Regentone ARG79 advice

[Guineafowl]

Right, some positives:

If I jump over the preamp and feed audio into the final amp, it works.

On FM, I can receive stations if I tap the grid of the preamp into a normal amplifier.

Hopefully, then, if I replace V4 and somehow sort the IF transformer, it should all work. Thanks very much to all for your help - I’ll keep you updated.

A

[crackle]

Well that's good news. Dont forget to check the valve pins on V4. What happens if you wiggle it around while the set is on and tuned in, do you get any crackling and stations.

I have had a fault on an IF can where one of the wires had broke/corroded between the coil and the connection point, I was able to solder a short piece of wire to bridge to the can connection.

Can you post a close up photo of the V4 valve holder from underneath.

Mike

[Guineafowl]

Yes, plenty of wiggling and cleaning - no joy.

Now I’ve found an FM station, the V4d anode voltage has dropped to 205V (should be 70V, but was 244V on AM) and I could very, very faintly hear Kylie through the speaker, full volume, next to my ear.

Low emission V4d? Hope so. One on order.

[Guineafowl]

Sorry, didn’t see your last sentence. Here is V4 valve holder, from underneath:

[Station X]

Originally Posted by Guineafowl

Yes, good idea.

The cathode resistor of the preamp V4d is nearly 6.9M, when it should be 5.6M. When I measured it a few days ago, it was nearer 6M. Perhaps it’s degrading under use.

Would this be enough to put V4d out of action?

Sorry to have to correct you, but V4d has no cathode resistor. What you're referring to is the grid resistor.

It certainly looks like V4 is shot and unfortunately I don't have one which I could test for you.

[crackle]

I have a few EABC80 valves spare, I will go through them and test in a working radio to see if there is a good one.
If there is you can have it for the postage. But I wont be able to check till tomorrow afternoon.

What you need to do is buy more radios and start a collection, then you can have spares standing by.

Mike

[Guineafowl]

Originally Posted by Station X

Sorry to have to correct you, but V4d has no cathode resistor. What you're referring to is the grid resistor.

It certainly looks like V4 is shot and unfortunately I don't have one which I could test for you.

Yes, of course you’re right. I had got a bit confused trying to follow all the advice at once!

[Guineafowl]

Originally Posted by crackle

I have a few EABC80 valves spare, I will go through them and test in a working radio to see if there is a good one.
If there is you can have it for the postage. But I wont be able to check till tomorrow afternoon.

What you need to do is buy more radios and start a collection, then you can have spares standing by.

That’s very kind of you, but I have already ordered one from eBay. It’s used, not new old stock, so I guess there’s no guarantee it’ll work, though.

More radios? Well, up until I found this one last week I had almost no interest in valve technology, but they do grow on you.

The availability of schematics seems much better for something made 60 years ago than for something made 6 years ago. Solid state stuff is getting very highly integrated now, and can be almost impossible to troubleshoot compared to the open layouts of the old machines:

1. Trace problem to microcontroller.
2. Check clock signal.
3. Check reset signal.
4. Throw board into parts bin.

[John10b]

That’s very true, in my home Town we used to have four Radio and TV shops now we have none. I repaired my granddaughter tv the other day, new pcb, absolutely no job satisfaction at all, apart from pleasing my granddaughter and saving her money.
Cheers
John

[regentone001]

I may have a pair of IF transformers for this set but am unwell at the moment and not up to digging through the junk room. But will have a look later in the week
Steve

[Guineafowl]

That would be much appreciated. Thanks Steve.

I have rewound the open coil of the IF, after a fashion, and now have voltage on the V2b mixer anode. The rewind was a ‘nothing-to-lose’ type repair, and I don’t trust it.

Still using an external amp feeding off the preamp input, I can’t get any AM stations. Possible problems(?):

1. My AM aerial is a loop from A to E - only about 6m total length - any good?

2. The IFs are completely out of alignment, due to the rewind, and so sensitivity is low.

Is there any way to ballpark the alignment with a scope? Check the LO?

A

[buggies]

1. My AM aerial is a loop from A to E - only about 6m total length - any good?

2. The IFs are completely out of alignment, due to the rewind, and so sensitivity is low.

Is there any way to ballpark the alignment with a scope? Check the LO?

1. Try just connected to Ae so just a piece of wire.

LO checking - couple of suggestions in this thread:-
https://www.vintage-radio.net/forum/...874#post108874

[Guineafowl]

Thanks. No joy with the aerial, but the LO appears spot on - 470 kHz above whatever the dial is tuned to.

I’ve bitten the bullet and ordered an old AVO HF 134 RF signal generator. Hopefully this will help me align the AM side, at least.

[buggies]

Ah well - another valve refurb job then...
Good that you oscillator is working. Depending on the receiver you used to check it, you could maybe do the reverse and see if your aerial wire can pick up the receiver's oscillator.

[regentone001]

I am wondering why you need a long wire aeriel for this chassis as it should have a ferrite rod for LW and MW a long wire should only be necessary for Short wave; Is the ferrite rod there or is it missing?
Steve

[Guineafowl]

The ferrite rod aerial is there, but the coils are moveable on the shaft as they’ve become unstuck. Also, I wasn’t getting any AM stations at all, so hoped the wire might help.

Would it be feasible to trace the aerial signal through the various stages with a scope? I’ve tried, but not sure what I’m looking at. I guess it would be easier on a working set...

[crackle]

For now move the coils back to where they were, there should be some sort of sign where they have been sat on the rod all this time.
When you get your signal generator set it to 470kHz and follow the instructions in the service document to align the IF transformer you have taken apart. I would not touch the alignment of the other IF transformer at this stage.
If you can't get the repaired IF transformer to peak, then I suggest you take up the offer of the replacement.

Mike

[Guineafowl]

V4 (EABC80) finally arrived and fitted, and now the audio works properly.

AVO HF134 sig gen also here. I’ve used it to align the oscillator and RF stages.

However, I think the AM IF stages need some sort of sweep generator (wobbulator?) which I didn’t notice before. The Trader procedure refers to a response curve.

I did a ‘different’ sort of alignment by feeding in a 470 kHz signal modulated with 400 Hz tone and peaked the IF transformers by watching a scope trace of the speaker output.

Anyway, now there is some reception of AM signals, although not very strong. Have I done the right thing?

Edit: New addition to the collection is a Cossor 501AC in a poor state. Watch this space...

[crackle]

You normally do the AM IF alignment first and then the AM RF alignment. But it shouldn't make too much difference.
I believe you only use a sweep generator if doing the FM IF alignment, and to be honest that is not really essential, but if the FM reception is working I normally leave it alone.
The FM discriminator electrolytic capacitor C54 can sometimes need changing, If it is leaking badly it can make FM sound distorted.
Without going back and reading all the posts, I have forgotten what has been done so far. But checking the valve voltages against the service information is the next thing I would be doing.
There may be one or more leaky paper & foil capacitors (waxies or mouldseals) dragging the screen and HT voltages down. If this the case then changing them can help improve the gain and hence reception.
I dont worry too much about the resistors unless they are way off. I normally leave them unless they are more than 20% out. Except the cathode resistor on the OP valve, if that has dropped much in value the bias voltage will have lowered and the valve could be stressed.

Mike

[Guineafowl]

Thanks for the help - the radio unit is now working and back in its cabinet.