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-   -   Lemco dogbone capacitors (https://www.vintage-radio.net/forum/showthread.php?t=187977)

Helder Crespo 25th Jan 2022 7:37 pm

Lemco dogbone capacitors
 
1 Attachment(s)
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

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

Longespee 26th Jan 2022 12:05 pm

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.

vidjoman 26th Jan 2022 12:10 pm

Re: Lemco dogbone capacitors
 
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

Re: Lemco dogbone capacitors
 
Quote:

Originally Posted by G6ONEDave (Post 1443898)
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

Re: Lemco dogbone capacitors
 
Quote:

Originally Posted by Longespee (Post 1443917)
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

Re: Lemco dogbone capacitors
 
Quote:

Originally Posted by vidjoman (Post 1443918)
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

Re: Lemco dogbone capacitors
 
Quote:

Originally Posted by Helder Crespo (Post 1443925)
Quote:

Originally Posted by Longespee (Post 1443917)
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

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

Helder Crespo 26th Jan 2022 1:26 pm

Re: Lemco dogbone capacitors
 
Quote:

Originally Posted by Radio Wrangler (Post 1443939)
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

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

Helder Crespo 1st Feb 2022 8:12 pm

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


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