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Old 23rd Feb 2016, 1:55 pm   #61
Boater Sam
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Default Re: HMV 653 Broadcaster all wave.

Er, um, Lawrence ( got it! ) Just had a look at Trader sheet 732 for the similar Marconiphone set, and there is no reservoir cap!!
Knew I got it from somewhere, bewildering or what?

Sam
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Old 23rd Feb 2016, 2:15 pm   #62
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Default Re: HMV 653 Broadcaster all wave.

I'm now confused Sam....I'm looking at Trader sheet 732, the reservoir capacitor is designated as C25 (16uf) the +ve is connected to L17 and one side of the rectifiers heaters, the -ve is connected to the HT transformers center tap and to the bias resistors, it looks like a reservoir capacitor to me.

Lawrence.
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Old 23rd Feb 2016, 2:27 pm   #63
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Default Re: HMV 653 Broadcaster all wave.

There must be 2 sheets 732..
If L17 is the speaker mag coil, the cap is connected to the wrong side surely?
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Old 23rd Feb 2016, 2:42 pm   #64
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Default Re: HMV 653 Broadcaster all wave.

Only one trader sheet so far as I know Sam, the one I referred to is the same one as in the link you posted, and in that, C25 is connected to the rectifiers cathode (the heater) that's where the reservoir capacitor is connected to in all the CLC filters I've seen, the reservoir capacitor is the first capacitor in the network to cop the ripple.

Lawrence.
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Old 23rd Feb 2016, 2:59 pm   #65
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Default Re: HMV 653 Broadcaster all wave.

Apologies, told you I was tired. Did not spot the cross connection, no dot you see, thought it was a leap. The sun went down long ago, its another cuppa and bed for me.

I find it amazing how different these diagrams can look just because they is drawn from a different hand. I believe the Trader and some others reverse engineered their sheet from actual sets, heck of a job.

On tonight's performance its just as well I was not on the job!

Sam.
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Old 23rd Feb 2016, 8:00 pm   #66
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Default Re: HMV 653 Broadcaster all wave.

But as ever I'm appreciative of your help Sam and everyone else's on here. Will try and get these pictures uploaded later.
Dave.
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Old 24th Feb 2016, 2:11 pm   #67
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Default Re: HMV 653 Broadcaster all wave.

Quote:
Originally Posted by Boater Sam View Post
I find it amazing how different these diagrams can look just because they is drawn from a different hand. I believe the Trader and some others reverse engineered their sheet from actual sets, heck of a job.
There are many ways people have drawn circuit diagrams. The worst I've met was a convention where there were no blobs and no loops either. A T junction was a connection, a straight crossover wasn't and a crossover with connections had to be a staggered junction (effectively two Ts). Add a Nth generation scanned photocopy into the mix and you have a real recipe for disaster.
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Old 24th Feb 2016, 2:58 pm   #68
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Default Re: HMV 653 Broadcaster all wave.

Some Manufacturers would only release service information to dealers, others were more open, but still usually trade only. Publications like Trader and ERT had to create their own versions, hence the different styles and component references (and occasional errors) The quality of Manufacturers data also varied greatly. You could often recognise the Manufacturer from the draughting style.
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Old 24th Feb 2016, 9:08 pm   #69
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Default Re: HMV 653 Broadcaster all wave.

I have spent some time reading through both sets of service data for both the marconi and Hmv models. If you read about the internal speaker on the Marconi sheet it mentions about an additional coil was used in series between the secondary of T1 and the speaker magnetising coil to reduce hum. It then goes on to say their model was fitted with it but it is not shown on the diagram and later was completely omitted. It says to connect this to speaker tag connections 3 and 4, which is the connection for either side of the speaker magnetising coil. Connections 3 and 4 measure 1600 ohms as per the service data for the magnetising coil. However, this is mentioned in the Marconi service sheet and not the HMV sheet but the Marconi even though mentions it it's not shown in their diagram. So I figure one set of secondaries that measures 0.7 ohms goes to my speaker connections, the other secondary that measures 0.1ohms goes across the speaker magnetising coil, or could be completely omitted as has been done in later models. Please see photo of text. Are we all in agreement we now know where both secondaries go? It would seem Edwards and Lawrence suggestions were pointing in the right direction reading their earlier posts. Also as the rest of your replies suggested connect the speaker to the secondary and omit the other unknown one. I hope my findings can put this to bed and continue with the rewire. Just looking for some confirmation from you experts. Many thanks to all.
Dave.
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Old 24th Feb 2016, 9:25 pm   #70
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Default Re: HMV 653 Broadcaster all wave.

You'll have some fun if you connect the 0.1 ohm winding across the loudspeaker magnetizing coil...

Lawrence.
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Old 24th Feb 2016, 9:31 pm   #71
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Default Re: HMV 653 Broadcaster all wave.

Back to the drawing board then.
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Old 24th Feb 2016, 9:33 pm   #72
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Default Re: HMV 653 Broadcaster all wave.

In the first attachment, the service info snippet says that the bucking coil was "shorted" by a piece of wire between tags 3 and 4- but my understanding is that this is likely to be a short piece of resistance wire tweaked to adjust the amount of "reverse hum", as it were, injected into the speaker's feed by placing it in series with the speaker coil. (There's currently a pretty much identical field coil with its tagboard and resistive loop being cleaned up in front of me right now, but fixed to the oval speaker from a Marconi 559)
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Old 24th Feb 2016, 9:49 pm   #73
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Default Re: HMV 653 Broadcaster all wave.

