02-27-2022, 03:32 AM
I am restoring a 5 valve 90 volt miniature valve battery powered non-Philco radio.
I need 90v and 1.4v. Over the decades there have been many valve battery eliminator.power supply circuits, mostly all use regular mains AC transformer/s, bridge and 78xx regulation for the filaments. I am wondering if a $3 prebuilt Chinese PCB will solve my problems for B+ .
In 2022 - can we make use of power mosfet switchers? For new restorers, old mains transformers with taps, are getting hard to find, doulbly so as we are on 240v. BTW Wall Wart transformers seem to top out at 24v. There is a genuine shortage of valve mains transformers, but plenty of burnt out ones.
Newbies powering up old ones, which kills the paper/wax caps, inturn leading to burnt out transformers. Once the magic smoke comes out - it most likey ends up in the bin. Thrift stores in .au do not stock vintage electronics, because of perceived legal liability issues - so that souce also goes direct to landfill. Same for aging vibrator units with cotton covered wires. Here a transformer is a $90 or so in bill of materials, plus labour on top.
I ask can we use a minature SMPS or chopper flyback, say 2.3 by 2.3 inchs ? Reviewing the situation for valve battery eliminators afresh, I identified new off-the-shelf possible solutions.
1) LED driver Units. Fixed current using things like constant current valley fill. These are cheap and small <100mA. It is said they overshoot voltage when no load. If only I had the smarts to modify these. And if only they stopped rubbing the IC part number off. I want a solution/model that will be around for years to come.
2) Cheap Chinese classic 2 transistor MOSFET SMPS - one output voltage.
3) Interesting 12v to B+ multi-tap transformer from 110-172-200-220v AC combo,complete with PCM controller for under $3 USD. It would need UF1007's to rectify output. Possibly zener ladder if the voltages are not as advertised.
Option 4 would be a holiday in Saigon, and a trip to the district with transformers made on the spot while you wait - dealers.
Option 5 is buy something on Ebay or build off the usual circuits using zeners or voltage quadruplers.
We are now in the year 2022 and I have decided to re-think the problem using modern parts availability for economical functional repair - not a shelf object. I decided option 3 wins - A cheap Chinese made PCM inverter using a SG3525A, two IRF3205 MOSFET's. At 2.2 GBP I have little to loose. OK maybe 5 quid tops. The tap between 110 and 172v gives 62V AC *1.414 =87 odd volts.
The reviews say check the solder joints(bridges or dry), and the voltages. If over 70w, I suspect the weedy heat sinks would have to be supersized.
Shortlist SWOT analysis
1) Modern 12v inverter board module that can supply 200-220v AC or so < 150 Watt
2) Modern voltage reducer module - less than a dollar prebuilt
3) 12 Volt plugpack or brick SMPS - everyone has these - zero cost
4) Adding a 12v DC jack hole is less invasive than IEC socket from a junked computer
PSU, and adding X2 safety caps and fuse inside, plus modern AC cord.
5) Smoothing caps. Again, plenty in my junkbox.
6) Any 12v wall wart. Modify'. The trouble is each charger seems to have a different 8 pin IC that could be flyback/PWM or smps. I have not yet encountered a 90v DC wall wart. Not sure why.
Dangers:
1) Modern 20khz chopper ferrite SMPS module may introduce RF interference - mileage may vary.
2) Raw chopper AC may need Fast speed rectifier diodes - as not 60Hz ; ringing?; additonal smoothing caps. Note: Order Schottky UF1007's as the fast rectifiers from used computer PSU's are lower voltage - may not up to the job
3) That '150' Watt unit may be less than 1/2 that, but still plenty -
4) May have to mount it in a tin can for shielding.
Benefits:
Price and availability.
Great if you have lost your mains transformer or 169 watt voltage dropping resistor (see Bush Radio DAC 90 repair).
Great if the rectifier valve or ballast valve has gone.
Loose the cheater cord / curtain fire starter whatever.
Great if your circuit diagram lacks voltage points
Opportunity to make existing tubes last longer
From 12v to B+ current restricted. Overload protection. Live Chasis is there for a reason.
Small and light. Maybe drive a BT module somewhere. use 0v 110v to drive any old
sacrificial 5v phone charger, and add a $1 dc-dc dropper module to 1.4v for filaments.
POstage: Mains transformers and back to back lighting transformers- nuff said.
Might be able to use those other junk box SMPS ferrite transformers to derive other
voltages. Something you cannot do at 50/60Hz. This PSU could be in an external box, and a discrete jack added - for restoration purists. Or in the battery compartment.
