Hello everyone,
I have a question, but I need to provide a rather lengthy introduction before stating it.
I haven't been active on the forum for a long time since I built my first SSE: the Mancave version. As life has slowed down for me lately, I've found enough free time to work on some projects I started about 10 years ago—an SSE to replace the current amp in my main system (almost done) and a full-blown steampunk mancave SSE version (all the weird parts are sourced, and the PCB is done; it just needs an enclosure and final assembly). I will post more details on both later. I thought these two would be my final builds, but I realized I have another enclosure and enough parts to build one more SSE before I exit the hobby.
My previous and in-progress builds have all of the options plus an ability to gradually adjust the output tube bias via either a precision pot or a switchable resistor matrix. They also feature a 100 mA meters between R17/R27 and the common bus to monitor the cathode current. For what would be my final build, I've decided to take a "minimalistic" (in my understanding) approach, with the amp operating in just two modes: triode with no CFB biased for EL34, or ultralinear with CFB biased for 6550/KT-88 selected via a single switch. However, I still want to be able to monitor the cathode current, mainly to spot a bad or failing tube.
Here is my question: would it be okay to connect R17 AND R27 to the same pole of a single 200-300 mA meter, and the other pole to the common (i.e., inserting about a 2 ohm or less single load between both cathode resistors and the common bus)? Or is this a bad idea, and would I be better off using separate meters for each channel?
Thank you to those who read this post all the way through. I'd appreciate your thoughts.
I have a question, but I need to provide a rather lengthy introduction before stating it.
I haven't been active on the forum for a long time since I built my first SSE: the Mancave version. As life has slowed down for me lately, I've found enough free time to work on some projects I started about 10 years ago—an SSE to replace the current amp in my main system (almost done) and a full-blown steampunk mancave SSE version (all the weird parts are sourced, and the PCB is done; it just needs an enclosure and final assembly). I will post more details on both later. I thought these two would be my final builds, but I realized I have another enclosure and enough parts to build one more SSE before I exit the hobby.
My previous and in-progress builds have all of the options plus an ability to gradually adjust the output tube bias via either a precision pot or a switchable resistor matrix. They also feature a 100 mA meters between R17/R27 and the common bus to monitor the cathode current. For what would be my final build, I've decided to take a "minimalistic" (in my understanding) approach, with the amp operating in just two modes: triode with no CFB biased for EL34, or ultralinear with CFB biased for 6550/KT-88 selected via a single switch. However, I still want to be able to monitor the cathode current, mainly to spot a bad or failing tube.
Here is my question: would it be okay to connect R17 AND R27 to the same pole of a single 200-300 mA meter, and the other pole to the common (i.e., inserting about a 2 ohm or less single load between both cathode resistors and the common bus)? Or is this a bad idea, and would I be better off using separate meters for each channel?
Thank you to those who read this post all the way through. I'd appreciate your thoughts.
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If you are only using one meter use a shunt resistor in series with each cathode resistor, and then measure voltage drop across the shunt to get the cathode current. A 10 ohm shunt and 0 - 1 volt meter will measure 0-100 ma cathode current if my arithmetic is correct (I = V/R).
Use a DPDT switch with the meter at the common points of the switch.
A 1/4 or 1/2 watt resistor should be fine.
Win W5JAG
Use a DPDT switch with the meter at the common points of the switch.
A 1/4 or 1/2 watt resistor should be fine.
Win W5JAG
Thank you for the suggestion, I appreciate it.
My other builds have an adjustable bias and separate meters on each channel. This amp will have a fixed bias, and the only purpose of the meter would be to detect an abnormal rise in the combined cathode current if/when something goes wrong. So, I’m considering using a single meter permanently connected between both channel cathode resistors and ground to measure the combined draw. This way, if I’m running EL84s and the meter shows over 100 mA, I would know that something isn’t right.
So, the question is: Is this okay to do?
My other builds have an adjustable bias and separate meters on each channel. This amp will have a fixed bias, and the only purpose of the meter would be to detect an abnormal rise in the combined cathode current if/when something goes wrong. So, I’m considering using a single meter permanently connected between both channel cathode resistors and ground to measure the combined draw. This way, if I’m running EL84s and the meter shows over 100 mA, I would know that something isn’t right.
So, the question is: Is this okay to do?
I don't see why it wouldn't be ok, except that if the meter goes open your amp goes dead in both channels.
You could put it in the B+ lead and also pick up the current from the 12AT7.
Win W5JAG
You could put it in the B+ lead and also pick up the current from the 12AT7.
Win W5JAG