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Old 16th Oct 2020, 5:47 pm   #1
lesparapluies
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Default Dansette Major capacitor

Hello, just a quick one. Bad hum problems on this amp and I think as it has so few components I'm just going to replace all the caps while I've got it apart.The tone control cap, 0.05uF is a waxy-looking thing which, curiously has a black stripe at one end but is not shown on the schematic as polarised. Could anyone enlighten? I was going to replace it with a polyester but would something else be more suitable? Thanks, MD
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Old 16th Oct 2020, 6:01 pm   #2
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Default Re: Dansette Major capacitor

The black line is the outer foil and in this position it can be ignored. Polyester will be fine, I would use a 630vw minimum, may as well use 1000vdc.
Before doing major work check the cartridge, it requires a high out type which are virtually impossible to get or very expensive.
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Old 16th Oct 2020, 6:40 pm   #3
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Default Re: Dansette Major capacitor

Thanks Frank, yes that had crossed my mind, I've been asked to make one working model from two existing units plus a spare deck, so 3 cartridges, maybe one of them will be OK!
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Old 16th Oct 2020, 6:49 pm   #4
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Default Re: Dansette Major capacitor

Is that the EL84 model? If so it is likely to be the triple electrolytic and be aware the case of the electrolytic forms part of the circuit!
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Old 17th Oct 2020, 8:38 am   #5
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Default Re: Dansette Major capacitor

You will most likely need to replace the 3 in 1 can with discrete components. Don't forget when you have used the other player and the separate deck for spares, these in their own right, will be sellable. Also suggest you add a 3 core mains lead. BTW Even a dud cartridge can sell in order for it to be rebuilt.
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Old 17th Oct 2020, 10:39 am   #6
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Default Re: Dansette Major capacitor

Yes it's the single EL84 with a metal (selenium?) rectifier. As usual, what I thought may be an hour or so's job gets a bit trickier.. the PCB is riveted to the chassis and the mains transformer prevents access to most of the bottom of the board, so have to decide whether to drill out the rivets and replace with nuts and bolts, or remove the transformer, which is bolted down and then covered with a liberal amount of wax or epoxy of some kind but.. in post-France quarantine so lots of spare time..!
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Old 17th Oct 2020, 12:35 pm   #7
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Default Re: Dansette Major capacitor

Quote:
Originally Posted by Edward Huggins View Post
You will most likely need to replace the 3 in 1 can with discrete components. Don't forget when you have used the other player and the separate deck for spares, these in their own right, will be sellable. Also suggest you add a 3 core mains lead. BTW Even a dud cartridge can sell in order for it to be rebuilt.
Thanks for that Edward, yes I did think about putting a 3-core lead on and I will do. I could probably get two working models from what I've got; unfortunately it's cosmetic items such as the plastic speaker grilles and the plastic turntable mats which have become brittle and have fallen apart which tend to complicate things. Re the cap can, I did think about having a go at "re-stuffing" the can; I've never tried this before; maybe it's more relevant in a vintage radio chassis than in something like this where it would be simpler just to add a tag strip with the new caps on...
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Old 17th Oct 2020, 1:48 pm   #8
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Default Re: Dansette Major capacitor

It certainly would be simpler - you are unlikely to be able to stuff new caps into that very small can! The high-output cartridge might make or break this project. Mono-only BSR TC8H clones can still be bought in the UK for 35-00.
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Old 17th Oct 2020, 7:59 pm   #9
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Default Re: Dansette Major capacitor

Just wondering about the 2 HT caps, which are 32uF and 16uF; I'm sure I've seen other EL84 circuits where they are both the same value and wondered if anything would suffer if I used a dual can 32+32?
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Old 17th Oct 2020, 8:54 pm   #10
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Default Re: Dansette Major capacitor

I too have seen other EL84 valve amplifiers using a dual 32+32uF can. It won't do any harm and may reduce the hum. They may have used 32+16uF to keep costs down. Fidelity did the same on their later UY85 - UL84 amplifiers.
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Old 18th Oct 2020, 7:25 am   #11
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Default Re: Dansette Major capacitor

Quote:
Originally Posted by lesparapluies View Post
Quote:
Originally Posted by Edward Huggins View Post
You will most likely need to replace the 3 in 1 can with discrete components. Don't forget when you have used the other player and the separate deck for spares, these in their own right, will be sellable. Also suggest you add a 3 core mains lead. BTW Even a dud cartridge can sell in order for it to be rebuilt.
Thanks for that Edward, yes I did think about putting a 3-core lead on and I will do. I could probably get two working models from what I've got; unfortunately it's cosmetic items such as the plastic speaker grilles and the plastic turntable mats which have become brittle and have fallen apart which tend to complicate things. Re the cap can, I did think about having a go at "re-stuffing" the can; I've never tried this before; maybe it's more relevant in a vintage radio chassis than in something like this where it would be simpler just to add a tag strip with the new caps on...
Be careful when thinking about adding a 3 core mains lead to these Dansette amplifiers. Although they use a properly isolated mains transformer, the chassis metalwork is often the HT negative connection. You could just earth the record deck metalwork (making sure the signal earth from the amp is isolated from the metalwork) but you may well find that this introduces hum.
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Old 18th Oct 2020, 10:41 am   #12
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Default Re: Dansette Major capacitor

