I note a reference to a 0.02pF cap bet its not.

Hi Marrc

Your right, its MF not pico.

I did the tests for IR, but I cant understand my reply (ha). Do you think the booster is salvageable, the vibrator sounds to be working, so it only needs new caps and electrolytes.

What do you think?

Hi Ads
Been v busy at work and a bit sick so sorry for the late reply.
The pics help a lot. What you are calling the "booster" is in fact the power supply for the radio. It makes the approx 200 volts that are needed for the valves. It fits in the box with the speaker. Then some wires go from the power supply and speaker to the radio itself.

"Ok, pins 3/4 on the 6v6 run to as follows> one wire goes into the booster harness (ie to the secondary unit), two

other wires on 4 go to three little black barrels. The two larger ones are cracked, the smaller one is .02pf 600v

seems ok and holds one wire from 6v6."

The speaker has its transformer attached to it. There are two wires, brown and blue, that come out of that transformer. These wires should make their way, via the 4 pin plug and socket, back to pins 3 and 4 on the 6V6. Can you see where the two wires are supposed to connect? If not, use an ohm-meter to trace them back to the power supply and connect them there.

"
Yes there is some mess and corrosion, but perhaps salvagable. The black barrels here too are cracked, so we can

assume they all are. I measured the ohms-r between 3/5 of the 6x5, it is> 0.96 on the 20kilohm setting. There is a

sqare item (cap?) there between. "

Good news that you can read the ohms between pins 3 and 5, bad news that it sounds a little low. The cap may be short circuit and will need to be disconnected and tested. What colour is this square cap, what does it seem to be made of, how big is it and can you see any text on it?

Checking this cap and, if it's not short circuit and it's a type that doesn't need to be replaced, (report back to me with what you find), connecting the wires as above will probably result in some sound from the speaker. Then we start fixing the other faults we find, and replacing the barrel-shaped black caps one at a time, checking in between that you haven't broken anything.

Remember you will need to connect an antenna, the radio is well shielded (has to be in a car) and won't pick up anything without one.

Enjoy!

Thanks IR

I will be back in a few days with the news.

Message for IR

I did the tasks, results are:> There is a loud consistent buzz/hum from the speaker when connected at its place. This is unaffected by channel sweep or volume control. And I think consistent with the stable voltage and amps measured there. I'm pretty sure that if it was functional both a&v would oscillate. A quick touch at the back of the 6v6 at pins 3/4 was the same. The cap on 6x5 on pins 3/4 is:> 5mm x 15mm x 20mm. 220pF, (symbol) 20%, 1000 DC. Brown in colour, is quite sturdy, and appears intact. It remains attached. Brand name: Simplex SM.

I'd have to check the circuit but 220pF is too small, you need about 8200pF in that position. Still, you may get away with it for a short time. My guess is there used to be a .008μF cap (that's 8000pF) there and it has exploded, caught fire or been removed for such a reason. Many "techs" didn't understand its importance. Its absence explains the buzz. Without it, there will be great stress on your Simplex mica cap.

Well, now is the time to connect a long wire to the antenna, turn up the volume, turn the tuning and see if you can pick up anything.

If not you'll need to start measuring some voltages. But first things first.

Don't run it for any longer than you must, you really need to locate an 8.2nF 2000v cap - here is one:

http://au.element14.com/epcos/b32672l8822j000/cap-film-pp-8200pf-2kv-rad/dp/2469027?st=8.2nF

Don't even THINK about using anything else here, it will go up in smoke in seconds.

Install that in place of your Simplex cap.

Buzz or hum from the speaker is promising: But. Can we stop calling the power supply the booster. It is essentially the electro-mechanical predecessor of the switch mode power supply and is by any other name a power supply.

Note that, that vibrator unit is a resonant circuit and circuit values should not be changed. Note the voltages on the circuit diagram. The common replacement nowadays will be the 630V types for most of the round black ones. There are exceptions and you will see 1000V specified for the buffer capacitor: Do not go below it. Due to the spikes that particular cap was unreliable. I have never had one of those black AWA rectangular pF caps fail electrically. As I have said on many occasions I have used mains rated line caps in that section.

Hum is quite often due to overload & failed capacitors. I believe that you are now at the point where a lot of capacitor replacing is order.

Check resistors as you replace them. Paint markers are good for dabbing where you removed something. Circuit board spray removes it.

