There is PCB and then there is PCB

[woodyc]

I've only seen a few really badly designed boards. (The only one I can think of right now was in the Madison Divinity II and the guy went out of business.)

From a repair perspective, there are some "PCB-related" problems that come up a lot. I'll mention two. One is when people put heavy parts on boards in combos and the solder joints fail from vibration, i.e. reissue Fenders. Another is when people don't know how to de-rate parts when they are PCB-mounted. For example, a 1N4007 is only good for its current rating if you keep it at room temperature. Here's what the board looks like under some 1N4007s in a Mesa Heartbreaker:

[teemuk]

I've only seen a few really badly designed boards. (The only one I can think of right now was in the Madison Divinity II and the guy went out of business.)

As far as I know, the Madison Divinity, as well as many other Madison's amps, were OEM designs bought from Smarvo Pro Audio Corp., which is still in business, I bet runs on a fairly nice profit, and continues to supply amps for dozens of brands like Randall, B-52, Eden, Ashton, etc. Madison may be out of business but likely not so much due to bad board designs but other reasons.

Another is when people don't know how to de-rate parts when they are PCB-mounted.

Indeed. Or realize that some components or tracks might actually do things like arcing and you'd need to take that into consideration in the design process. I should try to dig up some photos of Ampeg's SVT (the early tube models) boards. Those had a habit of not just charring but literally catching in fire and burning large holes to the boards.

[diagrammatiks]

5 or 10 minutes.

snip snip and slipstream the components back in.

Mil spec wiring like that is never meant to be repaired. To be compliant again that entire section would need to be rebuilt.

30 or so minutes for that.

That entire section didn't take more then 45 minutes to build tops.

Any repair would take less then that.

For a pcb amp, even if it's double plated through hole you'd still need access to the bottom. I would hardly call snipping the legs off a component on the top of the board and soldering a new part to the snipped legs a reasonable or good repair on a pcb. In fact, I wouldn't take my amp to a guy that was known to do that.


That picture you have up there is just about having the right parts and tools.

In fact just from that picture I can tell that starting from the stage on the right you've got 2 plate resistors at 100k.

the grid stopper is obscured but that looks like a .022 630vdc cap connected to the plate of pin 1 on the right valve
pin 6 is 100k, .022 630vdc.
grid input on pin 7 is the obscured grid stopper coming from the pot or in this case going into the pot..
cathode resistors are 1.8k and 1. something k.

The next tube is weird since pin 2 is grounded but it's 2 100k plate resistors with a cap coming off pin 6 obscured pin 1 is a .0033uf 630vdc into a 100k pot

R looks like a 4.7meg with what looks like a cdm mica cap across it.

thing would be a piece of cake on the bench.

I wouldn't even need a schematic.

[R.G.]

For a pcb amp, even if it's double plated through hole you'd still need access to the bottom. I would hardly call snipping the legs off a component on the top of the board and soldering a new part to the snipped legs a reasonable or good repair on a pcb. In fact, I wouldn't take my amp to a guy that was known to do that.

Well, on the other hand the tech's mantra should include something like the physician's "first do no harm".

There are situations - the Thomas Vox "Big Head" amps being one illustration - where simply getting at the back of the board may cause more troubles than correctly putting in a component by removing the old, clearing holes, and properly mounting a new one. In those cases, snipping leads and mounting from the top side is less likely to cause consequential damage than putting a replacement in properly. The size and weight of the component thus placed, and whether the leads are looped and crimped before soldering make a big difference. If you get a two-loop crimp and then solder on parts up to the size of a 1W resistor, I'd say it may well be reliable enough.

If it's a big cap or a 10W resistor, suspended above the board and especially if it gets hot like the 10W, that's a different thing again.

My favorite bad example is the Fender DeVille series and their resistor droppers for the +/-15V supplies. These resistors often get so hot they unsolder themselves from the PCB, and often leave charred PCB under them. I would not replace that setup, proper or not, with the same components properly mounted. The circuit as is is a design disaster.

You gotta pick your harms.

[diagrammatiks]

haha...i think if enough techs refuse to work on junk.....

but i agree rg that it should be situational. but i think we can agree that if you were gonna work on a good pcb and do a good swap of somethings boards gotta come off.

[R.G.]

haha...i think if enough techs refuse to work on junk.....

but i agree rg that it should be situational. but i think we can agree that if you were gonna work on a good pcb and do a good swap of somethings boards gotta come off.

As Arlo Guthrie said, it'll be a Movement... 8-)

There is one amp I can think of that the PCB never needs to come out. I designed the Workhorse amps so that a plate comes of the back of the chassis and you can then get to the bottom side pads of every PCB component. I was kinda bummed because I wanted to make the board holder/chassis tilt so the chassis didn't need to come out of the wooden enclosure, but I couldn't make it work. As it is, you can replace controls, switches, jacks, etc. without taking the chassis out of the box. But to get to the PCB pads, you do have to remove the chassis from the box and drop off the back plate.

