ericj
Headphoneus Supremus
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- Aug 2, 2005
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Some data for people building or rebuilding / repairing / upgrading energizers. Since in my research i have found that some questions get asked over and over and sometimes the answers received are wrong or a near miss.
The zener device in an SRD, marked Z1100 in the SRD-7 Mk2 datasheet, is a bidirectional TVS diode. transient voltage suppressor. You want one with a 100v breakdown voltage (not a 100v working voltage, or a 100v clamping voltage). Based on data here: http://www.datasheets360.com/part/detail/z1100/6016642548585695874/
For my project i have selected an MCC brand P6KE100CA-TP, 45 cents at Mouser.
You can use two 100v zeners nose to nose, but, i don't want to.
For the rest of the diodes of course we mostly use 1n4007 but really anything from 1n4003-1n4007 will work. But owing to popularity, the 1n4007 may be cheaper. And within that range it hardly matters. All of these are way better diodes than ever made it into most energizers.
On the SRD-7 Pro and Mk2 schematics you see four devices represented by a big Z marked ZL01 through ZL04. It turns out that these are MOVs. Just like the devices in a "surge protector" type power strip, but at a different rating.
Spritzer tells me that some later devices used high voltage zeners instead, but the MOVs will be quieter because they lack the switching noise inherent in a zener.
The datasheet for the original device is here, but it's mostly in japanese: http://www.datasheetlib.com/datasheet/681268/enb461m-03a_fuji-electric.htm
archive.org has the text of a whitepaper for another member of the "Z-Trap" line of devices here: https://goo.gl/3Tz6Nn -- it is clearly stated that they are metal oxide varistors, not zeners.
So we're looking for a very low capacitance MOV rated for about 460v. Turns out these are currently available from a few vendors.
I have selected the Littelfuse V470ZA05P -- rated at 470v vs. the 460v of the original part (close enough!) and 35pf rather than the 40pf of the original device. 64 cents at mouser. They are tiny 5mm diameter discs.
The PTH devices marked BD100N in the SRD-7 Mk2 schematic are still available. The current, full part number is PTGL07BD100N2B51BO - buck 20 each at mouser. I didn't see anything that looked like a more modern or superior device that does the same job, but since materials science has come such a long way since the 1970's, the current product is undoubtedly superior to the old one.
These are here to protect both your transformers and your amplifier so if you for some reason think thermistors are ruining the sound, please at least replace them with some power resistors which should also serve to protect your amp from the reactive nature of a transformer load (and the DC resistance of the stax transformer is around 1 ohm, so this is a concern).
These are rated at 10 ohms each, used in parallel, so you'd want maybe a 5 ohm resistor in their place. The old SRD-7, fwiw, has a 4.7ohm thermistor in parallel with a 27ohm wirewound resistor.
Other than that, just keep in mind when building that most resistors are rated for maybe 350v, and in a Pro bias energizer the resistor on the bias line will be looking at 570v. Look for a resistor with a working voltage rating of 700v or 1kv for that position. Like Vishay HVR3700002204FR500.
The zener device in an SRD, marked Z1100 in the SRD-7 Mk2 datasheet, is a bidirectional TVS diode. transient voltage suppressor. You want one with a 100v breakdown voltage (not a 100v working voltage, or a 100v clamping voltage). Based on data here: http://www.datasheets360.com/part/detail/z1100/6016642548585695874/
For my project i have selected an MCC brand P6KE100CA-TP, 45 cents at Mouser.
You can use two 100v zeners nose to nose, but, i don't want to.
For the rest of the diodes of course we mostly use 1n4007 but really anything from 1n4003-1n4007 will work. But owing to popularity, the 1n4007 may be cheaper. And within that range it hardly matters. All of these are way better diodes than ever made it into most energizers.
On the SRD-7 Pro and Mk2 schematics you see four devices represented by a big Z marked ZL01 through ZL04. It turns out that these are MOVs. Just like the devices in a "surge protector" type power strip, but at a different rating.
Spritzer tells me that some later devices used high voltage zeners instead, but the MOVs will be quieter because they lack the switching noise inherent in a zener.
The datasheet for the original device is here, but it's mostly in japanese: http://www.datasheetlib.com/datasheet/681268/enb461m-03a_fuji-electric.htm
archive.org has the text of a whitepaper for another member of the "Z-Trap" line of devices here: https://goo.gl/3Tz6Nn -- it is clearly stated that they are metal oxide varistors, not zeners.
So we're looking for a very low capacitance MOV rated for about 460v. Turns out these are currently available from a few vendors.
I have selected the Littelfuse V470ZA05P -- rated at 470v vs. the 460v of the original part (close enough!) and 35pf rather than the 40pf of the original device. 64 cents at mouser. They are tiny 5mm diameter discs.
The PTH devices marked BD100N in the SRD-7 Mk2 schematic are still available. The current, full part number is PTGL07BD100N2B51BO - buck 20 each at mouser. I didn't see anything that looked like a more modern or superior device that does the same job, but since materials science has come such a long way since the 1970's, the current product is undoubtedly superior to the old one.
These are here to protect both your transformers and your amplifier so if you for some reason think thermistors are ruining the sound, please at least replace them with some power resistors which should also serve to protect your amp from the reactive nature of a transformer load (and the DC resistance of the stax transformer is around 1 ohm, so this is a concern).
These are rated at 10 ohms each, used in parallel, so you'd want maybe a 5 ohm resistor in their place. The old SRD-7, fwiw, has a 4.7ohm thermistor in parallel with a 27ohm wirewound resistor.
Other than that, just keep in mind when building that most resistors are rated for maybe 350v, and in a Pro bias energizer the resistor on the bias line will be looking at 570v. Look for a resistor with a working voltage rating of 700v or 1kv for that position. Like Vishay HVR3700002204FR500.
