Dansette HI-FI

[newstart]

Hi all.
I have no knowledge of the workings of record players i'm afraid.
Turning on my Dansette HI-FI record player yesterday I found I had no volume, you could faintly hear the record playing down near the cartridge. I did notice that the two valves were not lit up (I think they usually are ?) I took both valves out and I think they are BRIMAR ECL82. I had the player serviced up in Leicester about 2years ago. The turntable is a Garrard AT6. Any ideas please.
Regards.....Dave.

[Station X]

Are you sure the valves are not lighting up? You may have to observe them from the right angle in the dark to see.

There are two reasons why valves don't light up. Blown (open circuit) heaters, or failure of the Low Tension (LT) power supply.

You can easily check for blown heaters by measuring the resistance between pins 4 and 5 of the valve, which must be removed from the player in order to carry out the test. Valve pins number clockwise from the gap when viewed from under the chassis.

http://www.r-type.org/exhib/aaa0052.htm

Low resistance (a few ohms) indicates a good heater.
Infinite resistance indicates a blown heater.

Before making the test, touch you meter's leads together so you know what a low resistance looks like.

Report results and we'll advise you what to do next.

[Station X]

Circuit here:-

https://www.vintage-radio.net/forum/...0&postcount=20

If the pilot light comes on this would indicate that the LT supply is present, but there may be a fault with the heater wiring.

[Edward Huggins]

Note the the circuit in Post #3 is for the later ECL86 version. Is the OP experienced enough or can he use a DMM to measure as advised? Check the cartridge connectors out (oxidisation?) and touch if possible to see if there's a "Buzz" in the speaker. Edward

[Station X]

If you or any other forum member has the circuit for the ECL82 version I'm sure we'd all be pleased to see it.

Regarding the OP's experience, it would appear from his opening sentence that he has no experience at all. He has a choice of either gaining knowledge through replies to his post or taking the player to a suitably qualified and experienced repairer.

As he's posted in this section rather than in Repair and Restoration Services wanted I assumed he wanted to attempt a repair himself. Based on the symptoms he described (in particular valves apparently not lighting up) I gave him the best advice I could. It's up to him whether he decides to follow it.

We all started with zero knowledge and experience. Some of us gain these skills, some don't bother and some find it impossible to do so.

[Station X]

The circuit in this thread may help, but it doesn't show the heater wiring.

https://www.vintage-radio.net/forum/...ad.php?t=73504

[Edward Huggins]

I don't have the circuit, but the one within Post #6 shows this as an Ultra Linear type which must make this near unique for an ECL82 PP amp. Edward

[newstart]

As mentioned I have no experience re. the workings of record players.Last night in a dark room I removed the pilot bulb that lights up the Dansette logo to check whether the valves were lighting up and I could not see a glimmer. As Graham is not to far from me I wondered if he would be interested in making a repair and a service on the player.
Best regards.....Dave.

[Station X]

The fact the pilot light is illuminated indicates that the LT supply is OK, so it's probably a simple wiring fault. I doubt that both valve heaters would blow leaving the pilot light intact.

I could certainly look at it for you, but there may be a forum member in North Essex who could help. I can't offer a while you wait service so you'd have to make two round trips.

As for "servicing", I'd fix the fault and replace any suspect components. I don't dismantle and relubricate decks.

Drop me a PM if interested.

[Herald1360]

Originally Posted by Edward Huggins

I don't have the circuit, but the one within Post #6 shows this as an Ultra Linear type which must make this near unique for an ECL82 PP amp. Edward

Definitely not unique, the Pye G63 does it in stereo.

There's a Mullard suggested design for p-p ECL82s which is UL.

http://www.bonavolta.ch/hobby/en/audio/ecl82_2.htm

[Michael Maurice]

Dave, I'm going to Woodbridge tomorrow.

I could service the record player on my way, I'll send you a PM.

[Station X]

Dave brought this player round to me yesterday and this afternoon I found time to start work on it. It's the first time I've worked on a record player in over 40 years.

As it had died on active service I felt that it was safe to plug it in and switch it on without using a lamp limiter. The 6.3V pilot lamp glowed brightly showing that the LT winding of the mains transformer was OK, which was one thing to be grateful for. Having allowed time for warm up I gently stroked the stylus, but there was no sound. It was just the same when I removed the head shell and touched the contact pads in the end of the arm with a screwdriver. Then I remembered that some decks have a muting switch underneath which short-circuits the cartridge during autochanging to supress clicks and bangs. I screwed in the transit screws and tried to play a 45. Total silence once again.

