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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 25th Aug 2011, 5:21 pm   #1
Courtney Louise
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Default Grid coupling Capacitor aka "That" cap.

Hi,

Please excuse me for asking this but just which capacitor is 'That Capacitor'

I did a search and couldnt find the answer...

Thanks

Andi
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Old 25th Aug 2011, 5:36 pm   #2
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Default Re: That Capacitor?

Any control grid capacitor, line output valve, field output valve, audio output valve. Or any other control grid capacitor which is leaky and needs replacing.
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Old 25th Aug 2011, 6:10 pm   #3
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Default Re: That Capacitor?

A Ha, Thanks for that
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Old 25th Aug 2011, 7:34 pm   #4
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Default Re: That Capacitor?

Although Geof is correct strictly speaking, it usually means the capacitor feeding the output valve control grid in a radio or class A amplifier.

It's referred to like that because it's so notorious in typical old valve electronics. Even a small leak will put significant positive volts on the grid, causing the valve to pass lots of current. This can wreck the valve and the output transformer.

That Capacitor is a change on sight item if it's a waxie or Mouldseal. With ceramic or plastic film caps you can check the grid voltage and replace if necessary.
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Old 25th Aug 2011, 10:14 pm   #5
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Default Re: That Capacitor?

Perhaps for the benefit of newbies we should stop calling it 'that' capacitor and refer to it as the grid 1 coupling capacitor.

Al
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Old 25th Aug 2011, 10:39 pm   #6
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Default Re: That Capacitor?

Not sure a Heptode is Newbie
Have fun

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Old 25th Aug 2011, 10:40 pm   #7
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Default Re: That Capacitor?

Hi.
I agree with Alistair, I have never referred to the G1 coupling cap as "That" Cap.
Often it is thought that "That" cap is just the capacitor that goes to the audio output valve, this of course is not the case, and any coupling capacitor that goes from anode or even cathode in a P-P amp or a cathode follower stage to a following stage (G1) could be termed a "That" Cap.
Capacitors that couple oscillators to frame output and line output stages also come under this category.
My personal opinion is that we should use the time honoured way of describing this component as a "coupling capacitor"!
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Old 25th Aug 2011, 11:01 pm   #8
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Default Re: That Capacitor?

no, not a newbie, but also not very techie either if that make sense, I pick up tips and learn on the way, and I have seen it referred to as 'That Capacitor' for ages now but couldnt find the source.

The TV24 I am doing now will almost deffinately be a Waxie and yes would change on sight
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Old 26th Aug 2011, 12:00 am   #9
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Default Re: That Capacitor?

Hi All, I have been in the repair trade for forty years and have to admit when I joined the forum I was confused as to what "that cap" was. I now of course realise what everyone was talking about. It is more helpful as Trevor says to refer to the cap by it's proper name of grid coupling capacitor. The least confusion in the repair of vintage equipment the better. Best regards to all. Norman
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Old 26th Aug 2011, 12:48 am   #10
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Default Re: Grid coupling Capacitor aka "That" cap.

I have to admit, I do not like the popular expression "that cap", I never have, and I think this thread shows why I never use it.

The first time I ever saw it was in a Chas Miller article many years ago, which also gave it an explanation, and was rather amusing... as is Chas' style.

Since then it has been used without any explanation.

After being coined by Chas as being the coupling capacitor to the output pentode/tetrode of a standard radio set, it seems to have assumed a wider and somewhat variable meaning which is not completely clear to people who aren't "in the know", and which even obfuscates the original use.
QED.

Pete
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Old 26th Aug 2011, 12:54 am   #11
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Default Re: Grid coupling Capacitor aka "That" cap.

The point about using the proper name ie 'Grid coupling cap(acitor)' is a very fair one. However, the term "That cap" has been used in the forums many times over many years so a change to its proper name may cause confusion for new members, given that two terms for the same component would be present.

To help alleviate the situation I've updated the title of this thread to embrace both terms; the idea being that this thread will be found when searching using either term as keywords.

Talking of confusion, I've also seen the cap across the mains (famous for going bang) referred to as 'That cap' although the use of the term in that context seems to have died out in recent years.
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Old 26th Aug 2011, 8:01 am   #12
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Default Re: Grid coupling Capacitor aka "That" cap.

It may have been a spelling mistake made years ago that has 'stuck'. What was probably meant was 'That cat'. J.
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Old 26th Aug 2011, 8:39 am   #13
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Default Re: Grid coupling Capacitor aka "That" cap.

