Dansette Conquest Auto

[ms660]

Originally Posted by DonaldStott

I'm 95% of the way through updating the text on the manufactures schematic to make things clearer - thanks to Lawrence for the figures in Post #33 above.

Having a bit of difficulty with some of the voltage figures although so far I have ascertained 56V just above V.R.2., 10V just above R5 and 10V just above R11. The voltage above R5 is 1v, the position of the 56v is wrong, more likely to be the anode of the triode (V1a pin 9)

Can't really make out the main voltage coming out of T.2, the voltage and amps to the left of the FC.116 and the voltage to the left of R10 - don't want to guess for obvious reasons. AC out of T2 is 225v and 6.3v, the voltage at the reservoir capacitor is 248v, load current is 28mA, voltage out of R10 looks to be 150v.

I'll Post the updated schematic as a PDF once it is complete.

So far as I can make out.

Lawrence.

[DonaldStott]

Originally Posted by ms660

...the position of the 56v is wrong, more likely to be the anode of the triode (V1a pin 9)

Thanks for the clarification Lawrence - surprising that this voltage label is so far from it's correct position??

[DonaldStott]

Some good initial readings for the Pentode section of the ECL82:-

Pin 6 (Anode) : 248V

Pin 2 (Cathode) : 10V

Not so good news for the Triode section but I'll have to sort out R6 first - this should be 220kΩ but now out of circuit is reading 2.61MΩ !!!"

[ms660]

The voltage between pin 2 and pin 3 should be approx. the same as the cathode voltage, the voltage between pin 2 and chassis should be approx. 10 volts if all's well.

Lawrence.

[DonaldStott]

Originally Posted by ms660

The voltage between pin 2 and pin 3 should be approx. the same as the cathode voltage, the voltage between pin 2 and chassis should be approx. 10 volts if all's well.

Access to the valve pins which are located underneath the mains transformer (good design!) is extremely challenging - I'll try again tomorrow!

Meantime I've attached my first attempt at a cleaned up version of the Conquest Auto MKII schematic - a big thanks once again to Lawrence.

I've re-labelled all the text where I can and tidied up some of the graphic symbols - those associated with the valve and transformers are still a bit rough! I've also removed the "rogue 56V" label as discussed above.

Any feedback welcomed.

[DonaldStott]

I've now replaced R6 with a new 220kΩ resistor and went back and measured the valve pin voltages.

Pentode section of the ECL82:-

Pin 6 (Anode) : 248V
Pin 2 (Cathode) : 12V
Pin 2 (Cathode) to Pin 3 (Control Grid) : -11.5V

Triode section of the ECL82: -

Pin 9 (Anode) : 68.5V
Pin 8 (Cathode) : 0.97V
Pin 8 (Cathode) to Pin 1 (Control Grid) : -0.96V

Removed the valve and checked that I had 0.00V on Pin 3 - I think this implies that there is no leakage (?) from the audio coupling capacitor (C4) which is a mustard cap. So no need to replace??

Hopefully looking much better - still have a couple of resistors to replace.

[Station X]

Looking good.

I don't generally check the cathode to grid voltage where auto-bias (cathode resistor) is used.. Measuring from chassis to grid should show 0V or very slightly positive. Not more than about 0.1V. You'll soon know if you have a leaky coupling cap, as the voltage will be way higher than this.

[DonaldStott]

Thanks Graham - both Pin 1 (Triode Control Grid) to chassis and Pin 3 (Pentode Control Grid) to chassis are measuring 0.00V.

Still only getting 0.86V across that blue electrolytic - a bit low but probably passable??

Replaced all out of tolerance resistors and squirted inside Volume and Tone controls with De-Oxit - no more scratchiness.

Now for that Dansette hum ... I know there are two main culprits: -

1. The smoothing and reservoir capacitors in that big can - comprises C5 (32μF), C6 (25μF) and C7 (32μF) - expensive to replace!

(Cricklewood do a 32μF + 32μF 500V Dual Electrolytic Can Capacitor for £7.80 and a 22μF 450V Radial 105 deg Capacitor for £1.14 although a much lower voltage component would seem fine in this location

2. The wires/connectors associated with the external sockets at the rear of the case.

Any other possible causes??

[Edward Huggins]

This simple circuit can still work for years (sub-optimally) with many components badly out of tolerance, so you seem to have had a real struggle with this one.
The other causes of hum can be the routing of the PU screened cable from the tag on the underside of the BSR autochanger to the volume control and the mains carrying lead to the turntable motor. If you do replace the 3 caps in the large can, this will also include the ECL82 pentode cathode cap. Replacing that can often have a beneficial effect on the volume level.

[Techman]

You need to get used to the causes of hum.

As a general rule if it's regardless of volume control setting it's the smoothing, but if it increases with volume setting, then it's likely to be wiring placement etc.

[DonaldStott]

Originally Posted by Edward Huggins

... so you seem to have had a real struggle with this one.

Or maybe it's just me!

Originally Posted by Edward Huggins

The other causes of hum can be the routing of the PU screened cable from the tag on the underside of the BSR autochanger to the volume control and the mains carrying lead to the turntable motor.

I'm inclined to disconnect the PU screened cable and the wires running to the sockets at the back of the case but leave them in place to allow any future owner to reinstate them if required? Seems a somewhat circuitous route to connect the speakers in parallel??

I suppose I could look at additional screening in some way for the mains carrying lead and other similar cables or look at re-routing them?

Originally Posted by Edward Huggins

If you do replace the 3 caps in the large can, this will also include the ECL82 pentode cathode cap. Replacing that can often have a beneficial effect on the volume level.

I replaced these 3 caps in my previous Dansette Monarch restoration but this didn't impact on the hum to any significant degree?