Is this a problem? The chassis on most radios with isolating transformers is HT- too. No problem with earthing those. Most even had a specific connector for just that. Helpfully labelled "E" usually.
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Old 26th Oct 2020, 10:23 pm   #13
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Default Re: Dansette Major capacitor

Thanks for all replies so far. I've replaced the smoothing caps and the tone control cap and the amp now runs well. I did order some 1N4007s and 150R 5W resistors, but it seems that the original metal rectifier works fine, so is it worth replacing it just for the sake of it? Also good news, all 3 cartridges work fine with a good clean output. One mechanical problem I have is that the motor is running slow. Definitely the motor - I've cleaned the jockey wheel, set the correct height, cleaned turntable inside rim, cleaned and re-greased the central ball race, etc, and have removed the cam so the auto-mechanism is not in play; turntable spins freely when disengaged, so I think dismantling the motor and cleaning inside it may be the next step. Incidentally, as I previously mentioned, I actually have 3 decks and all of them run with varying degrees of "slowness" so I'm concluding that years of inactivity have caused this...
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Old 26th Oct 2020, 11:08 pm   #14
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Default Re: Dansette Major capacitor

You will need to dismantle the motor lower bearing and clean and add some light oil. That should cure the speed fault. Give the pulley a good yank after reassembly to ensure it's all centred!
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Old 26th Nov 2020, 12:27 pm   #15
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Default Re: Dansette Major capacitor

Hello, just an update on the Dansette, which is proving far trickier than the original "quick job" I envisaged! I repaired the amp and as far as I can tell, it's working fine - except the only thing I can try it with is the cartridge... where another problem occurs: I tested the original cartridge with a separate amp and it seemed to perform well.. so I married up the deck with the repaired amp and... very low volume! I think the mistake I've made, which is staring me in the face in retrospect, is that the other amp I used to test the cartridge is obviously a modern one with a much higher gain than the single EL84 one, and it's hidden the fact that the old cartridge has in fact deteriorated and is giving a good tone but with a much reduced output.. does this make sense? Further strange goings-on... I ordered a new cartridge online and it's giving a 2-3V output as you'd expect but it sounds very distorted... supplier replaced it and the second one sounds the same. Bit of a chicken-and-egg thing, I don 't know for certain that the newly-restored EL84 amp is definitely OK and I don't know for certain that the new cartridge(s) are faulty or OK. I don't have an oscilloscope so the only way of testing the amp would be by ear really. What kind of input could I feed into the EL84 amp to verify its sound quality in order to do a process of elimination? I was thinking maybe the output from a portable radio, through a coupling capacitor, but this would be a low impedance signal into a high impedance input so probably would be inconclusive - any ideas? Thanks
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Old 26th Nov 2020, 12:47 pm   #16
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Default Re: Dansette Major capacitor

Feeding a signal from a low impedance source into a high impedance input is no problem, eg: imagine what difference connecting a 1meg resistor across a loudspeaker in a loudspeaker circuit will do....not a lot.

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Old 26th Nov 2020, 1:26 pm   #17
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Default Re: Dansette Major capacitor

The issue is that your player was designed to work with an (orange bodied) BSR TC8H Mono cartridge. You can (still) buy a replacement for 35-00 - but do remember this will not be suitable for playing Stereo records and most of your LPs will be Stereo. What type of cartridge have you bought as no cartridge that I know of can give as much as 2-3 volts output, except on occasional highly modulated peaks? Your assumption of why it may sound "loud" on a much higher gain amplifier is quite correct.
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Old 26th Nov 2020, 1:51 pm   #18
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Default Re: Dansette Major capacitor

It is an orange-bodied TC8H, identical to the old one, for 35.00.. yes I get everything re stereo etc, the new cartridge sounds very distorted both playing a 78 and a mono 45, not just an "overloaded input" type of distortion but an unpleasant uneven distortion.. I was prepared to accept that it could have been a faulty new cartridge but when the replacement item also sounded the same I had to re-think things. Re the output voltage, I understood that these cartridges could deliver up to 3V. I've measured the output while a record is playing, probably not a very scientific method, with a DMM set on AC, and it's reading between 2 and 3V using this method. Both the new cartridges sound much worse than the 60-year old one which had been fitted when it arrived. Thanks for the bit about impedances; I can see that perfectly as you put it like that; I think I'll try to eliminate amplifier problems first. Ironically I've got a big collection of working vintage gear but I just don't have another record player with the EL84 / crystal cart combo that I could use to compare various parts...
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Old 26th Nov 2020, 10:01 pm   #19
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Default Re: Dansette Major capacitor

Hi, could it just be that the selenium rectifier is showing its age and you haven't got enough HT now?
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Old 26th Nov 2020, 10:16 pm   #20
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Default Re: Dansette Major capacitor

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Hi, could it just be that the selenium rectifier is showing its age and you haven't got enough HT now?
Yes, good point, that was an avenue I was going to explore, the HT seems OK and have replaced filter caps but I think I'm going to try a 1N4007 with a 150R resistor and see if that improves things
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