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Old 15th Mar 2018, 2:34 pm   #61
DonaldStott
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Default Re: Dansette "Monarch"

Thanks George - absolutely brilliant!
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Old 16th Mar 2018, 11:18 am   #62
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Default Re: Dansette "Monarch"

Hi George - I notice in your very helpful PDF that there are numerous references to Item Nos. - is there another document that illustrates which parts are being referred to??
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Old 16th Mar 2018, 4:59 pm   #63
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Default Re: Dansette "Monarch"

PM sent.
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Old 16th Mar 2018, 7:24 pm   #64
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Default Re: Dansette "Monarch"

Thanks George - PM acknowledged.
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Old 17th Mar 2018, 2:15 pm   #65
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Default Re: Dansette "Monarch"

Two questions today: -

1. Are there any issues with mounting the 25uf, 25V electrolytic capacitor underneath the board - that way there is less chance of the leads coming into contact with the dual can capacitor? Or should I just heat-shrink the leads??

2. Any tips for cleaning up the covering material - Foam Cleanser and a toothbrush help but the edges still look very tatty? (see picture below).
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Old 17th Mar 2018, 2:18 pm   #66
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Default Re: Dansette "Monarch"

If you mean the cathode bypass cap. no problems of which I'm aware. Usually, I fit an axial 22 or 33uf cap on the underside, close to the valve base.
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Old 17th Mar 2018, 4:03 pm   #67
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Default Re: Dansette "Monarch"

Thanks again LIVEWIRE - of course there is no reason why the new cathode bypass cap has to use the connection vacated by C6 from the old triple cap can. There is the connection point for one end of R11 to Pin 2 of the valve - I'm assuming that would be o.k. with the other end of the new cap going to the common ground?
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Old 17th Mar 2018, 5:09 pm   #68
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Default Re: Dansette "Monarch"

You can clean the more dirtier edges with "Cif" (used to be "Jif") with the toothbrush, but don't over do it. Frayed edges and loose Rexine covering can be made good with contact adhesive. From your pics, I can see the particular colour of your player, and this is known to fade badly. I can also see the original BSR TC8M Mono only (brwon bodied) cartridge still in there.
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Old 17th Mar 2018, 7:16 pm   #69
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Default Re: Dansette "Monarch"

Today I've replaced C3, C5, C6 and C7 - left the mustard coloured caps in place as reportedly they are reliable.

All the resistors are within tolerance and voltages (AC and DC) on the rectifier are both fine!

Everything rewired and back in the box - switched on and guess what, I still have that hum, AARGH!!!

Good news though is that when I now touch the pins connected to the cartridge I get a very loud scratchy noise from the speakers - so that part of the circuit seems fine?

What further testing can I do??
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Old 17th Mar 2018, 7:35 pm   #70
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Default Re: Dansette "Monarch"

Quote:
Originally Posted by Edward Huggins View Post
You can clean the more dirtier edges with "Cif" (used to be "Jif") with the toothbrush, but don't over do it. Frayed edges and loose Rexine covering can be made good with contact adhesive. From your pics, I can see the particular colour of your player, and this is known to fade badly. I can also see the original BSR TC8M Mono only (brwon bodied) cartridge still in there.
Yeah, it cleans up ok but the problem is the faded colour!

The BSR TC8M will be replaced once the BSR X5M arrives.
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Old 18th Mar 2018, 5:07 pm   #71
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Default Re: Dansette "Monarch"

Checked out all my new components to ensure I had good connections and continuity.

Checked all the Pin voltages and there are a couple of surprises:-

Pin 1: See below
Pin 2: 13.5V
Pin 3: See below
Pin4: Heater 6.8V AC
Pin 5: Heater
Pin 6: 230V
Pin 7: 159V
Pin 8: 0.88V
Pin 9: 68.6V

When I touched the meter probe on Pin 1 I got a loud buzzing noise and no reading i.e. 0.00V. With Pin 3 there was a faint buzz but once again 0.00V.

Once the valve cools down I'll clean the valve pins again along with the valve sockets.

Looking at the circuit diagram it seems that Pin 1 and Pin 3 are Control Grids and also that Pin 1 is associated with the Treble control??

