Hi all,

I managed to score a nice KRIESLER 11-81A mantle valve radio today, for the hefty sum of $20. It will require a little bit of restoration, but is otherwise pretty nice for a first valve radio!

I have a few questions which I'll gradually post here in regards to it.

1) It uses a two-core mains lead, but I'm unsure of which is active and which is neutral. Both wires run to the power/volume switch, but one runs through a large transformer mounted on the chassis. Am I right in guessing that is the active wire?

2) The glue joints holding the base, front and sides of the case have cleanly broken (just the glue, not the case itself), so what glue should I use to re-bond the case back together.

3) The label on the base lists the valve line-up as 6AN7, 6N8, 6BD7, 6AQ5 and 6V4. All the valves are correct, except there is no 6BD7. There are two holes in the chassis that look like they were designed for a valve, but there doesn't appear to have been one. Is this just a factory modification to the circuit design, or has someone been playing silly buggers inside of my radio?

4) There are two wires running out of the rear of the set - E (black) and A (red). Am I correct in assuming these stand for chassis Earth and Antenna? If so, should I connect the earth wire to the earth connection on a three core mains plug (Active, Neutral & Earth), and what do I do about the A cable?

5) There are three holes in the rear, two of them marked as 'PU' and 'E', and they look as if they were designed for a probe (voltmeter?) or something similar. What is the story with these?

6) The case is pretty rough on top, and part of it (above the transformer) looks partially heat-melted. What can I use to restore the case to decent condition?

Sorry about all the questions, but this is my first valve radio restoration, and I know very little about valve radios (or any radio in fact!).

Thanks,

Chris

Oh, and is this an AM or FM set (showing my lack of radio knowledge here!). It has what appears to be an AM coil inside, but why would it then need an external antenna cable (assuming that 'A' wire means antenna).

Chris

[Repeat post deleted]

Congratulations on your first radio. There are many other members here better qualified to answer most of your questions but I'd first get hold of the circuit for your radio, you might find it clears up a few things. Kevin Chant's website has an 11-81 circuit, not sure if the 11-81A is the same.

Glue for the cabinet depends on what it's made from. I use either superglue or slow setting Araldite on Bakelite depending on what I'm repairing. Superglue will damage some plastics.

Yes, the A and E are aerial and earth and your set is AM. Most earlier Australian radios used a long wire aerial for AM reception, I think there was a discussion elsewhere on this forum regarding the reasons. PU socket is for a Pick Up, a record player but not modern magnetic cartridges. Although not recommended, I've run MP3's into these for testing. It works but I'm in the process of making an isolator out of a couple if little audio transformers to combine the stereo and isolate any MP3 source from the high voltages.

I use Brasso or very mild car polish on Bakelite, Brasso works well on most plastics too but test a small patch first, I've seen it start to dissolve some plastics!

Good luck with the restoration,

Warren

I'll answer a couple to start with.

It's definitely an AM set and radios of that vintage definitely need an external antenna wire.

The PU stands for Pick Up, and is where you would attach the two-core cable from a mono record turntable. I'm guessing that E is either the return or the shield for that PickUp input. In those days, many homes would amplify their record player through the family radio. You need an old-fashioned high-gain magnetic pickup, or a preamplified signal. You might find you could drive the Pickup input with the signal from a headphone output on something like an iPod, or a portable FM radio. It will probably not work so well with the modern RCA-type audio line output. But first, you will need to get the radio working...

Maven

I would need to see the circuit to confirm it ..but.... If there are three holes at the PU point, as is the case with the 11-7 I have spread out on the bench at the moment..... one is earth and there is a wire link between the other two.

That link is removed when the turntable is connected. That cuts off the RF section.

If it is missing, the RF remains cut off and stations will not be heard.

Marc

I've found that sanding with 180 grit sand paper is helping remove the marks on the case. The marks are rather odd - brown 'stain' marks which won't come out. Luckily, a bit of sandpaper and elbow grease fixes that. I then use some steel wool and Brasso, which smooths off the case and restores some level of lustre to it.

As for the other details, I'm in the process of posting some photos to my Flickr account (to save Brad the trouble of uploading a dozen or so photos), so I'll link it here when I'm done.

In the meantime, any ideas of how to wire the mains lead? I'll have a look for a circuit diagram and see if it distinguished between active and neutral.

Chris

In the meantime, any ideas of how to wire the mains lead? I'll have a look for a circuit diagram and see if it distinguished between active and neutral.

With power leads, ultimately what matters is how the plug is wired. If it's wired correctly the active is on the left as you look at the plug from the back (screw) side with the earth pin at the bottom. Of course, this also assumes that power point is wired correctly.

As I expect you know, active is coloured brown in modern cables and red in older cables.

On the existing switch as described, both active and neutral is switched for safety when using a two wire mains cord without colour for active and neutral. That way when the switch is off both active and neutral are disconnected.

If you want to put a three wire lead on it, go ahead and switch both active and neutral as now, and connect the earth wire securely to the chassis via a nut, bolt and star washer. Use a solder tag on the earth wire for a good chassis connection.

