Hi guys,

I picked up an Philips 4462 and am looking around on the web for related info.

On the radio museum site, it mentions there is an article in the "Radio Waves (HRSA)" No. 56 | 1996-04.

The title is "Philips model 4462,- The bookies wireless" by Darryl Kasch. If anyone has a copy of the article, can you share it please?

Cheers
Kevin

Check your email.

According to the article, "these sets were used extensively around Toowoomba by SP bookies who appreciated their long-range capabilities".

Thanks GTC, it is a very informative reading.

The valves line up in the article is different from the one on the radio museum site.

The second valve is ECH33 instead of 6J8G.

The power transformer on mine is different from the ones in the article and on the web. It is larger and cover the two holes on the chassis.

Also the service sheet said it is for 220 to 240AC. However, the back of the radio indicate 220 to 240 and 240 to 260.

I guess there are some changes during the production run.

I will recap the radio and hopefully get it to work again.

The chassis in mine looks clean, unfortunately the dial glass is broken and missing some pieces.

Cheers
Kevin

I do get the occasional set with most of the Pentagrids being the wrong one: This producing interesting behaviour. If its to be ECH33 superseded by ECH35; Check pin 1 it will be grounded, Pin 1 on 6J8 is NC and may need / have a shield?

In most cases one will run in the others place. Wartime saw a lot of odd valves factory substituted and many just plain substituted because it worked, or one was not available.

Make sure that you check the resistors when changing caps, 2nd detector plate valves & OP tube grid resistors have a high fail rate & Pentagrids do not like low element voltages.

Thanks Marcc.

Got it working after recap and changed 4 out of spec resistors.

However, the volume gets louder after turning on for a while.

What may cause this?

Cheers
Kevin

Sorry, Marcc. The auto correct changed it.

You can change it with the 'edit' button.

Possibly faulty AGC.

Thanks Brad, have edited the post.

Thanks GTC, will check AGC,

Have changed most resistors and one mica capacitor(c40 ) 100p.

Nothing changed. The problem is still there.

Try to get some 6J8G and 6U7G valves to try.

The AVC voltage is gradually down from -5V to -1V.

Run out of ideas.

Hi, good idea to try a couple of valves to prove them.
If the AGC is dropping as the sound drops, that indicates the front end of the set is dropping gain and so the AGC that is a derivative of the IF signal level is dropping.
.you could try shorting the AGC line out and see if the effect is still there cold to hot.
While the sound drops you may be able to check the valve bias levels (if they are self biased) or see if there is a change up or down of plate or screen voltages. Anything to give you a clue as to where something is changing.
Ulitmately I would be scoping signal levels at grids and plates to get a base reading and then see where the level changes.
Fred.

I would be scoping signal levels at grids and plates to get a base reading and then see where the level changes.

Yep, do it step by step. The tried and true method. Given that you say it's a progressive thing, it should be traceable.

The real buggers are the intermittents which never happen while you're measuring, only when you're not.

After replace the IF amplifier 6U7G, the AGC voltage is more stable. With a one metre long antenna, the sudden volume level change disappeared.

However, without an antenna, it still happen.

Hard to understand why.

With no antenna it will be unstable: It's rather like FM transistor sets with a weak signal & you walk between it & the signal path.

6U7 un-shielded is a nightmare. Its as stable as a bucket of weeping gelignite & I often see why 6K7 predominates in a lot of US sets. Un-shielded 6U7 is guaranteed to cause havoc, like oscillation & major instability.

Did you check pin 1 of the 6J8 socket to see if it was factory grounded? If you have no 6J8, sub with a 6A8, that will give an indication of a valve issue.

If that has delayed AGC? IF alignment can be a factor, however, often delayed AGC signal is from the plate of the last IF. If that cap is leaking it will send the AGC line more (or totally) positive.

Also look at things like dirty socket connections and bad jointing. Chopsticks are good for probing.

Marc

Hi, just to emphasise what Marcc is saying about the 6U7.

A set can exhibit all sorts of odd behaviour because of the non shielded construction of the valve type.
Don't assume an external shield that is fitted over the valve is actually working.
I have had a shield clearly fitting correctly to its metal base but still not connected to chassis as the base had insulated its self by corrosion in the face of the base, face of the chassis and the two metal rivets clamping the assemblies together!

Putting a clip lead from the shield to the chassis removed all the supersonic instability and weird changes of gain etc.
Only then by drilling out the rivets, cleaning the paint/rust off the parts then bolting the sod of thing back would the shield work.
Similarly "GOAT" shields can be clamped on the bottom fingers ok but still not make metal to metal contact.

I often wonder how many sets with 6U7's perform poorly or weirdly and never fixed because of this.
The 6U7 plate structure sits in the valve like a transmitting antenna can be running at hundreds of volts potential in RF and IF stages and if you could SEE the radio waves it would be glowing like a fluro lamp!! That "glow" just feeds back to other sensitive grid input wiring and the stage can be running flat out at RF or IF frequency causing all sorts of variations in the intended operation.
Fred.