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Old 29th Nov 2021, 4:23 pm   #21
dougietamson
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Default Re: Octal valve partially wrapped in brown paper...

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I was given a box of approx 100 valves today, xmas came early
Ah, a few of those appeared on the Edinburgh scene a few weeks ago.

David
I picked up the box yesterday from a very pleasant Irish lady in the Edinburgh New Town area. She said her father was an engineer and told me some of her fond memories of him buying broken TVs for 10s fixing them and selling for 50s, we had a 'guid blether'. I recounted some on my fathers stories from when he was a GPO engineer in the 50s/60s. I'm always reminded of him when driving past Hearthill on the M8 as he used to climb those tall masts.
Her father died 12 years ago and she was now having a clear out of her flat so instead of throwing in the trash she put an add in gumtree for £1.
She didn't even want the £1.

Photo from the add attached.

Doug.
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Old 29th Nov 2021, 4:49 pm   #22
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Default Re: Octal valve partially wrapped in brown paper...

She's probably happy that they're going to get used and appreciated.

A radio amateur in the Edinburgh area died this year, and some members of the local club have had the job of disposing of his stuff. He used to have an amateur radio shop and also a business doing PMR/Marine stuff.... he was ex-GEC. There were several boxes of valves auctioned a couple of weeks ago amongst a lot of stuff. I bought one and it only went for four quid. They all seem to be new, from his PMR/Marine stores. So I have a lot of 6V6, ECC81, N78, VR150/30, and the top cap metal jobs that make me think of HROs.

A couple of dozen audio types I passed on to Andy, to help distract him from waiting for motorbike injuries to heal. I think I'll take the rest of the ones I don't have uses for up to David in Aberdeenshire when I next feel like a long run. Maybe amalgamated with a loop round the North coast.

There were a vouple other boxes, so I'd wondered if one had gone your way.

Lothians radio soc's 6-monthly junk auctions are a real treat.

David
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Old 29th Nov 2021, 5:16 pm   #23
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Default Re: Octal valve partially wrapped in brown paper...

Here's my dad in a telephone exchange (London) standing on left.
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Old 29th Nov 2021, 9:07 pm   #24
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Default Re: Octal valve partially wrapped in brown paper...

Regarding testing power valves like that without a tester (which aren't all that good with high power valves anyway, I don't think) I always just triode strap them and connect them up with three AVOs and three power supplies. I don't even bother with a base socket, I just use small insulated croc clip leads and put little bits of torn off cardboard between the pins if there's a likelihood of shorts between the clips. You can take all the required readings and even plot a graph if you want to - I wouldn't bother with trying to knock up an amplifier, unless you just want the fun of doing it and have all the bits to hand.

Regarding cheap boxes of valves, the modern day 'ham' doesn't understand, or even have the interest in them - they're only interested in buying modern 'plug and play' transceivers at these sales, so people like me/us, end up buying all the stuff that no one else wants, to save it from being dumped. My interest is in valves, parts and meters etc...plus any other old scrap that's interesting (to me) and nobody else wants!

Last Friday evening I went to pick up another box of valves that someone had donated and dropped off at someone's house local to me. They were nearly all boxed in original boxes and as I commented at the time, I said that I bet they're all 'pulls' put back in the boxes, and after opening a few boxes they were in fact all used. However, as you can see in the pictures below, there was a slightly different story to these valves, as many were marked as having been tested back in the very distant past. I found one ECL80 which looked absolutely brand new, but marked as tested in April 1965...at least all those PCL83s should keep my PYE Black Box fed and watered for the foreseeable future, all in all I was very pleased with them.

Regarding sticking valve bases back onto the glass, I've never done it. I just leave them as they are and make sure I'm careful removing, handling and reinserting, but perhaps I should have a go at 'sticking' them back together. I've got another KT66 which has a base that's adrift, so being a big valve, that would be a good candidate for a repair. However, I'm not interested in selling valves and all valves that I get are for my own use in experiments, repairs and restorations (or even ornaments) etc. I wonder whether some of those exotic valves that you see for sale with highly polished bakelite bases and pins, that have probably had some hard setting glue applied between base and glass if they've had a loose base, whether a few months down the line the new owner of said valve finds a little crack in the glass and the valve has gone to air - too late for a comeback by then!

