Before I spend too much energy on this approach, any comments on whether it is necessary or desirable, and has anyone already got a working circuit?
thanks,
doug
Resort to Ebay if nothing else. Sure, if you are in New SOuth Wales, Brisbane, etc, the prices are going to be high due to shipping and exchange rates, but if you are in the USA, Canada or the UK, shop around for good prices, or search out good used tubes.
:I've got several old radios with bad rectifier tubes, some very expensive to replace. My intent is to by-pass the tubes with solid-state diodes and let the tubes filaments still run (especially for series sets). I have heard about cathode stripping, though, and worry about damaging the other tubes by the sudden application of B+ before their filaments are warmed up. So, I've been looking into an SCR-based rectifier circuit with a slow RC timeconstant on the gates to delay the B+ for, say, 15 seconds after power on.
:
:Before I spend too much energy on this approach, any comments on whether it is necessary or desirable, and has anyone already got a working circuit?
:
:thanks,
:doug
1st, there are amplifiers that were produced in the 1950s and 1960s, both AC/DC and high power AC (such as a Lesley Rotary Speaker) that use solid state rectifiers. Most have no provision for soft start conditions. All of the cheap one tube phonographs that I have had in my childhood (I was born in 1979, by the way, if that sounds strange to you) had solid state rectifiers. No provision was made for a soft start effect. The only piece of equipment I have ever owned, and still do own, that uses a sort of soft start device, is my RCA crosshatch/dot/color bar generator. It has a special disc shaped resistor thingie in series with the entire power supply. Both the tube heaters and the solid state diode get a soft start. Within the period of a few seconds, the tubes and the pilot lamp slowly receive more and more power. Other than being a soft start device, I see this component having no real value within the generator. The hotter it gets, the LESS resistance it has. That said, it would not serve to regulate line voltage, because if there was more voltage available at the socket, the component would get hotter and would pass more voltage to the generator.
2nd, all of the amplifiers and radios with indirectly heated cathodes in the amplifier sections (RF and AF) and filamentary rectifiers in the power section, have the problem of power being available within one second of radio/amplifier turn-on, which is long before the 6 to 10 seconds it takes for indirectly heated tubes in an AC radio to warm up.
Still, with all of these devices, tube life is long and well enjoyed. Many of our radios and amplifiers with filamentary and/or solid state rectifiers still use their original tubes, and many of our cheap one tube phonographs still work fine with their original tubes, electrolytics and all.
Thomas
i've been wondering about this i have put silicon diodes in a few sets and have never had a problem some peaple put a switch so the filaments can warm up first but i figure i have 90 some sets so any one of them is not going to get used much. butch
1st, warming up the filaments puts extra strain on the diodes. When they are switched on, they will have to charge the electrolytics and feed the warmed up tubes all at the same time. As I said before, there are TONS of tube type devices: amplifiers of many types and power ratings, televisions, phonographs, all of which have instant start diodes--the diode supplies as soon as the power switch is turned on. No provision is made for pre-warming the tubes or a soft start device or anything of that nature. The devices provide years of dependable service. The biggest risk involved is stress to the diodes themselves, as solid state devices cannot handle surges as well as tubes. By using diodes that can handle both the surge of powering the electrolytics and the surge of powering the electrolytics and the tubes at the same time when the set is turned off warm and then right back on warm, you can reduce the risk of frying the diodes. There are many devices that, to this day, still work fine, and use solid state diodes in the power supply.
As I have stated before, ANY RADIO THAT USES A #80, 5Y3, 5U4, 5Y4, OR OTHER FILAMENTARY RECTIFIER, HAS THE EXACT SAME PROBLEM AS USING A SOLID STATE DIODE. THE FILAMENTARY RECTIFIER IS WARMED AND OPERATING *LONG* BEFORE THE OTHER TUBES HAVE WARMED UP. These radios, millions of them, have provided years of dependable service.
