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Old 14th Dec 2018, 9:59 pm   #21
TrevorG3VLF
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Default Re: Danson D540 mono amp "can we make it work" project..

You have a 6.3V 50Hz signal source used to provide the heater supply. Put in a 100k resistor in a piece of wire and touch this on the valve grids. Work back from output valve till the signal disappears.
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Old 7th Jan 2019, 12:18 pm   #22
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Default Re: Danson D540 mono amp "can we make it work" project..

I havn't fried my brain yet.... still waiting for the capacitors i ordered before christmas to turn up before I can make any more progress. Lost in the post, seller sent some more. Still waiting....
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Old 9th Jan 2019, 6:16 pm   #23
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Default Re: Danson D540 mono amp "can we make it work" project..

Capacitors came eventually so I have changed them. Voltages at various points seem low, is this because the limiting lamp is still in circuit? (havn't tried it without the lamp yet). One other thought has crossed my mind today, the speaker connector has 3 pins middle one is earthed to the chassis. Do I need a "special" speaker to work on this amp? just been looking at schematics for other projector amps and the seem to have a transformer in the (separate) speaker cabinet. At the moment I just have a normal 8 ohm speaker connected to the centre (earthed) pin and one of the other two. Still havn't had any output, just a bit of feint mains hum and a "click" when switched on and off when its warm.
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Old 9th Jan 2019, 10:46 pm   #24
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Default Re: Danson D540 mono amp "can we make it work" project..

Is that earth pin actually connected to the output TX secondary? If it isn't, the speaker should go between the other two pins.
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Old 10th Jan 2019, 7:30 am   #25
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Default Re: Danson D540 mono amp "can we make it work" project..

Voltages will be low. Your lamp limiter is restricting current, less current = less voltage drop across resistors etc, basic ohms law.

No special speaker needed, if you have a junk speaker try it on various pins. In a nutshell you should have at least two wires out of the output transformer, one might go to ground, but might not. Follw the wires, attach said speaker to these.

BTW, it's advisable to use a junk speaker on first start up of an amp, don't want your Klipsh or whatever getting zapped. If you havn't got one old TV's/PC monitors are a good source, if not I've a few, your welcome to a few.

Andy.
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Old 11th Jan 2019, 10:42 am   #26
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Default Re: Danson D540 mono amp "can we make it work" project..

Quote:
Originally Posted by Herald1360 View Post
Is that earth pin actually connected to the output TX secondary? If it isn't, the speaker should go between the other two pins.
The output transformer has 3 wires going in and 3 coming out. One of the three coming out goes to the centre of the three speaker connections and also to the chassis and mains earth.
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Old 11th Jan 2019, 10:59 am   #27
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Default Re: Danson D540 mono amp "can we make it work" project..

Use your meter on low ohms range (200ish) and check for continuity between each output connection in turn. You are expecting 1 or 2 ohms for the true output pair.
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Old 12th Jan 2019, 2:45 pm   #28
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Default Re: Danson D540 mono amp "can we make it work" project..

Speaker is wired to outer pins, see picture.
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Old 12th Jan 2019, 5:21 pm   #29
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Default Re: Danson D540 mono amp "can we make it work" project..

Quote:
Originally Posted by Bomber county View Post
The output transformer has 3 wires going in and 3 coming out. One of the three coming out goes to the centre of the three speaker connections and also to the chassis and mains earth.
I might hazard a guess that the connection might be for say 8 ohm and 16 ohm or 8 ohm and 4 ohm or some such combination, with the centre pin as the common return. It's usual for the "negative" phase connection of an output transformer to be connected to signal ground.

I'd try that combination first rather than across the other secondary taps.

DC resistance wouldnt tell you much as the secondaries will have a very low resistance. But I guess a really good ohm meter that can accurately measure fractions of an ohm will give you an idea if you meter between the earthed pin and the others and then the other two to gether.

A.
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Old 21st Jan 2019, 6:44 pm   #30
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Default Re: Danson D540 mono amp "can we make it work" project..

Found a bit of tinker time today and It seems we have issues with some of the coarse looking resistors. These two are supposed to measure 1.8m ohm and 47k according to the schematic above. First one is open circuit and the "47k" measures 546M ohms. No voltage to EF40.

How do you work out the colour codes on these old resistors? what wattage rating do I replace them with?

A bit of grid probing with a 50 htz signal produced a buzz from the speaker from the EF40 and ECC40 but nothing on the EL41's.
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Old 21st Jan 2019, 7:07 pm   #31
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Default Re: Danson D540 mono amp "can we make it work" project..

