Lemco dogbone capacitors - UK Vintage Radio Repair and Restoration Discussion Forum

Helder Crespo · 25th Jan 2022, 7:37 pm

Hi
I wonder if anyone has Lemco dogbone capacitors, 3000pF (Hi-K series, 500 or 750V) like the one in the photo. I'm looking for 10 more of these for an RF section.
Many thanks
Helder

G6ONEDave · 26th Jan 2022, 10:28 am

Hi Helder,
I have some 3nf tubular capacitors that are similar to your Lemco one. These are light brown in colour and measure approx 17mm long x 4.5mm dia, they don't have any voltage stated on them. Having tested a couple they measure 2583pf and 2658pf which if at 20% tolerance are a bit low but still in tolerance. I can send you 20 of them for cost of post, PM me if it is of help.

Dave

Longespee · 26th Jan 2022, 12:05 pm

Hi Helder,
I may have some, let me check, although I get the feeling they are 1000pf.

I'm looking for some at 500pf in the same style, but they do seem quite difficult to pin down.

Sean.

vidjoman · 26th Jan 2022, 12:10 pm

Think these were also sold by Radiospares back in time so might find them with the RS logo on.

Helder Crespo · 26th Jan 2022, 12:17 pm

Quote:

Originally Posted by G6ONEDave

Hi Helder,
I have some 3nf tubular capacitors that are similar to your Lemco one. These are light brown in colour and measure approx 17mm long x 4.5mm dia, they don't have any voltage stated on them. Having tested a couple they measure 2583pf and 2658pf which if at 20% tolerance are a bit low but still in tolerance. I can send you 20 of them for cost of post, PM me if it is of help.

Dave

Thanks Dave, that's very kind of you. I will take your offer in case I can't get the later make epoxy coated red ones.
Helder

Helder Crespo · 26th Jan 2022, 12:24 pm

Quote:

Originally Posted by Longespee

Hi Helder,
I may have some, let me check, although I get the feeling they are 1000pf.

I'm looking for some at 500pf in the same style, but they do seem quite difficult to pin down.

Sean.

Thanks Sean. I also think they're hard to find which is why I'm now trying with the forum after a long period of fruitless online searches. You can get 1000pF and 2000pF on eBay right now, but I've never seen 3000pF ones.
I checked my small stock of these, but unfortunately I don't have any 500pF. I have 1x1500pF, 2x2000pF (one of them RS marked) and 3x1000pF, in case you're interested.
Helder

Helder Crespo · 26th Jan 2022, 12:49 pm

Quote:

Originally Posted by vidjoman

Think these were also sold by Radiospares back in time so might find them with the RS logo on.

Yes, I have seen them with several different markings, including RS. Thanks.

Longespee · 26th Jan 2022, 12:55 pm

Quote:

Originally Posted by Helder Crespo

Quote:

Originally Posted by Longespee

Hi Helder,
I may have some, let me check, although I get the feeling they are 1000pf.

I'm looking for some at 500pf in the same style, but they do seem quite difficult to pin down.

Sean.

Thanks Sean. I also think they're hard to find which is why I'm now trying with the forum after a long period of fruitless online searches. You can get 1000pF and 2000pF on eBay right now, but I've never seen 3000pF ones.
I checked my small stock of these, but unfortunately I don't have any 500pF. I have 1x1500pF, 2x2000pF (one of them RS marked) and 3x1000pF, in case you're interested.
Helder

Thanks Helder, I just had a look and they are a mix of 1000pf and 2000pf.
Thank you for looking, very kind. This particular project will also allow me to use the Lemco/RS 500pf Mica rectangles, but even so these are still hard to find.

Sean.

Radio Wrangler · 26th Jan 2022, 1:19 pm

Better known as tubular ceramics. They've stood the test of time quite well.

There were 'High-k' ones in the 1000pF region, as well as low tempco ones in the 1-100pF region.

