I would like to replace the tubes in my SB-200, but I want to make sure I do it safely.
I have done the reading and know there are lethal voltages etc., but I have not been able to find walk through anywhere on the internet.
The amp has a Harbach PM-200 power supply module installed. It also has the soft-start and soft-key installed.
Here's my understanding of the process.
Assuming the above is correct, questions:
Looking at the original schematics and construction manual it would appear that the HV plate wire is a large blue wire (which is I confirmed is still as originally built) and connects to "H" on the Harbach PS module (diagram attached).
Moving on, I have two options for tubes, some used, tested, and been sitting for unknown period Cetrons and also new Taylor/RF Parts tubes.
Once the new tubes are in place what is the best next steps as I have seen conflicting information (gettering).
So what am I missing? Where am I lacking? Comments or criticisms?
*When building a chicken stick, is a resistor recommended or not? I was thinking a single ~40k 3-5 watt resistor would be in the ball park were I to use one.
Thanks!
I have done the reading and know there are lethal voltages etc., but I have not been able to find walk through anywhere on the internet.
The amp has a Harbach PM-200 power supply module installed. It also has the soft-start and soft-key installed.
Here's my understanding of the process.
- Disconnect from power and ensure it can't be connected to power until completed.
- Allow voltage to dissipate, understanding that the HV reading on the meter may or may not be accurate and voltage may still remain even though it reads zero.
- Open case, remove cage to allow access to the internals.
- At this point all steps are a one handed operation with the other hand in back pocket to avoid creating a circuit that could lead to a very bad day.
- Using a chicken/jesus/oh-sh*t/capacitor discharge stick*, bleed off any potential high voltage from the power supply capacitors (and any other large caps?).
- Remove anode clips.
- Remove tubes.
- Install tubes, anode caps, and reverse the rest of the above steps.
Assuming the above is correct, questions:
Looking at the original schematics and construction manual it would appear that the HV plate wire is a large blue wire (which is I confirmed is still as originally built) and connects to "H" on the Harbach PS module (diagram attached).
- I would use the chicken stick to dissipate HV at connection point "H"
- - are there any other areas or capacitors that I should be concerned about?
- Should I then remove the anode clips using insulated handle pliers, or is it better to remove the RF chokes from the door knob capacitor and then remove the clips?
- Gently remove and replace tubes (soft cloth, no greasy fingers etc.)
Moving on, I have two options for tubes, some used, tested, and been sitting for unknown period Cetrons and also new Taylor/RF Parts tubes.
Once the new tubes are in place what is the best next steps as I have seen conflicting information (gettering).
- Do I not connect the anode clips, bring power to the tuibes and run them for 8-12 hours?
- Do I connect the anode clips, re-assemble and use a variac (I really would prefer not to have to find a variac)?
- Do I re-assemble completely and let it run for a while before transmitting?
- Does it matter that one set is new as of 6 months ago and the other set has been on the shelf for xx years?
So what am I missing? Where am I lacking? Comments or criticisms?
*When building a chicken stick, is a resistor recommended or not? I was thinking a single ~40k 3-5 watt resistor would be in the ball park were I to use one.
Thanks!
