On page 38 of the October 2025 issue of Radio Waves, there's an article about successfully dealing with silver migration problem in 6M5s by way of a 500 volt Megger employed as a zapper.

Is this a problem peculiar to 6M5 valves?
There is a similar method for clearing leakage in UL41 valves.
I cannot get Radio Waves here in the UK so I cannot read the article.
Sam.

Yes you can, if you are quick. Joining the HRSA will get you four editions per year, plus access to other goodies. As far as I remember, on being accepted for membership, you get the previous edition thrown in.

http://hrsa.org.au/

Thanks Brad.

A bit pricey for us cash strapped UK pensioners at £35, a shame its not on the web.
Sam.

Two reasons it happened on (early) 6M5s:

1. The pins were silver plated

2. G1 is right alongside G2 - unfortunate pin-out puts a pin with 250 volts on it right alongside the grid 1 pin.

A bit pricey for us cash strapped UK pensioners at £35

Radio Waves is great value for money, and production quality is getting better by the year.

If the Silver is on the pins, it will transfer some to the socket and tracking is not out of the question. It is therefore wise to check, clean, or replace as necessary.

As for the Silver and other dirty miniature tube pins. I find dipping their little bottoms in Hydrochloric Acid (Spirits of Salts) seriously effective at getting Silver & grot off of the pins and envelopes, across the board and within seconds.

Usual precautions for nasty chemicals apply. Rinse in water.