I have a different and more ruthless approach than many as I commercially fix. If its not good enough for a commercial fix its not good enough. I hate rework. I also consider fault finding in a set with wax-paper caps & tired electrolytic caps, time wasting. Whilst it may not be as much fun, you more often than not, get rid of the problem, when you get rid of them & any dud resistors.

Leave the squarish Bakelite ones alone, they rarely fail. At change point I only leakage test, if they are out of circuit one end.

Resistors with green body & yellow stripe (Green Black Yellow) 500K (470K now) and Green Black Orange 50K (47K now) have a massive attrition rate do not leave unchecked, I replace them by the bucket load.

Thanks IR/Marcc

I have a better chance of getting fish-n-chips from Jaycar, or anywhere else around here, than the right parts.

So I was hoping you guys there at Vintage could put together a parts parcel. I see people advertising, so maybe internally this could be done.

I am thinking we should start with the power supply (PS). I could write a list of caps/resists (I hope) and pay for them somehow or another. We could include the cap for the 6v6. Marcc mentioned the catalytics. Should we just do caps/resists first, then move on to bigger and I spose more expensive parts?

I might have a hard time identifying the resistors properly. Maybe the radio we should list and do at the same time. I could send the chopped out parts to you. Or maybe eybay is a good option.

You guys know what to do and say, so I leave it up to you to suggest. I am also thinking about trading the Amp/Gizmo for equivalent value. But I want to make the radio go, and to keep it. I don't have a receipt for the gizmo though.

What do you think?

I gave you a link for the most important part to replace. You can order it on line and it will be delivered next day.

A mains safety cap is NOT suitable for that position. Safety caps have internal fuses and so will quickly fail open circuit due to the amount of current the cap is required to handle in this circuit. That is why they are called safety caps. I did not choose that part lightly.

You can get suitable caps for the other places in the radio at that site, but let's not get ahead of ourselves. When it comes to that, I can give you Element14 part numbers to order the right ones.

I agree you'll need to replace all the paper caps. But being a neophyte, you should try to get the radio running, however badly, first. As you replace each cap you can turn it on again. If it doesn't work now you'll know exactly where the mistake was made. If you change a whole lot of them in one go and it doesn't work, how are you going to find your mistake?

Resistors? Yes, but go there if nothing works. And measure voltages first, don't chop them out to test them, you may well put back more faults than you started with. An off-value resistor in a radio will rarely stop it from working in some fashion. Standard tolerances for those resistors was +/- 20%. If, for example, a plate load resistor for the 1st audio amp goes from 250k to 2000k, (way more than 20%) it will still work, just not perfectly.

So, change the cap I suggested first and connect a big antenna wire. Then tell me what you get and we can take it from there.

Ok, back in a week or so.

Hi

Im returned. I put in the new cap across 6x5. It didnt make any difference. So I ran it for a minute, and the big noise out the speaker remained, unaffected by volume control. The buzz is at about the same speed as the vibrator. When I disconnected from negative side battery, I felt the new cap and it was cold. It did seem to be sensing channels, but the buzz was overwhelming; as before.
Does this mean that this part of the circuit is inoperative?

What next to do?

Check that a cap in the audio that's meant to go to ground & shares with a heater pin is actually grounded, or on a heater pin that isn't grounded.

Um

(please point>

https://www.kevinchant.com/uploads/7/1/0/8/7108231/902a-903a-904a-905a-906a.pdf

ta

One cannot point to an individual cap but what can happen is that a cap during a senior moment can end up on an AC pin like a heater, or in the case of a vibrator supply to the vibrator side of the transformer. or the HV secondary.

Where there are printed circuits, cracks in tracks and in both types, dry joints (bad soldering).

Where a volume control fails to operate, its earth end can be open, but when you have buzz its possibly a power supply filter issue but more likely a fault between the volume control & speaker, which is why I wonder about the above issues.

DC heaters should not produce buzz.

Marc

There are many possible causes of buzz (actually referred to as "hash") in a vibrator set, including dried-out electrolytics (in those large brown cardboard tubes). Since you say that you think you can hear some signals behind the hash, try bypassing the two large high voltage electros with replacements. I strongly suspect you'll need to replace these electros. You may have to consider gutting them and fitting the new parts inside the cans, there doesn't seem to be anywhere else they could go.

Do you have a scope? If so, check for AC ripple (hash!) on the B+ line. There should be no more than a couple of volts P-P. That will confirm the diagnosis.

Having made the vibrator circuit safe, you are getting close. Replacing the electros and the wax paper caps one or two at a time should get you home.