Dansette Major component values

[Old Sparky]

I'm currently in the process of repairing one of these fairly basic one-valve players, and am wondering how critical the few components are.  The screen feed resistor read over 6k, so  I replaced it with  4k7 (the correct value) with no discernable or measurable difference in either performance or voltage readings.  Because the 0.05uf tone correction cap. was a black Hunts type I replaced it with a yellow axial 0.1uf 630v one ( I didn't have an 0.047uf to hand). Now, in theory of course, doubling a capacitors value halves it's impedance at any given frequency, but, again, to my ears the amp. still sounded O.K., despite only having a frequency response of about 100Hz-9kHz.  The HT, b.t.w. is about 205v after warming up, with the original metal rectifier and reservoir/smoothing caps. in use.  I'd have expected it to be a little higher than that.  The EL84 anode draws about 35mA, whilst the screen current is maybe 5 or 6mA, all measured with my DMM.

[ppppenguin]

Generally very uncritical. You may have reduced the treble response a bit but if it sounds OK to you then don't woryy. The EL84 operating conditions seem OK to me. HT seems a little low, possibly a tired rectifier. But again, if it works OK then don't worry.

[Old Sparky]

You've basically confirmed what I felt, Jeffrey. If I can find an 0.047uf capacitor, I may fit the correct value, if not, it can stay as it is.

[Terry]

There were lots of these one-valve record players and they probably had many different component values in what is essentially an identical circuit!

I'd check the value of the cathode bias resistor if I were you. The chances are that it has been running at the upper limit of its power rating and may well have dropped in value.

[Old Sparky]

It actually measures 120 ohms, Terry, but according to the color code it should be 100 ohms, so it's just on the upper end of 20% tolerance.

[Refugee]

The grid capacitor is unlikely to have an effect on treble.
It might extend the frequency response below the response of the transformer and speaker so you should not be able to hear any change.
There is no need to change it again.

[Old Sparky]

That 0.05uf cap I replaced with a 0.1uf is actually in the anode circuit of the amp, as the tone control is effectively in parallel with the o/p tx. primary. There is no grid capacitor-the volume control doubles as the grid leak resistor, with the pickup connected between it's wiper & ground.

[ppppenguin]

Here's the schematic, at least I assume it's the right one: http://dansetteworkshop.blogspot.com/201...hi-fi.html or possibly this one: http://dansetteworkshop.blogspot.com/201...c1961.html

The only surprise is that they didn't use a UL84 with the heater tapped off the motor. That mains TX is a significant cost in such a cheap and cheerful design. The cartridge would have been a high output crystal type such as the TC8H. Not to be used on stereo records or anything precious except 78s.

[Terry]

Well, those two demonstrate what I said about different designs having different component values but neither is the right one! The one with the volume control configured as described by the OP has a 120Ω bias resistor and the other uses 100Ω!

Having the cartridge connected to the wiper of the volume control makes no sense to me as a crystal cartridge should be fed into a high impedance output to get a level response. The bass cut at low volume settings must make it sound dreadful!

I'd recommend rewiring it so that the cartridge always sees a 1M load with the wiper connected to the grid as in the MC 1961 design.

[Old Sparky]

Thanks, both. The player on which I'm working is a Dansette Major (not Major Deluxe) although the only difference I can see is the way the tone control is wired (mine is across the o/p tx primary), and the fitting of a pilot lamp (mine doesn't have one) It's possible that someone could have re-wired the pickup connections before I got the machine(or it's wired partly as a so-called 'de-luxe' ex factory), which has been fitted with an SC11 (M or H- I haven't looked yet!) to replace the original TC8. I may have to replace the volume control any way as it has a 'dead' spot, possibly a crack in the track. In any case it's an easy job to swap over the connections to the v/c.