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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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23rd Aug 2015, 9:42 pm | #21 |
Dekatron
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Re: HMV 653 Broadcaster all wave.
Hi Dave,
Does it get warm or even hot after 5 mins? Nearly 100mA equates to nearly 25W of power being dissipated, which is not trivial. "Rapid clicking" does sound a bit like arcing to me, so be a bit cautious at this stage. You don't think that this noise was arcing because the insulation on the wires from the HT secondary is shot? Nick. |
23rd Aug 2015, 9:50 pm | #22 |
Dekatron
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Re: HMV 653 Broadcaster all wave.
You are assuming that the 100mA current is in phase with the mains voltage. If the transformer primary appears as a pure-ish inductor then the current could be almost 90 degrees out of phase with the voltage. In which case almost no (real) power is dissipated.
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23rd Aug 2015, 9:51 pm | #23 |
Dekatron
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Re: HMV 653 Broadcaster all wave.
Ah, thanks Tony
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23rd Aug 2015, 10:11 pm | #24 |
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Re: HMV 653 Broadcaster all wave.
The clicking does sound a concern but the current is probably OK. Did you earth the chassis? With a suspect transformer, it is very important to check leakage to chassis as this is a common failure mode and could result in a fatal electric shock.
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24th Aug 2015, 6:02 pm | #25 |
Octode
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Re: HMV 653 Broadcaster all wave.
The clicking was very faint and like a consistant pulse just like it was the 50 Hz I could hear. It dissapeared after about a couple of mins as the transformer warmed up.Would the arcing be more intermittent sounding? More so every so often?
To help matters I will repeat the test this evening and for longer. Dave. |
24th Aug 2015, 7:08 pm | #26 |
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Re: HMV 653 Broadcaster all wave.
It sounds like it could be the lamination's buzzing, I think you would see (or smell) if it was arcing!
A transformer with shorted turns would get hot very quickly, and could draw enough current to take out a 1A fuse pretty quickly! Mark |
12th Dec 2015, 11:13 am | #27 |
Octode
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Re: HMV 653 Broadcaster all wave.
I attempted another power up of the transformer this morning. This is with all the valves removed so in effect the transformer has no loads and is running removed from the circuit. It is drawing 95 milli amps steadily, no buzzing, clicking or arcing sounds this time whatsoever. It is not warm in the slightest and the mains plug is running a 1 amp fuse. Does every one agree with Tony Duell in post #22 ? If this is the case I will continue with the rewire. The transformer has been running for 15 mins or so with no heat or blown fuses, just a steady constant 95 milli amps being drawn. Many thanks.
Dave. |
12th Dec 2015, 5:36 pm | #28 |
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Re: HMV 653 Broadcaster all wave.
Sounds promising. Do the outputs from the transformer measure roughly right with a meter?
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12th Dec 2015, 5:50 pm | #29 |
Octode
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Re: HMV 653 Broadcaster all wave.
I will check these next Nick. I will do this tomorrow when I have a bit more time to carefully work out the transformer output configurations, exposed dodgy wiring and stuff literally strung together all over the place , I need to be careful and exercise caution. This set has been badly got at, dodgy previous repairs all over. The capacitor block is missing and they have been replaced under chassis tied with string. I'm trying to fathom the speaker wiring that gas become disconnected from the chassis side. Most confused but I'll get there, I hope. This set shall be a real challenge and perhaps a long term project that I shall fill in between with some easier little battery transistor portable sets. Many thanks.
Dave. |
16th Dec 2015, 2:05 pm | #30 |
Octode
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Re: HMV 653 Broadcaster all wave.
Well, this set is a real mess and will need a complete rewire. I've spent my last few sessions on it simply trying to cross reference the wiring diagram to the set and follow for a start the HT rail from V5. Most of the HT circuit makes sense and is wired correctly corrosponding to the diagram, but there are also some incorrect wiring arrangements. The HT comes off V5 to a tag strip where there are two spurs taken off from the same tag. One goes to supply R22,R2 and R3 resistors and C26 which is missing. The other spur taken from the tag strip goes to feed L16 speaker field coil which acts as a smoother. This is where things get strange. The other side of L16 then goes onto feed the HT rail C28 and C24 and the output transformer T1. I've found that C24 is connected correctly to the output transformer side of L16 but c28 is connected to the loudspeaker side of L16 in the diagram? The diagram shows they should be connected together from the HT supply after L16 then connected T1. I'm just a little worried that have I read it wrong and got confused with cross referencing it to the set. But then I've traced the rest of the HT supply and components it feeds and it all makes sense and is correct. The other problem is the wire coming from L16 to C24 and C28 is disconnected where it should join C28 and C24. So do I rejoin the wire to C24 on the left of L16 or to C28 which is currently on the right of L16 (not according to me or the diagram is in the right place). Or move c28 back to where it shold be in the diagram and attatch the left side of L16 in the diagram to c28 and C24. It just worries me why some one has soldered c28 on the wrong side of L16? The capacitor block that should be above the chassis is missing that houses C7,C11,C25,C26 and C28 is missing and they have been replaced underneath the chassis and tied up with string. This is when I think C28 was soldered incorrectly on the wrong side of L16. C26 is not fitted (missing) and there are two huge 16uF caps fitted when the data sheet only quotes one! Unless some has somehow wired in another 16uF to replace multiple other electrolytics as one, this may explain why C26 is missing.
