Dansette Major (early type) Issues

[paul1962]

Hi everyone

I'm having issues with an early Dansette Major that I can't seem to find any schematic for.

The scenario is that this appears to be a UL84 variation of the later EL84 type. It has mains hum like crazy and changing the triple Mains Cap for modern equivalents has made no difference, nor has changing the .05 uF tone control cap, making every capacitor on the board new.

I have valve tested the valve and it passes with no issues. The rectifier (a type 06e 11/8 ) has output of 282v ac.

The valve readings (again ac) are ..
Pin 1 0v (but hums like crazy when you try reading it)
Pin 2 As Pin 1
Pin 3 16v
Pin 4 heater negative
Pin 5 heater positive 45v
Pin 6 149v
Pin 7 219v
Pin 8 219v
Pin 9 148v

The only other thing done to the player is to fit a 3 core mains cable (earthed to the volume pot). The last thing of note, is that the record deck is disconnected (motor and pickup wires)

The board has the numbers 157/4 and I can't seem to find any reference to that anywhere in the Dansette Schematics I have seen, hence why I can't check specs, voltages etc.

Can anyone throw some light on the subject ?
All answers gratefully received.

Kind Regards
Paul

[Analogue man]

I would reconnect the audio lead to the deck, you may well find that this will cure the problem.

[Cathovisor]

I once found that if the PCB wasn't firmly soldered to the metal chassis carrier it caused this - have a look.

[Sideband]

If this uses a UL84 it suggests a live (non-isolated) chassis and therefore should not be earthed. Is it an oddball that uses a proper mains isolation transformer? If not, the earth you have introduced could be the problem.

[Edward Huggins]

Your amplifier is a later and interim version of the one first found in the Dansette "Automix" which used a UL41 valve. Using the same mains TX, this later had a UL84 (same heater voltage) before the final EL84 version. With a 3 core mains lead, this amplifier should possess a fairly low hum level, hum only being noticeable over the last 25% of travel of the volume pot. Re-connect as advised above and make sure you do not introdce any earth loops.

[paul1962]

Originally Posted by Sideband

If this uses a UL84 it suggests a live (non-isolated) chassis and therefore should not be earthed. Is it an oddball that uses a proper mains isolation transformer? If not, the earth you have introduced could be the problem.

It is a UL84 valved circuit, as from my understanding, the heater voltage on a UL is 45v and the later type EL84 is 6.3v.
This one does incorporate a mains transformer, rather than using a UL85 valve (from schematics) and seems exactly the same circuit at the EL84 type apart from a different rectifier.
But I will disconnect the earth and see if that is the cure. If so, I owe you a pint

[paul1962]

Originally Posted by paul1962

It is a UL84 valved circuit, as from my understanding, the heater voltage on a UL is 45v and the later type EL84 is 6.3v.
This one does incorporate a mains transformer, rather than using a UL85 valve (from schematics) and seems exactly the same circuit at the EL84 type apart from a different rectifier.
But I will disconnect the earth and see if that is the cure. If so, I owe you a pint

I disconnected the earth and the situation got worse. It seems that it does actually have an isolation transfomer fitted to it.

[paul1962]

Originally Posted by Cathovisor

I once found that if the PCB wasn't firmly soldered to the metal chassis carrier it caused this - have a look.

Many thanks for your input. I have done continuity checks and also ohms tests from board to earth and reading 0.00 on the scale. This doesn't appear to be the issue I'm afraid.

[paul1962]

Originally Posted by Analogue man

I would reconnect the audio lead to the deck, you may well find that this will cure the problem.

I would say that you deserve full marks Analogue man !!

I removed the original wiring to the deck and fitted some co ax, connected that back to the deck and the noise levels are now back to acceptable Dansette levels.

I definitely owe you a beer, unfortunately, as you are nowhere near me, will a virtual one do ?

Many thanks to everyone's answers. All valid and helpful and for that ... I thank you all !!!!

[Analogue man]

My pleasure, I shall be in Thames Ditton next Friday but alas I shall be attending an AGM until late evening so a virtual pint it will have to be!