Qualifications: I make no money on the link referrals below, this is just a guide to what is presently available that looked to have B+ application.. Prices can vary a lot, as can postage. Each country will have a portal for cheap mail order stuff and parts. Ratings are variable - and refitting bigger heatsinks might be an idea. The 20KHz squarish waveform will probably give a misleading voltage indication on many budget multimeters for the inexperienced. This is just a concept. Yes, there are some cheaper suspect constant current LED driver boards out there for about $1 that might be pressed for use - However if only B+ HT - should be plenty. My theory is PWM chip should have some decent protection circuity in it.RT and CT allow frequency to be changed. (Pins 5 and 6?). I like the fact this part has silk screened part numbers,and recognizable part numbers (not sanded off). IMHO a smart design/product.
Keywords: to refind the part if the link fails or you want to find others selling what looks to be the same. 150W Car DC 12V to AC 110V 220V on Aliexpress.com or similar online hawkers.
Component Sourcing as at Feb 2022
https://www.aliexpress.com/item/1005001570148962.html
For about USD $3 (postage extra) you get a 2.3 by 2.3 inch Power inverter board with multiple AC out taps to create many voltages.(Range 3-16 dollars for the same thing) The unit pictured contained SG3525A pulse width modulator integrated circuit and two
IRF3205 MOSFETS. A tap between 172V and 110v should yield 62V if rectified (fast diodes or fast rectifiers ) = 87 volts odd - close enough. I do NOT know how things stand if input voltage varies. 172*1.414 on a bridge should yield 243v odd. If the 220v tap really was 280v then 395v DC means we are in KT88 grid zone.
Other links
See https://www.youtube.com/watch?v=Ktn4JEURLjQ Bush Radio DAC 90 repair - the original mains dropper. Finding a 169 watt, 800 ohm resistor
https://www.amazon.com/Voltage-Boost-Con...merReviews
As you see, pay a LOT more using Amazon, or the extra plastic terminals added.
Review: Load testing gave 170ma into 350v, perfect for my tube tester. Those who are reporting no VAC out probably have meters than wont read a 20khz ac signal. The output is 20khz not 60hz. Cheap dvms will not read above 1khz usually.
I will update this when my schottky UF4007's and Zener assortment arrive from China. I am told valve rectifiers will rectify 20KHz.
I need 90v and 1.4v. Over the decades there have been many valve battery eliminator.power supply circuits, mostly all use regular mains AC transformer/s, bridge and 78xx regulation for the filaments. I am wondering if a $3 prebuilt Chinese PCB will solve my problems for B+ .
In 2022 - can we make use of power mosfet switchers? For new restorers, old mains transformers with taps, are getting hard to find, doulbly so as we are on 240v. BTW Wall Wart transformers seem to top out at 24v. There is a genuine shortage of valve mains transformers, but plenty of burnt out ones.
Newbies powering up old ones, which kills the paper/wax caps, inturn leading to burnt out transformers. Once the magic smoke comes out - it most likey ends up in the bin. Thrift stores in .au do not stock vintage electronics, because of perceived legal liability issues - so that souce also goes direct to landfill. Same for aging vibrator units with cotton covered wires. Here a transformer is a $90 or so in bill of materials, plus labour on top.
I ask can we use a minature SMPS or chopper flyback, say 2.3 by 2.3 inchs ? Reviewing the situation for valve battery eliminators afresh, I identified new off-the-shelf possible solutions.
1) LED driver Units. Fixed current using things like constant current valley fill. These are cheap and small <100mA. It is said they overshoot voltage when no load. If only I had the smarts to modify these. And if only they stopped rubbing the IC part number off. I want a solution/model that will be around for years to come.
2) Cheap Chinese classic 2 transistor MOSFET SMPS - one output voltage.
3) Interesting 12v to B+ multi-tap transformer from 110-172-200-220v AC combo,complete with PCM controller for under $3 USD. It would need UF1007's to rectify output. Possibly zener ladder if the voltages are not as advertised.
Option 4 would be a holiday in Saigon, and a trip to the district with transformers made on the spot while you wait - dealers.
Option 5 is buy something on Ebay or build off the usual circuits using zeners or voltage quadruplers.
We are now in the year 2022 and I have decided to re-think the problem using modern parts availability for economical functional repair - not a shelf object. I decided option 3 wins - A cheap Chinese made PCM inverter using a SG3525A, two IRF3205 MOSFET's. At 2.2 GBP I have little to loose. OK maybe 5 quid tops. The tap between 110 and 172v gives 62V AC *1.414 =87 odd volts.
