DAC90A Beginner

[Murphyv310]

One other point about wax capacitors. Generally the small picofarad wax covered silver mica caps will be perfectly good so these cannot be lumped together with the tubular paper wax covered capacitors.

[boater sam]

One other point about wax capacitors. Generally the small  picofarad wax covered silver mica caps will be perfectly good so these cannot be lumped together with the tubular paper wax covered capacitors.

Indeed, they are usually perfectly OK but there has been some disturbing reports of later one, 60s and 70s, failing.
I have very rarely had to replace any in pre war sets or stuff from the 50s'

They are in the tuned circuits in the set front end and the problem if you do change them is that the alignment will be all over the shop afterwards, probably for  no good reason. 

So I will reiterate, no CCC.

[Terry]

As Mark is new to this it might be a good idea to explain what we are talking about!

Silver mica capacitors are rectangular and consist of a sandwich of thin paxolin outer layers, for strength, with several layers of thin, silvered mica between them with the connecting 'wires' - actually narrow strips of thin metal - riveted onto each end. They were dipped in wax to protect the capacitor from moisture ingress like this (although it is not easy to tell if this has lost most of its wax coating due to heat or is actually varnished instead):

Later, the wax was replaced by a cement coating, often dark red or brown, as here:

They were, as you can see, very close tolerance capacitors.

[pwdrive]

Tektronix used wire on wire connecting strips, wire on wire for component replacement is ok if it's done skillfully, any service engineer in the R&TV trade that hasn't done that must have either a bad memory or not actually fixed much.....

Replacing a silvered mica capacitor in a receivers tuned circuit with one of the same value is not very likely to cause the alignment to be "all over the shop"

Some times replacing capacitors en mass is actually the less damaging route.

….Just sayin'

Lawrence.

[Murphyv310]

Nice one Terry. Not back to my usual self I'm afraid so that's great you've taken the time to post up pictures, it will be of use to the OP.

[Murphyv310]

Tektronix used wire on wire connecting strips, wire on wire for component replacement is ok if it's done skillfully, any  service engineer in the R&TV trade that hasn't done that must have either a bad memory or not actually fixed much.....

Replacing a silvered mica capacitor in a receivers tuned circuit with one of the same value is not very likely to cause the alignment to be "all over the shop"

Some times replacing capacitors en mass is actually the less damaging route.

….Just sayin'

Lawrence.

Well that depends on the person that they don't make a mistake. If you do then you land up in a guddle and have to sort out the man-made faults. If anyone intends to replace en mass then do the two important ones first (mains filter and coupling cap to output valve) test the set and move on one by one powering up the set after each one.

[pwdrive]

With some receivers that's not always advisable, replacing en mass is the only practical route if it takes ages to strip down a part of the receiver to gain access, replace one wax capacitor reassemble, switch on and check, dismantle, replace another wax capacitor, reassemble, switch on and check and so on...so many strip down and replacements down the line, wires can snap off, bandchange switches, coils or other vital bits can get damaged in the process.

Lawrence.

[Murphyv310]

Hi.
There is a point to that Lawrence but any beginner really should be working on a simpler set that doesn't require a major strip down to gain access to replace caps. Can you imagine the mess some people would get into working on an inaccessible set and doing a blanket component change? Some experienced engineers landed in trouble with blanket changes, I'm sure you are quite aware of that!
I am afraid I stick to my guns with cap replacement unless you are experienced and even then any of us can land up in trouble, none of us are perfect and I make mistakes like anyone else does. Best to fix the mistake when youv'e done it rather than later and its a problem to find.

[boater sam]

Hi.
There is a point to that Lawrence but any beginner really should be working on a simpler set that doesn't require a major strip down to gain access to replace caps. Can you imagine the mess some people would get into working on an inaccessible set and doing a blanket component change? Some experienced engineers landed in trouble with blanket changes, I'm sure you are quite aware of that!  
I am afraid I stick to my guns with cap replacement unless you are experienced and even then any of us can land up in trouble, none of us are perfect and I make mistakes like anyone else does. Best to fix the mistake when youv'e done it rather than later and its a problem to find.

[boater sam]

Hi.
There is a point to that Lawrence but any beginner really should be working on a simpler set that doesn't require a major strip down to gain access to replace caps. Can you imagine the mess some people would get into working on an inaccessible set and doing a blanket component change? Some experienced engineers landed in trouble with blanket changes, I'm sure you are quite aware of that!  
I am afraid I stick to my guns with cap replacement unless you are experienced and even then any of us can land up in trouble, none of us are perfect and I make mistakes like anyone else does. Best to fix the mistake when youv'e done it rather than later and its a problem to find.

You get my vote there T, sorry Lawrence but still think that just changing any part just because you can is not fault finding or professional.

I bow sometimes to your all encompassing knowledge of the world and the universe but for beginners it needs to be simple and correct.

Else they learn nothing and get into a muck sweat and chuck it out.