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Posted: 4/15/2024 10:14:42 PM EDT
[Last Edit: Jambalaya]
Somewhere in storage I have an Elenco bench power supply kit. It's been close to 15 years since I built it, but IIRC it has adjustable AC voltage output.
If I remove the transformer from a tube amp from the circuit, can I (relatively) safely test it using this low AC voltage power supply? I'm am thinking I need to check the primary and secondary windings for continuity, isolation from the core/case, and make sure the transformation ratio from primary to secondary (and any taps) is correct. It's possible there may be issues that only appear at full line voltage, but this might be good enough to tell me whether to proceed with this transformer or to order a replacement right off the bat. Anything else I'm missing? |
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Posted: 4/15/2024 11:00:49 PM EDT
[Last Edit: wheel]
[#1]
I think you can do it as you described. Also of course you can check some things like continuity of windings, isolation (at least at low voltage) etc. using an ohm meter.
I would put a low voltage (like 5-10V AC) across the primary and measure the secondary output. Not knowing the turns ratio, beware the secondary voltage may still be a bit high so be careful. You could also do the reverse - apply a small AC voltage to the secondary and measure the primary. ETA: You cannot predict from such tests whether the transformer will withstand full line voltage. The only way to tell is to test it. In my experience an isolation fault is rare. With full line voltage applied to the primary, measure the AC voltage from the core to ground (third wire) or to neutral, it should be zero (or close to it). |
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Posted: 4/16/2024 12:15:13 PM EDT
[#2]
After checking for continuity and shorts, couldn't you hook
the primary winding to a Variac and bring the voltage up slowly while looking at the secondary output with a volt meter? Is that what the variable AC supply you mention does? |
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Posted: 4/16/2024 6:31:10 PM EDT
[Last Edit: Jambalaya]
[#3]
Quote HistoryOriginally Posted By KB7DX: After checking for continuity and shorts, couldn't you hook the primary winding to a Variac and bring the voltage up slowly while looking at the secondary output with a volt meter? Is that what the variable AC supply you mention does? It's not really a variac, and I don't have one. This is the supply: https://www.elexp.com/products/32xp720kac-dc-requivated-supply-kit |
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Posted: 4/16/2024 6:51:16 PM EDT
[#4]
Wheel is correct.
On your supply the 3 binding posts near the switch will output AC. The output voltage is 6.3 V either yellow to black or 12.6V yellow to yellow. Just remember...the output voltage will be far above 6 (12) volts. Keep everything except the meter probes away for the output terminals. Quote HistoryOriginally Posted By wheel: I think you can do it as you described. Also of course you can check some things like continuity of windings, isolation (at least at low voltage) etc. using an ohm meter. I would put a low voltage (like 5-10V AC) across the primary and measure the secondary output. Not knowing the turns ratio, beware the secondary voltage may still be a bit high so be careful. You could also do the reverse - apply a small AC voltage to the secondary and measure the primary. ETA: You cannot predict from such tests whether the transformer will withstand full line voltage. The only way to tell is to test it. In my experience an isolation fault is rare. With full line voltage applied to the primary, measure the AC voltage from the core to ground (third wire) or to neutral, it should be zero (or close to it). |
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Posted: 4/16/2024 8:18:22 PM EDT
[Last Edit: KB7DX]
[#5]
That power supply has a fixed AC output. Looks like a 12.6v center
tapped AC output which is a common "filament transformer" with 6.3v per "side". Cheap Variac from Jeff I had a few variacs I got from an estate years ago. Sold most of them at the local hamfest. I have a GIANT one out in the shed. That thing is probably 8 inches in diameter and was used in a homebrew battery charger. Looks like Dr. Frankenstein built it. Part of my haul..    |
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Posted: 4/16/2024 8:58:35 PM EDT
[#6]
Quote HistoryOriginally Posted By KB7DX: That power supply has a fixed AC output. Looks like a 12.6v center tapped AC output which is a common "filament transformer" with 6.3v per "side". Cheap Variac from Jeff I had a few variacs I got from an estate years ago. Sold most of them at the local hamfest. I have a GIANT one out in the shed. That thing is probably 8 inches in diameter and was used in a homebrew battery charger. Looks like Dr. Frankenstein built it. Part of my haul.. https://www.ar15.com/media/mediaFiles/108158/DSCN4596_JPG-2341582.jpg https://www.ar15.com/media/mediaFiles/108158/DSCN4590_JPG-2341577.jpg https://www.ar15.com/media/mediaFiles/108158/IMG_20180202_195450_130-2341578.jpg Wow! You could build a ton of power supplies. |
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Posted: 4/16/2024 9:09:29 PM EDT
[#7]
You could also fab up a dim bulb tester.