The hum certainly reduces in volume when the Bass, Treble and Volume controls are turned to zero - but there is still a pronounced hum. Not just a background hum which I would expect to hear with my ear up against the speaker(s) but a hum you can clearly hear from 2-3 metres away.
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Old 20th Mar 2018, 10:38 am   #72
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Default Re: Dansette "Monarch"

These always had a hum due to the output transformer picking up the field from the mains transformer.
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Old 20th Mar 2018, 11:06 am   #73
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Default Re: Dansette "Monarch"

is the hum with or without the deck connected? If with have you connected the wires to the deck the wrong way around? The screen of the lead should be to the chassis of the deck.
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Old 20th Mar 2018, 1:19 pm   #74
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Default Re: Dansette "Monarch"

Quote:
Originally Posted by peter_sol View Post
These always had a hum due to the output transformer picking up the field from the mains transformer.
If this is a known "feature" is there any way to screen the output transformer from the mains transformer?

Quote:
Originally Posted by regentone001 View Post
is the hum with or without the deck connected? If with have you connected the wires to the deck the wrong way around? The screen of the lead should be to the chassis of the deck.
The deck has never been disconnected so no possibility of me connecting the wires the wrong way round?

You mentioned the "screen of the lead should be to the chassis of the deck." - not sure which cable this is? Still finding my way around.
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Old 20th Mar 2018, 1:31 pm   #75
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Default Re: Dansette "Monarch"

Look at the third picture in post #54. You'll see two screened cables (ie one for each channel) running from a tag strip to the amplifier. It appears that the screens are strapped across to the centre chassis tag?
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Old 20th Mar 2018, 2:32 pm   #76
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Default Re: Dansette "Monarch"

Thanks Graham - I'll ensure that the centre chassis tag is making good contact.
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Old 20th Mar 2018, 2:47 pm   #77
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Default Re: Dansette "Monarch"

Try grounding each control grid in turn and noting any effect that may have on the level of hum.

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Old 20th Mar 2018, 5:19 pm   #78
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Default Re: Dansette "Monarch"

Thanks to everyone for their ongoing support.

Did some detailed circuit tracing to try and ascertain what was going on with the strange values on Pin 1 and Pin 3 detailed in Post #72 above: -


Pin 1 - This is where the additional components not detailed in the Circuit Diagram are located - see first picture below.

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We have a 1MΩ resistor and a 0.047μF capacitor shown in RED. Touching the multi-meter probe on any part of the circuit between Pin 1 and the Treble control gives me a loud buzz? Not sure what this resistor and capacitor are supposed to be doing??


Pin 3 - Traced the circuit from the mains transformer, through the FC116 Rectifier to Pin 3 - voltages are shown in RED in the second picture below.

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All the values are within tolerance until we get to C4 0.01μF - I think this is the audio coupling capacitor which I haven't replaced as I thought these mustard caps were reliable??


Any feedback welcomed as usual - thanks in advance.

NOTE: Hopefully I haven't breached any Forum rules by Posting sections from Circuit Diagrams - I cropped as much as I could.
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Last edited by DonaldStott; 20th Mar 2018 at 5:20 pm. Reason: Typos
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Old 20th Mar 2018, 5:54 pm   #79
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Default Re: Dansette "Monarch"

""Not sure what this resistor and capacitor are supposed to be doing??""

The capacitor is a coupling capacitor, the resistor is the grid resistor, the grid needs a -ve bias voltage, in this circuit the bias voltage is developed across the resistor that's in series with the cathode, the cathode becomes +ve with respect to the chassis due to the current flowing between cathode and anode, that means the chassis is -ve with respect to the cathode, since the grid is connected to chassis via the grid resistor it means that the grid is also -ve with respect to the cathode, that's what the bias voltage needs to be, -ve with respect to the cathode. The grid bias for the output pentode is developed in the same way.

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Old 20th Mar 2018, 6:05 pm   #80
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Default Re: Dansette "Monarch"

There are parts of those circuits that just don't look correct. In my experience of this amplifier, and although it is quite crude, there should be no noticeable hum at 3 feet away from the speaker at 65/70% volume and only a moderate hum beyond that. The tone controls on this model are seperated from the main chassis and this can induce hum/noise. Moving the output transfomer so that it is at 90 degrees to the mains transformer might help. Also as it unlikely that you will ever use them, carefully remove the 3 trailing leads to the phono sockets located at the rear of the cabinet. These can be very hum inducing.
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