Defiant MP4 with AT6 Turntable refurbish

[Station X]

Looking at those pics I'd say that your player is wired exactly as per the diagram apart from the mains transformer and indicator lamp arrangement.

I can clearly see the 390R and 12k resistors wired across the smoothing caps, the 560k grid capacitor, the 100k anode load resistor for the triode section of the UCL83 and C3 the coupling capacitor.

If you can confirm that the 25uF electrolytic and a 390R resistor go from pin 7 of the UCL83 to chassis, that would clinch matters.

[vidjoman]

Back in post 26 in the photos - the mains to the turntable from the transformer is wired with screened cable and the screens just left twisted together in space which could touch the live mains. This looks to me as it's not original and someone has 'modified' it. Dangerous if left as it is. Also might add to my previous comment about the transformer has been transplanted from somewhere else or the TT and wiring is not original.

I've looked at any Defiant circuits that I have, including those mentioned above, and they have never shown a bulb used a fuse. Maybe that is also a mod?

[ms660]

Doesn't look like screened cable to me, the "screen" looks like string unless I'm not seeing proper.

Lawrence.

[Station X]

Coming back to that "indicator lamp".

From the picture the filament looks perfectly OK to me and as I've said previously it would be unusual for a lamp to fail short-circuit.

I have a selection of dial lamps here and I've measured several using the lowest ohms range on both analogue and digital meters. None of them measure less then 5R and most measure considerably more.

I can only conclude that there is something wrong with the OP's measuring technique or dare I say it, his meter.

Graham. You might like to try measuring some other lamps if you have some.

You must be suffering from information overload by now, so I would suggest replacing components as necessary and then getting back to us with voltage readings.

[vidjoman]

Originally Posted by ms660

Doesn't look like screened cable to me, the "screen" looks like string unless I'm not seeing proper.

You might be right - was only looking on a small screen so difficult to tell.

[Station X]

Originally Posted by vidjoman

I've looked at any Defiant circuits that I have, including those mentioned above, and they have never shown a bulb used a fuse. Maybe that is also a mod?

It appears that the lamp shines through a red "filter" next to the controls, that being the case it won't be an addition, but as you say the circuit may have been modified.

[ggg1234]

Thanks Guys for all your input. I'm going to do some further investigation and will report back.

It is possible that my new meter is 'sus' but I did try with my old analogue one and it did read zero ohms as well . . . . (but I wouldn't rule out that I'm doing something wrong with both meters sadly !!!)

The Red filter housing certainly does look original as does the metal hanging rail the bulb holder slips on to underneath.

I'll do some checks and revert guy's

Graham

[ms660]

Sometimes a meters resistance range setting can muddle up the interpretation of 0 (zero ohms)

Lawrence.

[Edward Huggins]

Try another new Bulb, it looks standard enough and is not a fused type. Yes, it shines through a red "Lens" as they are called.

[Station X]

What would be the point of that Edward? We know that the lamp lit before, but doesn't light now. The filament is intact, so clearly there's a fault elsewhere, possibly insufficient HT current, preventing the lamp from lighting up. You haven't suggested a rating for the new lamp either.

I've suggested in earlier posts that the OP measures the cathode resistor and the voltage across it so that the HT current can be calculated. We can then take things from there.

[ggg1234]

Hi guys sorry for the delay. . .

Graham.
a. The resistance across R4 (390R) on my ‘new’ auto ranging meter reads 450k Ohms. - Am I doing something wrong or is that what you might expect?

b. I confirm the 25uF electrolytic and a 390R resistor go from pin 7 of the UCL83 and then is soldered to a lug on the chassis.

c. Should I replace the 0.02uF Hunts?

Lawrence/vidjoman
a. I can confirm the twisted mains to turntable cable to the motor - is in fact twisted string (which has now fallen off) and is not twisted metal braid.

Please confirm what other readings would you like me to test?

regards
Graham

[Station X]

Originally Posted by ggg1234

Graham.

The resistance across R4 (390R) on my ‘new’ auto ranging meter reads 450k Ohms. - Am I doing something wrong or is that what you might expect?

Graham

There's something really not right here. The reading is over 1000 times too high. I might believe a reading of 450R, but not 450k.

Have you waited for the reading to stabilise whilst the electrolytic charges up?

I understand you meter is auto ranging. Do you have the leads plugged into the correct sockets (generally COM and +ve)? What does the display actually say? Have you tried your analogue meter, carefully zeroing it first. Try measuring some of the other resistors.

Unless we get readings we can trust it's difficult to advise you.

[Edward Huggins]

I would replace that Hunts with a (nearest value) 0.022uf.

[ggg1234]

Hi Graham

Apologies in my haste to type I left out the decimal point.
I attach a pic of the actual meter reading .450k Ohms

Regards
Graham

[Station X]

That's better! 450R!

Check that its colour code is Orange, White, Brown denoting 390R. If so it's gone high in value and you'll need to replace it.

While you're at it check the other resistors. You'll need to disconnect one end of R3 in order to measure that and R1, as they "shunt" each other via the speaker. The general rule is to replace any resistors which are more than 20% off value.

For vintage valve equipment I generally use 2 watt flame proof type resistors.

[ggg1234]

Hi Graham

Sorry about that - careless me !
Colour code is indeed 'Orange, White, Brown'. I will test the rest and order up some new parts and report when I have replaced them all (when they arrive I will replace all the components one at a time and power up the machine after each replacement to make sure it still works - just in case !!!)

Regards
Graham

[julie_m]

According to the diagram here, the indicator lamp is in series with the anode circuit. If the cathode resistor has gone high, the cathode will become more positive, so the grid will become more negative WRT the cathode; this will mean the valve will pass less current; and therefore less current will flow through the lamp.

That might well be enough to extinguish a small tungsten filament lamp; below the rated current, it could be glowing too dimly to see, or even only in the invisible infra-red region.

[ggg1234]

High Graham

Just ordering some parts up and I need a little advice. The 390Ohm resistor replacement I'm not sure the wattage I should use. Would an

ER74 Series Axial Wire wound Resistor 390Ω ±5% 3W 0 → +60ppm/°C

be OK or do I need higher wattage?
Regards
Graham

['LIVEWIRE?']

A 390 ohm 3W resistor will be perfectly adequate as a replacement for the Cathode bias R., as the dissipation should be <2Watts IMHO

[Station X]

A half watt resistor would do the job. However resistors are physically smaller these days for a given power rating.

I'd use something like this. It looks the part and can handle the high voltages found in valve equipment. At the end of the day it's down to personal choice:-

http://uk.rs-online.com/web/p/throug...stors/2141894/