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Posted: 4/16/2024 9:20:38 PM EDT
[#8]
 How to bench test an unknown vintage tube high voltage power transformer |
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Posted: 4/16/2024 9:27:46 PM EDT
[#9]
Quote HistoryGood info, thanks! |
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Posted: 4/16/2024 9:30:22 PM EDT
[#10]
Quote HistoryOriginally Posted By Jambalaya: Good info, thanks! Quote HistoryOriginally Posted By Jambalaya: Good info, thanks! No problem. Uncle Doug has a few on this too, but I couldn't remember which one was best so Terry from DLab is just fine too! |
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Posted: 4/18/2024 9:53:31 PM EDT
[#11]
Well, I got this big pig out of the amp, along with having to desolder a lot of other stuff, and I hope I can get it back together without having to study schematics. It was filthy dirty and I'm going to have to really scrub the amp to get it clean. But at least it's out. Testing is next.
 Attached File Attached File |
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Posted: 4/18/2024 10:22:11 PM EDT
[#12]
What amplifier is that? Looks like the staining is rodent pee.
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Posted: 4/18/2024 11:24:50 PM EDT
[Last Edit: Jambalaya]
[#13]
Quote HistoryOriginally Posted By KB7DX: What amplifier is that? Looks like the staining is rodent pee. It's a Heathkit SB220. My FIL gave it to me. His neighbor a couple of houses down moved away (and passed away) and had left it in the trunk of a junk car sitting outside for years. I put it in my garage for more years. It very well could be mouse droppings. It was a LOT dirtier last year when I first opened it up, but there were a lot of spots I just couldn't get to without disassembling it. Of course, in doing so, I have to keep track of how everything went together. I have taken a lot of pictures with my phone, and I think I will be able to get it back together. When I first dug into it, both breakers had been tripped, and there are a few other signs that it wasn't working. The biggest red flag was the CB radio found in the trunk along with it.  I figured testing the transformer would be a good first step. Hopefully I won't need to replace the breakers. I did buy all the Harbach kits for it and thise are assembled and ready to install. None of the transformer leads appear to be shorted to the core, so that's good, and there appears to be the correct continuity between primary windings and taps, and secondary windings. I'm going to clean up as best as I can and get the transformer soldered back in. In the process I'll install the Harbach kits. I might spray paint the transformer black just to make it look less shitty. Then I need to remove the variable capacitors and I'm going to try cleaning them in an ultrasonic cleaner. Same goes for the 2 big coils. This was how it looked right out of the garage.  Attached File |
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Posted: 4/19/2024 8:57:40 PM EDT
[#14]
Wow! That's pretty grungy! Take your time and a lot of pictures.
You may want to download the manual. I borrowed one of those back in the early 90's to use on 10 meters. The solar cycle was raging and an amp wasn't really needed but I had absolutely no trouble busting pileups with 1500 watts into a 5 element beam. 
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Posted: 4/19/2024 11:03:11 PM EDT
[#15]
I had to tear it down pretty far to get at all the dirt. I hope it freaking works after all this effort.
I still need to buy a legal limit dummy load and eventually a tuner that will handle the power. I will also need to make a cable to key it.  Attached File |
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Posted: 4/19/2024 11:18:25 PM EDT
[#16]
Wooohooo! An SB 220 revival! Yours looks mostly stock. You might be better off to take the tuning caps completely apart and lightly surface all the plates, rather than ultrasonic them if there is any arching damage at all. Make sure you do the meter protection diodes mod, since the meters are unobtainable. Also, upgrade the filter bank and diode boards, and ground the grids.
Mine during the last repair when a filter cap shorted and took out a bunch of other parts. 
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Posted: 4/19/2024 11:29:37 PM EDT
[#17]
When working on this, jesus stick all of the high voltage components, the ground the high voltage with a jumper before sticking your fingers in the amp. You'll want a high voltage probe to test the output of the transformer, it should be around 1200VAC on each leg since the SB220 runs a voltage doubler rectifier. Also DO NOT try keying an SB220 with a modern radio, the keying circuit in a modern radio doesn't like keying the 120vac t/r relay in this amp, install the Harbach soft key board or use a keying isolator. While you are at it, replace both of the RF connectors with new high quality Teflon insulated ones, the stock ones are junk and have caused many sb220 failures. Finally update it to the horse shoe style parasitic chokes.
