Here, I demonstrate why it's not usually a good idea to substitute solid state rectifiers in place of a tube rectifier. Generally, if a circuit originally used a tube rectifier; then, you're better off sticking with a tube.
It just goes to show that old technology + old technology = perfect match. Old technology + new technology= trouble. Great video with crystal clear explanation.
As always a great video. I can see someone using that replacement diode pack if they could not find a proper tube, like back in the late 80's and early 90's before the internet was a thing.. I mean now you can find rectifier tubes online but back them it was a dark era when tube equipment was widely replaced with solid state and part houses quit carrying tubes, this diode pack would be your only option.. I have seen modifications of equipment I have worked on using these plug in packs to replace tube rectifiers, where the device had a small IC (555 or 556) based timing circuit to fire a relay to supply the B+ to the tubes after all the other tubes have warmed up so your not applying HVDC on the plates of a cold tube.. The latest modification I have come across was in a guitar amplifier that had an arduino nano as a timing device to trigger some FET's to supply the B+ from a diode pack to preheated tubes. This is more versitile as you can program the nano to whatever delay time you want.. I know it's blasphemy but people do what they must I guess to get equipment working and to save money.. personally I would have just found a proper tube rectifier and called it repaired.. On a side note I have rebuild resistor packs that plugged into tube type sockets in the past.. I don't see to many tube devices come through here anymore, the occasional guitar amplifier or old 2-way radio finals for a ham radio operator or the classic 5 tube table top sets that need electrical restoration but that's every blue moon..
I was surprised to hear that commercially made diode packs do not typically include a replaceable thermistor (ie: "light"bulb?) and/or SCR to limit the inrush current in a soft-start (and to add to add a non-poison standby mode?) ; before considering most common things were made to be cheap and happen to be durable, were also simple. Have you seen no example of either in your work in the years since the above comment?
I seen in a Tektronix scope, it had a tube that would slowly heat up...keeping the filament voltage from going right to the tube's when first started, making sure the other tube's heat up first. It had what looked like relay contacts that moved over when it got hot, and made the power to connect to the filament leads.
Think this is good general advice if you are not sure. Otherwise it's really no issue using solid state rectification in any equipment - if you do it right. There is no problem with output valves or any valve getting HT before the heaters warm up, As long as you keep voltages under control all should be fine, and your mains transformer may like it better in the long run by running cooler not burning a few watts on your GZ34 or whatever. An NTC thermistor will mimic warm up if you want it to cheaply stop surges. Though I do prefer to have a valve there myself and wouldn't want a solid state replacement,
I came across this video after losing a power transformer in my EICO 460 'scope. I'd replaced the original HV rectifier 1v2 tube with two HV diodes in series (PTC205's) and the scope seemed fine. But the last time I turned it on, one of the 0.1uF 1000V ceramic caps downstream shorted out, taking out the transformer. I didn't expect this sort of cap to break down. I'd wondered about surge voltages due to the diodes being the problem. Looking at your video, in your testing, the instantaneous surge voltage might be much higher than 400V. Parsing the video frame-by-frame shows 889V for several frames before reading ~ 400V. Not sure if this is an artifactual "bootup" display error, or whether your multimeter can react that fast, but it might be a real spike. Things might be even worse than you suspect! Thanks for the discussion!
When necessary I have used diodes to replace a tube rectifier or selenium rectifier with a dropping resister but I've always added a thermistor to the line in to avoid surges. It does add to the heat load and proper placement and venting is necessary.
Yeah, I cringe whenever I restore a vintage guitar amp & see 1 of those installed! Usually means automatically the filter caps are shot or worse, shorted from the high surge current when 1st turned on and possible power xformer damage! I've seen it all when I've gotten vintage guitar amps in for restoration/repair! IF someone INSISTS that they want to use one of those solid state subs for a tube, I install a huge resistor in series with it to absorb some of the current when 1st switched on
Dropping resistor values vary from 1k to 220 ohms for 6x5 to 5y3. Can be as low as 100 ohms for 5u4 replacement with silicon diodes. usually 2 or 3 in4007 in series is a good idea. 1 1n4007 is usually not enough in practice even though looks ok on paper. bypass capacitor ranging in value from 1000pf to 10000pf are a good idea to prevent rectifier noise with silicon diodes.
