Hi,

Does anyone have any 6M5 valves that they are happy to sell?

Cheers
Scott

6M5s are getting rare. Be aware the early Mullard ones with the funny glass base suffer from silver migration between the pins, causing crackling noises.

Retro audio (tube-amp-nutter-audiophile) market uses 6BQ5, which has similar spec but a different pinout. Easy wiring change and readily available - they are still making them!

Hope Brad doesn't mind me posting this link. I've always found them competitive for TV valves, they stock nearly everything and the delivery is fast.

https://www.tubedepot.com/products?utf8=%E2%9C%93&keywords=6BQ5

The HRSA valve bank have 8 new ones and 33 used ones on their valve list. If you email me I can send you the complete list of what they have.

The 6M5's with the funny glass base are called a "Innoval" type. These Innoval valves were developed by Philips Miniwatt in Australia based on war time research with the EF50. Australian Innoval style techniques were also used in the later versions of the European Rimlock series of valves.

The Innoval type valve's were manufactured in Australia from 1949 until about 1959. After 1959 the Australian Innoval series changed to normal noval type valves and were manufactured until the early 1970's

As for 6M5 replacements the 6BQ5 or EL84 is the best choice. A common TV valve, the 6CK6 with socket wiring changes, is also a good sub for a 6M5.

You could even use a 6BM8 and you get a bonus extra triode (if you wish to make use of it).

Thanks guys, I would still prefer to use 6M5 if I can find them. I have 4 Philips radiograms that all use it.
In terms of having to substitute, if I have to go down that path, what's the changes I'll need to make to the sockets?

Cheers

Easy-peasey.....

Just move the wire that's on pin 1 (6M5) to pin 9 (6BQ5).

It's wise to make sure there's nothing connected to pins 1, 6 or 8 because they are listed as "I/C" (Internal Connection) Although 6M5 also lists pins 6, 8 and 9 as I/C sometimes some bright spark will look inside the glass, see the pin disconnected on a particular bottle and use them as tie points.

Baissing, gm and plate impedance are all about the same so performance will be unaffected. I have found the 6BQ5 seems to be a tougher bottle than the 6M5 but I have no real evidence to support this.

One of the reasons for the innoval (thanks MCTV, I had forgotten what they were called) 6M5 problems is the proximity of G2 right next to G1 on the pinout. The innoval pins were silver plated and the silver would migrate across the glass over time. Very sensible of the 6BQ5's designers to move G2 to the other side of the index gap!

On the subject of using a 6BM8, biassing would need to be changed, a 6M5's bias will cook a 6BM8. A better choice would be the 6GW8 if you want to go down that path, but 6GW8s are Highly Desirable ($$$) so you might be better to consider the 6GV8, similar spec, different pinout, relatively unknown, undiscovered TV valve that's much easier to get and cheaper.

I looked at using the 6GV8 to replace the unavailable 6BV7 in my AWA TV but in the end the existing bottle was still OK so I left it. Not too much of a pinout change to drop a 6GV8 in place of a 6BV7 and you can use the triode to replace the diodes if you need to. Or if you don't need the diodes, rewire to get some more audio gain instead. The 6GV8 was used by Kriesler successfully in the last valve mantle radios. They were using up surplus stock (their B/W TVs by then were solid state). The 6GV8 is not really an audio valve but have a look at the Kriesler circuit to see how they used it.

I have some old second hand ones, They all seem to work OK but all the ones I have checked so far look as if they have had a hard life.
I'll keep looking. How many did you want?
JJ

This guy has been listing them regularly on Ebay.

http://www.ebay.com.au/itm/322235248517

The 6M5s I have used look like they have had a hard life but measure ok

Josh

The HRSA ones are only 8 bucks new and $4.50 used

The video output pentode 6CK6 is virtually the same as 6M5 and I would not be surprised if it wasn't the same Pentode in several other valves
like 6GW8.

The is a mod to do. The 6M5 has dead pins (6, 8 & 9) as G3 is tied to the Cathode internally. Pin 8 is an internal shield on 6CK6. The critical is pin 6 which is a live pin G3 & needs to be tied to the cathode.