This probe is available on Amazon for about $100. 
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Posted: 4/20/2024 12:29:41 AM EDT
[Last Edit: Jambalaya]
[#18]
Quote HistoryOriginally Posted By FlatlandBusa: When working on this, jesus stick all of the high voltage components, the ground the high voltage with a jumper before sticking your fingers in the amp. You'll want a high voltage probe to test the output of the transformer, it should be around 1200VAC on each leg since the SB220 runs a voltage doubler rectifier. Also DO NOT try keying an SB220 with a modern radio, the keying circuit in a modern radio doesn't like keying the 120vac t/r relay in this amp, install the Harbach soft key board or use a keying isolator. While you are at it, replace both of the RF connectors with new high quality Teflon insulated ones, the stock ones are junk and have caused many sb220 failures. Finally update it to the horse shoe style parasitic chokes. This probe is available on Amazon for about $100. https://www.ar15.com/media/mediaFiles/457325/1000003080-3192952.jpg I decided to just stick the transformer back in without metering the voltage. The windings tested okay for continuity and isolation. I did buy all the Harbach kits last year including the soft key module, and the soft start, along with the new capacitor bank and metering board as seen here.  Attached FileI will definitely make a chicken stick. But for now it hasn't seen electricity for years. These capacitors are new and I shorted them before soldering them into the board. I know the soft start module needs to connect to some of the power wires coming off the input breakers but I figured it would be best to wire everything up as original first before doing the mods, to reduce the chances of a mistake. |
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Posted: 4/20/2024 12:57:33 PM EDT
[Last Edit: Jambalaya]
[#19]
Quote HistoryOriginally Posted By FlatlandBusa: Wooohooo! An SB 220 revival! Yours looks mostly stock. You might be better off to take the tuning caps completely apart and lightly surface all the plates, rather than ultrasonic them if there is any arching damage at all. Make sure you do the meter protection diodes mod, since the meters are unobtainable. Also, upgrade the filter bank and diode boards, and ground the grids. Mine during the last repair when a filter cap shorted and took out a bunch of other parts. https://www.ar15.com/media/mediaFiles/457325/1000002356-3192939.jpg Yeah the caps are dirty enough that I can't tell if there is damage or not beyond the corrosion that I see in places on the chassis. Looking at the picture you posted, there is a fuse on the post for the shorting bar that isn't mentioned in the manual. Is that one of the upgrades? I'll have to look up the meter protection mod. My meters had a bunch of junk rattling around inside. It was a coating on the light bulbs that had deteriorated and flaked off. I don't think any got stuck in the movements but I don't know if any of it works or not. I half expect it to pop and sizzle when I first power it on, and then need to be sent off for repair. Really I'm just cheap and don't want to spend the money for a modern amp. But given the storage conditions and the fact it was used by a CB'r who probably didn't know anything about it, I think there is a fair chance there is something messed up somewhere. But at least it will get a second chance at life with new capacitors.
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Posted: 4/20/2024 4:47:06 PM EDT
[#20]
Very nice project, Murdered out heatkit amps are the best amps!
Looking for an SB-220 to keep my SB-200 happy. I am going to keep my SB-200 as a backup when I replace it. I got it for $300 from a guy that got a steal on another amp. Had all the Harbach stuff in it, protection Diodes on the meter with an LED kit in it. Blacked-out face and black armor shell. I was surprised when I pulled the panel today that it is a powder coated panel front and back that was silk-screened and not the Vinyl sticker. Keep us posted on the progress of this thing. Suggestions on the HV probe is smart, picked up an old one from the Hamfest for $50.  Attached FileMy SB-200 |
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Posted: 4/21/2024 4:21:05 PM EDT
[#21]
Quote HistoryOriginally Posted By stanprophet09: Very nice project, Murdered out heatkit amps are the best amps! Looking for an SB-220 to keep my SB-200 happy. I am going to keep my SB-200 as a backup when I replace it. I got it for $300 from a guy that got a steal on another amp. Had all the Harbach stuff in it, protection Diodes on the meter with an LED kit in it. Blacked-out face and black armor shell. I was surprised when I pulled the panel today that it is a powder coated panel front and back that was silk-screened and not the Vinyl sticker. Keep us posted on the progress of this thing. Suggestions on the HV probe is smart, picked up an old one from the Hamfest for $50. https://www.ar15.com/media/mediaFiles/199367/IMG_9756__1__JPG-3193436.JPG My SB-200 That's a nice looking amp! I am not going to worry too much about cosmetics until I get it working. If it does work, after buying a dummy load and a tuner, I'll probably paint the cabinet and get a new front panel overlay. For now, I did at least polish up the terminals for the tubes. The one on the left isn't polished yet.  Attached File |
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Posted: 4/21/2024 6:08:29 PM EDT
[#22]
Some pics after cleanup and in the process of re-assembly.