[Edward Huggins]

I would not leave these long trailing leads in situ as they can still induce hum whether connected to the rear sockets or not. It is highly unlikey that you will ever use these, so they can be removed....BUT do remember that the LH and RH cartridge channels will need to be bridged and the speakers correctly wired in parallel as they will no longer be connected by those switched sockets at the rear. If the hum is still present at nil volume, then the 3in1 can should be replaced - you can use seperate components.

[DonaldStott]

Originally Posted by DonaldStott

I'm inclined to disconnect the PU screened cable and the wires running to the sockets at the back of the case but leave them in place to allow any future owner to reinstate them if required? Seems a somewhat circuitous route to connect the speakers in parallel??

Just to clarify what I meant here - I'm looking to disconnect all the wiring to the rear sockets although I appreciate that this will mean re-routing the cable that comes from the tag on the underside of the BSR autochanger directly to the volume control. This tag has the connections from the cartridge but only two are needed as I will be fitting a BSR X5M stereo compatible cartridge - in this case the black and red wires.

This is the tag on the underside of the BSR autochanger (a bit blurry, sorry): -



So the plan is to re-use the screened cable that runs from the volume control and disconnect that at the rear socket - this would be re-connected directly to the underside tag (black and red wires). The other grey and white cables would be disconnected from the underside tag and rear sockets?

The wiring and connections at the rear sockets are a bit confusing (to me!) but don't you just love the Dansette craftsmanship: -



I think I've worked out what all the cables and wires do apart form the orange wire that runs from the Primary on the Output Transformer to the L.S. rear socket??

As for the connecting the loudspeakers in parallel, this seems fairly straightforward? This picture clearly shows the yellow and black twisted pair that come from the Secondary on the Output Transformer along with the red and black twisted pair that come from the rear sockets. A blue wire connects one set of tags across the speakers. I'm assuming it's just a case of disconnecting the red and black twisted pair and connecting another length of wire between the two other tags on the speakers. Of course all the other changes detailed above would have to be undertaken first.



Has anyone else carried out these modifications and with any degree of success??

[ms660]

Originally Posted by DonaldStott

I think I've worked out what all the cables and wires do apart form the orange wire that runs from the Primary on the Output Transformer to the L.S. rear socket??

So far as I can make out, the orange wire should be connected to the secondary, it should be the feed to the switch on the Ext. L.S. socket:

https://www.radiomuseum.org/r/danset...uest_auto.html

Lawrence.

['LIVEWIRE?']

Looking at your pictures, the wiring is the same as in a Conquest Auto Mk1 I repaired a couple of months ago, and the orange wire does indeed go from the secondary of the o/p Transformer to the extension speaker socket switch, so the two speakers can simply be wired in parallel at the speaker terminals, and the orange wire discarded. Unfortunately I didn't take any pictures of the player I repaired, which has been back with it's owner for several weeks now, but the modifications are straightforward. However, I presume you realise that you need to wire the two channels of the cartridge in parallel at the tagstrip to obtain proper mono reproduction. (Apologies if I'm stating the obvious) B.T.W., what is/was the difference between the Conquest Auto Mk1 & Mk2? Reading this thread, they appear to be electronically the same thing, and very similar in appearance, too.

[DonaldStott]

Originally Posted by ms660

So far as I can make out, the orange wire should be connected to the secondary, it should be the feed to the switch on the Ext. L.S. socket.

You are correct of course - it does connect to the Secondary on the Output Transformer. Still safe to remove it??

['LIVEWIRE?']

As I noted in post # 55, yes, as long as you wire the two speakers in parallel.

[DonaldStott]

Originally Posted by 'LIVEWIRE?'

However, I presume you realise that you need to wire the two channels of the cartridge in parallel at the tagstrip to obtain proper mono reproduction. (Apologies if I'm stating the obvious)

Thanks for this and no need to apologise - often as not things aren't obvious to people like myself! Sometimes it's difficult to articulate and demonstrate what changes are being made - if you popped round I could show you but Chipping Norton to Glasgow is a bit far!

Where I am confused is the way in which I have the black and red wires running from the cartridge to the tag strip but I also have the yellow and blue wires connected to the tag strip but not connected at the cartridge which, obviously in this case, only has two terminals.

• 1. The black wire goes to the shield and red wire to the conductor of the grey co-axial that connects to the TAPE socket at the rear.
  
  
• 2. The yellow wire goes to the shield and blue wire to the conductor of the white co-axial that connects to the STEREO socket at the rear.

I'm guessing (!) that I need to bridge the red and blue wires at the tag strip and these are the ones that need to connect to the cartridge or does one of the cartridge connections need to be the screen? Doubly confusing as the black and red wires are currently connected to the existing BSR TC8M cartridge?? The screens are already bridged at the tag strip.

And even more confusing for novices like myself, the grey co-axial cable that runs from the TAPE socket at the rear to the Volume control doesn't have it's shield connected at the rear socket.

Originally Posted by 'LIVEWIRE?'

B.T.W., what is/was the difference between the Conquest Auto Mk1 & Mk2? Reading this thread, they appear to be electronically the same thing, and very similar in appearance, too.

In Post #24 above Lawrence kindly provide a link to the Conquest Auto MKII schematic, here it is again: -

https://elektrotanya.com/dansette_pr...wnload.html#dl

In Post #45 above I attached my first attempt at a cleaned up version of the Conquest Auto MKII schematic.

Hope this helps?

[David G4EBT]

To be clear, to rewire the speakers leaving the Ext L.S socket in place but disconnected, the wiring needs to be like the R.H. pic below.

Apologies for the manky scan of the circuit.

[DonaldStott]

Thanks David - clarity as usual, much appreciated !

In Post #45 above I attached my first attempt at a cleaned up version of the Conquest Auto MKII schematic.