The problem with the output tubes is the increase in the rail voltage. Use ohms law to find the correct resistor to bring the rail voltage down to the original voltage. Or reset the bias to the output tubes. Normally, commercial equipment were designed to work in a lower plate voltage but the tubes are fine with as much as 40 volts, in average, increase in the plates, look at the charts, Pv= Plate voltage>>minimum>>maximum. lot's of people that try to explain this same thing they go for the lottery and have no idea to calculate the value of a resistor to drop a certain amount of voltage and try several of resistor until their are close....Waste of time, resources and human ingenuity..USE THE OHMS LAW!!!!!
Except for tube testers build ss83 and ss5y3 no issues. If used in audio amp etc. Try and use dropping resistors to drop voltage enough to match original tube
Philips did this with some of their TV sets, offering "solid state valves" to replace the original valves ( tubes ). They didn't generally run for long after the solid state was substituted, an old technician told me. Old and new don't make good bedfellows sometimes...
@@smokepeddler Been switching diodes for tubed since the 60's here is one of my videos requested from people that did not understand how homs law works. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-7uCUffwr_lQ.html
ive been reading up and this and understand the issues well enough only to ask a question, have you tried to use a ss rectifier in conjunction with a thermistor on the input line like an amphenol cl-90? my interest is tube radio and trying to reduce the transformer load and heat, i was even considering the possibility of using current limiters on the ss rectifier itself. the goal being to produce a true drop in replacement for a specific radio. its just thought at this stage.
Using those solid-state rectifiers intended for replacing actual rectifier tubes seems to open up a can of worms that would be avoidable. After all, the engineers who designed these vintage electronics intended for them to specifically accommodate for the specifications of those rectifier tubes.
Excellent and very informative. Thanks for sharing. Any chance you could do something on 1/2 wave and full wave rectifiers in the future? I don't understand the difference and how diodes function in both. Regardless - you do great instructional videos.
Imo, the appeal of vintage electronics is the glow of the tubes. Now, if you enclose it where you can't see the tubes anyway, it may not be as noticeable. I assume you are just replacing one tube with a solid state rectifier. I guess that's not too bad. I have a heat lamp just like that one. My folks bought it about 1970. I enjoyed looking at the reflection of the heating coils.
Re bias plate voltage. Change resistance on b plus voltage. Problem solved. It's done on guitar tube amps all the time. Rectifier tubes can SAG and Rob output.
This used to confuse me. I thought that Direct Current flows from neg cathode to pos anode or B+ plate. But it seems that it should go from pos to neg, or in the opposite direction. Then it was explained to me, inside a battery, it does go from pos to neg, so that is why outside the battery, DC goes from neg to pos. A rectifier doesn't allow for AC to flow both ways, but only in one direction, to change the transformer AC output to ripple DC. Brian, just curious, was that solid state rectifier with four diodes? Did you look inside? I suppose a 25watt ballast resistor could be used in seeies where you inserted the ma meter. But um wondering if a voltage regulator or SCR could be used? Don
I just don't understand the point of replacing a vacuum tube rectifier with a solid state one. Most common vintage NOS rectifier tubes are still easy to find, and they are still relatively cheap.
What is wrong with instant voltage???? the caps can handle the problem and the resistor between the filter caps can also handle the current rush. Non seance. Also there is no problem for B+ hit the tube plates before they are warm, they will simply will not conduct. They will start conducting slow as they warm up. I work Philips for many years and As you should know tubes work in a range of plate voltages. the key is in the biasing.