I washed the capacitors in hot soapy water and brushed between the vanes as best I could. They appear to be undamaged. Lots of dust and cobwebs in there. I don't see any evidence of arcing. I also cleaned up the fan and fan motor, and got the meters re-installed on the front plate. I also washed the knobs. One of them has a ding in the aluminum center.  Attached File Attached File Attached File Attached File |
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Posted: 4/21/2024 7:25:57 PM EDT
[#23]
Quote HistoryOriginally Posted By Jambalaya: Yeah the caps are dirty enough that I can't tell if there is damage or not beyond the corrosion that I see in places on the chassis. Looking at the picture you posted, there is a fuse on the post for the shorting bar that isn't mentioned in the manual. Is that one of the upgrades? I'll have to look up the meter protection mod. My meters had a bunch of junk rattling around inside. It was a coating on the light bulbs that had deteriorated and flaked off. I don't think any got stuck in the movements but I don't know if any of it works or not. I half expect it to pop and sizzle when I first power it on, and then need to be sent off for repair. Really I'm just cheap and don't want to spend the money for a modern amp. But given the storage conditions and the fact it was used by a CB'r who probably didn't know anything about it, I think there is a fair chance there is something messed up somewhere. But at least it will get a second chance at life with new capacitors.The fuse is to protect the rest of the high voltage circuit if a tube shorts. If this was run by a CB'r, they might have removed it, some of them drive the SB 220 with 200+ watts. Lol |
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TN, USA
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Posted: 4/21/2024 7:29:59 PM EDT
[#24]
The power supply is the weak link of that amp. Lots of information regarding replacement of the main transformer and the filter caps on the internet. Mine is still bone-stock but it hasn't been turned on in 20+ years and I'm not sure I want to try without spending some time going through the power supply, much like you are doing. They are good amps though. I'd recommend staying about 75% output because those 3-500Z tubes are hard to find and expensive!
Also be aware that the relay circuit will not work with modern radios. As I recall it works on 120VAC whereas today's radios expect something on the order of 5 VDC. I may be off on the exact numbers but you get the idea. It's pretty simple to stick a relay in there to handle it, I think, or you can buy a box to handle already built. |
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Posted: 4/21/2024 8:21:27 PM EDT
[#25]
Yeah I will be running this one on 120V because it would be prohibitively expensive to run a 240V line.
I'm planning to drive it at less than 100W anyway, to take it easy on the circuit that supplies the power for the amp. It's an older home and there are a lot of different things on the same breaker. The previous owner had installed a jet tub so there might be 240V available in that part of the house that I could access. But I don't mind running it at a lower output to make the tubes last longer. |
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Posted: 4/22/2024 5:41:41 PM EDT
[Last Edit: Jambalaya]
[#26]
Well I got it back together. Hopefully correctly.
I still need to deep clean the tubes and install the soft start module. I got the soft key module in so it should be able to work with a modern radio. So, things I still need: Dummy load rated for 2kw. Tuner rated for 2kw Watt meter, maybe. Some tuners come with one, and if I get a tuner that has a meter, I can probably hold off on buying one for a while. I guess these are things I'd need to buy anyway if I got a brand new amp, so either way I'll have to bite the bullet and buy them.  Attached File |
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Posted: 4/22/2024 10:22:02 PM EDT
[Last Edit: Jambalaya]
[#27]
While I have it open, I went ahead and dressed up the wire harness some. It was a mess. Some wires really should be a little lo ger. Others I had to trim down.