And make sure the power cord is well-anchored via a cable gland or similar.

Mains: Be careful there: You can do real damage if you get it wrong. If you do not know what you are doing with mains: You are playing with fire.

The days of the two wire cable and the knot in it are gone.

The two mains wires will go to the transformer primary. I need to look at the circuit (which I probably have) to see if there are tappings?

What you may have is the mains cable going to a Double Pole, Single Throw switch (DPST) which wil break both neutral & active. (switch is often on the back of either the tone, or volume control.

Sometimes the transformer will have one of its wires going to a terminal with a coloured dot: That is normally "Common" & connects, prefferably, to neutral. Trace the wire & make absolutely sure where it goes.

If it is DPST there is, unless damaged, likely no need to tamper with switch to transformer wires.

Transformers are not sensitive to being reversed in phase, so that is not something to stress about.

Going back to the chassis; The same chassis may have been used in several models. Quite often it was cheaper to make a run of multi use chasses, than make & re-tool the brake presses for a short stamping run.

The 11-7 chassis has a gapping hole for another IF transformer. Looks like it can take a bigger transformer.

Marc

The schematic and other tech information is here:

http://www.radiomuseum.org/r/Kriesler_11_81.html.


Maven

With regard to your missing valve, I wonder if you might have an 11-80 chassis in your 11-81. The 11-80 only has four valves but uses a 6BM8 for the output instead of a 6AQ5 on the 11-81.

According to Kriesler the cabinet is polystyrene, this might give you a clue as to what glue to use. The 11-81 had an inbuilt ferrite rod aerial but it looks like it might also have had a terminal for an external aerial, the 11-80 used only an external aerial. The fact that yours actually has a wire there makes me wonder more whether it's actually an 11-80?

Marcc is quite right about the PU socket, there should be a jumper in there otherwise there is no RF input to the output amplifier.

According to the 11-81 circuit the power switch is on the volume control but is only a single pole, the other wire going directly to the common on the transformer, although this wire might use an unused terminal on the volume control as a tag connector. Later versions might have had a dual pole switch to meet regulations. It also states "All electrical appliances are required to be fitted with an approved earth. Where the chassis is not grounded, hum may be minimised by correct phasing of the mains lead" The active lead should definitely be switched and the chassis earthed via a three core mains lead. I seem to remember reading somewhere that to meet the current Australian standards the earth lead must be mechanically attached to the chassis using suitable crimps and must not be soldered.

Having said all that, do not be tempted to just fit a new lead and turn it on, there's a lot of checks to be made first. Apart from safety, a lot of common faults on valve radios could do serious damage to your set if power is applied. Think about why the original owner stopped using it, more than likely because some sort of fault developed.

I found this series of articles on Paul Ledger's "The Bakelite Radio" website very helpful:

http://thebakeliteradio.com/page102/page102.html.

There is also a good article on the Silicon Chip website about starting a valve radio restoration: http://archive.siliconchip.com.au/cms/A_101834/article.html.

If you haven't already seen it, have a look at Brad's article on electrical safety, there's some good tips in this: http://vintage-radio.com.au/default.asp?id=safety-with-electricity.

I hope some of this is useful to you.

Warren

Hi all,

I've uploaded a dozen or so photos on ImageShack: http://imageshack.us/photo/my-images/829/img8711px.jpg/.

Does anyone have a circuit diagram for one of these that they could email me please? I'm having trouble downloading the diagram from Kevin Chant's site.

Chris

Hi Chris, I've emailed both the 11-80 and 11-81.

Cheers,

Warren

PS I just had a look at your photos, a definite bargain at $20! If I'm looking at the right photos, I count 5 valves? The mains wiring is much clearer. The wire that goes direct to the transformer is the neutral. The other wire is the active and goes directly to the switch. The other half of this twin wire returns from the switch to the other connection on the transformer. It looks a bit confusing because of the way they've wired it. Although that figure 8 wire is the same colour, if you look closely you'll see only one wire has a moulding mark down the side to help you trace them.

You probably don't want to hear this, but all those wax/paper caps will need to be replaced, I don't even bother checking them anymore, I've yet to find a good one. The mica caps should be okay. Some restorers (including myself) replace the electrolytics as well, but they may well be okay. I always check as many resistors as I can but many will have a parallel through a cap. A good time to check these is whilst swapping caps rather than lifting one end. I usually find about 4 or 5 out of spec resistors in each radio.

Thanks for that Warren!

Chris

The soldering of the wax paper on the volume control, is not of an acceptable standard. Many of those joints show evidence of poor technique and a too cold iron.

All of those wax papers need to go as suggested. I fix commercially and would recommend that all electrolytics be replaced. Those on cathodes do dry out & loose polarity , just the same as the filter ones.

I normally test any unsoldered resistor (one end only needed) and if a MIca is unsoldered I normally leak test it using high voltage. They rarely fail.

I find Kriesler output transformers have a high mortality rate. Crack a 9V battery across the primary to see if it and the speaker work.

I may sound critical, but I have in front of me the fourth radio in a month that has had shoddy workmanship and wrong components.

Marc