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

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Old 19th Nov 2017, 12:01 am   #1
rtbcomp
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Default Decca Deccalian Smoking

I've just tried my Deccalian and after about half a record it started smoking profusely.

One of the white electrolytics has failed so I'm replacing both those, the only modern ones I can find are 450v and about half the size of the originals, I'm assuming these will be OK? The manual says 450v, the ones fitted are marked 500v.

The volume control is shot so I'll be replacing that. It's a Log pot (which I expected) but looking at potentiomers I have the choice of Logarithmic or Logarithmic (Audio). Which to use? Any decent makes? The usual stuff on sale looks a bit puny.

Is it possible to get the 3-pin socket that the pickup plugs into (the one on the chassis)? I have a load of 78s to digitise and I was thinking of connecting the cartridge to a pre-amp to get the job done before I start faffing about with the amp. as it's a bit of a priority.

I also intend to replace some of the dodgy rubber mains wiring too.

Anything else I should be looking at whilst I'm at it?

Any help appreciated, thanks.

Roger
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Old 19th Nov 2017, 1:03 am   #2
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Default Re: Decca Deccalian Smoking

Are those the smoothing and reservoir caps? You don't mention a capacitance value. 450V WVDC should be OK. It would help if we knew the vintage of this Deccalian (they made the model for a lot of years) - post a photo or 2 if you are not sure. The 3pin socket is probably a variety of battery connector (used for all sorts of low voltage applications back in the day) - there was quite a range of orientations - again a photo and measurements would help.
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Old 19th Nov 2017, 3:45 am   #3
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Default Re: Decca Deccalian Smoking

Hi Roger,
If your Deccalian has the Decca XMS plug-in heads, then the disc equalisation is wired after that 3-pin socket and before the 3-stage amplifier. Taking an output direct from the head would sound very 'toppy'. And I don't think that standard RIAA EQ suits the XMS head either.

Assuming you can get the amp working again, my experience is that the best audio feed is to be had from the extension speaker jack.

Martin
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Old 19th Nov 2017, 8:30 am   #4
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Default Re: Decca Deccalian Smoking

Caps have shrunk, it is a tad disconcerting when compared side by side; the modern caps don't look right but they're actually better made in most cases. Get a decent brand if possible, Panasonic, Nichicon, Rubicon, Werth.... Vishay do some nice axial's and 105 degrees if possible.

" Logarithmic or Logarithmic (Audio). " They're the same AFAIK. Log is AKA audio taper.

Andy.
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Old 19th Nov 2017, 10:44 am   #5
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Default Re: Decca Deccalian Smoking

Thanks guys.

These threads identify the actual machine:

http://www.vintage-radio.net/forum/s...ad.php?t=20036

http://www.vintage-radio.net/forum/s....php?p=830839#

The one that's failed is a smoothing capacitor, connected to the cathode of the rectifier valve, the identical one is a decoupling capacitor. Just wanted confirmation as the physical size difference is quite significant.

I'll take some photos and do a drawing of the plug and socket a bit later on.
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Old 19th Nov 2017, 11:35 am   #6
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Default Re: Decca Deccalian Smoking

If it's directly connected to the rectifier cathode it is the reservoir cap, use the best you can find, it is worked hard.
I had a similar Decca and used a Chinese red and black cartridge fastened on the arm with a bit of ally and the existing screw that holds the socket. I fitted wires to the cartridge and just plugged them into the socket. Inelegant but easily removed, and it sounded fine.
Had to add a load of weight to the arm to make up for the XMS pickup.
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Old 19th Nov 2017, 12:13 pm   #7
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Default Re: Decca Deccalian Smoking

Got it now! I have a slightly earlier one (and one like yours). The 78rpm only version I substituted a Garrard 2025 deck with a Sonotone cart and it now does service in our living room - the amp, speaker and cabinet were far too good to be limited to just playing 78s. I also fitted it with a switched jack socket in the signal line so I can play CDs through it. Very well worth restoring - it will make a lovely noise!
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Old 19th Nov 2017, 12:29 pm   #8
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Default Re: Decca Deccalian Smoking

When I first got mine I was really surprised by the sound quality. Even at this last episode it went down singing!
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Old 19th Nov 2017, 1:22 pm   #9
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Default Re: Decca Deccalian Smoking

What component was the cause of the smoke?

Andrew
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Old 19th Nov 2017, 2:02 pm   #10
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Default Re: Decca Deccalian Smoking

It was the reservoir capacitor C12, or at least it looks like it's been smoking (See Post #5)

If I got 4 x 450v working caps (8 uf each) and connected them in series/parallel would that reduce the workload on each?

The first gramophone I got was a Dansette with a broken "tone" arm. I made a splint out of a lollipop stick and Sellotape, lasted for ages.