The goal was to make room for the soft start module. You can see the soft key module already installed next to the opening for the fan. Before:  Attached FileAfter:  Attached FileI still need to shorten a couple of wires and installed the soft start module. Harbach suggests gluing it in with RTV, but I would much rather find a way to bolt it in place. |
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Posted: 4/22/2024 10:32:17 PM EDT
[#28]
That looks great!
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Posted: 4/22/2024 10:43:50 PM EDT
[#29]
The bottom of mine with the soft key module installed. I wouldn't bother with the soft start module, I have one that I would sell if someone else wants it.
Also upgrade to the horse shoe parasitics. When you first turn it on, leave the high voltage disconnected from the tubes and make sure both filaments light, then let them sit on for several hours before bleeding down the high voltage and hooking it up. 
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Posted: 4/23/2024 12:39:42 AM EDT
[#30]
Quote HistoryOriginally Posted By FlatlandBusa: The bottom of mine with the soft key module installed. I wouldn't bother with the soft start module, I have one that I would sell if someone else wants it. Also upgrade to the horse shoe parasitics. When you first turn it on, leave the high voltage disconnected from the tubes and make sure both filaments light, then let them sit on for several hours before bleeding down the high voltage and hooking it up. https://www.ar15.com/media/mediaFiles/457325/1000002372-3195578.jpg Thanks for the picture. It looks like you've grounded the grids as well. I might do that while I still have the cover off. I read about de-gassing the tubes, and I'm guessing that's what the hours-long run time is supposed to do. When you say leave the HV disconnected, that's the contacts at the top of the tubes, right? I don't know where to get reasonably priced parasitic suppressors, because the ones on ebay are like $30 or more plus additional shipping for a couple of resistors and some wires. Everyone says to replace them, but why? If its the old resistors going bad, then ALL of the resistors in the amp should be replaced using the same logic, no? I'm new to tube equipment and amplifiers in general so these might be stupid questions and assumptions. I read somewhere yesterday that the factory Heathkit breakers are 8 amp, but the Harbach replacements are 10 amp. I don't know if I will need to replace those until I try to power it up. But they were both tripped when I got the amp. I think it's possible the previous owner turned it on with the cover off and the safety interlock engaged, or removed the cover with it powered on. Nothing was obviously burned or popped from a visual inspection and a lot of the old circuitry was replaced with the Harbach stuff anyway. Nice thing about the Harbach metering board is the protection diodes are included. I'll probably go ahead and install the soft start since I already built the kit, I just need to work out how I am going to mount it. I think I can bolt it to some fiberglass and glue the fiberglass to the chassis. This won't interfere with anything g on the top side and it will still allow me to remove the board if needed for servicing (like changing to 20 Ohm resistors if I ever get a 240V outlet in the shack). I'll probably just run it in CW/TUNE mode all the time and be happy with whatever output I can get. If I get 1000W out of it that will still be a noticeable improvement on the other end of the contact. |
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Posted: 4/23/2024 7:19:01 AM EDT
[Last Edit: FlatlandBusa]
[#31]
The high voltage is the the top of the tube, leave it unhooked when first powering up. Also see if you can get a high voltage fuse back in it since that will help protect the rest of the high voltage circuit if a tube shorts. The horse shoe style parasitic suppressor is more effective, you can make your own, I'll look later for the plans.
The Harbach board does include some meter protection, you'll want to put the two protection diodes directly on the meters as well. |
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Posted: 4/23/2024 9:39:46 AM EDT
[#32]
Quote HistoryOriginally Posted By FlatlandBusa: The high voltage is the the top of the tube, leave it unhooked when first powering up. Also see if you can get a high voltage fuse back in it since that will help protect the rest of the high voltage circuit if a tube shorts. The horse shoe style parasitic suppressor is more effective, you can make your own, I'll look later for the plans. The Harbach board does include some meter protection, you'll want to put the two protection diodes directly on the meters as well. The only thing you really need to be careful with running the SB-220 after you getter the tubes is if you run AM. The HV transformer is geared toward SSB and is light ampere handling catagory. This was made as a SSB amp for 1200 watts when SSB was relatively and it was marketed as a SSB amp. It was NOT made for 1200 watts PEP using AM. I limit mine to 150 watts carrier and I limit transmissions to a few minutes at a time. No buzzard transmissions. With 100% modulation that will give you 600 watts PEP or so. I never had a problem doing that. I did run 1200 watts or so SSB without issue. I will be selling my SB-220 with all the harbach mods and new caps this week at NearFest along with y AL-80B and a spare tube. You will love the amp. Mine is still running a pair of non-graphite 3-500Zs and still makes full 1200 watts PEP on all bands, though it has been a few years since I used it hence why I am going to sell it. |
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Posted: 4/23/2024 7:21:33 PM EDT
[#33]
Wife and kids are out of the house for a concert. I'm too rural for there to be a source for replacement parts for the parasitic suppressors so I will have to roll with what I have.