Why 2 diodes in series? Thats never done commercially and there are usually small caps in parallel with the diodes to suppress the noise. Put that in a tv and watch the b+ go from 350 to 480 and cause all kinds of issues
+shango066 would that increase the current ability, like from one amp to two? I was thinking a diode in series with a 10watt ballast resistor would make more sense. Don
***** Maybe the designer of the plug in pack was thinking of a size factor, A 10 watt power resistor would be kinda big and produce / dissipate a fair amount of heat. All part of that grey/black era where people were transitioning from tube to solid state and shops quit supplying tubes, this was supposed to be an easy temporary fix until your rectifier tube actually came in but I guess people used these "disasters in a tube base" on a more permanent basis.. I can't imaging anyone with any electronic sense sticking one of theses in a TV set for any reason...
Engineers had to design tube circuits to deal with tube problems. Every stage related to other stages of the circuit. Diodes and selenium rectifiers do not emulate vacuum tubes, so some modifications are necessary to work properly. It's not simple R&R, Plug in and Play - that's what Bryan demonstrated here. It's the same principal of dropping in a transistor to replace a tube. It's all linked together. It's very possible to use a solid state power supply, like it would be to use a solid state transistor preamp, as long as it matches up with the circuit loads down the line. Overloads, and underloads cause undesired troubles. Consider loading a power amplifier designed for 8 ohms with a 2 ohm load. Mismatching can overheat the circuits. Diodes are OK if properly adjusted to match the circuit load. Selenium rectifiers are a good case in point, THEY SHOULD BE REPLACED WITH DIODES, not with rectifier tubes, but a slight mod is needed to use a proper ballast resistor in series with the diode. Solid state diodes can be substituted for tubes OK, but with an adjustment to compensate for efficiency and load match. Using wrong e-caps can also cause surge overloads, regardless of rectifiers. The job of a rectifier is to block AC and pass DC voltages. Diodes do that better than tubes or selenium rectifiers. Then there are SCRs... ?
So why replace tubes with diodes? Consider this: A couple diodes and resister are two bits. One NOS 5U4 on ebay is at least 5$. Risks: Damaged or lost in mail, bad tube, time it takes to get it etc., so there are disadvantages. But then you get your new rectfier tube, and even change those ecaps. Plug it in, poof, blown tube! WHY? Shango and Bryan can explain what blows new tubes. So it's back to ebay...
I know this is four years old, but I just thought I'd point out the B+ power is 4 watts with the 5Y3 and is 8 watts with that little solid state gem. That means that all the other tubes in the set are running at TWICE their design power. Not a real wonderful thing.
+Synthematix There really is no such thing. Solid state was specifically made so you didn't need high voltage any more and make electronics more reliable and not waist energy by generating so much heat. It would be like putting gasoline in a diesel engine. It just doesn't work.
+Synthematix One of the instructors I had years ago mentioned SS replacements for the tubes in test equipment like oscilloscopes. The biggest claim about these things was that matched pairs would stay matched for longer. I assumed they used single or multi-gate N-channel FETs with maybe a few resistors to mimic the behavior of the tube being replaced. He said they didn't work very well most of the time, since the circuit was designed around the tubes, warts and all. I guess "better" is only an improvement when you aren't counting on the things that were "worse".
This kind of stuff would have long been thrown away if it wasn't for the internet and latest technology to keep it Alive, the internet and all the latest gadgets have allowed people to film and show this kind of stuff and that has renewed interest in it. People can learn and see how circuits are working with this ancient stuff, most of it has been replaced by I.C's, can't test for a failed transistor when 50 of them are stuffed inside a tiny black blob. Modern electronics are made small, compact, cheap and fairly robust, many of these old tube sets have been repaired dozens of times and if you were actually paying for these repairs you'd have spent out 3 or 4 times what the set originally cost to buy in the first place, which was a damn site more than a new one today. Like I said the only advantage is because a low tech guy can explain and repair something like this, a modern computerised set is beyond their skill,but you can bet your bottom dollar their homes are filled with the latest tech, 4k video, internet,modern cars sets etc
Connect the 5Vac rectifier tube filament in series with the primary winding to drop the resulting higher voltage from using solid state rectifiers. Be sure that you connect the 5 vac winding such that is reduces the output voltage from the HV windings. Use a voltmeter to verify that you have connected it properly. If it is connected opposite, it will raise the output voltage rather than reduce it.
