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Old 10th December 2012, 03:28 PM   #91
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I've heard stories about the early Dynaco solid-state amplifiers - like the ST-80 - PCBs starting on fire due to some power supply dropping resistors being mounted directly against the board. So no, it just isn't a tube issue, it's a heat-related issue - which could be true with anything that runs hot - resistors, power tubes, or any poorly designed layout.

The thing I hate most about PCBs is trying to desolder/wick out tube sockets, especially with some of the junkier sockets being produced these days.
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Old 10th December 2012, 03:43 PM   #92
marce is offline marce  United Kingdom
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If you dont want to save the socket, cutting the pins and taking one out at once is an old trick used in the past with IC's to prevent the PTH barrel being pulled out with the pin. These days with SMD its not used as much.
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Old 10th December 2012, 04:08 PM   #93
qusp is offline qusp  Australia
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Quote:
Originally Posted by marce View Post
These days with SMD its not used as much.
these days with SMD there are not that many pins
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Old 10th December 2012, 04:24 PM   #94
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CST suite for one has a thermal management section . When you have a 125 watt cpu in a less than 2 square in square heat will effect the board.
kstagger what I have seen on the ols ST-80 Dynaco boards was not a fire but a well burnt pcb with a good sized chard fiberglass spot . If you get the fiberglass to burn it will burn very hot in my experience.
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Old 10th December 2012, 05:26 PM   #95
marce is offline marce  United Kingdom
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LOL thats sort of what I meant
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Old 10th December 2012, 05:38 PM   #96
marce is offline marce  United Kingdom
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A lot of the newer SMD packages are designed to get the heat away from the actual chip, QFN's LGA's etc or bottom terminated components, IPC-7093 is a good guide if you can find one. The increased thermal density, power density, pin density and increasing rise times has changed how we design PCB's and also the ancillary concerns with a design, never mind trying to get all thye routes in. If you look at a lot of commercial gear in metal enclosures you will often see heat sink fins moulded in to the case design. As I have said on other threads, you have to think about the whole system with todays design, PSU, electronics, case, EMC, thermal, signal integrity etc etc especially when doing high reliability designs (class 3 PCB's) where failyre of the system can cause death.
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Old 10th December 2012, 07:13 PM   #97
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....In the earlier post ..all the carping about that rather discoloured wirewound on the PCB; Here is the reason:-
The place on top side is occupied. A large electrolytic has encroached the footprint area of the resistor; the CAD library incorrect. Anyone should see the electrolytic would have quite a shortened life if the wirewound was "cosying" up to it.
Mistakes like this happen alot of the time even in the best of equipments and where series modifications are done without pad updates.

richy
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Old 10th December 2012, 08:04 PM   #98
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Three decades back....I taught radio & TV electronic servicing in evening classes twice weekly at the local tech. In that era, amateur radio HAM rig work was still popular using PTP and even with most guitar amps.
The two pics show for themselves the construction principles.
Still many amp constructors go for the short and dirty of prototyping PTP "birds nest" in a wooden box.
Compare with a pic of a decent PTP, the owner of this amp has taken care and trouble over the locations of parts etc. Centre PCB is heater supply. It is infinitely more reliable than the "birds nest".
Like doing it proper; then show oneself what one is capable of. Like a car; most want to see under the bonnet.

r.
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Old 13th December 2012, 12:45 AM   #99
SandyG is offline SandyG  United States
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Quote:
Originally Posted by p. jordan View Post
In 1957, Juke box manufacturer Seeburg produced two models, KD200 and l100. In previous years, all models were PTP using tubes. Due to the many issues
surrounding cracked circuit paths, caused by heating and cooling, this was the only
year circuit boards were used with tubes. Seeburg continued with circuit boards, after
transistors were used for amplification and control, several years later.
I have an L100 and I think the problem was the materials used for the PCB. I have one that is in good condition and works ok. I find that I have more problems with the connectors then anything. They were way ahead of their time I think.

Sandy
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Old 13th December 2012, 01:19 AM   #100
SandyG is offline SandyG  United States
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Quote:
Originally Posted by richwalters View Post
....In the earlier post ..all the carping about that rather discoloured wirewound on the PCB; Here is the reason:-
The place on top side is occupied. A large electrolytic has encroached the footprint area of the resistor; the CAD library incorrect. Anyone should see the electrolytic would have quite a shortened life if the wirewound was "cosying" up to it.
Mistakes like this happen alot of the time even in the best of equipments and where series modifications are done without pad updates.

richy
So the design was bad, not the PCB, if you can't see that a something like this going bad before you do the work on the PCB you likely shouldn't be doing them. Also I can guess that that PCB and likely design was made to be as low cost as possible just due to the 'simulated' double sided board wire jumpers, ie, save money anywhere including the designer.

Doesn't matter what you do if you at least start with common sense and ask for help at DIY AUDIO

I have done PCB for fun for quite a while using PROTEL/ALTIUM pcb software and most of the stuff I have done has been smaller digital based boards.

Doing tube based were somewhat of a challenge at first as it has a very different style to doing a board. To start but the first thing I did was create my own PCB patterns for anything of high heat or have potential for mechanical issues making sure that pads were robust and not default, then be generous with track size and spacing. Time consuming yes, but worth it in the long run.

I'll see how long the boards I did last but I will say that I do like the 2oz copper with the thicker boards. I do like the simplicity of mounting the tube sockets to the PCB but one thing that I make a big effort is to make sure the board has MANY anchor points to the chassis keep things rigid when swapping tubes not just at the corners as I have often seen which I think is a big problem for some designs.

Common sense stuff like that helps keeps you out of some trouble. Mounting anything that generates a lot of heat should have some hole for heat to escape, etc. etc.

And remember PCB's don't kill... people do... wait... is that guns I can never remember that

Use what you like and are comfortable with that's really the bottom line. No shortage of successful projects built with either method.

Sandy
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