I was looking around with a ruler measuring things to see if I could come up with a piece of aluminum to use to help mout the soft start board, when it occurred to me that the ruler itself was aluminum and the perfect thickness.  Attached File |
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Posted: 4/23/2024 7:32:17 PM EDT
[#34]
Quote HistoryOriginally Posted By KB7DX: Looks like Dr. Frankenstein built it. I love shit that looks like it came out of a Frankenstein movie. I used to have a big heavy oak electric chair in front of the TV but the wife made me get rid of it when another woman sat in it and I slapped a wet sponge on her head and put down the metal skullcap. Women have no sense of humor. |
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Posted: 4/24/2024 2:21:28 AM EDT
[Last Edit: Jambalaya]
[#35]
I got the bias mod done, and I completed installing the soft start module. I made that aluminum brace to go across two of the transformer mounting screws. I replaced them with longer 5/8" long 8-32 screws.
 Attached FileSince the Harbach diode metering board came with new standoffs, I used the two insulated standoffs from the old board to mount the soft start module to my aluminum strap.  Attached FileThis fit nicely in the space I made after dressing up the wire harness, and I didn't have to drill new holes in the chassis. It has about 3/8" of clearance to the bottom of the chassis, but I will hot glue some fish paper to the bottom just as a safeguard.  Attached FileAll that remains now is grounding the grids and new parasitic suppressors. |
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Posted: 4/24/2024 12:17:31 PM EDT
[#36]
Nice work!
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Posted: 4/24/2024 3:20:49 PM EDT
[#37]
Okay, after digging around the garage for some missing screws for the top cover, and relocating the safety interlock peg so that it makes better contact with the brass spring tab, I put the outer cabinet on and installed some brand new rubber feet.
I'll be honest, I am afraid to plug it in because if something doesn't work or if it pops and sizzle, I'll be terribly disappointed! The tubes aren't even in it right now. But I have some questions for those familiar with these amps. Can I do the tube degassing without any coax connected? Is it okay to just plug it in and turn it on without tubes in it? What are the chances it will be damaged if I try to operate it with the original parasitic suppressors? I still need to order or make a keying cable for it. I know I have some mini DIN plugs I bought for a different project, but they might not be the right number of pins. This whole project would have been completed a lot sooner if I had just trusted my own ability to do it. I tend to get stuck in this mindset of "better not move forward, you might mess it up" and so it sits. In my youth I used to just dive right in, but I broke a lot of things that way. Anyhow, it's a little "scratch and dent" cosmetically, but it looks so much better than it did. Before:  Attached File Attached FileAfter:  Attached File Attached File |
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Posted: 4/24/2024 3:37:17 PM EDT
[#38]
Looking good!
You can turn it on with the tubes out or with the tubes in and the high voltage disconnected. You do not need a coax hooked up to turn the amp on, you can even briefly key the amp without coax to test the keying circuit and relay. Meter protection diodes:  The meters are unobtainable. |
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Posted: 4/24/2024 4:30:52 PM EDT
[Last Edit: Jambalaya]
[#39]
Quote HistoryOriginally Posted By FlatlandBusa: Looking good! You can turn it on with the tubes out or with the tubes in and the high voltage disconnected. You do not need a coax hooked up to turn the amp on, you can even briefly key the amp without coax to test the keying circuit and relay. Meter protection diodes: https://www.ar15.com/media/mediaFiles/457325/1000003127-3196875.png The meters are unobtainable. Good to know, thank you! |
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Posted: 4/24/2024 5:48:36 PM EDT
[#40]
Use a dim bulb tester I mentioned above. It's just a 100w incandescent lamp in series
with one of the AC lines. This will limit current and save you some trouble if things go south. |
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Posted: 4/24/2024 7:51:08 PM EDT
[#41]
Quote HistoryOriginally Posted By KB7DX: Use a dim bulb tester I mentioned above. It's just a 100w incandescent lamp in series with one of the AC lines. This will limit current and save you some trouble if things go south. I'll have to see if I can find a socket somewhere. I don't think I have one, but I might have an old chicken incubator socket I could use. Then finding a non-LED light bulb will be a challenge all by itself.