In the recent acquisition of older type valves I got, there was a few really good examples of perhaps how not to stick a base back on...I'll have to look out some of the best examples for a photo shoot - one is completely wound with tape head to toe, so don't know what was going on there!

I did take a picture of one of these valves that's been really spoiled with a base that's been stuck with something that can only be guessed at. It looks a mess, but it's solid, so I'm not bothered, as it's for my own use anyway. It could be some of that old type insulating tape (like my dad used to use when I was a kid and is actually used on some other valves to stick the bases on) and it's either been deliberately melted on or the heat from the valve has melted it over time.
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Old 29th Nov 2021, 9:17 pm   #25
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Default Re: Octal valve partially wrapped in brown paper...

Re-attaching valves to their Bakelite bases - the 1950s/60s Military approach was to use a short length of gray adhesive-lined heatshrink tube.

I've got a bunch of WWII-vintage VR100/KTW62/VR101 and similar valves used in Marconi B28/CR100 receivers thst have been re-attached this way.

Not sure if it would work so well in a power-valve where the envelope-temperature would normally be well above the softening-point of the heatshrink glue.
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Old 29th Nov 2021, 9:26 pm   #26
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Default Re: Octal valve partially wrapped in brown paper...

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a short length of gray adhesive-lined heatshrink tube.
I've also got a few valves like that - seems to work well enough.

The valve that I mentioned that was wound with tape head to toe is done with the same colour tape - perhaps it was an attempt at doing the same thing, but the person got carried away
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Old 30th Nov 2021, 1:45 pm   #27
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Default Re: Octal valve partially wrapped in brown paper...

I completed the loose base fix for the GEC KT66 suggested by GJ and while I was enjoying the nail varnish fumes I found some more candidates for the same fix:

Brimar 6V6GT and 6X5GT, a Russian 6V6GT clone and a 6L6GC.

All nice and steady now, will wait a few days longer to allow them to fully dry before heating them up.

Doug.
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Old 30th Nov 2021, 1:55 pm   #28
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Default Re: Octal valve partially wrapped in brown paper...

While checking all my octal base valves I found some Russian 6L6 clones (6n3c/6p3s).
These are identical to the Bentley Acoustics Corporation Ltd KT66 vales.

These are often sold as equivalent to a 6L6GC but this is quite wrong, they are more like a 6L6G maxing out at 350v on the anode as compared to 500v for the 6L6GC. Red plating awaits... the one in the photo was glowing red for a while and now just crackles and pops.
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Old 30th Nov 2021, 7:37 pm   #29
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Default Re: Octal valve partially wrapped in brown paper...

I fired up the GEC KT66 along side a 6L6CG and the 2 fake Russian KT66(6P3s) in a test push pull amp and took some readings.

The filament measured 1Ω and there were no shorts to other pins.

A while back I wound a bench amp PSU transformer with a choice of 0-275,300, 325(CT),350,375,400 and 650v ac 40v bias supply and 4A 6.3v and 5v. For this test I chose the 300 tap and bridge rectifier.

Filtered HT to the OT settled down to 288vdc after a 5 minute warm up.

The bias supply was adjusted to -28vdc

For the KT66 and 6L6GC pair

Cathode pin 3 via 1Ω resistor to ground
V3(KT66) = 0.031vdc = 31mA
v4(6L6GC) = 0.027vdc = 27mA

Vdrop across CT to anodes
V3 1.52v with 69Ω dcr from CT to anode = 25.4mA
V4 0.975 with 59Ω dcr from CT to anode = 16.5mA

screens at pin 4 measured 274vdc

For the 2 fake Russian KT66, these turned out to very well matched.

HT to OT CT 284vdc
Bias measured at 128.4vdc

Cathode Pin 3 via 1Ω resistor to ground
V3(6P3s) = 0.021vdc = 21mA
v4(6P3s) = 0.022vdc = 22mA

Vdrop across CT to anodes
V3 1.18v with 69Ω dcr from CT to anode = 17.1mA
V4 1.08 with 59Ω dcr from CT to anode = 18.3mA

screens at pin 4 measured 272vdc.

Doug.

Last edited by dougietamson; 30th Nov 2021 at 8:07 pm. Reason: correct error
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