Hi all,
Odd markings on the base of this valve in my Astor HMQ. Was in the rf position which should be a 1M5G, same as the IF.
The radio works ok, though it does work better with the valves swapped i.e. 1M5G in the rf position and this one in the IF.

I've been over the glass with a magnifier and can't find any hint of any other markings.
It is an AWV valve and is a pentode.

Any clues appreciated.
[hope the below bb code for the image works.
If it doesn't, the marking is a D then an arrow pointing up then another D.
The characters are quite large and 'hot branded' into the base

Image Link

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Currently restoring Astor HMQ 32vdc
Completed and working great!!

Hello Rob

The D arrow D is a department of Defence mark & doesn't identify the valve.
You could try putting the valve in a freezer for ten minutes; then take it out and condensation may show up the valve ID.

http://www.hws.org.au/RadioHistory/manufacturers/astor.htm gives the valve lineup as
1M5G, 1C7G, 1M5G, 1K7G, 1L5G
So it looks like the RF & IF valves should be the same. Does the internal construction of the two valves look the same? One may be weak or there may be an alignment issue. Have you checked the caps and resistors for deterioration?

Cheers
Graham

Hi Graham,
Ah, DoD. Thanks for the enlightenment
Yes, they do look identical internally.
I have checked alignment but am yet to do a thorough component check.
The only component I've had to change so far is a noisy AF coupler cap.

It would seem that the DoD valve is happier at IF frequency than RF.
Mind you, there's not a huge difference, just noticable.

Will try the freezer trick and see what I get.

Cheers,
Rob

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Currently restoring Astor HMQ 32vdc
Completed and working great!!

Interesting talk about the D^D. I've seen this symbol in the past and had no idea of what it meant.

Is this a symbol added to signify that the valve was purchased under a government contract?

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A valve a day keeps the transistor away...

It could be that, or maybe the Australian equivalent of the US JAN valves - Joint Army Navy - military spec stuff

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Currently restoring Astor HMQ 32vdc
Completed and working great!!

I guess so. The arrow is an old government issue symbol - hence the arrow on convict clothes, as much to prevent them flogging the clothes as to identify them as convicts. I have noticed it on some but by no means all surplus valves I used to pick up at a scrap yard at Bulli (now alas closed) that used to sell surplus defence material. The CV valves never had it. Picked up some nice signal generators there too.

Ah, the arrow....convicts....of course! Thought I recognised it as something I had worn...er...seen somewhere

So it would then be more likely for these to be regular valves, just branded with DD to indicate gov purchase/issue.

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Currently restoring Astor HMQ 32vdc
Completed and working great!!

QUOTE: You could try putting the valve in a freezer for ten minutes; then take it out and condensation may show up the valve ID.

Tried that but no luck.

I'm pretty sure now that it is in fact a 1M5G.
After chasing some intermittent problems out of the set and tweaking the alignment, the set is performing really well and can now pull in 6MD in Merriden at night with just a bit of wire hanging off the antenna post.

Swapping the 1M5's around now makes no difference. Doing that before was triggering another issue, which was poor earthing of the metal shield around the IF valve, which seems to be critical in this set.
If the shield is not earthed, you get nothing.

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Currently restoring Astor HMQ 32vdc
Completed and working great!!