The reviews say check the solder joints(bridges or dry), and the voltages. If over 70w, I suspect the weedy heat sinks would have to be supersized.
Shortlist SWOT analysis
1) Modern 12v inverter board module that can supply 200-220v AC or so < 150 Watt
2) Modern voltage reducer module - less than a dollar prebuilt
3) 12 Volt plugpack or brick SMPS - everyone has these - zero cost
4) Adding a 12v DC jack hole is less invasive than IEC socket from a junked computer
PSU, and adding X2 safety caps and fuse inside, plus modern AC cord.
5) Smoothing caps. Again, plenty in my junkbox.
6) Any 12v wall wart. Modify'. The trouble is each charger seems to have a different 8 pin IC that could be flyback/PWM or smps. I have not yet encountered a 90v DC wall wart. Not sure why.
Dangers:
1) Modern 20khz chopper ferrite SMPS module may introduce RF interference - mileage may vary.
2) Raw chopper AC may need Fast speed rectifier diodes - as not 60Hz ; ringing?; additonal smoothing caps. Note: Order Schottky UF1007's as the fast rectifiers from used computer PSU's are lower voltage - may not up to the job
3) That '150' Watt unit may be less than 1/2 that, but still plenty -
4) May have to mount it in a tin can for shielding.
Benefits:
Price and availability.
Great if you have lost your mains transformer or 169 watt voltage dropping resistor (see Bush Radio DAC 90 repair).
Great if the rectifier valve or ballast valve has gone.
Loose the cheater cord / curtain fire starter whatever.
Great if your circuit diagram lacks voltage points
Opportunity to make existing tubes last longer
From 12v to B+ current restricted. Overload protection. Live Chasis is there for a reason.
Small and light. Maybe drive a BT module somewhere. use 0v 110v to drive any old
sacrificial 5v phone charger, and add a $1 dc-dc dropper module to 1.4v for filaments.
POstage: Mains transformers and back to back lighting transformers- nuff said.
Might be able to use those other junk box SMPS ferrite transformers to derive other
voltages. Something you cannot do at 50/60Hz. This PSU could be in an external box, and a discrete jack added - for restoration purists. Or in the battery compartment.
Qualifications: I make no money on the link referrals below, this is just a guide to what is presently available that looked to have B+ application.. Prices can vary a lot, as can postage. Each country will have a portal for cheap mail order stuff and parts. Ratings are variable - and refitting bigger heatsinks might be an idea. The 20KHz squarish waveform will probably give a misleading voltage indication on many budget multimeters for the inexperienced. This is just a concept. Yes, there are some cheaper suspect constant current LED driver boards out there for about $1 that might be pressed for use - However if only B+ HT - should be plenty. My theory is PWM chip should have some decent protection circuity in it.RT and CT allow frequency to be changed. (Pins 5 and 6?). I like the fact this part has silk screened part numbers,and recognizable part numbers (not sanded off). IMHO a smart design/product.
Keywords: to refind the part if the link fails or you want to find others selling what looks to be the same. 150W Car DC 12V to AC 110V 220V on Aliexpress.com or similar online hawkers.
Component Sourcing as at Feb 2022
https://www.aliexpress.com/item/1005001570148962.html
For about USD $3 (postage extra) you get a 2.3 by 2.3 inch Power inverter board with multiple AC out taps to create many voltages.(Range 3-16 dollars for the same thing) The unit pictured contained SG3525A pulse width modulator integrated circuit and two
IRF3205 MOSFETS. A tap between 172V and 110v should yield 62V if rectified (fast diodes or fast rectifiers ) = 87 volts odd - close enough. I do NOT know how things stand if input voltage varies. 172*1.414 on a bridge should yield 243v odd. If the 220v tap really was 280v then 395v DC means we are in KT88 grid zone.
Other links
See https://www.youtube.com/watch?v=Ktn4JEURLjQ Bush Radio DAC 90 repair - the original mains dropper. Finding a 169 watt, 800 ohm resistor
https://www.amazon.com/Voltage-Boost-Con...merReviews
As you see, pay a LOT more using Amazon, or the extra plastic terminals added.
Review: Load testing gave 170ma into 350v, perfect for my tube tester. Those who are reporting no VAC out probably have meters than wont read a 20khz ac signal. The output is 20khz not 60hz. Cheap dvms will not read above 1khz usually.
I will update this when my schottky UF4007's and Zener assortment arrive from China. I am told valve rectifiers will rectify 20KHz.
