150K-RC with 350V working voltage L=16 mm. The NTE L=24.5 mm. Leads would have to bend and double back a little.
Option 3:
Single 150k 3W metal film with a 750V rating.
If metal film resistor is okay for R2, R4, etc. Vishay PR03000201503JAC00 (L=19.5 mm) and TE RR03J150KTB (L=15 mm) look good.
Thank you in advance for any advice. Please forgive me if I missed an existing discussion and re-direct. I am hoping to learn more and continue making my shopping cart.
For SSE build, the full 500V B+ at bleeder resistor R2 exceeds the data sheet 350V working voltage with a similar situation at R4, etc. All metal oxides this size that I am finding are 350V.
Is metal oxide specified for cost and performance (noise) tradeoff? Or is the surge capacity of metal oxide necessary?
The parts list specifies:
Metal oxide in the power supply R2, R3, R4. Also R14/R24, R18/R28.
Wirewound R1, R17/R27.
Metal film everywhere else.
I had considered a few options, but am not sure how to proceed.
Option 1:
Two 75k 2W metal oxides in series to step down.
Fitting two 75k metal oxide 2W (MOS2CT52R753J) in a series zigzag in the R2 space would each see 250V and dissipate 0.8W each. They are rated to 350V and could step down the B+ without exceeding rating and benefitting metal oxide if this is needed.
Option 2:
Single 150k 3W metal oxide with a 500V rating, such as NTE 3W415 (it is bit larger).
Royal Ohm, SR Passives, and NTE have some metal oxides with list 500V working voltage. Problem is they either require minimum orders or become physically larger. For reference, the holes are 25.4 mm apart. The parts list R2 is metal oxide 283-150K-RC with 350V working voltage L=16 mm. The NTE L=24.5 mm. Leads would have to bend and double back a little.
Option 3:
Single 150k 3W metal film with a 750V rating.
If metal film resistor is okay for R2, R4, etc. Vishay PR03000201503JAC00 (L=19.5 mm) and TE RR03J150KTB (L=15 mm) look good.
For a bleeder resistor the type of resistor is irrelevant. It just has to eat power.
In your case I would use for instance the Mouser search function, starting with the needed standoff voltage and power and value, that will funnel you to available devices. Then select the cheapest one.
Jan
In your case I would use for instance the Mouser search function, starting with the needed standoff voltage and power and value, that will funnel you to available devices. Then select the cheapest one.
Jan
That is why we used Carbon Film resistors back in the 50s, 60s, 70s and 80s.
They drift around but don't mind lots of voltage across them.
MO and MF are much cheaper now. Select what you require from the manufacturers specification sheet, not from what someone suggests.
They drift around but don't mind lots of voltage across them.
MO and MF are much cheaper now. Select what you require from the manufacturers specification sheet, not from what someone suggests.