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Posted: 4/24/2024 8:51:32 PM EDT
[#42]
Well, she's dead, Jim.
Plugged in and flipped the power switch. I got no meter lights and no fan. No scarey sounds or smells though. I unplugged and opened it up (just the underside) and working carefully with one hand in my pocket, checked for AC voltage at the breaker outputs, and the soft start module output, and the power switch. All of that appears to be working as expected. I don't have my high voltage meter probe yet so I stopped my investigation there. The amp's multi-meter is set to the HV position and nothing reads there either. It is possible that both meter bulbs, the meter itself AND the fan are all dead, but I think it's more likely something wrong with a transformer. Not sure which one. I did test for continuity on the big transformer's windings and continuity to the core while I had it removed. It appeared to check out okay. This means the capacitors probably did get charged up with HV, since their power appears to come from that transformer, assuming it isn't malfunctioning and is wired correctly. I've got the schematic downloaded and I will just need to look it over and make sure the wiring is correct. The fan not coming on is strange because it just gets 120V right off the switch before the transformer. Unless the fan is bad, it should work even if the transformer is bad. |
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Posted: 4/24/2024 8:56:28 PM EDT
[#43]
Quote HistoryOriginally Posted By Jambalaya: Well, she's dead, Jim. Plugged in and flipped the power switch. I got no meter lights and no fan. No scarey sounds or smells though. I unplugged and opened it up (just the underside) and working carefully with one hand in my pocket, checked for AC voltage at the breaker outputs, and the soft start module output, and the power switch. All of that appears to be working as expected. I don't have my high voltage meter probe yet so I stopped my investigation there. The amp's multi-meter is set to the HV position and nothing reads there either. It is possible that both meter bulbs, the meter itself AND the fan are all dead, but I think it's more likely something wrong with a transformer. Not sure which one. I did test for continuity on the big transformer's windings and continuity to the core while I had it removed. It appeared to check out okay. This means the capacitors probably did get charged up with HV, since their power appears to come from that transformer, assuming it isn't malfunctioning and is wired correctly. I've got the schematic downloaded and I will just need to look it over and make sure the wiring is correct. The fan not coming on is strange because it just gets 120V right off the switch before the transformer. Unless the fan is bad, it should work even if the transformer is bad. Put a multimeter in Continuity mode and you can test the meter, should read about half scale when connected to the meter leads |
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Posted: 4/24/2024 10:24:54 PM EDT
[Last Edit: Jambalaya]
[#44]
Quote HistoryOriginally Posted By stanprophet09: Put a multimeter in Continuity mode and you can test the meter, should read about half scale when connected to the meter leads I'll give that a shot. I know there have been a few attempts to repair the meters, and some people have made substitutions they managed to get working, but that's perhaps more than I want to bite off if these aren't working. I had a couple of days off this week, but I am back to work tomorrow, so I probably won't get into the inside of the cabinet until the weekend. I need to make a Jesus stick before poking around any of the HV stuff,and I'll go get the materials this weekend. I've also got an HV meter probe ordered. Hopefully it will arrive before the weekend. I have been thinking it might be the filament transformer that's bad. The relays for the soft start module get their power from the filament transformer. I never heard those relays click, so it's possible the fan (which is downstream from the soft start module) simply won't run with the soft start resistors in line, even if everything else is working. A bad filament transformer would also explain the lack of meter illumination. |
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Posted: 4/24/2024 10:42:51 PM EDT
[#45]
Quote HistoryOriginally Posted By Jambalaya: I'll give that a shot. I know there have been a few attempts to repair the meters, and some people have made substitutions they managed to get working, but that's perhaps more than I want to bite off if these aren't working. I had a couple of days off this week, but I am back to work tomorrow, so I probably won't get into the inside of the cabinet until the weekend. I need to make a Jesus stick before poking around any of the HV stuff,and I'll go get the materials this weekend. I've also got an HV meter probe ordered. Hopefully it will arrive before the weekend. I have been thinking it might be the filament transformer that's bad. The relays for the soft start module get their power from the filament transformer. I never heard those relays click, so it's possible the fan (which is downstream from the soft start module) simply won't