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

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

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.

Re: Lemco dogbone capacitors
 

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

Re: Lemco dogbone capacitors
 

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

Re: Lemco dogbone capacitors
 

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

Re: Lemco dogbone capacitors
 

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

Re: Lemco dogbone capacitors
 

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.

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

Re: Lemco dogbone capacitors
 

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

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

Re: Lemco dogbone capacitors
 

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