Regentone ARG79 advice

[Guineafowl]

Hi all,

I’d like to get this radio/record player going again, and would appreciate your advice. There’s a thread on here called “Regentone radiogram advice” that doesn’t quite conclude, but I’ve downloaded the linked manuals.

Ideally, I want to get it powered up without causing damage, then start replacing less critical components to improve performance and at the same time learn some valve stuff. I haven’t powered it up yet - what should I replace before this?

I have a decent DMM, scope and various other bits of test gear, as I do solid-state electronics repair as a hobby.

TIA
Andrew

[John10b]

Hi Andrew hope you enjoy forum you will find a wealth of information from very experienced folk.
I’m not familiar with the Regentone so I can’t help you there, however if you look on the forum you should find plenty of advice which hopefully will guide you in the right direction.
As you have test equipment and fault finding knowledge, and I presume you understand the dangers of working on mains powered equipment, I would suggest you do a visual first, no Mains connected of course, and do some simple tests on Mains transformer etc, which I think is fitted to this model. All the best.
Cheers
John

[Edward Huggins]

Your Radiogram comes from 1955 and, if it's still in it's original condition, is only suitable for playing Mono records. This could be updated later. The chassis on this is mains isolated. Ideally you should carefully power is up with a Lamp Limiter. You'll not know what to replace until it can be tested. Make sure that there is a 3A (not 13A) fuse in the mains plug.

[Guineafowl]

Thanks to you both.

I checked for obvious shorts and burnt components, then replaced C60, the final audio decoupler (‘that capacitor’), powered on with a series lamp limiter. All good. Even the panel bulb works.

Powered on with no lamp, and all the valves glowed. The unit stabilised at about 250mA for a few minutes, then started to climb beyond 350mA and I switched off.

Some oozing from the electrolytic filter can, and from one of the wax caps. These will be replaced, but I have a few questions in the meantime:

1. I’m keen to eventually earth the chassis - is this generally done?

2. The schematics don’t give the voltage ratings for the three electrolytics in the can - what would they typically be? They also don’t indicate which terminal is which cap, but I think I’ve traced that out.

3. Is there a good technique for disconnecting component leads that have been wrapped round the tie strip? I have a powered desolderer but it’s not much help, as the wrapped/soldered lead is much stiffer than the tie point, and I’m afraid of breaking them. Is it really bad form to cut the old lead close and solder the new lead to the whole lot?

4. I only have the receiver on the bench at the moment, so no speaker. The original speaker wasn’t marked with the impedance value - can I use a 4 ohm?

Cheers
A

[crackle]

This radiogram uses a mains isolation transformer so it should be safe to earth the chassis.
Trying to unwrap component wires from tag strips can result in breaking the brass tags which can go very brittle with age.
On a machine such as this I just snip the old component out and solder the new ones to the remaining legs of the old component as neatly as possible. The longer the overlap on the component leads the stronger the solder joint.
If it looks like the new component may stress the old wires due to vibration you can make little spirals of thin copper wire to slip over the solder joint.
If there is any chance of excessive heat being generated in the new component, like dropper resistors, then it is essential to fix the new component solidly to the original solder tag, in this case leave as much spare component lead as is safe to help dissipate the heat before it gets to the solder tag.
The 3 HT smoothing capacitors should be 450v, it should be marked on the old can, use the same voltage or higher.
They normally have coloured terminals. Red for the reservoir which goes to the rectifier C64 32uF, yellow the the smoother C63 32uF, and probably plain for the other terminal which is for C59 8uF (Trader references)
Dont forget to check the V5 cathode bypass cap C62 25uF and the 180 ohm resistor.
But most importantly change C60 the 0.05uF AF coupling capacitor.

Measure the resistance of the original speaker if it is about 2.5 ohms then a 4 ohm speaker will be fine.

You may want to change all the waxy capacitors, they will all be leaking electrically to some extent.

Mike

[Guineafowl]

Again, many thanks.

The order has gone in to RS! Your list looked similar to my list, which is nice. Perhaps I’ll get the hang of these glowing things one day.

I switched on with a speaker connected - nothing for ten seconds, then a very loud 50hz hum began to grow independently of the volume control. No stations or static - just hum. The scope trace on the audio output showed a distorted sine, while scoping the three filter caps showed a tremendous amount of ripple. I didn’t stop to measure or analyse anything, just switched off before something terrible happened. HT voltage fell VERY rapidly after switch-off.

I guess I’ll wait for the caps to arrive...

In the meantime, would it be at all feasible to fit a line-in jack so I can feed my guitar amp’s ‘headphone out’ into the amplifier section? If so, where? Obviously I’ll need to earth the chassis properly first.

A

[Guineafowl]

Right - changed all caps as suggested and the loud hum has disappeared. However, no sound/stations other than a slight hum which sounds normal.

