Last Modified: 21 Nov 2018


Condensed from a forum topic.


Thu Nov 03, 2016 7:57 pm


  bought this! The Dansette Conquest Auto was a late 50’s model and featured a slightly larger cabinet thatn previous models, that houses two large (-ish) elliptical loudspeakers for improved bass response. The BSR UA12 auto-changer turntable (hence 'Auto') is the 4 speed model (16, 33, 45 and 78 rpm), which can be used manually, one record at a time, or can stack up to 8 records when used in the automatic mode. The amplifier uses a single ECL82 valve in a traditional circuit that includes negative feedback, and independent treble and bass tone controls. We had one at home when I was a kid, also a red one, but ended up being scrapped because it had woodworm.







Edit: that's not my table BTW, or even my room...



Fri Nov 04, 2016 6:01 pm

Was trying the Dansette last night, works quite well!

There are a couple of minor bijou problem-ettes though that I would like to investigate:

1. IT HUMS LIKE BUGGERY!!!!

2. it's a bit too quiet. (I mean the loudness of the music.)

1. Not too surprising as the mains transformer is directly underneath the circuit board, so the mag field permeates every last component on it. What it really needs is moving away out of there. I do remember our one at home did that too, well they all would do, made like that.

2. it's had a replacement cartridge, to a BSR X5M, 'M' meaning 'medium' (output). What it means is, a lot of the time the Volume knob has to be whacked right up to the stop. However according to circuit diagram, the amp has NFB so ought to be possible to increase the gain.

I am about to get it up onto the table for a good coating of looking at...



Fri Nov 04, 2016 6:05 pm

Appendix: I also want to be be to play 78's on it too, so have had to order this morning a LP / 78 stylus for it; the one that's on it is a flip-over, but both for 'LP', no '78'.



Sat Nov 05, 2016 1:38 am
Oo-ar!

Well it is better.

Currently playing Kate Bush The Red Shoes and she sounds not arf bad.

I moved the mains traffo to the back of the cabinet, and put in a screened lead for the arm to board link. Formerly a twisted wire pair! Madness!

Still hums but nothing like as bad as before.

Changed a couple of caps, put in a Maplin audio grade for V1 anode to V2 grid coupling, and changed a couple of resistors, V1 anode resistor supposed to be 100k but measured as 75k, and to tweak the NFB to up the gain to x15-ish, formerly 5.5 (!), contrary to schematic I've got, the actual NFB values on the board were 68Ω (!) + 15Ω, whereas schematic shows 100Ω + 18Ω. Also given it a bridge rectifier. Also replaced the valve (ECL82) with a Brimar, the Mullard is unknown age and very dirty looking.

The cartridge currently in it is NOT a BSR X5M, the 'spare' I was also given is, but it doesn't work, is obviously what was taken out (it had been serviced before); I found out when I tried swapping them over. Didn't test it first! Doh!

So that wasted an hour or so.

So the cartridge in there now is the replacement stereo 'FOX' thingy, so 2 channels have to be wired in series. Want to try an actual X5M cos it's actual mono (stereo compatible).

Photos later.....


Sat Nov 05, 2016 6:51 pm

1. Deck out...




... to get at the electronics.




Out on the table.









Sat Nov 05, 2016 6:55 pm

Removing the mains transformer. First need to take off plate what holds the pots, also contains the tone control network.









Mains TX all unsoldered and off...




Underside of board now has unrestricted access.





Sat Nov 05, 2016 7:12 pm

Sorry about the yellow pix, I've tried increasing the blue raster, successful in some cases, but for others, can't increase what ain't there!


Two new resistors and two changed caps. 1 resistor value was >20% out (V1 anode resistor), other to change the feedback ratio and increase gain. Yellow coupling cap, albeit replaced before with what looks like contemporary type and same kind of apparent vintage, was changed to Maplin audio grade. Definitely an improvement. ('Fuzzy/scratchy' sound before.) The other change was also to put in a more modern elec for the V1 stage cathode bypass. Also 'new' valve, a Brimar, possibly an improvement.













Mains TX now screwed into back of cab:










Mon Nov 07, 2016 9:56 pm

Still hums a tad so put a CLC 'pi' filter in it today. Still hums a tiny bit but seems a 'cleaner' sound. Problee the unbalanced heater supply, earthed only on one side.



Here showing bridge rect and extra cap added to the board:





Here is 10H choke ensconced under what will be front left corner of the deck:





Scribbled diagram (but after I'd soldered it together ) :





Working:





Tue Nov 08, 2016 5:18 pm

A BSR X5M arrived today, to replace the non-working original one, so have just put that into the Dansette and we'll see how that performs a bit later on.

The thing is, this is proper mono (only 2 pins) the Fox replacement that was in there is stereo so 4 pins, which have to be bodged together somehow to make a mono output.

I have a choice of 2 tracking weights - the arm is cast alloy and the VTF is achieved by a tensioned coil spring and a metal strip full of holes like a colander, you hook one end of the spring into a hole nearest to what weight you want. The spring exerts an upward pull on the arm, so more stretched = less VTF. For the X5M I can have 4.3 grams, or 5.5 grams, so I opted for 4.3. (cartridge specs say range is 4 - 6g.)


It occurred to me only this afternoon, I've been doing this mod and this mod and that mod, just like that, whereas the last time I had anything to do with one of these exact same players was over 40 years ago, at which time I was struggling to understand how the amplifier circuit works, never mind adding any improvements to it!

---