Interesting tale Satelliteman!,scarey stuff!!!, will let you know about the heat issue soon. Have replaced all the old sus caps as I have found them available from various sources.
Also have found a couple of ouput transformers to try instead of my first attempt with a Jaycar line tranny!!
Just need to determine the output config as class A needs 5k & AB=8k
All valves are in the correct sockets!!-digital cameras & a quick sketch come in very handy.......

Clas AB is normally push pull with two 6V6's 8K plate to plate is a centre tapped transformer with lots more volts on it.

Download the valve specs from Franks Electron tube pages.

At 250V plate 5K load is recommended with a grid bias of -12.5V developed by a cathode resistor around 270 ohms (if not back biased).

In most cases the grid stopper resistor & grid leak normally 50K &500K (not looked at the circuit) and the cathode bypass capacitor (if fitted) will be stuffed. Check them.

Marc

Finally I get a chance to work on the Rymola chassis again...it’s not consistent to above schematics...different valve/component line up.

6V6 issue sorted by replacing the old leaky Ducons & using the correct O/P former, no more hot 6V6, thanks to all for comments & brain joggers.

But one last thing has me stumped....the value of this black AWA cap which I have sent a pic to Brad if he can post...Thanks!!
A 9V battery is captured next to it for an idea of size

It's totally stuffed - but I can't figure out if it’s 0.25, 2.5 or 25 uf?? The markings scuffed enough to make reading confusing. Double dots before the 2 add to the dilemma & the dot between the 2 & 5 appears to be where part of the two is worn?
Hopefully someone with some experience with these Black AWA Caps can identify it.

lastly is it polarity sensitive? - It has a white band running around it - but no label to clarify polarity.
Voltage is easy to read at 400v wkg
Thanks
PS: the bizzare thing with this cap is that it tested OK several months ago but now is a near dead short!!!!?

We will await picture. Confucius say they are worth thousand words.

Question is where did you get it and what was it attached to? Or is it still there?

At 400V and physically big it may be a bypass cap. If it's an electrolyitic I would expect a reference to the polarity; Otherwise its probably "outside foil" and the white end went towards earth?

Paper caps ususually come in three types viz:-- Good (Rare), Leaky (normal), or short (common).

Marc

G'day Marc & others...This AWA Cap is the only one in the Rymola Chassis I have been working on, possibly alien as the resistor next to it also looks out of place when compared to others.

Photos are at
Image Link
Image Link
Hope I did that right.....

This Cap is connected to pin 4 of the 6U7G - Screen & to Chassis earth & tied into the input switch cct to another "tin can" elctro mounted on the top of the chassis

Marcc your reply makes me confident that its a 25μF electro , white band Chassis Earth., so yes polarity conscience.

Have been using a megger to test these & paper type caps at the nearest voltage under the caps max value.
Most tested as leaky or short.
Is this a good method of testing or is likely to "kill" the cap being tested?.....nearly all I have tested seem to fail!!

Thanks Again Paul

Well I stuffed that up somehow......
Sorry, have to do it the old fashioned way of copying & pasting the link...

http://i860.photobucket.com/albums/ab167/pjfitzy/BlackCap.jpg
http://i860.photobucket.com/albums/ab167/pjfitzy/PB010023.jpg

G'day Paul,

You forgot to include a / in the closing tags - not to worry though, it's easy to fix now that the edit facility is available.

Please see this article for more information.

In 250 plus radio's, I think we found about two paper caps that were, perhaps, useable. There is a message there.

A megger at their opperating voltage is about the only realistic method that there is for testing non polarised capacitors. If the Megger punches the cap through at its rated voltage, then the HT will do the same thing.
That's why it's realistic and I do it. You can test the Mica's the same way, but they rarely fail. Do it if one end is out of circuit regardless.

That is rather what I thought. It's a paper "Mud" type, Outside foil non polarised and stuffed. Use a 0.22 mfd 630V. Check your pinouts, I cannot clearly see where it is on the valve but it appears to be pin 5.
5 is the suppressor; 6 is the tag strip; 7 is a heater, 8 cathode all going to ground, one wire is heading to pin 2 of another tube which is probably also very likely, its heater.

Pin 6 of a 6U7 is not connected and that one has no pin in 6. Check the way you are reading. Numbering goes clockwise looking at the base (wiring side) starting at the spigot.

That capacitor is associated with the switch not the 6U7.

Get rid of the rest of the papers in that, they will all fail. do a rough check on the resistors especially if one end is out of circuit.

Marc

Marc, such a big cap for only 0.25 μF? thats suprising.

Many thanks, I was pretty well convinced it was 25μF due to its size, thank Brad for this website & you for responding!!

Have already replaced the other waxy ducon caps - photo is of virgin unit.

Thanks for clarification on cap testing, I was starting to think my IR tester was killing them as I was testing them, even though I always started on the lowest voltage & worked my way up to the rating of the cap.

These black AWA "mud" caps? seem a very well sealed unit what goes wrong with them & how??
If anyone has an explanation I would be interested to read.......

Its not uncommon for that size cap. The older the set, the bigger they often are. I have an AWA on the bench at the moment which has 8mfd papers on the HT. the double one is as big as the 4 gang tuner.

You can google the net for paper caps. Basically most of them were made like a roll your own cigarette. however there was Aluminium foil with waxed paper sandwitched in between.

Unfortunately the wax dried out & hardened, there was also a tendency for a small amount of moisture to be present.. Paper is porous and fragile.

With a large number of caps, they are self healing. When the dialectric dries out and cannot move or melt; The capacitor will not self heal & punches through.

Marc

Interesting, on one web site I stumbled on relating to vintage radio restoration the auther claims he has "low baked" caps in his oven to re-birth them, interesting to know how long that would last!!

Paul

You might get away with heating on some, but reliability is another factor as you do not know the condition of the paper or the size of the hole.

"Self healing" relys on something, be it the dialectric, or some thing added, to melt into the holes in the dialectric to seal it and restore the insulation. Clearly if there is insufficient material to accomplish this and it cannot melt, the capacitor will fail.

The other thing is that if you go too high in temp. you will loose wax

Considering the overall reliability of paper caps I would not bother.

Left field ..... I note NAV killing a Virus while I writing this? Virus obviously written by another Moron needing to go find a life.

Marc

Nasty nasty, well the virus industry or should I say anti-virus industry? is a billion dollar affair these days....lucky for them we don't all run macs or unix based OS's, talking of which have been playing around with ubuntu lately, magic stuff...self healing software, a friend of mine hosts railpage.com.au on it but ther is also a client version which is very good...just another flavour of linux.

Anyway fast forward 50 odd years & the Rymola is now alive & sounding very good.
I was a bit worried I would lose some tonal quality after reading on the web certain types of caps are supposedly better for tonal response & I just used readily available polypropylene ones from RSComponents...differences in ESR cited as having an effect?
The RS ones look the part as they are yellow & if you buy the 1000V ones similar in physical size as well.

It just seems to have one strange issue, when tuning on SW or MW but in a different single position on the tuning gang the radio makes a "dusty pot" sound which nulls out the recieved station & projects the speaker cone forward some what as it "crackles"

Maybe the slight differences in the new cap values from the old have thrown it out of alignment somehow? but it does seem more than just that.........

Paul