run with the soft start resistors in line, even if everything else is working. A bad filament transformer would also explain the lack of meter illumination. Yes the bulbs typically are upstream of the tubes on the filament lines so if you do not have filament voltage then the meter lamp will not burn. I would go through carefully and check for opens and broken solder connections. Do not assume you do not have HV due to the meter. The meters are commonly messed up due to issues and the reason why almost everyone puts protection diodes on them because they are hard as hell to find. The transformers from what I understand are kind of weak on the SB-220. There is a lot of info on W8JI website on the SB-220 and from what I inderstand he was somehow involved in the design of them or Heath based it on a design he made. He also talks about improvements that can be made to them and things that should be done. |
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Posted: 4/24/2024 11:29:50 PM EDT
[Last Edit: Jambalaya]
[#46]
Quote HistoryOriginally Posted By stanprophet09: Put a multimeter in Continuity mode and you can test the meter, should read about half scale when connected to the meter leads Okay both meter needles deflect when the continuity tester is applied. Both bulbs check out as well when removed from the sockets. So that's encouraging. I think even if the filament transformer was bad, I should still show a reading on the HV meter when the amp is turned on though. The power switch shows continuity in the on position on both sets of terminals. I should add that when I removed the lid for the RF deck there was no spark when the safety engaged, and I believe the bleeder resistors did their job (if there ever was HV to begin with). I have the lid back on and I'm going to go through the schematic paying attention to the switches and the voltage selector bar where the power and transformer leads are attached and make sure the colors and positions match the schematic. There is probably a reason this amp was abandoned.
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TN, USA
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Posted: 4/25/2024 8:06:57 PM EDT
[#47]
A bad transformer will do that...beware of old brittle xfmr lead wires, the insulation hardens and movement can break the conductor. Broken insulation is also an arcing and shock hazard.
DO NOT use that unit, especially as filthy as it was, without restoring the grounds on the air variable caps!!! I saw a bouncing Load cap ground in my Drake TR3 turn the plate inductor into a roman candle. White flash and 5 turns of vaporized copper wire. That caused a reflected pulse that was probably up to 6 KV- the PA tubes are rated to 6.8 KV. There was a bad spot in the already grossly oxidised ground contacts that opened up. Make new supprrssors, cant check the resistors in place with an ohm meter. Its cheap. |
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Posted: 4/25/2024 10:17:57 PM EDT
[#48]
Quote HistoryOriginally Posted By k8byp: A bad transformer will do that...beware of old brittle xfmr lead wires, the insulation hardens and movement can break the conductor. Broken insulation is also an arcing and shock hazard. DO NOT use that unit, especially as filthy as it was, without restoring the grounds on the air variable caps!!! I saw a bouncing Load cap ground in my Drake TR3 turn the plate inductor into a roman candle. White flash and 5 turns of vaporized copper wire. That caused a reflected pulse that was probably up to 6 KV- the PA tubes are rated to 6.8 KV. There was a bad spot in the already grossly oxidised ground contacts that opened up. Make new supprrssors, cant check the resistors in place with an ohm meter. Its cheap. Thank for the advice. By restoring the grounds, do you mean cleaning them where they connect to the chassis, or disassembling the capacitors and ensuring contact between all of the fins? I've been over the schematic a ton of times at this point and I still can't figure out why it's behaving this way. I'm actually seeing 120V on BOTH sides of the power switch, regardless of switch position. Also looking at the original schematic, and pictures of other SB220s, it looks like for some reason a couple of the power leads bypass the circuit breakers. Someone made a revised schematic that shows the breakers wired after the voltage selector terminal strip. |
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Posted: 4/25/2024 11:03:20 PM EDT
[#49]
" I'm actually seeing 120V on BOTH sides of the power switch, regardless of switch position. "
That sounds like the primary wiring is incorrect somehow. When I've been stumped on repairing a piece of gear, I'll "just walk away" /Humongus/ and take a day or two break from it. A lot of the times when I return to it the problem is right there staring me in the face. Especially a good idea when messing with high voltage. |
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Posted: 4/25/2024 11:23:32 PM EDT
[#50]
See if power is going through the soft start. I don't think there is normally power on both sides if the switch.
Is the terminal block jumpered for 120volt operation or 240volt operation? |
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