David

Helder Crespo · 26th Jan 2022, 1:26 pm

Quote:

Originally Posted by Radio Wrangler

Better known as tubular ceramics. They've stood the test of time quite well.

There were 'High-k' ones in the 1000pF region, as well as low tempco ones in the 1-100pF region.

David

Thanks David. In my searches I have been using both terms (dogbone and tubular ceramic). Still hard to find. They do seem to be quite robust, and I've read elsewhere that the only time someone found a faulty one this was due to mechanical breakage. However, they do seem to be a bit on the low side nowadays. Usually still within tolerance, but low nevertheless. Perhaps some degradation/oxidation in the metallic coating over time in spite of the epoxy coating, e.g. due to trapped residual contaminants.
Helder

Helder Crespo · 26th Jan 2022, 2:06 pm

On the other hand, the High-K ones have a rather large positive temperature coefficient, and their capacity increases by 10-20% for a temperature change of only a few degrees. So perhaps they were designed for an operating temperature slightly above room temp. Just guessing here.
Helder

Helder Crespo · 1st Feb 2022, 8:12 pm

I got a great set of 3000pF capacitors from Dave today, so this thread can be closed.
Many thanks,
Helder

25th Jan 2022, 7:37 pm	#1
Helder Crespo Hexode Join Date: Sep 2019 Location: Crystal Palace, Bromley, London, UK. Posts: 314	Lemco dogbone capacitors Hi I wonder if anyone has Lemco dogbone capacitors, 3000pF (Hi-K series, 500 or 750V) like the one in the photo. I'm looking for 10 more of these for an RF section. Many thanks Helder Attached Thumbnails

26th Jan 2022, 10:28 am	#2
G6ONEDave Heptode Join Date: Dec 2019 Location: Owston Ferry, North Lincolnshire, UK. Posts: 944	Re: Lemco dogbone capacitors Hi Helder, I have some 3nf tubular capacitors that are similar to your Lemco one. These are light brown in colour and measure approx 17mm long x 4.5mm dia, they don't have any voltage stated on them. Having tested a couple they measure 2583pf and 2658pf which if at 20% tolerance are a bit low but still in tolerance. I can send you 20 of them for cost of post, PM me if it is of help. Dave __________________ Quote "All is hyperthetical, until it isn't!" (President Laura Roslin, Battleship Galactica)

26th Jan 2022, 12:05 pm	#3
Longespee Pentode Join Date: Jun 2009 Location: Leominster, Herefordshire, UK. Posts: 185	Re: Lemco dogbone capacitors Hi Helder, I may have some, let me check, although I get the feeling they are 1000pf. I'm looking for some at 500pf in the same style, but they do seem quite difficult to pin down. Sean.

26th Jan 2022, 12:10 pm	#4
vidjoman Nonode Join Date: Jun 2013 Location: East Sussex, UK. Posts: 2,881	Re: Lemco dogbone capacitors Think these were also sold by Radiospares back in time so might find them with the RS logo on.

26th Jan 2022, 1:19 pm	#9
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 19,575	Re: Lemco dogbone capacitors Better known as tubular ceramics. They've stood the test of time quite well. There were 'High-k' ones in the 1000pF region, as well as low tempco ones in the 1-100pF region. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

26th Jan 2022, 2:06 pm	#11
Helder Crespo Hexode Join Date: Sep 2019 Location: Crystal Palace, Bromley, London, UK. Posts: 314	Re: Lemco dogbone capacitors On the other hand, the High-K ones have a rather large positive temperature coefficient, and their capacity increases by 10-20% for a temperature change of only a few degrees. So perhaps they were designed for an operating temperature slightly above room temp. Just guessing here. Helder

1st Feb 2022, 8:12 pm	#12
Helder Crespo Hexode Join Date: Sep 2019 Location: Crystal Palace, Bromley, London, UK. Posts: 314	Re: Lemco dogbone capacitors I got a great set of 3000pF capacitors from Dave today, so this thread can be closed. Many thanks, Helder