Need to fix old valve radio

The radio must be Italian? At least some of the markings on a cap were Italiano...

Geocities just stopped allowing access to the photos. I saw a few then a message appeared saying that your "data transfer" limit has been exceeded.

It is odd isn't it ? And the electrolitic has Russian writing??? (Maybe it was at the repair shop once or twice, just a guess)

Also, the front panel has the writing "Air King" which was once a radio manufacturing company, so is it Lafayette or Air King, very misterious indeed, or perhap Air King was the overseas arm of Lafayette ???

John, I have put a smaller version of the pictures on the following site, hopefully it will not run into these download limitations problems.

following

putting the

amp,

input

testing

Bob, can please explain were do I measure, from the pin of the canned capacitor to where? If both pins of the capacitor are almost at the same level, why is it a 200V rating?

I will check the speaker for you. It is mounted on a transformer, I need to get another picture for you. BTW, John has noticed one capacitor with Italian markings, and I noticed that the canned capacitor has Russian writing. This may suggest the originals were replaced. If so, this could be a recurring problem.

The sound becomes also louder.

Schematic now available, at

I thought I was following this thread but I'm wondering if I lost something along the way.... the pictures/schematics shown in said website, are they for the radio (Lafayette brand?) that this post was originally about? Was this radio made by Air King/sold under Lafayette? Or am I presuming the radio to have been a "Lafayette" due to the name of the poster?

By the way, thanks for the info... Though "I" didn't need it, I collect any decent info I find - just in case.

I looked at some of the pictures. My guess is that you basically need to measure every resistor and capacitor in this set. You most likely have several resistors that have gone WAY up in value and several capacitors with excessive leakage resistance. Do not be surprised if you have to replace every one of those wax coated capacitors and many of the resistors as well. A usual suspect for your symptom is the resistor that feeds the plate of the audio amplifier (6SQ7) which should be in the 100K to 470K ohm range.

David

Hi...

Don't have any idea how valid it was, but back in the days when the dinosaurs were walking around we used to gently squeeze the wax caps with a long nose... if they were soft, they were replaced on general principle.

Take care.

Ken

at

Great for the schematic. Now we can get going. The case of the electrolytic is the "ground" The two terminals are for two separate sections of the electrolytic that share the same case and a common ground.

Looking at the schematic, they are probably two of the three capacitors shown as C14a, b, and c, at the output of the 6x5 rectifier, pin8, shown as . You will have to trace the DC voltage developed at the pin8 of the 6x5 through resistors R13 and R12. The voltage rating on the capacitors is 350 V, so I would expect the voltage developed at pin8 is at least 250Volts DC. See what you measure on pin 8 and then on the other two capacitor points, and then we'll go from there. If you want, you can e-mail me directly, or else we can do it this way, whichever you prefer. I have a meeting to go to for the next several hours, will be back later on.

Bob Hofmann

at

shown as K on the schematic.

There are several possibilities, but the first 2 that cross my mind are: speaker voice coil jammed against pole magnet, due to corrosion or debris bad connection, might be due to corrosion of a friction contact. The other thing is that most of those caps look like waxed or oiled paper types, which have a bad reliability record IME.

There are other things that can cause the distortion too, such as a break in the output transformer, or a bias failure.

If you dont have a scope, there is a simpler way to check for signal distortion at points along the signal path. Get yourself a very low power audio amplifier, under 1 watt, hook it to a speaker and use this to probe various audio signal points. To protect the amp you'll need to put some components on the input:

X--||----/\/\----+----+--- amp signal input | | __ -- \/ /\ | -- radio chassis | |

-----------------+----+---- amp ground

Now, as long as output power is low, your ears will survive ok.

I'd start by checking voltages around the place, such as on the supply lines, or capacitor + tags.

You can check the speaker by hooking up an external one in parallel. Dont disconnect the original for the test, if a system like this has no load even for a fraction of a second it can do itself considerable damage.

Lytics can fail, but IME are quite far down on the list of most likely failures.

NT

I don't have such an amplifier. I have a DMM. Regarding the speaker, if it is jammed then I wouldn't here anything, or would I? My inclination is leaking condenser/s, all the components inside look very shining (a wet look) so I think a lot of condenser liquid has vaporised inside. I hope it is not a health hazard (did they use pcb's in such typical radios), but this would explain a reduction in DC level and increase in DC ripple. If anyone knows exactly what the DC level should be and what the AC ripple level should be, I think this will be extremely useful. Also, there is this mysterious problem of the schematic mains voltages, which reads 110-125V whereas this radio was always used with 230V

I wouldn't worry about the 115 -230 issue as if it wasn't ok, you would have fried all the tubes and pilot lamps by now.

What is the DC voltage on the C14-a, b, c capacitors? Measure from the capacitor terminal to chassis ground.

Bob Hofmann

The problem is likely to be a bad resistor or capacitor, somewhere in the last two audio stages (6SQ7 and 6V6). The plate of the 6SQ7 should be somewhere around 50 volts. The cathode to grid voltage of the 6V6 should be around 20 volts (negative side on the grid!). Anything wildly different than that may be a problem.

I would replace all the wax capacitors in that area just on general principles. They're probably at least a bit leaky and will not be getting any better over time.

Also check the resistors, they tend to go up in value.

And oh, it could be the speaker rubbing-- try moving the speaker cone by hand to see if it rubs or is stuck.

Personally, in this sort of situation I reckon the shotgun approach is the way to go - just replace all the crappy caps, and all resistors over 50k - saves a lot of time and in many cases fixes the problem in a short time. If the fault is still there there is not a lot more to check

David (a different >

Check the main filter (16/16/20 uF) voltages. Expect to see around 350 VDC there.

That is a typical radio here in the USA . The problem it has is most likely bad paper capacitors and filter capacitors . Replace those and spray the tube pins and volume control with cleaner and it should work fine . That radio is not worth much . Its an ugly style . More of a fun project than anyhing else .

an inappropriate idea.

NT

They are so common I bet you have. An old pair of pc speakers, old walkman, pocket radio, unused cdrom, anything with low volume audio output. If not, try the $ store for something with one in, or any junked audio kit. Or make one, its fairly simple.

When they jam, they jam at one point. The voice coil & cone is not perfectly rigid, so a very tiny amount of movement is still possible.

If this is so you may have an issue, as PCBs were the chemical of choice. A good clean out may be called for. You cant steam clean wax coated caps of course.

Unlikely, but if you give us the voltages we can tell you if theyre reasonable or out of whack. You can also look up valve data for electrode voltages, but bear in mind valves werent always used in the way the mfr published.

if it worked on 240 then there's no further issue. Thats assuming the mains lead you removed wasnt a resistance dropper.

As always with these things, theres little point guessing, you need to test it out bit by bit. Vale rads are easier to do checks on because the valves all become o/c when no heater power is applied, so most components can be reliably checked in circuit.

An analogue meter for this kind of work has the advantage that variations and poor connections are clearly visible, which is not so with a dmm. A DMM should do it though, in most cases.

NT

You obviousely have never had to work as a TV or radio tech where time is a cost to your customer

David

snipped-for-privacy@care2.com wrote:

way

fault