Re: New Member intro and needing help


Hi Mike,
I likely have a VTVM in my collection that needs a little TLC as, getting those mercury batteries....

Kind regards,DBN aka John

On Saturday, July 2, 2022 at 04:12:32 PM EDT, Mike Dinolfo <mdinolfo@...> wrote:

The method suggested by John Kolb is somewhat similar to a method
described at

And although the "London Sound" method was apparently intended to apply
to vacuum tube audio equipment, I suspect it's equally applicable to
older vacuum tube Tek scopes. I tried the London Sound method only once;
it was successful in the sense that an old vacuum tube radio transmitter
powered up without any component failure.

But as they say- "caveat emptor."

Mike Dinolfo

On 7/2/22 13:01, John Kolb wrote:
In my younger days, I've turned on a long unused scope, and after a
couple of minutes, heard a loud bang as a cap exploded.

The electrolytic cap anode is a metal with a thin insulating oxide
layer.  After long idle periods, the oxide layer disappears. When
voltage is applied without the insulating oxide layer, large current
flows, causing heat, pressure, and eventually BANG.

I power up unknown equipment by turning power on for 10 sconds, then
off again, Wait awhile so that if heating occurred, the cap can cool
off again. Another power on, 15 seconds, this time; another cooldown.
The process continues with increasing on time periods until I run out
of patience. The applied voltage causes the oxide layer to form again

I don't know if this theory is correct or not, but I haven had any
explosions while using it.


On 7/2/2022 8:17 AM, David C. Partridge wrote:
Bring it up slowly on a Variac. This has the advantage of giving
alum electrolytic capacitors time to reform before they get full
Just don't do this if the 'scope has a switching Power Supply (like
most 7000 series and later 'scopes).

Just plug in an turn on (after checking the voltage selector is set

Dim bulb approach is fine.

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