Is it best on recaps and restores to test the unit at stages.

[Ken Boyd]

Just wondering it when others do a full recap, and/or replacing all the resistors if it might not be best to do it in stages, and then power the unit up to listen to the results. Or is it best to just go full bore and replace everything? Currently I amworking at replacing all the carbon caps with new metal caps. I had already replaced all the caps but one, an old bumble bee cap, and have been listening to it for a while.

Just thinking it might be easier to trouble shoot if I did something incorrect, to catch it at the bud if I was to do a few and then put it in the system and power it up.

 

[jefferylhenr]

All depends how good your craftsmanship and documentation is. The rule of thumb is to not shotgun. And it depends on how difficult it is to access boards. I have been doing this for a long time and I don’t like to disassemble things multiple times. If you have an extensive parts inventory it help as you might find values different than the schematic. Waiting on parts orders can be frustrating.

 

[Lavane]

I start with power supplies, do some testing, then off to the next stage, rinse and repeat until done. If you shotgun a piece of equipment with new caps and other parts if needed and there's a problem it can makes it harder to find the problem.
If there is an issue to start with fix that first, then go on to do a restore.
I've seen more than a few threads where someone has posted that something was wrong after recapping a piece of equipment. They replaced all the caps at once, and maybe other parts that are known to possibly not age well, made some modifications, etc. And now have no clue what went wrong.

 

[wd40addict]

In stages so functionality and voltages etc can be checked at each stage. The internet is littered with people saying "I changed all the capacitors in my xyz and now it doesn't work at all".

However, I do agree that if much disassembly is needed every time this can get painful. I have an oscilloscope that has to be dismantled to gain access to the channel amplifiers, but then has to be reassembled before they can be tested.

 

[tubelectron]

• First, I identify and search for the problems.
• Second, I identify and search for the problems.
• Third, I identify and search for the problems.
• Fourth, I identify and search for the problems.

This involves looking, listening, smelling, tests and measurements.
NO hasty conclusions... Especially if it is an intermittent issue !

Then, only after, I study what can be done at best, according to the needs.
My rule being "if it works as expected, don't fix it", the systematic replacement of parts is not my strategy.
So it is indeed a step by step approach, as suggested by @Lavane and @wd40addict.
And of course a function of your documentation, troubleshooting experience, knowledge and tooling, as pointed by @jefferylhenr.

I'd say that it is a case-by-case basis !

But it's me, OK ?

T

 

[GordonW]

Many times, the units I get, are in such bad shape, that they need extensive re-capping just to work. Cracked coupling caps, bulging electrolytics, can caps with tar oozing out of the vent holes, and such. I don't have a choice, but to replace everything that is likely bad.

I do make it a point, to do one section at a time. Make sure that each replacement is installed exactly as the old one came out, before moving onto the next one. That minimizes the probability of an error causing things to not work.

Mind you, I do occasionally run into a defective part. But, fortunately, that's rare, and usually it's not too hard to find one defective part in a unit once it's test-fired for the first time.

Now, I DO just replace caps first. If there's resistor issues, those can wait until the caps are done. Unless resistors are actually blown up or broken to the point of no function whatsoever, I leave them for a second round.

Regards,
Gordon.

 

[kvflyer]

I have to agree with the above. What has gotten me into trouble (and it's on the back burner!) is when you are working on an item and several capacitors are crowded and buried. I have tried to be very careful and replace them all at the same time, to avoid going back to the same tube lug more than one time. I have been successful most of the time, but burned more than once. It gets complicated and detailed drawings (which do take time) and many photos will help.

 

[Ken Boyd]

I start with power supplies, do some testing, then off to the next stage, rinse and repeat until done. If you shotgun a piece of equipment with new caps and other parts if needed and there's a problem it can makes it harder to find the problem.
If there is an issue to start with fix that first, then go on to do a restore.
I've seen more than a few threads where someone has posted that something was wrong after recapping a piece of equipment. They replaced all the caps at once, and maybe other parts that are known to possibly not age well, made some modifications, etc. And now have no clue what went wrong.

Pretty much what I have done, as this unit I have replaced all the caps, other than missing one. I then put this in service and have been using it a few months. Now I have developed a problem as it starts emitting static and it is in time with the gas regulators flickering. So now I am back in with plans to replace all the carbon resistors. So far, all the resistors I have pulled out all are not too far off, just a bit higher in resistance than what they should be. I am also double checking all my prior solder joints making sure none of them look like cold solder joints.

These are mono units, old RCA theater amps, and the other unit is working great with just the caps changed out.

 

[gadget73]

I usually try to bring things up un-touched if I can to get an idea of working status, and go from there. If its got a hard fault immediately, I'll change that cap or whatever to get some signs of life. If its obviously burned, leaking, damaged, etc I'll change it before even applying power. No point in putting voltage to a cap thats obviously puking its guts out already.

Also depends what sort of parts we're talking about. Film caps I'm usually not so worried about doing, power supply caps tend to be bad, paper caps are always bad. Once I have some sort of baseline about what works and what doesn't I'll proceed accordingly. If everything works, I often just shotgun the thing if its not too annoying to deal with. If its not fully working I'll work on the section thats broken first to try and get it going without introducing more variables than needed. If the power supply is working OK that might get done last, or in something I'm rarely going to use, maybe not at all.

Resistors I tend to just check in circuit, mostly with tube gear they will read OK. if its low, something is across it. if its high, its bad. If one is bad I'll try to change it with a cap on the same terminal if possible, just to minimize the amount of meddling with tube sockets and terminal strips.

 

[Mr Boochie]

Just wondering it when others do a full recap, and/or replacing all the resistors if it might not be best to do it in stages, and then power the unit up to listen to the results. Or is it best to just go full bore and replace everything? Currently I amworking at replacing all the carbon caps with new metal caps. I had already replaced all the caps but one, an old bumble bee cap, and have been listening to it for a while.

Just thinking it might be easier to trouble shoot if I did something incorrect, to catch it at the bud if I was to do a few and then put it in the system and power it up.

Check and clean all connections, sockets, and tube pins first! This could save you a lot of work.

I go stage by stage, as needed. The noisiest stages tend to be those with the highest gain — such as the input.

You can demo this by pulling tubes section by section.

With all the tubes in, how’s the baseline noise? Swap the rectifier tubes with a known-good one. Does the noise problem get better? Then, that is your problem.

If not, put the rectifier back in and pull the input tubes. Does the noise go away? Then the problem is in that section. Tubes, resistors, and/or caps. Check the grounding!

If not, put the input tubes back in and pull the next stage (second gain, tone stack), then on to the phase inverter. If none of that solves the noise issue, then it’s probably in the output stage (tubes) or the power supply.

I avoid wholesale change-outs. Because what if you somehow miss the culprit and the darn thing is still noisy? Yes, this does happen. It’s better to be methodical, even though it takes longer, at least in my way of thinking.