Hi Rod. Does the C1 47uF capacitor need to be audio grade? I'd like to replace mine with a 50V in my GM70 regulator.
Thanks,
Adrien.
Something reasonably known-good. But many low-cost types work well, like Nichicon VR, and Panasonic AM.
Please take care, when considering high voltages. The standard regulator operates safely with input voltage up to about 45V, using 50V C1. Higher values require some parts changes (to Q1, Q3).
OK. There is a possibility that if a GM70 filament blows, the voltage will climb to around 45 volts with no load. Then when the tube is replaced, the caps could discharge from 45 volts residual charge. So given this, should I be using a bleeder resistor or protection circuit to deal with this issue?
Thanks,
Adrien.
I can do that. So to confirm, C1 is the only component at risk with 45V DC and no load?
Thanks,
Adrien.
Hi Adrien, Yes, C1 is usually the lowest voltage item, followed by Q1,Q3 which are 50V rated. The rest of the Regulator is able to withstand 100V.
Higher voltage versions are also possible, and make a nice regulator for fixed-bias voltages (grid bias). They have the same advantages of the filament regulator - lowest possible noise, and zero coupling from the music signal to the regulated voltage.
Higher voltage versions are also possible, and make a nice regulator for fixed-bias voltages (grid bias). They have the same advantages of the filament regulator - lowest possible noise, and zero coupling from the music signal to the regulated voltage.
Hi Tim,
Yes, they are already in use in a number of Field-Coil Speaker designs (Vegard's 215EXC is the latest). They can operate right up to 6A of field-current, and any voltage found in the usual speakers.
The 25-turn trimmer makes the Regulator a practical solution for trying out the sound at different voltage/current points, and the ultra-low noise is well worth having.
(Survived storm, by heading West. Only 13mm rain, no wind!) cheers, Rod
Yes, they are already in use in a number of Field-Coil Speaker designs (Vegard's 215EXC is the latest). They can operate right up to 6A of field-current, and any voltage found in the usual speakers.
The 25-turn trimmer makes the Regulator a practical solution for trying out the sound at different voltage/current points, and the ultra-low noise is well worth having.
(Survived storm, by heading West. Only 13mm rain, no wind!) cheers, Rod
I use these Rod:
Buy Terminal Posts Single sided PCB terminal pin,1.3mm dia Vero Technologies WP6819 online from RS for next day delivery.
Not quite those as I have the old lead watch out version but the same thing.
My two reg boards have been in three breadboards and are now finally at home. Goodness knows how many times I have re-soldered to them and it's been fine.
Those screw terminals have caused me no end of trouble over the years on pre-PLC industrial stuff.
I would love to know the manufacturer of the screw terminals on Mitsubishi PLCs because they are excellent. I had one that we used for training, it got abused by technically inept monkeys day in day out for nearly ten years and the terminals although battered are still good.
Cheers
Matt.
Buy Terminal Posts Single sided PCB terminal pin,1.3mm dia Vero Technologies WP6819 online from RS for next day delivery.
Not quite those as I have the old lead watch out version but the same thing.
My two reg boards have been in three breadboards and are now finally at home. Goodness knows how many times I have re-soldered to them and it's been fine.
Those screw terminals have caused me no end of trouble over the years on pre-PLC industrial stuff.
I would love to know the manufacturer of the screw terminals on Mitsubishi PLCs because they are excellent. I had one that we used for training, it got abused by technically inept monkeys day in day out for nearly ten years and the terminals although battered are still good.
Cheers
Matt.
At first this type of connector may be rock solid. However, if the connector is just a screw terminal and the position of connection is not automatically adjusted to the copper (which more or less flows over a longer period) then resistance goes up or worse, there will be only intermittend contact, which both will attribute to the noise.
How much resistance is needed to generate audible noise ?
Once you have answered this question, my next question will be:
With that resistance in series with the tube, what will be the remaining filament voltage ?
One should estimate what noise voltage is audible, first. My calculations and experience shows that that is 1mV at the speaker terminal.
At the filament of a 300b that translates to about 10mV (no balance or hum potentiometer applied, so this is a worst case situation).
10mV of resistor noise, in a bandwidth of 20kHz, requires a resistor of 30k-ohm.
Now you connect 30k-ohm in series with your filament and figure out what happens......
Thanks for the feedback everyone. As for my experience, I used some Cinch Jones connectors rated at 10 amps for my umbilical running at 3 amps. I did occasionally get some noise so the connectors needed to be reseated. So I suspected that if the screw terminal contacts were not of good quality, I may have similar problems. That was what I was thinking. Contact noise as opposed to resistance noise.
Based on your feedback, the screw terminals are in the bag where they will remain. I soldered all the wires so they are well connected.
Adrien.
Based on your feedback, the screw terminals are in the bag where they will remain. I soldered all the wires so they are well connected.
Adrien.
So you are saying that these types of terminals show a resistance in the range of k-ohms ?
I use Lumberg and never experience problems, not even with the low noise filament supply modules, which are used in linestages where the sensitivity is even 30dB higher.
best