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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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8th Aug 2018, 7:05 am | #21 |
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Re: Dansette Major Deluxe - too quiet
If you do sub the BSR TC8M in for a test, remember that is only has half the output of the BSR X5H.
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Edward. |
8th Aug 2018, 8:37 am | #22 |
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Re: Dansette Major Deluxe - too quiet
The voltages in post 16 are the same as I got on a recent service to a Major Deluxe. The cathode resistor seems to vary in different players - I've seen 100 ohms through to 220 ohms. Maybe they fitted whatever they had available - it will, of course, alter the voltage found on the grid.
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8th Aug 2018, 10:39 am | #23 |
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Re: Dansette Major Deluxe - too quiet
So it has! Thanks Edward.
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8th Aug 2018, 4:13 pm | #24 |
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Re: Dansette Major Deluxe - too quiet
Don't make hard work of this.
Just touch/stroke the stylus (flip to 78 side is best) and observe noise/sound, or lack of it, on full volume. Then un-clip the cartridge and carefully remove the tangs. Then remove the tangs from the TC8 on the other record player and connect them to the X5H and touch stroke the stylus with it just hanging there, again on full(ish) volume and observe sound - job done. No need for any removing, swapping over, unscrewing or otherwise messing about. The 'carefully' bit is to avoid flexing the internal connections of the cartridge, as this is what causes a lot of the problems with them in the first place. |
16th Aug 2018, 9:27 pm | #25 |
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Re: Dansette Major Deluxe - too quiet
Thanks Phil - I shall try that. In puzzling over this horror I have come across a horrible waxy cap with an almost indecipherable colour code - is it an 1800uF 6.3V? What does it do? And could it be the problem?
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16th Aug 2018, 9:45 pm | #26 |
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Re: Dansette Major Deluxe - too quiet
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16th Aug 2018, 11:28 pm | #27 |
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Re: Dansette Major Deluxe - too quiet
Thanks - I have a schematic with values that appear to be in uF - as in 0.05 - the one I changed - that was correct. The 1800 is marked as exactly that - hence the query- and it turns out there are 1800uF caps at 6.3V - what are they for? Here is the link - http://dansetteworkshop.blogspot.com...uxe-hi-fi.html
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17th Aug 2018, 12:40 am | #28 |
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Re: Dansette Major Deluxe - too quiet
From the voltage readings I don't think that capacitor is likely to be the cause. I also personally don't see how a shorted turn or two in the output transformer will particularly alter the DC conditions on the anode as stated in post #17, although it would cause the low output. I wouldn't be surprised if it's just a duff cartridge - the fact that you get some buzz when touching the pickup connection indicates that the amplifier is probably working, as with a single stage amplifier like this there's only going to be a low level of buzz anyway.
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17th Aug 2018, 7:38 am | #29 |
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Re: Dansette Major Deluxe - too quiet
That link shows 3 different amp circuits - the only one with an 1800 shown is for the 14-3 fitted to a Major DeLuxe. It's a very poor re-drawn diagram. If you fitted an 1800 uf (microfarad) then you will have effectively shorted the signal and will have a very low, or none at all, output. As I said before it will be 1800 picofarad at 630 volts - at least 400 min. There are no 6.3 volt caps shown on that diagram.
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17th Aug 2018, 8:38 am | #30 |
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Re: Dansette Major Deluxe - too quiet
FWIW I think those diagrams in that link are very neatly drawn, certainly better than many of my recent efforts. However I agree that the cap. between the anode & cathode of the EL84 is 1800pf, and needs to be at least 400v, preferably 600v working, since it's wired between the anode & cathode of the valve.
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17th Aug 2018, 11:08 am | #31 |
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Re: Dansette Major Deluxe - too quiet
Thank you gents. When I was teaching and a student expressed a value without units I would write n- what? Oranges? Half bricks? Indian sub-continents? I feel rather the same about that schematic. I am leaning towards the cartridge as being at fault. There is an x3H available on the net - approx 700mV? Would that do? As a matter of interest what is the application for an 1800uF cap, 6.3V? Something to do with the heater circuit?
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17th Aug 2018, 11:16 am | #32 |
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Re: Dansette Major Deluxe - too quiet
It's shown as a 1800pF capacitor in a schematic I'm looking at....No mystery.
Lawrence. Last edited by ms660; 17th Aug 2018 at 11:29 am. |
17th Aug 2018, 11:34 am | #33 |
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Re: Dansette Major Deluxe - too quiet
Point taken about the lack of units on those diagrams. Confusing for beginners, especially! As to the purpose of that capacitor, after all the years I've spent building & repairing things, I should know. My guess is that it provides negative feedback, since a portion of the amplified signal at the anode, which is out of phase with the input, is coupled to the cathode via the 1800pF cap., but quite why this is necessary I know not!
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17th Aug 2018, 12:22 pm | #34 |
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Re: Dansette Major Deluxe - too quiet
No negative feedback unless the cathode decoupling capacitor is shot.
It's there as the "tone correction" aka fast HV spikes across output TX primary suppression cap. It's perfectly placed to cause maximum grief if it goes short. I'd go with at least 1000V rating if it's replaced and I'd prefer to see it across the output TX primary rather than anode to cathode/ground.
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17th Aug 2018, 1:41 pm | #35 |
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Re: Dansette Major Deluxe - too quiet
All the ones I’ve seen were tubular ceramic types and normally 1000 volt, unless some phantom repair person has been involved.
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17th Aug 2018, 2:31 pm | #36 |
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Re: Dansette Major Deluxe - too quiet
I presume the low audio is not distorted. The reason I say this is because I did have one rp to repair many years ago with low output and it turned out to be the Loudspeaker! Sounds (pun intended) unbelievable but it was the speaker.
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17th Aug 2018, 4:24 pm | #37 |
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Re: Dansette Major Deluxe - too quiet
There's certainly a whole host of possibilities with this very simple single stage amplifier!
It's certainly true that a short circuit of the capacitor in question would probably ruin the output transformer, so it would be wise to replace it with one suitably voltage rated. It's not quite so bad if there's a resistor in series with it as there is in some designs. I had one that had started to fail in a set with this configuration once. The fault symptom was that due to the set having a selenium rectifier, HT was present at switch on which caused an instant low hum and crackling sound in the speaker before any valves had the chance to warm up. On inspection the resistor was about fried and I seem to remember that little sparks could be seen running across it. The resistor had also gone considerably lower in value. It was lucky that the capacitor hadn't gone completely short circuit, just very leaky. It could have been a very close call for the output transformer in this instance. |
17th Aug 2018, 4:33 pm | #38 |
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Re: Dansette Major Deluxe - too quiet
There's quite a lot going on here about that 1800pf cap. It clearly needs to be a high voltage type. The thing is, on most of Dansette's single-stage amplifiers, this cap is omitted. I've never known Mr. Margolin to add in a component where there seems to be no need for it! Is it there for HF instability or tone correction?
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17th Aug 2018, 5:11 pm | #39 |
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Re: Dansette Major Deluxe - too quiet
No doubt about it!
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17th Aug 2018, 5:26 pm | #40 |
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Re: Dansette Major Deluxe - too quiet
So it is - someone has helpfully added units to that one - sadly not in the one I found while trawling the interweb - see link above. There is a helpful chat on a youtube vid that goes with it - but it was a bit technical for me. I'm sure this old Dansette is aware of the scorn I have heaped upon its ilk (since they started getting silly prices) and is exacting revenge!
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