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Old 20th Nov 2019, 4:32 pm   #21
mickm3for
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Default Re: Dansette conquest output transformer

Hi i would remove the lead from transformer to pin 6 of the valve the anode remove valve
switch on mesure HT if you have no ht its a short between the primary of transformer to ground . What lamp limiter have you used . A short to the HT will blow fuses or the mains transformer will get hot if on full mains but if the lamp limiter is low wattage bulb the current/voltage may not be enough to supply the current required to give full HT voltage.
Have you checked restance from pin 6 of valve to chasis for a short across valve bace etc as if this has been wet and pluged in you could have tracking causing a short . So
remove wire tx to pin 6 post result lamp lim watts ?
post result resistance on 20m ohm range on meter post result we can then help with fault Mick
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Old 20th Nov 2019, 5:22 pm   #22
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Default Re: Dansette conquest output transformer

That resistor looks diabolical! How long was it 'underwater'? I presume the van completely filled with water as the player would have been packed in some sort of box. Looks like it was completely submerged. J.
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Old 20th Nov 2019, 5:24 pm   #23
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Default Re: Dansette conquest output transformer

Quote:
Originally Posted by simonbridge View Post
Right chaps...
Anyway have I got a knackered output transformer and an obvious 18ohm resistor or is it 180ohm?
Yes, Brown, Grey, Black, Silver is 18 ohms @ 10%.
And yes again, from the last description, it does now look as if you have a faulty OP transformer. Either a low resistance between the primary to secondary or a low resistance between the primary to transformer frame.
I would remove the 4 wires from the transformer and do a continuity test primary to secondary and primary to chassis. Maybe we are just catching you up...

To check the 100 ohm resistor, remove the lead to the 25uF section of the can capacitor and re-measure. If it returns to 100 or a bit more, the cap will need replacement.
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Old 20th Nov 2019, 5:29 pm   #24
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Default Re: Dansette conquest output transformer

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Originally Posted by simonbridge View Post
Anyway have I got a knackered output transformer and an obvious 18ohm resistor or is it 180ohm?
You need to get your units right first

Is that the 18K as marked on the circuit diagram? That is eighteen thousand ohms - a massive difference from 18 or even 180 ohms!

While there could be something wrong with the output transformer, I would very much doubt that there is at this stage.
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Old 20th Nov 2019, 5:59 pm   #25
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Default Re: Dansette conquest output transformer

I think he is talking about the resistors connected to the secondary of the transformer.
Cheers
John
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Old 20th Nov 2019, 9:49 pm   #26
simonbridge
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Default Re: Dansette conquest output transformer

Yes the 18ohm in series with the 25uf Cap
thats the one that has disintigrated.
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Old 20th Nov 2019, 11:05 pm   #27
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Default Re: Dansette conquest output transformer

Ah, cheers for that, I see which one you mean.

However, don't go splashing (pun intended) out for a replacement transformer just yet.

Some more thinking and testing needs to be done first and fingers crossed it's something simple (and cheap), but do check the insulation (ohms range/s on your meter) from the primary winding to both the transformer frame AND the secondary (speaker side).

Edit: Reviewing back through some past posts, I now think that it's unfortunately looking like it may be the output transformer after all, but the tests will prove one way or the other - you may well have been right all the time.

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Old 23rd Nov 2019, 11:08 am   #28
simonbridge
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Default Re: Dansette conquest output transformer

will a 1/2 w 18ohm resistor be ok as a replacement?
I think the o/p transformer is knackered so going to replace that and obviously the resistor.
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Old 23rd Nov 2019, 11:26 am   #29
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Default Re: Dansette conquest output transformer

Quote:
Originally Posted by simonbridge View Post
I think the o/p transformer is knackered so going to replace that.
You could well be right, but changing a component because you "think" it may be faulty is not a good fault finding technique or repair method.

You need to do some tests. You've received plenty of advice on how to do this.
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Old 23rd Nov 2019, 12:30 pm   #30
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Default Re: Dansette conquest output transformer

I have tested the transformer out of circuit there is no leakage from windings to case.
The only reason i suspected the transformer is it looks like its been under stress and with no valve and only that in circuit it was indicating that was the culprit.

So station X i am not just suspecting its that I am using elimination..

Anyway if that 18ohm resistor is O/C then maybe that's the only issue. i have a replacement coming so will see what that shows up.
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Old 23rd Nov 2019, 12:34 pm   #31
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Default Re: Dansette conquest output transformer

You should be able to connect something like a 200R resistor in place of the O/P TX primary.

The player won't work of course, but you should get a sensible set of voltage readings.
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Old 23rd Nov 2019, 12:34 pm   #32
ms660
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Default Re: Dansette conquest output transformer

If there was no overheating during the observations in Post#19 then it suggests high resistance in the HT circuit as well.