Quote:
Originally Posted by Heatercathodeshort View Post
It may have been a spelling mistake made years ago that has 'stuck'. What was probably meant was 'That cat'. J.
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Old 26th Aug 2011, 9:01 am   #14
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Default Re: Grid coupling Capacitor aka "That" cap.

Darren has made a very interesting point and I agree that grid coupling capacitor is probably more helpful to a newbie for understanding what is happening.

The output valve coupling capacitor is so notorious that when it is used in describing a restoration, in "success stories" I have had no problem in understanding what is meant. The first time I came across it in that context I felt it lightened the tone a bit and made it more like a story than an engineering report.

Where that gets me I don't know! Perhaps I have just confused myself. I must admit that it had never realised that it might be used to mean any other.

Not being a Prime Member (I prefer dogs to cats) It never occurred to me that it was a mis-spelling or typo. Perhaps it explains the occasional finds of dead flies or spiders when people have needed to feed the cat.
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Old 26th Aug 2011, 9:04 am   #15
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Default Re: That Capacitor?

Quote:
Originally Posted by Norman Raeburn View Post
Hi All, I have been in the repair trade for forty years and have to admit when I joined the forum I was confused as to what "that cap" was.
I, too, was confused about what it meant when I first joined the forum. But I have to say that it only took a very short while for me to have the opportunity to find out what everyone meant by it - and to apply it to my very first repair.h Now I think it's a nice bit of in-forum jargon that should stick. A bit of curiosity will soon unearth the meaning, and now there's a thread for the potentially confused to search in the future.

Those who want to use a technical reference to the part can still go ahead and no harm done.
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Old 26th Aug 2011, 10:31 am   #16
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Default Re: Grid coupling Capacitor aka "That" cap.

I think it could be useful for beginners to make this post a sticky and possibly show a couple of examples of 'That Capacitor', specifically the output valve grid coupling capacitor, on actual circuit diagram sections.

I just recall when I first started reading this forum having to work out for myself what 'That Capacitor' was and where it might be found on a diagram. It's also a regular direction when beginners venture on here looking for help, 'Remember to change That Cap' and they're sitting at home looking at their new radio thinking 'Which capacitor is that, there are twenty-five of the flippin' things in here!'.

Andrew
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Old 26th Aug 2011, 3:54 pm   #17
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Default Re: Grid coupling Capacitor aka "That" cap.

The term "That Cap." confused me as well initially but reading about the fault sypmtoms it was associated with it did not take long to figure out what it meant.
I suppose it could relate to any old (or sometimes newer) capacitor of a type that we know is prone to failure which could make it confusing ie: which "that cap" are they on about, then "That Cap." would become meaningless unless referenced to a specific component number or specific part of the circuit it is located in.
I have used the term "That Cap." or "That Resistor" on odd occasions myself.
My own preference is its circuit description as there is no doubt as to its function, ...grid coupling capacitor, screen decoupling capacitor etc. especially when communicating by electronic media with someone unknown.
Knowing it's correct name helps those less in the know learn more by questioning it's specific duty in life and the reason why that type of particular component was fitted...grid coupling capacitor, screen decoupling capacitor etc.

Or was it "Boost Connie" or "Bypass Connie" Fropt, froptx or fropty, lopt, loptx or lopty, PCL85 or Puckle 85.

I'm confused now.

I guess it's "That Cap." for the initiated.
And grid coupling capacitor if you don't know what "That Cap." is.
I will use the circuit description more than saying "That Cap." most of the time.

Lawrence.
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Old 26th Aug 2011, 8:24 pm   #18
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Default Re: Grid coupling Capacitor aka "That" cap.

Bear in mind that 'that cap' does no harm in some valve sets, where the output pentode is driven straight from the detector e.g. Pye P45. It would have to be very leaky to have much effect, and even if there is no other DC block the detector output is negative so will have the opposite effect of the usual circuit.

Personally, I don't like the term 'that cap' and had never heard it before coming to this site.
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Old 26th Aug 2011, 8:40 pm   #19
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Default Re: Grid coupling Capacitor aka "That" cap.

I don't think I had heard the term 'That capacitor' either, but having dealt with a couple of 5-valve superhets while still at school, both of which had faulty capacitors coupling to the output valve, I recognised the potential damage that could be caused.

Visiting this Forum, coming across the term 'That capacitor' for the first time, I instinctively knew what it must be. After all, it couldn't be anything else, could it??
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Old 26th Aug 2011, 11:21 pm   #20
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Default Re: Grid coupling Capacitor aka "That" cap.

Nothing wrong with the occasional "in" joke. It adds to the character of the forum imho
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