Dansette Major seems a bit quiet.

[AD360 Rob]

Morning all, just started on this dansette major. Amp is working but seems a bit on the quiet side. The cartridge it came with appears to be a BSR Sc12H but is unmarked so could be anything. It's output has been mixed for mono using a couple of resistors (10K) I subbed in an sx5H which made no real difference to the max output. Measuerment shows the voltage out of the rectifier to be 156Vdc with some 256vAC going in. Nothing gets hot even after an hour (apart from the EL84 obviously) and the sound is undistorted and hum levels are low.
My question is what output should I expect from this type of rectifier? (circuit doesn't show voltages)

Thanks
Rob

[Edward Huggins]

I suspect the amp may be OK, but the problems may lay with the type of cartridge being used. Whilst the BSR SC12H and SX5H (not originally fitted to this player) are good in that they are stereo-compatible, they do not give sufficient output for the single EL84 valve amplifier. You need a true high output type such as a BSR X5H. The "H" suffixes on your cartridge means they have a higher output than is average for a ceramic cartridge, but are not high enough for your needs in this case. If you only want to play Mono records you can buy a BSR "HTC8" re-manufactured type. I would also remove those resistors as these may inhibit output.

[ms660]

According to a Dansette schematic I'm looking at which is a different amp (ECL82 for the Dansette Monarch) it shows 225 AC in and 248 DC out.

Lawrence.

[barrymagrec]

Sounds like the rectifier is duff.

[AD360 Rob]

My thoughts exactly regarding the rectifier Barry, just wanted to be sure. Specs for the TC8H and SX6H quote output at 800mV for the TC8H and 700 mV for the SX6H so fairly close but lower as you say Edward. I understood the resistors to be the accepted method of mixing a stereo output down to mono as they somewhat isolate the left and right outputs from interacting but I will try it without them.

Thanks

[PJL]

Even if the rectifier is weak, the gain won't change much with increased HT. I would go with Edward. Another option is a pre-amplifier and there are further threads including one from Edward https://www.vintage-radio.net/forum/...d.php?t=121557.

['LIVEWIRE?']

I've never included those 'mixing' resistors when fitting a stereo cartridge to a mono player, but simply paralleled the two channels on the tagstrip under the deck. They usually work well enough that way, but, as others have said, either a higher o/p cartridge or a pre-amp. may be needed to obtain max. o/p from this and other one-valve players. (I should have added-sort out the HT first, as it may improve the volume a little, besides which the rectifier could fail altogether at any time.)

[ms660]

I would sort the HT out first.

Lawrence.

[Station X]

There's a thread here relating to low HT on the UL84 version:-

https://vintage-radio.net/forum/showthread.php?t=149889

[ms660]

The OP's is the EL84 version, his HT measurement looks way too low to me for the measured AC input, the UL84 will operate at low HT but the power output will be less, same goes for the EL84.

Lawrence.

[Station X]

Sub the rectifier with a 1N4007 with series resistor and see if there's any difference?

[AD360 Rob]

Hi Graham, would I need a series resistor as the rectifier is only for ht? There isn't one with the original and ht is present at switch on.

[Station X]

When replacing a metal rectifier with a silicon diode it's usual to use a series resistor to reduce switch on surge and compensate for the forward volt drop of the metal rectifier.

220R 2W seems to be a popular value.

[Techman]

I would agree with getting rid of the silly 10K resistors and replacing the duff rectifier with a diode and series resistor. Personally, I'd go with higher than 2 watts for the resistor, regardless of the calculations, it'll run hot and may be unreliable, so go with at least 5 watts.

[AD360 Rob]

I quickly tacked in a 1N4004 (all I had in stock) just to test, HT up to 209v with 226v ac input so rect isn't very well (4007s and resistor on order), has made a difference to the output but not massively so. The 10ks in the input are actually 39k and shorting them made no noticeable increase, in output. The 2 carbon resistors on the board measure within spec as does the tone cap although it's a black hunts so will be replaced as it will no doubt leak in the future. I might try a few different EL84s when I can find my "other" valve box. It's doubtful I will go to the expense of getting another higher output cart as the overall condition of the player is not that great (it's tidy enough but not mint by any means)..

[Chris55000]

Hi!

I can help with the EL84 issue – most manufacturer's under–run the EL84 slightly to cut down on the heat dissipated and prolong its life – in most cases the cathode resistor used is 220 ohms and anode/screen voltages (measured to chassis) of about 230/240V, which gives an anode current of about 36mA, a screen–grid current of about 4mA, with a voltage drop across the 220 ohm cathode resistor of about 8.5V.

If the cathode–bias resistor fitted is 150 ohms, about 7.5V can be expected across it with an EL84 in sound condition.

EL84 pinout:–

1:– i.c. 2:– g1 3:– k, g3, 4:– h, 5:– h, 6:– i.c. 7:– a 8:– i.c. 9:– g2

EL84 heater 6.3V 760mA

Va 250V, Vg2 250V, Ia 48mA Ig2 5.5mA Rk 135 ohms Vg1 –7.3V Ra 5.6k Pout 5.7W for D=10%.(voltages relative to cathode)

Chris Williams

[electrogram]

As has been said your issue is probably the cartridge. Is the cathode resistor bypass cap ok, if it has lost capacity it will noticeably affect the volume

[Techman]

That HT voltage reading is a bit strange - is something dragging it down?

You do realise that you MUST completely disconnect the old rectifier when 'tacking' in a diode. Fitting it it series or paralleling it across the old rectifier should NOT be done. The old rectifier as well as having increasing forward resistance due to age, may also have some reverse leakage.

I suspect a cartridge problem. The old SX5H will likely be lower on output due to its age and the SC12H is basically equivalent to a medium output cartridge, regardless of it having the 'H' suffix.

I would also agree with others regarding checking such things as the cathode bypass capacitor etc.

[Herald1360]

A suitable preamp to boost the lower cartridge output can be built for a few pounds worth of bits. Quite possibly nothing if you have a reasonable junk box.

[RojDW48]

I had one with a similar fault - tried all sorts of solutions, changed most of the components. In the end it came down to a faulty transformer (how unlikely is that?) and I fitted it with a cheap class D amp from China. Cop-out I know, but it sounds OK now.