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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 24th Jun 2018, 1:54 am   #1
petervk2mlg
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Default Loctal B8G inherent weakness?

Have others noticed an inherent weakness in the integrity of Loctal valves and their bases? I bought a new 14S7 valve and on unpacking it noticed that the base was detached from the glass envelope. How were they originally attached? I guess I could try reattaching with some epoxy glue.
Peter
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Old 24th Jun 2018, 4:17 am   #2
joebog1
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Default Re: Loctal B8G inherent weakness?

I have not had ANY problems with loctal valves, APART from some valve bases
( sockets) having very small contact area, can become noisy after time.
ALL the loctal valves that I have are ex aussie military though, so that may have some bearing on reliability/build quality.
Some valve bases I have, are simply two tiny "clamps", like a pair of tweezers, that hold onto the 1.25mm diameter valve pins, on either side of the pin. i.e. micro contact area, even though the "clamps" have quite strong spring action.
These seem to be the "worst" type base I have, even though the contacts are silver plated phosphor bronze.
Apart from that problem I am doing a lot of things with loctals as I have access to quite a few of them, alas not high gain twin triodes.

Joe
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Old 24th Jun 2018, 9:42 am   #3
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Default Re: Loctal B8G inherent weakness?

The weren't much used in the UK, though a few manufacturers made sets using them in the late 40s between the Octal and B8A Rimlock eras. Philips/Mullard were pushing the B8A standard hard in Europe at that time.
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Old 24th Jun 2018, 10:01 am   #4
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Default Re: Loctal B8G inherent weakness?

Cossor seemed quite fond of the loctals and although the adopted the B7G very quickly for post war battery sets, didn't seem fond of the B8A.

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Old 24th Jun 2018, 11:22 am   #5
petervk2mlg
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Default Re: Loctal B8G inherent weakness?

Thanks guys. The 14S7 was a spare for my Sobellette radio - so a UK set.
I attach a pic of the valve.
I’ve glued the base back on with 5 minute epoxy.
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Old 24th Jun 2018, 11:29 am   #6
paulsherwin
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Default Re: Loctal B8G inherent weakness?

I didn't mean to imply that they weren't used at all in the UK, only that they were used by manufacturers without strong ties to Philips/Mullard or Mazda and then only for a few years. I know Regentone used them for a couple of years.

Wasn't the Loctal originally a rough service design for US military use?
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Old 24th Jun 2018, 12:22 pm   #7
petervk2mlg
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Default Re: Loctal B8G inherent weakness?

Understood Paul.
I’ve read that the loctal sockets were developed by Sylvania for ruggedised applications such as car radios.
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Old 24th Jun 2018, 12:23 pm   #8
TonyDuell
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Default Re: Loctal B8G inherent weakness?

I had the base shell come off one of my Loctal valves. I can't remember what I stuck it back with, but I never had any problems.

I seem to remember that the seals round 7 of the pins are circular, but D-shaped round the eighth. And the holes in the metal shell are similar. This means it will only fit properly one way, with the locator in the correct position.
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Old 24th Jun 2018, 9:45 pm   #9
G6Tanuki
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Default Re: Loctal B8G inherent weakness?

I had that happen with a 1299/3D6 battery pentode some decades back - I cleaned-out the old adhesive and used a blob of Evo-Stik to reattach it.

The 'Loktal' base always seemed an oddity to me, in the same spirit of "being different just to be difficult" as the Mazda Octal! I much preferred the B9G base as used on little power-tubes like the QV04-7 and of course the EF50. The valveholders with the screw-down retaining ring are particularly nicely engineered.
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Old 24th Jun 2018, 10:21 pm   #10
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Default Re: Loctal B8G inherent weakness?

I've struggled to rationalise their existence, too- the socket has much the same footprint as International Octal, so no space saving there and with less reliable contacts. IO even lived on for decades in power relays as a tribute to its reliabilty and current and voltage capability. Loktal did at least introduce the concept of the glass, low-loss base and short interconnections for effective use into the VHF range, certainly better than pinch-type construction with long lead-outs and lossy bases- but even there, the metal octal valves that had preceded loktal had short internal leads and base insulator materials improved over time.

Perhaps they could be seen as serving to give valve-makers experience of the construction and manufacturing techniques that were then refined and miniaturised in subsequent valve series.
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Old 24th Jun 2018, 11:06 pm   #11
joebog1
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Default Re: Loctal B8G inherent weakness?

I believe they were developed as Paul says. All the loctals I have are rated to silly G forces, and most have guaranteed service ceiling of 60,000 feet. I do know that the 5B/254's I have were for RAAF Canberra bombers in the 50's.

I should mention that the only experience I had with them was in imported radios.
Namely Canadian and South African
j.b.
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