I then find another large huge cap tied up not connected to anything but the cap has a card type wrapper with no markings at all. The HT smoothing caps and supply have severely been messed with and I'm just looking for confirmation I'm heading down the right repair route not the wrong one. Other than this there are stubs of wire off tag strips that have been cut where stuff has been rerouted or simply cut out and not replaced. Hope that the forum members can shed some light. Many thanks. Dave. |
16th Dec 2015, 2:20 pm | #31 |
Octode
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Re: HMV 653 Broadcaster all wave.
Perhaps my drawing on the diagram will help matters.
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16th Dec 2015, 2:28 pm | #32 |
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Re: HMV 653 Broadcaster all wave.
Looks like someone has bypassed the speaker magnetising coil which also serves as a smoothing choke.
Your speaker won't work and you'll get hum. Has the speaker perhaps been replaced with a permanent magnet type?
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16th Dec 2015, 2:28 pm | #33 |
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Re: HMV 653 Broadcaster all wave.
Hi again Dave,
You've taken on a real challenge this time! Previous bodged repairs can be a nightmare. In your case, where they are so extensive, perhaps a complete rewire will actually be the quickest and easiest way.
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16th Dec 2015, 5:59 pm | #34 |
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Re: HMV 653 Broadcaster all wave.
A quick check of the field coil continuity would likely be informative. I would think it's open circuit and has been bypassed to get the set running on an external speaker. A bodge but at least it would make sense.
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16th Dec 2015, 6:17 pm | #35 |
Octode
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Re: HMV 653 Broadcaster all wave.
I'm away till tomorrow evening (birthday celebrations). I will check the field coil tomorrow evening. It definately has the original speaker and field coil fitted. I took some photos before I left this afternoon. You will see what a mess it is and the speaker that's original. Speaker has four wires to it, two to the speaker and two to the field coil , either side of L16. Thanks for your replies.
Dave. |
17th Dec 2015, 9:40 pm | #36 |
Octode
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Re: HMV 653 Broadcaster all wave.
The speaker magnetising coil L16 measures 1566 ohms.
So this would appear to be ok. Measured on my DMM. Lord knows what's gone on with C28 where it is. Dave. |
18th Dec 2015, 11:03 am | #37 |
Octode
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Re: HMV 653 Broadcaster all wave.
Sorry I may have confused you with my drawing . The arrowed line is to show where C28 positive connection has been moved to, not indicating a wire bypassing L16 . After drawing this arrowed line I thought why didn't I just draw a cap symbol, this has lead to confusion. Ignore the arrowed line. The wire leading from L16 to where C28 SHOULD BE and where C24 IS, is cut/disconnected. So C28 is connected to the loud speaker side of L16 in the diagram and C24 is connected to T1(output transformer ) side of L16 . The wire coming out of L16 is cut as shown in my drawing. If I connect the loose wire to c28 I will be connecting the HT back through L16 again because c28 is misplaced . If I connect it to C24, c28 won't be acting on the HT where it shold be as c28 is now before the smoother field coil. So I am thinking as long as my diagnosis is correct i need to move c28 back to after L16. My burning question is why? Why is c28 moved to before L16? Why have I got 2 x 16 uF caps and missing C26 and the 4 uF caps? Has some one wired in 1 x 16 uF cap to replace the missing couple of 4 uF? Then there is a huge cardboard tube type snipped out of the circuit with no label markings. I guess I need to snip the lot out and start again from the diagram rather than continue to waste time trying to understand why and what someone else has done. Many thanks.
Dave. |
18th Dec 2015, 11:18 am | #38 |
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Re: HMV 653 Broadcaster all wave.
I wouldn't waste any time trying to work out why C28 has been moved. Just put things back to correspond with the circuit.
I've experienced similar things with sets that have been "got at". Often new smoothers of, whatever value the repairer had in their junk box, are just bodged in.
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22nd Feb 2016, 2:53 pm | #39 |
Octode
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Re: HMV 653 Broadcaster all wave.
Progress is being made with this basket case of a set. I'm slowly putting together the HT rail from the mains transformer and rectifier valve 5. However, I've noticed something strange going to wire in the output transformer. I've noticed that the secondary has 4 wires coming out of it. Two obviously go to the speaker but then there is like a pair that come out of the secondary together. You will see from the photos . I have two wiring diagrams for this set. One is of the marconi, an identical set and one of the HMV. One diagram shows an earth connection to the transformer and the marconi diagram does not. Seeing how this opt was not connected it's not obvious to me how this should be wired to chassis.
If any one could shed some light please? There is continuity between all 4 wires between 0.5 and 0.7 ohms. Any advice greatfully received. This set is a total mess. Enjoying the challenge though. Regards Dave. |
22nd Feb 2016, 7:24 pm | #40 |
Dekatron
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Re: HMV 653 Broadcaster all wave.
Maybe they saved some money by specifying the output TX with flying leads long enough for all the places it's connected.
0.5 -0.7 ohms sounds like just the meter leads. To discriminate for sure try putting some ac- 24V should be plenty- onto the primary and measure the voltage and phase of what appears on all the secondary lead configurations. That should identify everything.
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