Preventing HV flashover on socket pins - diyAudio
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Old 27th April 2012, 07:41 AM   #1
nazaroo is offline nazaroo  Canada
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Question Preventing HV flashover on socket pins

It occurs to me that one obvious cause of flashover on higher voltage tube amp designs is unfortunate increases in humidity in an environment and/or dust accumulation.

One way to cut down on this likelyhood (and even one flashover can be devastating to amp or tube) is to do the following:

(1) make sure that any likely expected repairs will not involve resoldering pin tabs. Mount for instance 1 ohm cathode resistors on a small turret or tab, and run a wire to socket.
Or make a mini-circuit board for resistor clusters around tubes.

(2) Carefully cleaning socket bottoms and covering pinholes, then spray High Voltage laquer / insulator on socket bottoms.
Do this lightly to prevent runs or leaks into socket holes. Bake dry with lamp to prevent dust pickup. Do a few coats.

Now in theory there will be much less opportunity for flashovers, traces, wormlines. The amp could be roaded into more difficult and harsh environments, including dusty smokey clubs and humid, drizzly outdoor concert venues.
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Old 27th April 2012, 11:55 AM   #2
M Gregg is offline M Gregg  United Kingdom
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Just for interest,

I use this idea on vero board projects..I just clean the flux off and spray with HT sealer/lacquer...Its important I think to use the sealer you can solder through and some even act as a flux..slightly different situation to above but it stops corrosion and tracking..I don't use it on the component side just the track side same on PCB's..

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Old 27th April 2012, 12:22 PM   #3
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I wouldn't use veroboard on HV projects.

However, I can't recall flashover being a problem with my experience of valve amps.

I think common sense prevails. Once the design is working, then any form of insulation will work. Heatshrink tubing is probably easier and less messy to use.
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Old 27th April 2012, 12:37 PM   #4
M Gregg is offline M Gregg  United Kingdom
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Quote:
Originally Posted by KatieandDad View Post
I wouldn't use veroboard on HV projects.
I built the oscilloscope project in the 70's from Practical wireless (vero project)..I think vero is OK as long as you know what your doing and don't put HV tracks right next to each other and cut away what your not using..

But yes heat shrink is good..The problem is some lacquers once on you can't solder through them and some you can't dissolve with cleaners..then it gets messy..

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Old 27th April 2012, 01:01 PM   #5
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It's funny how now that tube amps are less common it seems like these problems have gone away.

This used to be a common problem with tube gear, most frequently PA and instrument amps, TV sets, and transmitters, where the voltage is over 500VDC.

I wonder if teflon sockets are more resistant to permanent tracking.

Circuit boards can be conformal coated. Some of the formulas are solder-through but of course you need to recoat after repairs.

You can spread the pins out to 0.2 inch spacing or stagger the pads on to-220 packages > 300VDC.
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Old 27th April 2012, 01:08 PM   #6
M Gregg is offline M Gregg  United Kingdom
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Quote:
Originally Posted by Michael Koster View Post
It's funny how now that tube amps are less common it seems like these problems have gone away.

This used to be a common problem with tube gear, most frequently PA and instrument amps, TV sets, and transmitters, where the voltage is over 500VDC.

I wonder if teflon sockets are more resistant to permanent tracking.

.
LOL...The brown old circuit boards around the HT doubler/tripler and the line time base... CICK CLICK CLICK PHUT.....white dot on the tube off line me thinks..LMAO

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Old 27th April 2012, 01:08 PM   #7
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At higher voltages you will get static attraction of dust.

Valve TVs, I can remember them, I was knee high to a grasshopper then. YES, Mum and Dad had an old 405 line VHF B&W set. We had to go to my Grandparents to watch a colour TV and that was transistorised (I think, an ITT back in 1970s)
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Old 27th April 2012, 01:10 PM   #8
M Gregg is offline M Gregg  United Kingdom
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I'll just solder a new socket in..

Er where is the circuit board..lump of carbon with copper tracks hanging in the air and a tube base swinging in the wind...

LMAO why did we go to circuit boards...LOL...the old point to point was better (saying in the late 70'S)..Huh its got cheap circuit boards,,,,It'll never last.

That was the other one...the dry joint of hell/// that gets hotter and hotter and strips the track of the board then blows like a fuse and tracks across the what used to be circuit board now carbon based life form.....

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Old 27th April 2012, 01:14 PM   #9
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PCBs have never been a favourite with Valve Amp projects.

The Orientals love them, probably because of repeatability.
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Old 27th April 2012, 01:34 PM   #10
M Gregg is offline M Gregg  United Kingdom
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As above,

Dust and HT is a major problem...mix that with damp and condensation, then green/blue copper corrosion and you have the future of the tube circuit.. one person said to me..well you can't stop the dust or damp but. If it can't come into contact with the circuit conductors then it should last.. Untill it burns out..LOL

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