Видео

That's sad news. I did not know.

Yes some switchers do need a minimum load or they can't regulate properly. The data sheet for this model says that for less than 1 volt regulated output you need at least 500 mA. So for typical use at higher voltages as marked on the modules a minimum load isn't needed. Certain types of ceramic surface mount caps are prone to failing from stress as it cracks them or damages the structure since they have no flexible leads. There are surface mount caps designed to take flexing stress probably not what was used here. Yes the Dynaload has a current sample output. I recently did a video on another Dynaload model that needed repair ..you may be interested in seeing that.

Glad you enjoyed it, thanks for watching!

I think the values are chosen for what makes the most useable attenuation range. 0.25 dB would require the two top T configuration resistors to be 719.51 milliOhms perhaps more difficult (or costly) to make such small value of resistance? Also going up to 255 dB is such a huge attenuation it is not useful at low RF levels. This attenuator is 1 watt max. As it is 130 dB is down to fraction of a microvolt.

You're welcome and thanks for watching!

It's normal for the GFA5500 to pop when powering off. There is no speaker protection relay so the speakers are connected to the output stage at all times. As the power supply rails collapse the amp becomes unstable and a short pulse of voltage is applied to the speakers. It is not damaging, and the voltage is less than what the speaker is subjected to when playing loud music.

@@EriksElectronicsWorkbench Thank you. Maybe I should clarify. The pop I referred to is more of a "whumph" (not loud but audible). The cone movement is quite noticeable and, as I mentioned, the event is only on one speaker. Your assessment is probably correct and there is nothing to worry about but I am going to sell this amp and do not want to pass on a faulty product. I'll see if there is a local expert on this amp. For now I am using a Schiit amp and I am very pleased with it. Much thanks!!!!!!

@@charlesclifton5896 I would check the amp for meeting rated output power, no distortion issues, etc and if all looks good then the turn off thump is not a concern and for whatever reason the one channel is just more prone to it. Agree good idea to have it tested to be on the safe side.

I appreciated the compliment! Glad the video was helpful for you.

If the unstable readings are happening on both channels I suspect the issue is with the meter or probes you are using, perhaps picking up noise as the meter is trying to measure in the millivolts range. Keep sources of noise like switch mode power supplies away from the test area. The bias potentiometers may be dirty and making poor connection. The AC line voltage could be varying excessively. If just one channel bias is unstable it could be its bias pot, or a defective transistor. Make sure the transistors are securely attached to the heatsinks and with thermal paste. Look for broken solder connections on the power transistors and emitter resistors. Heating and cooling over years can stress the solder joints. I hope these ideas help. And thanks for watching!

@@EriksElectronicsWorkbench I tried it with the clip type this time but still no luck, I got all zeros with every range setting. Perhaps I have a different/earlier version of the GFA 555 II with different bias points and 1800VA at the AC input whereas the later version has 1440VA, don't know what that means but that's the different I've spotted. That may sound unlikely but I just can't think of why am I not getting any meaningful reading. Anyway, thank you so much Erik.

@@georgeho8997 The bias is taken across an emitter resistor. The upper resistors are easier to reach. You don't have to use the test points, technically, to read the bias as any of the resistors will give a reading. You may not have bias due to a fault thus no voltage reading. The bias pots are very sensitive to adjustment. No bias will result in cross over distortion. Excessive bias will make the amp run hot or even blow a fuse. Make sure your meter is on DC millivolts, not AC volts. The VA rating is not related to the bias, that's just the AC power consumption under full load.

@@EriksElectronicsWorkbench What might be the reason for the problem if there is a fault like this?

@@georgeho8997 if there is no bias voltage it could be a bad bias potentiometer, bad bias transistor on heatsink, a bad transistor or component in the preceding stages. Just some general ideas. If you have no bias reading on both channels look at your meter setup and the test points you are using as it would be unusual to lose bias on both channels.

The very early 1960's RCA 2N3055 were hometaxial with a considerably lower transition frequency, but that process was changed to epitaxial many years prior to when these were made (these are dated in the mid 80's). There was a special H version but would be marked as such on the device. I have never seen a temperature sensitive paint on transistors, although not a bad idea for monitoring purposes, I've only seen colored markings for matching identification.

Glad the video was helpful, thanks for watching!

I have a can of Glyptol that was given to me, unused still. I didn't think about the possibility that Glyptol was used on the trimmer pots. Thanks for mentioning.

Thanks for watching! The external modulation could be thought of as a remote control input. The DC load coarse and fine controls become a gain control for the external signal. At full gain, 6 volts DC in will allow 60 amps or up to the current/power limit for voltages over 16.66 volts. I tested inputs of sine and square waves to 20 KHz and the dynaload responded correctly. Other waveforms could be used too and you can modulate on top of a continuous current.

@@EriksElectronicsWorkbench Thanks :)

The new 2N3055 transistors all tested base-emitter voltage range of 0.631 +.004 / -0.000 volt @ base current 5ma so all were well matched in that regard.

Calibrated fingers with mil spec temperature specification don`t come cheap :)

Definitely useful to have!

There is a PDF download here with a schematic but it is not the best scan bee.mif.pg.gda.pl/ciasteczkowypotwor/dynaload/Dynaload%20DLP50-60-1000%20Intruction.pdf I can take a scan of my schematic just email me (address in about this channel section) and I will reply back. Note there are some minor changes in the newer version models from the original schematic mostly in the pulse generator circuit and I don't have the newest schematic version.