Lawrence.

Last edited by ms660; 23rd Nov 2019 at 12:40 pm. Reason: clarify
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Old 23rd Nov 2019, 1:28 pm   #33
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Default Re: Dansette conquest output transformer

Simon,
A silly question, but when you say, ''Disconnecting the HT supply from the top of the primary winding at the junction with the 18k resistor I get 300VDC again no valve installed''. Does that also remove the connection to the 32uF smoothing capacitor too? (I have assumed it does not.)

From the way the circuit is drawn, with the valve removed, only the 32uF reservoir capacitor or a leaky OP transformer could draw enough current to pull the HT down and light the limiter bulb?
Alan
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Old 23rd Nov 2019, 3:24 pm   #34
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Default Re: Dansette conquest output transformer

snowman the 32uF cap was still in circuit I just removed the wire connecting the top of the primary.
Basically isolating the the main circuit from the supply.
If I reconnect the circuit with no valve it still pulls too much current. Only seems fine with the transformer primary removed.

anyway i have another conquest which should be coming soon so will be able to swap out the transformer from that and see what the issue is.

Appreciate all you help my knowledge of valve amps is improving already ....
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Old 23rd Nov 2019, 3:56 pm   #35
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Default Re: Dansette conquest output transformer

What is the fault with the transformer, a short between primary and frame or primary and secondary. Are you sure there isn't a short between the anode connection of the valve holder and somewhere

Last edited by electrogram; 23rd Nov 2019 at 4:24 pm.
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Old 23rd Nov 2019, 4:05 pm   #36
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Default Re: Dansette conquest output transformer

Quote:
Originally Posted by simonbridge View Post
If I reconnect the circuit with no valve it still pulls too much current. Only seems fine with the transformer primary removed.
Have you actually measured the current? You can do this directly by inserting your meter in series with the anode supply or indirectly by measuring the voltage across the cathode resistor.

Quote:
Anyway i have another conquest which should be coming soon so will be able to swap out the transformer from that and see what the issue is.
How do you know that the O/P TX in the second player is any good? If there's a fault with the original player causing to much anode current to flow you might end up with two faulty O/P TX's.
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Old 23rd Nov 2019, 4:35 pm   #37
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Default Re: Dansette conquest output transformer

I agree - he might burn out the second transformer if there's still another undiagnosed fault. He still hasn't checked for a primary to secondary short as I advised earlier, although these sort of faults in output transformers are very unusual, and I've certainly never encountered it before.

I'd thought about the possibility of a high resistance in the HT as mentioned, which would immediately cause the voltage to be killed, but I seem to remember he mentioned that the lamp limiter became over bright once things were connected up which would seem to rule this out.
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Old 23rd Nov 2019, 4:37 pm   #38
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Default Re: Dansette conquest output transformer

This has become confusing, at least I think so, I’m not really sure how to advise you. However let’s press on.
1. you say you have tested the transformer out of circuit and it does not indicate a leak etc.
2. You say you have 300vdc when tx is out of circuit and valve out of circuit.
3. You say the 18ohm resistor is open circuit.
Can you confirm above or correct me as succinctly as possible.
Cheers
John
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Old 23rd Nov 2019, 5:16 pm   #39
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Default Re: Dansette conquest output transformer

Quote:
Originally Posted by electrogram View Post
... Are you sure there isn't a short between the anode connection of the valve holder and somewhere
This is a possible problem too.
Could be the anode connection (pin 6) of the valve holder is tracking to the chassis following being switched on when wet.
Have a careful look at the holder for signs of blackening or even a small crack? You can check it with your multi-meter on ohms, but better if you use the 300 volts HT you have on hand.
With the transformer and valve out of circuit, put your -ve meter lead on pin 6 and the +ve lead on the 300 volt point. Set the meter to 1000 volts DC. Now switch on. If you read zero or very low volts, the pin is fine. If you read a high voltage, then there is something wrong.

I expect you have discovered this already, but just in case, you count the valve pins clockwise from the component side (not the valve side) as below.

Alan
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Old 23rd Nov 2019, 6:21 pm   #40
simonbridge
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Default Re: Dansette conquest output transformer

I have just tried something else. Again no valve installed and on light limiter
with the secondary winding wires disconnected and the primary connected light limiter not pulling any current and 300VDC present
If i now connect the secondary wire that connects to the now non existant 18ohm resistor light limiter now quite bright and no HT

does this indicate a short between primary and secondary windings. This is not evident from measuring resistance with multimeter.
Could it be the 18ohm resistor causing the issue
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