Off came the panel covering the amp and controls. I could see that the valves weren't lighting up, just as Dave had reported, and touching them with a finger showed that they were stone cold. I removed the valves and did a continuity check on the heaters. Both were intact, which was another thing to be grateful for. Inserting thin probes into sockets 4 and 5 of the valve holders confirmed there was no LT. It was obvious that there was a fault with the heater wiring.

Out came the amplifier so I could access the underside of the chassis. At first I could see nothing wrong. I could see that the mains transformer had been changed at some time for one of RS manufacture. A closer look showed that one of the heater wires had just been wrapped loosely round the tag on the mains transformer and had never been soldered. It had obviously given up the struggle to make electrical contact.

I unsoldered the remaining two wires from the tag, cleaned everything, rewrapped the wires round the tag and resoldered the joint.

Fortunately the wires leading to the amplifier are long enough for it to be stood on top of the front panel and make voltage tests on the underside. This time the record played loud and clear. I stacked some 45's on the spindle and spent a pleasant quarter of an hour listening to them. A pair of ECL82's in push pull certainly sound a lot better than a single UL84!

I'm going to have to do some preventative maintenance work on the amplifier. Two of the chassis fixing holes have been crudely drilled out without deburring, presumably to make it easier to refit to the cabinet. The nuts associated with those holes were missing, so the chassis was only fixed at one end.

The amp has received "attention" at some time in the past. One of the coupling caps has been replaced, but I'm not sure about the other. I'll fit two new ones for peace of mind.

As mentioned the mains transformer has been replaced and a semiconductor rectifier has been fitted in place of the original. There is a 1.5K resistor in series with the DC output of the rectifier, presumably to compensate for the reduced forward volt drop of the new rectifier. I think its value is far too high though as the HT is only 160V at the pentode anodes. ECL82's deserve more than that. I'll try a 100R resistor instead.

[Station X]

A 500R series resistor gives about 220V at the centre tap of the push pull output transformer. However with 40VDC across the 3 watt resistor it's obviously being overrun. I'm going to have to fit a higher power resistor or think again.

Any suggestion as to what the HT voltage should be? The circuit diagram for the ECL86 version doesn't give any voltages.

[ms660]

Originally Posted by Station X

Any suggestion as to what the HT voltage should be? The circuit diagram for the ECL86 version doesn't give any voltages.

I don't have the info for that model but I just pulled off the web a schematic for an Ekco record player that uses two ECL82's in push pull, the anode voltages are quoted as 228 volts, the screens are 175 volts, that circuit uses a common cathode bias resistor of 180 ohms.

If that's any use.

Lawrence.

[Aub]

Hi Graham,

The Mullard 7 watt push pull ECL82 design shows 256 volts on the anodes of the push pull pentodes.

One of my old data books says 250 v at the anodes.

Hope this is of some use.

Cheers

Aub

[bobbyball]

I had a look at an Ecko/Ferranti circuit using two ECL82 valves and the HT on the anodes is given as 228 volts.

Another circuit from a radiogram using the same valves was 265 volts at the centre tap of the output transistor (anode voltages not specified). The Dansette circuit isn't as "sophisticated" as either circuits, having very few passive components so perhaps somewhere in between is a suitable value to aim for.

[Station X]

Thanks for the helpful comments.

I've replaced the coupling caps along with the dodgy looking 220k resistor which had gone high in value. It's the anode load resistor for the triode amplifier.

I'll revisit the dropper resistor tomorrow.

This is an ultra linear amp by the way. The circuit is similar to the ECL86 version, but almost all the resistor values are different. I'll reverse engineer it before reassembly.

[bobbyball]

A quick look online yesterday (searched "ECL82 push pull") found a circuit with ultra linear output and the HT was more towards that of the Ferranti circuit.

[Edward Huggins]

Thanks for the circuit downloads in Post#10. Very interesting. I think the version of the "Hi Fi" just (very thoroughly!) serviced with ECL82s used a 9" x 6" speaker. The ECL86 version had an 8" round. I've never heard a side-by-side comparisom. Edward

[Station X]

I think the value of the dropper resistor has been decided for me.

The label on the new mains transformer shows that the HT winding is rated at 60mA. I removed the dropper resistor and supplied the amplifier with HT from an external PSU with variable voltage. On slowly winding up the voltage, 60mA was reached at 165VDC. A reading of 11.7V across the 200R common cathode resistor of the pentodes indicated a current of 58.5mA. The rest would have been going to the triodes. I turned off the LT supply and the current dropped to near zero indicating that the smoothers weren't leaking. At 200V the current was 73mA, at 220V 82mA and at 250V 93mA.

I'll refit the original 1.5k dropper.