Quote:
How do you work out the colour codes on these old resistors?
It's the same colour code as the one used nowadays.


The body colour is the first digit.

The tip colour (the tip other than the one silver or gold) is the second digit

The spot or band round the middle is the multiplier.

If there is a silver tip as well, it's 10% tolerance. A gold tip means 5% tolerance. And no gold or silver tip is 20%

So the first one in the photo has a brown body, grey tip and green band.
Read that as 18*10^5 or 1.8 MOhms.

I can't see a multipler band or spot on the second one. If there isn't one, it would suggest it's yellow, like the body colour, which would make it 470k. If it really is 47k there would be an orange band or spot.
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Old 21st Jan 2019, 7:14 pm   #32
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Default Re: Danson D540 mono amp "can we make it work" project..

Quote:
Originally Posted by Bomber county View Post
Found a bit of tinker time today and It seems we have issues with some of the coarse looking resistors. These two are supposed to measure 1.8m ohm and 47k according to the schematic above. First one is open circuit and the "47k" measures 546M ohms. No voltage to EF40.

How do you work out the colour codes on these old resistors? what wattage rating do I replace them with?

A bit of grid probing with a 50 htz signal produced a buzz from the speaker from the EF40 and ECC40 but nothing on the EL41's.
The "47k" looks like 470k to me.

To read the value.....body colour=1st digit....coloured ring at one end=2nd digit...coloured ring towards the middle of the body=the multiplier....gold, silver or no ring at the other end=tolerance...….see fig.2 in the link below:

https://www.radioremembered.org/rescode.htm

1/2 watt jobs will do for those two.

EDIT: Post crossed.

Lawrence.
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Old 21st Jan 2019, 8:11 pm   #33
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Default Re: Danson D540 mono amp "can we make it work" project..

All makes sense now ( I have never come across that type before), looks like I have a few to change out that are a long way off what they should be.
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Old 6th Feb 2019, 4:50 pm   #34
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Default Re: Danson D540 mono amp "can we make it work" project..

Bit the bullet this afternoon and spent a couple of hours on this. Changed 90% of the resistors as the majority were well out of spec. It now works and has an output albeit with a small amount of "hiss" and mains hum. The voltage after the last 8uF cap is quite a bit lower than it maybe ought to and that capacitor isn't warming up much (its two neighbours are running at about 40 degrees). How critical are these voltages as most of them are wayward, some by quite a bit?
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Old 7th Feb 2019, 12:28 am   #35
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Default Re: Danson D540 mono amp "can we make it work" project..

If any electrolytics are getting warm they will need replacement. If you leave them they will most likely fail and leak electrolyte everywhere.
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Old 7th Feb 2019, 10:20 am   #36
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Default Re: Danson D540 mono amp "can we make it work" project..

Those parts in the top left of the diagram need to be isolated if you are trying to use it as an ordinary amp. They are only required to power the photocell that is used in the projector. Easiest way is to simply disconnect the 470k in the HT supply to the 8mfd.
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Old 7th Feb 2019, 12:21 pm   #37
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Default Re: Danson D540 mono amp "can we make it work" project..

Just been thinking about that, its got an aux in socket on it for a mic but it seems to work connected to an MP3 player OK. I don't need the big central "valve" socket that powered the projection lamps so I think I'll get rid of it and move the big smoothing cap to the empty hole. All the "magic eye" related stuff can go too. Out of curiosity can anyone explain why it has two volume controls? is one a pre-amp and the other the "power" amp or is it set up to run two speakers off a mono source. I can connect the top two or bottom two speaker connections to a speaker but both seem the same (not yet tried two on it).
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Old 7th Feb 2019, 12:56 pm   #38
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Default Re: Danson D540 mono amp "can we make it work" project..

An electrolytic capacitor shouldn't run noticeably warm at all. If you can actually feel any warmness on the canister, then this proves that it will be internally electrically leaking enough to drag the HT voltage down, which in turn causes more warming until it eventually goes off with a big bang!

Projector amplifiers often have one volume control for the film sound track and another for the projectionists microphone to make announcements regarding the film show etc.
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Old 7th Feb 2019, 2:02 pm   #39
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Default Re: Danson D540 mono amp "can we make it work" project..

What do you mean by top and bottom speaker connections, it should be a 3 pin plug?

https://www.vintage-radio.net/forum/...0&d=1547300719
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Old 7th Feb 2019, 2:09 pm   #40
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Default Re: Danson D540 mono amp "can we make it work" project..

It is, centre pin is offset slightly to one side and goes to chassis/earth.
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