[Steve Conner]

I would hardly call snipping the legs off a component on the top of the board and soldering a new part to the snipped legs a reasonable or good repair on a pcb. In fact, I wouldn't take my amp to a guy that was known to do that.

That is pretty hypocritical, you have posted pictures of complete dog's breakfasts that you made clear you intended to sell to a customer.

Tongue in cheek warning: My own amps are a real mess and I regularly do the snippy thing, but they're experimental and not meant for public consumption.

[diagrammatiks]

That is pretty hypocritical, you have posted pictures of complete dog's breakfasts that you made clear you intended to sell to a customer.

Tongue in cheek warning: My own amps are a real mess and I regularly do the snippy thing, but they're experimental and not meant for public consumption.

ha .

I think it really boils down to what you are used to looking at.

these old marshall pcbs are clean as heck but those leads give me ocd fidgets.



something like bc audio looks a lot messier at first glance...



but being able to trace the circuit just from a picture makes me a lot happier.

that being said I'm not qualified in any way shape or form to work on a pcb. There's a good chance I'll destroy it. I actually started out trying to mod pedals.

[Alex/Tubewonder]

ha .

I think it really boils down to what you are used to looking at.

How very true. Having seen pictures you posted of your work makes me wonder what it is you are used to looking at.

that being said I'm not qualified in any way shape or form to work on a pcb. There's a good chance I'll destroy it.

Therefore not qualified to pass judgement on pcb design either.
From your earlier posts I assume you haven't seen a PTP assmbly made to mils spec. BTW when you say "mil spec", which mil spec are you referring to? There are many, each has its own number and applies o different duty of the equipment. Mission critical, airborne, ground service etc. There's also a full instruction on how to repair this stuff so the relevant specs won't be compromised. I would be ashamed to say my amps are "built like a tank", rather "rugged industrial" but I guess you wouldn't have a clue as to what it means... I would suggest you learn more before passing judgements on matters you really know very little about. If someone came to me with what you have shown as example of your work I would throw it directly to the recycle bin. Cruel judgement? Yes, but a true one and based on some 40 years experience.

[diagrammatiks]

How very true. Having seen pictures you posted of your work makes me wonder what it is you are used to looking at.

Therefore not qualified to pass judgement on pcb design. You are not used to look at them by your own admission.
From your earlier posts I assume you haven't seen a PTP assmbly made to mils spec. BTW when you say "mil spec", which mil spec are you referring to? There are many, each has its own number and applies o different duty of the equipment. Mission critical, airborne, ground service etc. There's also a full instruction on how to repair this stuff so the relevant specs won't be compromised. I would be ashamed to say my amps are "built like a tank", rather "rugged industrial" but I guess you wouldn't have a clue as to what it means... I would suggest you learn more before passing judgements on matters you really know very little about. If someone came to me with what you have shown as example of your work I would throw it directly to the recycle bin. Cruel judgement? Yes, but a true one and based on some 40 years experience.

ouch. I guess I shouldn't mess with the genius behind vimag.

Quick question? When did I ever pass judgement? Stating a preference on how I like to build sure...passing judgement on pcbs as a whole?

I'm looking at the amps I own currently...a fryette pitbull UL and thd flexi 50. Both are pcbs.

40 years...guess that's how long it takes to come up with those innovations on your amps huh?

I'd settle down and work on my literacy grandpa.

[Alex/Tubewonder]

Aren't we touchy today? You stated your opinions (ok, not really judgements) in this post:
There is PCB and then there is PCB - Page 5
No, you shouldn't mess with geniuses. We get mad easily. That was a royal "We".
Now, I have more important things to do. Like inventing another revolutionary innovation or working on my literacy.
Have fun!

[diagrammatiks]

Aren't we touchy today? You stated your opinions (ok, not really judgements) in this post:
There is PCB and then there is PCB - Page 5
No, you shouldn't mess with geniuses. We get mad easily. That was a royal "We".
Now, I have more important things to do. Like inventing another revolutionary innovation or working on my literacy.
Have fun!

I like pcbs and I like not pcbs? ya real touchy opinions there.

you'd really design, simulate, and tweak a pcb if you were gonna build an entirely one off amp?

I'm sure it would be good with that level of dedication but that's pretty rare.

Don't get your infinitely variable impedances in a bunch now. If I ever see one of your amps around to snap a picture I'm sure I'd think it was great.

Been a while since that post though.

My favorite build shot right now is the Aiken Invader. Pcb and all.

[Steve Conner]

you'd really design, simulate, and tweak a pcb if you were gonna build an entirely one off amp?

Sure! Although strictly speaking this is a two-off since it's a hi-fi amp.

[kg]

Sure! Although strictly speaking this is a two-off since it's a hi-fi amp.

where the hell are the tubes?

[Alex/Tubewonder]

where the hell are the tubes?

Dangling on a long umbilical cord under the table?
The mojo surely is in how that power diode(?) is placed at an odd angle.