I'm an expensive transformer away from this happening properly:
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I don't think the Pioneer ends up being the driver though,
and I'm keeping the radio functional.

Yes the speaker output on the back of the unit in parallel straight to the converter then ex input on powered amp. Sounds amazing iv had to adjust the converter and amp down!

I will see what the situation is with that 11-77 if I am right about it. It belongs to a collector who was going to do something with it ? Lot of that disease about.

Wind is running at about 25 knots at the moment so I will avoid opening the container for a while.

Marc

Hi guys, well its been great listening to the 11-97 with the subby blaring out annoying the neighbours!! Still going well noone can believe it can sound that good!

Anyway I stumbled across another 11-77 I bought on the weekend which isn't working and haven't tried but I just wanted it for parts. The knobs all had the shiny centre and the on off switch works and the transformer isn't melted so I should be set. It also had a good pair of speakers so I swapped them over and my 11-77 is sounding pretty good now!

I do however have a persistent crackle in the left channel that doesn't swap channels when I swap the output tube over and doesn't seem effected by wobbling the balance/tone/volume controls so I dont believe the crackle is coming from them (I have used contact cleaner on them anyway).

Does any one have ideas on next step? I was thinking of swapping a speaker transformer over does this sound like a good idea? I have already changed all the capacitors over (well there are a couple of .0022 mf ones that I couldn't get) so the problem shouldn't lie there.

Thanks guys!!

Krieslers did have issues with output transformers. With early ones like Bee Hive (11-4) about one in 8 would not have cooked it.

The main reason the power transformer would run hot is from over load (Bad caps), or an internal short of which I have only seen two in 40 years.

Normally Mica caps are the ones that cause the "snap, crackle , pop & hissing".

0.0022 should not be hard to get EVATCO should have them.
If they are on the Plate of the OP valve do not go below 630V. That cap is one that had a very high attrition rate due to heavy load on it and the transients from the audio. Many sets use caps their in the KV range.

Thanks for that, yes i've heard the Krieslers tend to chern through the output transformers!!

I will have to change the remaining cap's first I think - I bought my caps from jaycar and they didn't have any .0022 or .0047 so I just left those at the time. All the caps I replaced were 630v except the electrolytics which were 450v I think.

I'll change them and go from there.

With the mica's is there any easy testing method / strategy to go about replacing them or just redo the lot?

Is there any way of knowing if one half of the 12ax7 valve could be responsible? I've read that valve problems are not too common though so its most likely a cap or output trans I guess.

In desperation the mains rated 275VAC I think go that low. They have punch through of around 1600V.

Australian Mica's rarely fail, albeit that one may have the little silver clear plastic encapsulated Styroseals. They had issues if one got over zealous with a soldering iron.

12AX7 could be arcing. You are liable to get arcing if the output is run with the speakers open circuit on the secondary as it can start "ringing".

Albeit that I have a couple of devices that will test leakage. For NP caps, I will use an insulation tester 500V for valve stuff.

Marc

Monaro,

With the crackling in one channel, are we talking about the 11-77 or the 11-97?

I'm not sure if I mentioned this before, but you could try removing the 12AX7 out of circuit and see if you still have the problem.

You may also have some noisy resistors. I have encountered this problem before with Kriesler stereograms.

If the capacitors in the output of the 11-97 are of the Philips mustard types (.0047μF X 4), they should be pretty reliable. Its only the Ducon wax paper types I'd be replacing.

The early type Simplex SM were fairly reliable but not infallible, one does get to occasional feral.

The ones that I have never replaced are the open (and sometimes same thing, encapsulated,) laminated types of around '38 used in a lot of AWA manufactured stuff.

Hi Monochrome,

It's the 11-77 with the left channel crackle.

I will take out the tube and see and let you know!

I have ordered the few caps that I haven't replaced yet (to replace the remaining wax paper .0022 & .0047's) and I already replaced all the electros. I also ordered a couple of 100pf mica's just to replace around the 12ax7 valve just incase.

With the resistors how would I go about checking them? I think i've read that they can read lower than they are supposed to because there could be some other circuit bypassing the resistor so just check for ones that have resistance higher than they are supposed to? Or when they fail do they usually look damaged visually?

The 11-97 is working brilliantly I replaced (most of) the paper caps, all the electro caps, cleaned the pot's, added a subwoofer and the sound is amazing. Just chasing a replacement dial scale as it has a crack in it but doesn't affect its operation.

Ok I removed the 12ax7 and the crackle stops.....so what does that mean? Is it likely the valve (i do have a spare I can try not that I know if the spare works!) or should I still change the remaining paper caps when they come (hopefully this wk) and see before I risk the valve?

I guess the fact the 12ax7 stops the crackle rules out the output trans at least and the output circuit.

The point of removing the 12AX7 is to rule out the 6M5's and output transformers. So I'd try another 12AX7 to rule that one out.

Do you get the crackle in the left channel with the volume control right down?

HI guys sorry i've been a total nut and got it the wrong way around!

It crackles with the 12ax7 out but doesn't crackle when I take out the output valve.

I did a few things before I got back to the computer and got confused sorry!

And swapping the output valves does not correct the issue.

So I guess that points towards the output transformers then does it? Or a resistor or mica somewhere there too I guess.

The crackle is independant of volume control so its not really noticeable at high volume but very noticeable at no volume or switched to gram with no record playing.

Ps. just tried my spare 12ax7 and same result!

So the problem lies after the 12AX7. I guess the next thing to do is to replace C24 & C25 (.0022μF X 2), that goes between the plates (pin 7) of the 6M5's and the 10K resistors to ground.

I'm always suspicious when it comes to any paper or mica cap that is taking HT voltages.