@@EriksElectronicsWorkbench Than you.

As was mentioned in the video the hfe is higher than the data sheet value because they are tested at very low current levels on the transistor tester. The hfe on the data sheet is when tested at several amps.

I'm glad the video was helpful and confirmed some things about your design. Yes you can drive many paralleled transistors.

There isn't a place to put the vents elsewhere. Even if the vents were on the sides the air is still circulating within the rack. Top and bottom covers are no good as it's assumed there will be equipment above and below. Probably need to have a cooling fan in the rack to bring in fresh air if this was running at high wattage dissipation. My other DLP series dynaload shown in video has never overheated under extend full power use.

🧐 ~ if I had designed it, the transistors and their heat-sink would be mounted in the top of the unit with the slot having an angled piece of metal “L” in front of it to direct the hot air up (away from the fans) and when off ~ the heat will dissipate through the lid [particularly if mounted on top of the rack] ✅

This model was designed in the early 70's and I don't think high power MOSFETS were as common at that time in this type of application. Modern electronic loads almost always use MOSFETS as they are easy to parallel and don't have thermal runaway.

@@EriksElectronicsWorkbench yes didn't think about the design being older than the unit oops

At 60 amps the transistors pass 3 amps each in this application so the gain is not comprised much. Higher current demands probably would be better to use a different transistor.

Many emitter resistors are tucked away under other components so was easier to check all the transistor cases but yes a hot emitter resistor will point you to the fault.

Check out hoppesbrain.com/category/adcom/ for upgrades, modifications, parts, etc.

What was meant is the the transistors are not being worked as hard to dissipate power near their specified max limit. It would be like replacing a resistor with one of a higher wattage rating. The component isn't being stressed as much. Nothing was modified in a way to make more power actually dissipated on the transistors. Depending on load current they can run fairly hot.

On the series 5 it could be R1, R3, or R16 that is out of spec. Or something wrong with the switch contacts in the Rx1 position.

This was built for the military and they have their own way of doing things. Yes other types of inverters existed at the time this was built.

I wouldn't really compare it to an audio amp style output stage as this uses two SCR's to drive the primary winding. Yes it saturates the transformer and clips the waveform by design.

Yes it worked fine for 20 years. I think the power switch was on its way out and I didn't realize it. The fuse holder plastic was old and disturbing it probably made its contacts become intermittent. The fuse was never touched in 20 years. The actual failure was the transistor.

I noticed numerous 83 date codes on IC's and capacitors. Fits with the contract date. Yes I have seen the fuse holders with incandescent bulbs colored as you mention.

No schematic inside the lid. I wish there was.

You're most welcome!!

You can find them on eBay. The lamp does not care about the frequency. Only the voltage is important. Yes it is made for 115-120 volts, you can use a lower voltage but the current draw is less therefore the power is less. Above 120 volts will shorten the lamp life or even burn it out immediately.

The bank of yellow capacitors are on the SCR's and primary transformer side but probably for spike and noise suppression. SCR's are more rugged than transistors and given this was built for the military in harsh use I'm sure that dictated circuit design. It would take many many paralleled transistors to handle the current that just these two SCR's switch. The 600 volt winding is in the large upper part of the windings, that is where the tap is placed and you can see the wire go into the windings.

Odd order harmonics, not even. The transformer would sound a _lot_ angrier if there were even harmonics due to the saturation effects thereof.

Thank you, I'm glad to know you enjoyed the video. Best of luck on your 160!

If your model is similar in design to mine, the potted/sealed high voltage module may have been damaged with the polarity reverse switch while on. But I would also check the power transistors on the heatsink for shorts or opens, drive signal to the power transistors and drive voltage to the high voltage module, and basic things like power supply DC voltages.

@@EriksElectronicsWorkbench Thank you for your swift response! Can I check the power transistors while they're still attached, or do I have to take them out?

@@EriksElectronicsWorkbench Also, yes it's practically the same model as yours, but it goes up to 3kV and 10mA.

@@BurakAhmetTufekci It depends on the surrounding circuit if it influences the readings to a great deal but you can try in circuit first. You should have a diode junction from collector to base and from base to emitter. And an open from collector to emitter. If you can unsolder just the base lead connection (depending on how they are mounted and wired) you may not need to remove anything else to get the C-B and B-E readings. In circuit may not give an accurate reading from C-E.

@@EriksElectronicsWorkbench You're right. Also, how could I check the sealed high voltage module? Thank you so much!

Thanks for sharing this information. It now makes sense why the capacitor voltage is so high.

Only universal brushed motors won't care about supply waveform. Induction motors care a lot since the harmonics can either result in a stator magnetic field that tries to stop the rotor or spin it the wrong way.

Thanks for sharing this information. I may revisit this inverter in a future video to look at the ferroresonant transformer in more detail.

Thank you for the information. You might like to see the follow up video ruclips.net/video/Q2KF4k_8daE/видео.html I do measure the output on a scope and adjust the frequency which as you mention raised the voltage. In the follow up video I ask if anyone has ideas about the 600 volt circuit. Your info is exactly right.

Nope, something went wrong in your math. At 300 watts it's drawing 412.8 on the DC side a net conversion loss of 112.8 watts. 72.7% efficiency assuming the bulb is actually drawing 300 watts.

Yes it is power hungry! The ferroresonant transformer runs in saturation and gets quite hot by design. Being that it was built for the military I think rugged and indestructible were the goals over being efficient.