It really helps to have the right schematic!?! 😀 Things make a lot more sense now.
More to come...
More to come...
RS1 Surgistor replacement
Does any one have advice on what type/rating of thermistor one could use to replace the RS1surgitor in the HF-87?
Thanks,
Ryan
Does any one have advice on what type/rating of thermistor one could use to replace the RS1surgitor in the HF-87?
Thanks,
Ryan
Hi Ryan,
Yes, absolutely! Don't use that type. Set up a timed relay to short the resistor out after the supply has mostly charged. You can use the heater supply for "housekeeping" functions.
That surgistor will cycle on and off for an hour before it finally stays open. The thermistor would work, but not nearly as nicely as a more complicated relay circuit. I have an HF-87 and plan to install what I suggested to you here.
-Chris
Yes, absolutely! Don't use that type. Set up a timed relay to short the resistor out after the supply has mostly charged. You can use the heater supply for "housekeeping" functions.
That surgistor will cycle on and off for an hour before it finally stays open. The thermistor would work, but not nearly as nicely as a more complicated relay circuit. I have an HF-87 and plan to install what I suggested to you here.
-Chris
Thanks Chris,
I looked at the diyAudio store version. Others on line. I don't want to reinvent the wheel here. Any advice? Your plans with specifics?
Thanks again,
Ryan
I looked at the diyAudio store version. Others on line. I don't want to reinvent the wheel here. Any advice? Your plans with specifics?
Thanks again,
Ryan
Hi Ryan,
I haven't designed mine yet. There should be boards that use a 555 timer as a "one shot" monostable multivibrator. It will probably be called a power-up reset circuit, or "power up one-shot". You just use the relay to short contacts when it times out. If you get a dual chip (556 timer), you can mute the input signal until things have warmed up and stabilized. That would avoid the heavy distortion as the tubes wander into their normal operating range. All you need is a pair of timers (the 556) and two time constants, one being a minute or so long. The other for 500 msec to 1 sec long. The relays would be 6 volt coils and maybe a resistor to drop the voltage across the coil(s -if you do input muting).
-Chris
I haven't designed mine yet. There should be boards that use a 555 timer as a "one shot" monostable multivibrator. It will probably be called a power-up reset circuit, or "power up one-shot". You just use the relay to short contacts when it times out. If you get a dual chip (556 timer), you can mute the input signal until things have warmed up and stabilized. That would avoid the heavy distortion as the tubes wander into their normal operating range. All you need is a pair of timers (the 556) and two time constants, one being a minute or so long. The other for 500 msec to 1 sec long. The relays would be 6 volt coils and maybe a resistor to drop the voltage across the coil(s -if you do input muting).
-Chris
Thanks Gents,
I agree with the more elegant solutions long term. In the mean time, would a cl-60 serve the purpose of getting me up and running?
Thanks,
Ryan
I agree with the more elegant solutions long term. In the mean time, would a cl-60 serve the purpose of getting me up and running?
Thanks,
Ryan
Actually, the surgistor is very clever old tech that works perfectly when it is correctly aligned. What happens is that there is a heater strip that heats up the bimetallic strip and which forces the contact on the bi metallic strip to close up and make contact on the fixed end. The heater wire allows the voltage to ramp up slowly and when the contact is made full AC will be enabled. So as long as the correct gap is set in the strip it works without problems with no circuitry or active components to potentially go bad. Those modern slow voltage turn on circuit boards are an impressive technology but, on my HF89 the surgistor is still working perfectly. How many years in an amp do any of the slow start circuits have? I don't think it is over 60 years.
Now, if yours is bad that would be a reason to change it but if it is working then it works better than CL, current limiter, which will only give you a few second of slow voltage increase.
Hi DAK808,
My surgistor is working as it should. But, once the resistor cools down it opens and then cycles a few times until the ambient temperature rises enough to keep it closed. Yours does this too, it has to. My surgistor is also mounted exactly where it was from the factory.
A few seconds are all you need to kill the surge. Applying the series resistor any longer than this is a waste of energy. As for technology lasting, the surgistor contacts go through several more cycles than a relay would, and the energy across the relay contacts is very low in this application. So the only thing that will age are the capacitors - like the rest of the ones used throughout the amplifier.
-Chris
My surgistor is working as it should. But, once the resistor cools down it opens and then cycles a few times until the ambient temperature rises enough to keep it closed. Yours does this too, it has to. My surgistor is also mounted exactly where it was from the factory.
A few seconds are all you need to kill the surge. Applying the series resistor any longer than this is a waste of energy. As for technology lasting, the surgistor contacts go through several more cycles than a relay would, and the energy across the relay contacts is very low in this application. So the only thing that will age are the capacitors - like the rest of the ones used throughout the amplifier.
-Chris
Hi Chris, i have watched the operation of the surgistor when doing testing in both my HF87 AND 89 where both just close after heating up. They don't open and close like you mentioned. It would not be good for the components if it cycled like that.
Hi dak808,
Actually, the only component that it wouldn't be good for is the surgistor. Everything else would just follow the gentle deviations of the power supply. I wish mine acted like yours, but if the environment doesn't heat up as quickly, then the bimetallic strip cools and opens the contacts again until the resistor heats it up again for another cycle. This has to continue until the surrounding environment is warm enough to keep it closed. Maybe yours has bad contacts and that generates the heat needed locally. But they should cycle as mine does if you think about it. The air and metal simply does not heat up quickly enough to keep the contacts closed.
-Chris
Actually, the only component that it wouldn't be good for is the surgistor. Everything else would just follow the gentle deviations of the power supply. I wish mine acted like yours, but if the environment doesn't heat up as quickly, then the bimetallic strip cools and opens the contacts again until the resistor heats it up again for another cycle. This has to continue until the surrounding environment is warm enough to keep it closed. Maybe yours has bad contacts and that generates the heat needed locally. But they should cycle as mine does if you think about it. The air and metal simply does not heat up quickly enough to keep the contacts closed.
-Chris
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