Beau Decca stopped working

[thejazzageuk]

Since about 2017 I've been happily listening to a beau decca restored with the help of this forum (see thread 'restore a beau decca').

However about a week ago the radiogram stopped working. It still works on the radio input, but there is no sound from any of the 3 gram inputs.

I've just removed the radio to start some trouble shooting but though it would be sensible to check if any one can suggest a possible cause before I start.

I've attached a photo which will be familiar to those who helped out in the original restoration.

[Hartley118]

Does your pickup head still show continuity? They do have tendency to fail open circuit.

Martin

[Techman]

I remember this one.

I remember that you blanket changed all the capacitors in the radio tuner against my best advice and then found that it didn't work. I'm afraid that I lost interest after that, as you could have introduced multiple man made faults. I thought that was a shame, as you'd done so well with the amplifier unit, but I guess you got the radio tuner working in the end, which I'm really pleased about, so well done!

You could do with doing a 'buzz test' on those inputs and I agree that it could possibly be the pickup gone o/c - there's a thread on a GEC radiogram restoration running at this very moment, which you might be interested in, particularly from post #16 onward regarding rewinding an o/c pickup, although thinking about it, you may have fitted a later deck with different pickup heads - I haven't looked up the old thread to check, so you'll have to tell us, or 'link' to that old thread to make it easier for members to check.

Link to GEC thread:-
https://www.vintage-radio.net/forum/...d.php?t=166758

[Michael Maurice]

If it works on radio then there's no point in taking the radio out.

You could do the buzz test as follows:

Remove the radio
Remove the knobs for the amplifier
Remove the top wooden cover
Carefully remove the screening can from the first EF37
Unplug the pick up wire from the amplifier.

Now switch the amplifier on, switch to gram, turn the volume up, let it warm up and put your finger on the top cap of the valve with the screening can.

Do you get a hum? Yes the amplifier is ok, No there is a fault around the first EF37.

If the answer is yes, first make sure that the cable from the deck to the plug is not crumbling and going short circuit, (it should have been replaced) then do a continuity check as Martin says.

[thejazzageuk]

Thanks all for your response.

..And thanks again techman, the gram has performed fabulously these last 3 years and your help was invaluable.

I've carried out the checks suggested by Maurice, here are the results.

I should have mentioned that I had tried both the garrard deck and an alternative audio input to confirm that the input signal was not the issue.

When I turn the volume up and touch the cap of V6, I heard no hum at first, but on turning up the volume you can hear a very quiet hum, but only when volume is around halfway or above.

(If I touch the cap of V7 in the same way, the amp produces a very loud hum).

If I turn the amp right up I can hear output from the turntable, bit it is very quiet.

I did try swapping V6 with another EF37 I have in a drawer. Possible very slightly louder but really the difference is minimal.

I've attached a couple of schematics which may be useful.

[thejazzageuk]

here is a link to the original thread

https://www.vintage-radio.net/forum/...d.php?t=119481

[snowman_al]

Measure the voltages round V6. Check at pin 8 (cathode) and pin 3 (anode) both to ground / 0 volt line.
Also make sure there is 6.3 volts between pins 2 and 7, if not the heater will not come on...

[Silicon]

It is interesting that the grid of V6 does not have the standard 'grid leak' resistor going to ground.

In this circuit, for V6 to be correctly biased, there must be some DC continuity through the pickup.

Voltage checks on V6 would be useful.

[Ted Kendall]

I'd be inclined to check C39 - it could be that V6 is working but the coupling of the output is compromised.

[Techman]

Originally Posted by Ted Kendall

I'd be inclined to check C39 - it could be that V6 is working but the coupling of the output is compromised.

I've just had a quick skim through the original thread to see if I could happen to spot whether C39 had already been replaced with a new one - I'd forgotten what a mammoth thread that was with 16 pages! C39, with others, were discussed in I think post #105 on that thread and I'd advised that it was one of the ones to replace and I think in post #134 the OP had advised us that he'd actually replaced it, with others mentioned in the earlier post. That was a bit of luck finding those posts, as I couldn't go through all of it, but all the information is documented there for anyone with the time to read through the whole lot, so thank you to the OP for kindly finding the thread and posting the link to it in post #6 of this thread, I'm sure it will be useful. It's probably still worth checking C39, even though the new replacement is unlikely to be faulty - although you never know!

[thejazzageuk]

Thanks all. Yes C39 has been replaced as advised by Techman. However C36 was looking dodgy and failed an ESR test so I've changed it with the 22mf cap shown in the photo (was 25mf). Still same result though, VERY low audio volume. Faint hum when touching the cap of V6, maybe a little bit louder but still very quiet.

Here are some result based on the checks suggested by snowman_al

Measure the voltages round V6. Check at pin 8 (cathode) and pin 3 (anode) both to ground / 0 volt line.
RESULT:I checked pin 3 - voltage measured -0.1V. I checked it again with the valve removed and there was 370V indicated.
Pin 8 (Cathode) measures 8.0V

Also make sure there is 6.3 volts between pins 2 and 7, if not the heater will not come on...
RESULT: Access to this valve from the rear is very restricted. I measured between pins 2 and 7 from the top with the valve removed. The voltage measures 3.8VAC. Valve heaters all appear to be glowing.

[snowman_al]

If there is no voltage on V6 pin 3 with the valve in, logic says either R26 and or R27 have gone high resistance. Sorry I've no schematic to know the values.

Are you sure there is only 3.8 volts AC from pins 2 to 7? You can do the same check on V7 to prove the point.

[thejazzageuk]

Thanks snowman_al

The schematic is in post 5.

I'll do some checks and post the results.

[Techman]

No component values shown on the diagram.

Sounds like resistor/s gone high in value causing voltage to be killed when valve conducting, or could even be a faulty valve, but resistor/s first.

Some meters won't read AC voltages (heaters) correctly and read low - try the probes both ways round - one way round may give a higher reading.

[thejazzageuk]

Thank you Techman

I'll check if the resistors are failing.

Here is a schematic that also shows the values.

[Sideband]

My first check would be the anode load resistor R27 (270K)...probably gone high. Even if it's gone high, with the valve removed there could still be a voltage present even if it's gone up to several megohms

[Silicon]

Another possibility is that C38 has a dead short or the valve holder pin contact is faulty.

Is there any voltage Across R26? That would indicate a current flow.

8 Volts at the cathode suggests that 2.5mA is flowing through R25, presumably destined for the screen grid.

[Techman]

I think C38 was mentioned in the other thread as looking a little bit distressed, but not sure if it was replaced, or possibly forgotten about. However, the fact that inserting the valve kills the voltage tends to indicate that the high value anode load resistor (R27, as mentioned) may have gone very high in value, so that would be the first check to make.

[Michael Maurice]

One thing you need to be aware of is that all coupling capacitors and HT decoupling capacitors should really be rated at least 400V as the rectifier warms up before the output valves and at that point the HT could go up to 500V.

Resistors must also be rated at 500V, do not use standard carbon resistors,

[thejazzageuk]

Thanks all.
Excellent news, it is now working. As suspected by most of you, R27 had failed. It measured O/C when checked. I did not have any 270K resistors so I used 3 x 100K resistors in series. The spec calls for a 0.5W resistor but i'm not sure of the wattage on the replacements- I guess they are well above this as they are much bigger that the standard resistors in my kit but I can't recall where they came from. I've added some pics of the resistors and updated amp. Perhaps I should purchase a dedicated 270k resistor to be true to the original circuit.

However it sound fabulous. I will try to upload a link to a video of playing.