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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 26th Mar 2023, 2:20 pm   #1
OldTechFan96
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Default Dansette Major HT?

Does anybody know the correct HT and anode voltages for the Dansette Major?

My example is from 1958. The amplifier is marked 'C157/4' on the PCB. It is fitted with a UL84 and a metal rectfier. It uses a 120Ω cathode resistor and a 10kΩ smoothing resistor. It does not have a pilot light.

I can't find an exact circuit. The closest match online is the MC/1961/.

All of the usual servicing has been done including three new electrolytic capacitors.

The HT is 129V (measured at the top end of the audio output transformer).

The voltage at the anode of the UL84 is only 115V.

I've had a run of low HT from metal rectifiers lately so I'm wondering if it is on its way out?
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Old 26th Mar 2023, 2:36 pm   #2
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Default Re: Dansette Major HT?

That does seem low. I'd expect it to be about 200V. You can easily parallel the metal rectifier with a diode to confirm it.

The other likely explanation is that the UL84 is pulling excess current for some reason.
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Old 26th Mar 2023, 2:46 pm   #3
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Default Re: Dansette Major HT?

I always change these metal rectifiers on sight and replace them with a 1N4007 (or similar), in series with a 120 ohm 5W (wirewound) resistor. You may have to vary the resistor value slightly. I don't think they ever quoted voltages on their circuit diagrams.
There are so few passive components, that I usually change them all.

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Old 26th Mar 2023, 3:16 pm   #4
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Default Re: Dansette Major HT?

The anode current is 47.6mA, which is fine according to the UL84 datasheet.

I'll have a look at exactly what MR is fitted and try and find a datasheet for it. Looks like a Siemens?
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Old 26th Mar 2023, 3:33 pm   #5
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Default Re: Dansette Major HT?

The MR is out and is marked 'E 125 C80'.

There does not appear to be any information about them online.

Thinking about it, '125' is probably the DC output of the rectifier and '80' is the current rating.

Last edited by OldTechFan96; 26th Mar 2023 at 3:48 pm. Reason: More info
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Old 26th Mar 2023, 4:09 pm   #6
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Default Re: Dansette Major HT?

There is 140VAC coming from the HT winding of the mains transformer.

I wonder if everything is actually OK?

I'll see what other members think.
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Old 26th Mar 2023, 4:44 pm   #7
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Default Re: Dansette Major HT?

Does it sound ok and have enough volume ?

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Old 26th Mar 2023, 4:56 pm   #8
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Default Re: Dansette Major HT?

The AC also seems low. I don't know this model though, and don't have a circuit. Maybe it's supposed to be like that for some reason.
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Old 26th Mar 2023, 5:53 pm   #9
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Default Re: Dansette Major HT?

I've been using this Major to experiment with modern ceramic cartridges and pre-amps to replace the now mostly unobtainable stereo compatible crystal types.

Feeding my phone into the amplifier via the pre-amp there is lots of volume.

With the cartridge, things are a bit quieter. It would probably sound better with everything in the cabinet.

I'll drop a 1N4007 in place of the original rectifier to see if I can squeeze a few more volts out of the PSU.

Below is the circuit I'm using.
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Old 26th Mar 2023, 6:04 pm   #10
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Default Re: Dansette Major HT?

I have one on the bench at present. This one has a 6.3 v EL84 - seems they made them with UL 84 and EL84, depending what was available.
On load voltages are 230v ac from transformer secondary and 200v dc HT.
I have sadly had a few mains transformers faulty on these recently. They usually have a good amount of wax around the base. Usually you can find a suitable one with a 6.3 v heater winding and change the valve to an EL84.

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Old 26th Mar 2023, 6:21 pm   #11
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Default Re: Dansette Major HT?

Quote:
Originally Posted by OldTechFan96 View Post
Does anybody know the correct HT and anode voltages for the Dansette Major?

My example is from 1958. The amplifier is marked 'C157/4' on the PCB. It is fitted with a UL84 and a metal rectfier. It uses a 120Ω cathode resistor and a 10kΩ smoothing resistor. It does not have a pilot light.

I can't find an exact circuit. The closest match online is the MC/1961/.

All of the usual servicing has been done including three new electrolytic capacitors.

The HT is 129V (measured at the top end of the audio output transformer).

The voltage at the anode of the UL84 is only 115V.

I've had a run of low HT from metal rectifiers lately so I'm wondering if it is on its way out?
Been here before:

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

Lawrence.
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Old 26th Mar 2023, 7:38 pm   #12
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Default Re: Dansette Major HT?

Quote:
Originally Posted by OldTechFan96 View Post
The MR is out and is marked 'E 125 C80'.

There does not appear to be any information about them online.

Thinking about it, '125' is probably the DC output of the rectifier and '80' is the current rating.
I think the first figure is the maximum AC voltage rating (RMS) and the second figure is the maximum load current rating in mA.

The half wave type usually have the prefix E before the voltage rating and the full wave bridge type have the prefix B.

Lawrence.
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Old 26th Mar 2023, 9:38 pm   #13
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Default Re: Dansette Major HT?

I tried a 1N4007 in place of the original rectifier and I have gained about 10V in HT.

The next step will be to button everything up and see how it sounds.
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Old 27th Mar 2023, 9:19 am   #14
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Default Re: Dansette Major HT?

They used the UL84 to finish the Mains TX stock from the previous UL41 amplifier version as used on the 1955/56 "Automix". From then on, the EL84 was standard. You will most definately need a simple OP/AMP pre-amp, maybe powered from the valve's cathode voltage. The signal from your 'phone is probably greater. I can never understand why someone, somewhere, has not offered a simple-to-fit pre-amp (made in small quantities and listed as a standard item) for the novice to use?
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Old 27th Mar 2023, 10:04 am   #15
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Default Re: Dansette Major HT?

Quote:
Originally Posted by Edward Huggins View Post
They used the UL84 to finish the Mains TX stock from the previous UL41 amplifier version as used on the 1955/56 "Automix". From then on, the EL84 was standard. You will most definately need a simple OP/AMP pre-amp, maybe powered from the valve's cathode voltage. The signal from your 'phone is probably greater. I can never understand why someone, somewhere, has not offered a simple-to-fit pre-amp (made in small quantities and listed as a standard item) for the novice to use?
Preamp designed for Dansette preamp EL84 power from heater voltage

https://www.facebook.com/groups/dans...4539723592606/

here at £20 from the Dansette face book group
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Old 27th Mar 2023, 11:46 am   #16
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Default Re: Dansette Major HT?

Thanks for this heads-up. I was never aware of this FB Group before!
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Old 27th Mar 2023, 12:43 pm   #17
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Default Re: Dansette Major HT?

Thanks for the information. I'm not on Facebook so I can't see the preamp details.

This is the preamp I have bought and this is the cartridge I'm using.

Just a thought: will impedance matching be an issue here?
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Old 27th Mar 2023, 12:56 pm   #18
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Default Re: Dansette Major HT?

There may be an input impedance issue. It depends on the op-amp used and the design. A 470k-1M series resistor may help if there's enough gain.
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Old 27th Mar 2023, 2:29 pm   #19
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Default Re: Dansette Major HT?

Yes, it's just possible that your cartridge, and if it does give up to 300mV output, might overload the first IC in spite of RV1.
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Old 27th Mar 2023, 2:59 pm   #20
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Default Re: Dansette Major HT?

The preamp is based around a TL071CP. The spec sheet lists the input impedance as 10k and the output impedance as 1K.

I'll think about changing the resistors on the input/output to better match things.
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