2nd, in most cases, increasing B voltage by 20 or 40 volts is not significant enough to worry about. Sometimes it is, but it usually isn't. In some cases, though, a resistor may be desirable.
Thomas Dermody
The soft start devices I mentioned are external to the radios themselves, they are like a plug strip like you have your computer components plugged into as just a physical type of example.
There are some soft start systems that people have incorporated into their own designed amps that allow for the heaters to warm up before any B voltage is applied, and when it is applied it ramps up from zero. This type of circuit is not practical to install insode of a tube radio, and considering the impacts on valuations, why you would want to do this much work to kill that much value would be a mystery.
:Two notes:
:
:1st, warming up the filaments puts extra strain on the diodes. When they are switched on, they will have to charge the electrolytics and feed the warmed up tubes all at the same time. As I said before, there are TONS of tube type devices: amplifiers of many types and power ratings, televisions, phonographs, all of which have instant start diodes--the diode supplies as soon as the power switch is turned on. No provision is made for pre-warming the tubes or a soft start device or anything of that nature. The devices provide years of dependable service. The biggest risk involved is stress to the diodes themselves, as solid state devices cannot handle surges as well as tubes. By using diodes that can handle both the surge of powering the electrolytics and the surge of powering the electrolytics and the tubes at the same time when the set is turned off warm and then right back on warm, you can reduce the risk of frying the diodes. There are many devices that, to this day, still work fine, and use solid state diodes in the power supply.
:
:As I have stated before, ANY RADIO THAT USES A #80, 5Y3, 5U4, 5Y4, OR OTHER FILAMENTARY RECTIFIER, HAS THE EXACT SAME PROBLEM AS USING A SOLID STATE DIODE. THE FILAMENTARY RECTIFIER IS WARMED AND OPERATING *LONG* BEFORE THE OTHER TUBES HAVE WARMED UP. These radios, millions of them, have provided years of dependable service.
:
:2nd, in most cases, increasing B voltage by 20 or 40 volts is not significant enough to worry about. Sometimes it is, but it usually isn't. In some cases, though, a resistor may be desirable.
:
:Thomas Dermody
Many times I have had to remove someone else's "improvement", because it impaired performance, or impaired value. There have a number of instances where the modifications were so messy, that the set was really only good for scrap, or as a novelty example.
Adding things like thermistors is not really practical as some of the soft start units that I have seen have actually been units that ramped up the supply voltage to the amps so that the amps themselves were not modified from their original valued form. If you were a serious collector and were concerned about your type 250 globes, an external soft start would be the way to go because you only need the one, and any radio you want to operate is just plugged into the device.
::There are "soft start circuits" in some of the audiophile magazines and news groups, however, the cost and effort to make one are far less costly than buying good used tubes, or shopping around for different tube prices.
::Since the tubes are available, the value of the radio will be diminished if you make such a modification.
::
::Resort to Ebay if nothing else. Sure, if you are in New SOuth Wales, Brisbane, etc, the prices are going to be high due to shipping and exchange rates, but if you are in the USA, Canada or the UK, shop around for good prices, or search out good used tubes.
::
::
:::I've got several old radios with bad rectifier tubes, some very expensive to replace. My intent is to by-pass the tubes with solid-state diodes and let the tubes filaments still run (especially for series sets). I have heard about cathode stripping, though, and worry about damaging the other tubes by the sudden application of B+ before their filaments are warmed up. So, I've been looking into an SCR-based rectifier circuit with a slow RC timeconstant on the gates to delay the B+ for, say, 15 seconds after power on.
:::
:::Before I spend too much energy on this approach, any comments on whether it is necessary or desirable, and has anyone already got a working circuit?
:::
:::thanks,
:::doug
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:i've been wondering about this i have put silicon diodes in a few sets and have never had a problem some peaple put a switch so the filaments can warm up first but i figure i have 90 some sets so any one of them is not going to get used much. butch
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