This is the socket that the pickup plugs into:
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Old 19th Nov 2017, 2:39 pm   #11
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Default Re: Decca Deccalian Smoking

It would but is unnecessary. A good quality 8uf @450v will be fine, its the ripple rating that matters with reservoir caps.
I make my own plugs for sockets like these. They are hard to find now.
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Old 19th Nov 2017, 2:45 pm   #12
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Default Re: Decca Deccalian Smoking

It's the socket I'm after. I'll probably have some female pins that will fit the plug as it's only a temporary fix I'm after.
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Old 19th Nov 2017, 3:19 pm   #13
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Default Re: Decca Deccalian Smoking

You can get an idea what the maximum voltage the HT capacitors can be subjected to by pulling the rectifier, powering up and carefully measuring the AC voltage between the chassis and one of the rectifiers anode connections on the rectifiers valve socket and multiplying that voltage figure by 1.414, that will give the AC peak voltage, that's equivalent to the maximum DC voltage that the reservoir capacitor and other HT capacitors can be subjected to under certain circumstances.

Lawrence.

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Old 19th Nov 2017, 4:14 pm   #14
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Default Re: Decca Deccalian Smoking

Quote:
Originally Posted by rtbcomp View Post
It's the socket I'm after. I'll probably have some female pins that will fit the plug as it's only a temporary fix I'm after.
Well, as those plugs are only tinplated, you'd get a satisfactory temporary solution, without doing damage, by soldering to the tips of the pins.

Martin
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Old 19th Nov 2017, 7:44 pm   #15
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Default Re: Decca Deccalian Smoking

Hi.

I would keep a close eye on those wax capacitors whilst you have it apart, they will be nearing the end of there life, but of course that is at your own discretion.

Paul.
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Old 21st Nov 2017, 5:15 pm   #16
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Default Re: Decca Deccalian Smoking

^^ Yes, and the resistors, the transformer insulation is getting a bit old, the insulation on some of the wires is a bit iffy, perhaps the valves are due for replacement.... sigh.

Seriously though are those wax capacitors at risk of failing? I'll probably end up doing it in stages, at least if it stops working after replacing some bits I'll know where to look.

EDIT - What would suggest replacing the wax capacitors with?

Last edited by rtbcomp; 21st Nov 2017 at 5:34 pm.
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Old 21st Nov 2017, 5:30 pm   #17
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Default Re: Decca Deccalian Smoking

Quote:
Originally Posted by rtbcomp View Post
It's the socket I'm after. I'll probably have some female pins that will fit the plug as it's only a temporary fix I'm after.
I've solved that one, the lead from the cartridge terminates on a tag strip so I just soldered a lead and jack-plug to the tags and it works quite well just plugged into the MIC socket on the back of my PC.

https://www.dropbox.com/s/bwakzj6r00...%20It.mp3?dl=0

The above is from a WAV, compressed to MP3 to save space. I haven't done any enhancements apart from remove DC offset.

FYI This part of the circuit diagram is wrong:

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The capacitor is connected to the top left and ground to the bottom pin.

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Old 21st Nov 2017, 6:47 pm   #18
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Default Re: Decca Deccalian Smoking

Quote:
Originally Posted by Stylo N M View Post
I would keep a close eye on those wax capacitors whilst you have it apart, they will be nearing the end of there life, but of course that is at your own discretion.
I believe that the waxies in your pic are in the tone control circuit. Yes they probably leak, but have only a minor effect. The most critical capacitor is the coupler on to the grid of the 6V6 output valve. Remove the 6V6, and switch on the amp. Using a DMM, measure the voltage on pin 5 (anti-clockwise from the spigot looking on the top of the valve holder) with respect to chassis. If it's more than a volt positive, replace the coupling capacitor.

Martin
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Old 21st Nov 2017, 6:50 pm   #19
Stylo N M
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Default Re: Decca Deccalian Smoking

Hi,

Chricklewood electronics, do quite a few yellow polypropelene foil wound capacitors, wich are ideal replacements for the waxies at verious votages, you can always go slightly higher with the rated voltage marked on the capacitor, for example if your wax capacitor is marked 350 volts you can replace that with 450 volts, or even 600 volts, as they will be smaller anyway to the original.

And i think you can still order, and pay by phone

Paul.
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Old 21st Nov 2017, 7:19 pm   #20
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Default Re: Decca Deccalian Smoking

Thanks for info guys, I'll go the whole hog, no point in spoiling the ship for ha'penny worth of tar. I've just had to replace the motor mounting grommets following a horrible graunching sound - thread to follow!

Good old Cricklewood - I remember their adverts in Practical Wireless from over 50 years ago!
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