All the valves are glowing except the tuning eye, which I’m not worried about for now.

HT about 244V

Audio preamplifier anode voltage is 140V, when it should be 105. Its load resistor is 258k, when it should be 220k (10%). Is this enough to cause the failure?

A

[Guineafowl]

Sorry, scratch above about audio preamp.

I hooked in an unamplified electric guitar to the ‘gram’ input terminals (chassis is now properly earthed).

No sound. But the guitar signal was making it to the grid of the audio preamp, but not to the anode. When I fed in the guitar to the final amplifier (just before ‘that capacitor’ then the sound came through to the speaker.

So it looks like a faulty V4(d) preamp EABC80. However, the anode voltage should be 70V, but is 244V. Is this because the valve is faulty, and drawing no bias current, or because it is fine and some other problem exists? No other voltages are quoted for this section.

[Station X]

Check that the valve lights up.

Check that the valve's anode resistors (R34 and R35 Trader sheet) haven't gone high in value.

BTW. Valves don't draw bias current. They draw anode and screen currents.

It's true that bias VOLTAGE may be generated by passing current through a cathode resistor, so producing a voltage across it.

[Guineafowl]

Yes, valve lights up. Oddly, the volume pot reads 1.2M total, although should be 500k.

Anode current is 0.0uA

Now, R34 is 2k2, 10% and reads 2.154k. All good.

R35 is 220k, 10% and reads 278k - this is out of tolerance.

However, replacing R35 did not change the anode voltage.

Also, I notice that the V4 EABC80 has three sections, and the preamp one is dark, slate grey while the other two are brighter.

What I don’t want to do is wait a week for a replacement valve, then find it doesn’t fix it. Have I done everything to call the valve dead?

Also, can I do any signal tracing on the RF side without a signal generator? I have a scope. It would be nice to check that is working.

[Station X]

It's rare for a valve to have absolutely no emission.

Before condemning the valve check that the pins are clean and that the valve holder sockets are clean. Sockets can get loose and require nipping up.

If you can, make sure that voltage is actually reaching the anode pin rather than just reaching the socket. Is the cathode pin correctly grounded? Is the grid resistor R33 OK?

[crackle]

Originally Posted by Guineafowl

No sound. But the guitar signal was making it to the grid of the audio preamp, but not to the anode. When I fed in the guitar to the final amplifier (just before ‘that capacitor’ then the sound came through to the speaker.

I hope you connected your guitar in after the Audio coupling capacitor, between C60 & R38, otherwise you may have shot 140v through the guitar pickup.

It is sometimes useful to use a little cheap transistor radio as a "tracer" you could connect a wire to the volume control of the transistor radio in series with a blocking capacitor and use that to trace if you have any signal coming from the radio detector under test.
Or you could use it to inject an audio signal into the AF side of the radio under test to see how far it gets.. It is better than using a guitar to trace the signal.
I agree with Graham, make sure all the pins on the EABC80 (and other valves) are clean and making good contact with the socket.
The anode voltage is probably high because the valve is not conducting, but remember that some voltages on high resistance circuits will read high if you are using a DMM instead of an old AVO.

Mike

[ms660]

Originally Posted by Guineafowl

the anode voltage should be 70V

Present fault aside, don't forget that the voltage given in the Trader sheet was measured using a 500 ohms per volt meter.

EDIT: Post crossed.

Lawrence.

[Station X]

If in doubt about the meter, check for a voltage across the anode resistor.

[Guineafowl]

Station X - yes to all those.

Crackle - er, yes, the guitar was before the cap. Seems none the worse for it, and it’s an old thing anyway.

We may have another problem - voltage at V2b (mixer) anode is zero and should be 230V. It looks like the supply comes through switch S22 (OK) and via IF transformer L26, which is open circuit.

Is there any chance of getting another IF transformer, or winding a new coil?

[crackle]

I take it that when you measured the voltage on V2b anode you had the set switched to MW.
With the set switched off and all the push buttons are released (up) measure the resistance across L26 and also across L28.
I dont know about you but I always find it easier when the circuit spread is over 2 pages to join them together in one page.
In the case of the PDF I am looking at the second page needs enlarging by 1%.
Mike

[Guineafowl]

Yes, MW.

L26 - open circuit.
L28 - 0.6 ohm.

[crackle]

Well what I would do I think is carry on getting the set to work on Gram, then get FM to work then think about tackling the 1st AM IF transformer L26 & L27.

Mike

[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?

[crackle]

I think that's R33 (trader) the on the control grid to chassis you are looking at. I wouldn't worry too much about that it is not going to stop it working, I have seen similar circuits with 10M resistors in that position.
Most of the resistors can be a bit out of spec. exceptions are the cathode resistors on the output valves as these normally control the grid bias voltage, they often go lower in value and then the valves will be over worked which could lead to problems.

Mike