Please forgive my confusion on this Lawrence. Still being fairly new to this hobby and not having vast experience such as yourselves, certain parts of these circuits I'm still learning. Especially OPT'S with two secondaries. And hum bucking coils is completely new to me. I'm not understanding why there would be a short between tags 3 and 4 . Was this instead of the coil not shown in the diagram or as well as. Struggling to get my head round this arrangement without a diagram to show it.
Dave.
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Old 24th Feb 2016, 9:55 pm   #74
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Default Re: HMV 653 Broadcaster all wave.

On the broadcaster sheet it shows the secondary winding with a tap, the loudspeaker is shown connected between the top end of that winding and the tap, the bottom end of the winding is shown unconnected, you've established that there are two separate secondary windings on the transformer you have in the receiver, it could be that the schematic was drawn but showing only three connections and not four because in reality the two separate windings were connected in series thus only three effective connections, if that were the case one would expect to see a connecting link somewhere in the receiver you have to connect those two windings together in series, as has been suggested by others earlier there is only couple of reasons I can think of that would warrant a tap or separate winding, one would be to change the output impedance of the transformer the other to provide a negative feedback winding, it looks as though the chassis was developed to fit several different models possibly with different budgets.

Either way, I would connected the loudspeaker across the secondary winding that has the highest resistance and leave the other winding disconnected completely.

I assume the primary winding is ok.

Lawrence. EDIT: Whoops....My post crossed.
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Old 24th Feb 2016, 10:22 pm   #75
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Default Re: HMV 653 Broadcaster all wave.

The HMV data also tells you how to reconnect the speaker wiring to its tag strip. On mine and from my photos in post #69 you can clearly see that the suggested connections to connect the speaker have never been used, or soldered to.
On my set, pins 1 and 5 measure 3 ohms across the speaker, the same is measured across the extension speaker tag strip.
Pins 3 and 4 measure 1572 ohms across the speaker magnetising coil.
Below the speaker two thin wires can be seen leaving the speaker magnetising coil and both wires terminate together at pin. If I measure across these two wires before the terminate at pin 7 I measure 0.1 ohms. I'm not sure what this connection is Please see photos . Will leave the extra secondary disconnected as suggested but I don't like mysteries. Many thanks for all your continued help.
Dave.
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Old 24th Feb 2016, 10:34 pm   #76
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Default Re: HMV 653 Broadcaster all wave.

The two copper wires terminated on tag 7 would appear to be from the hum bucking coil, which suggest the hum bucking coil has been shorted out, leave tag 7 as it is.

The other wires connecting to the other tags seem ok, but double check the connecting wires that connect to the magnetizing coil tags (3 & 4) to make sure the other ends are connected to what they are supposed to be HT wise, if they do then it would appear that all's well at the loudspeaker.

Lawrence.
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Old 25th Feb 2016, 12:10 am   #77
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Default Re: HMV 653 Broadcaster all wave.

It does sound as though the speaker you have is configured differently to descriptions in the sheets. The one I have here correlates to the published circuits in that the 1600 ohm magnetising winding is between tags 6 and 7, with the low resistance bucking winding between tags 3 and 4 and shunted by a low value resistor as in post #39 attachment 2 , yours sounds as though the magnetising winding was swapped to 3 and 4. I'd do as Lawrence says- go with what you find, and treat that bit of the service sheet description as misleading and for a different (earlier?) model speaker.
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Old 25th Feb 2016, 7:23 pm   #78
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Default Re: HMV 653 Broadcaster all wave.

Yes I'm going to take your advice, turretslug, Lawrence . My speaker is definately not configured to either service data's i have. It could be a different but similar spec / value speaker fitted. I've looked at photos online and the speakers are all configured to what the service data quotes. So just mine is the oddball but we can now see how it is configured and get round it. Pins 3 and 4 on mine measure 1597 ohms, so this is definately the speaker magnetising coil. I just need to make sure my HT line is wired correctly through it. Pins 1 and 5 are the speaker itself measuring 3 ohms. To this I will connect my highest value secondary from the OPT. The other mystery extra secondary I shall insulate and omit from the circuit completely. The humbucking coil is shorted at pin 7 . Il connect all up as described above and all should be ok. Lots still to do, sets a real mess so I'm sure I will face more non standard issues. The large electrolytics were just botched in all over crazy places. I will get this speaker arrangement corrected over the weekend and move on to the next section of repair. Will let you know my progress. Many thanks for all your help and input to everyone who has contributed.
Regards.
Dave.

Last edited by sobell1980; 25th Feb 2016 at 7:33 pm.
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Old 25th Feb 2016, 10:55 pm   #79
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Default Re: HMV 653 Broadcaster all wave.

One thing that occurred to me (and it's basically just my musing, don't let it distract from the main aim of the thread)- shorting the ends of the bucking coil together would detract from the inductance of the main magnetising winding. This latter needs as many Henrys as can be got if it's to fulfill its added smoothing brief, I wonder if the existing possibly large stocks of field coil assemblies simply had the now redundant bucking winding re-connected in series with the main winding on the basis that "these turns of copper have been paid for, they may as well do something and assist with inductance".

As I say, thinking out loud, but it's a curiosity.
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Old 1st Mar 2016, 9:53 am   #80
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Default Re: HMV 653 Broadcaster all wave.

Well, progress I being made slowly and carefully on the rewire. Along the way I've had to disconnect various resistors so at the same time I've taken the opportunity to test these. Some have tested ok some have not. There appears to be what I might describe as carbon type resistors fitted such as R7 and R3. These appear to measure low, out of circuit approx 2000 ohms both of them. I thought normally resistors only went high? Definately have the correct location and right resistor. I've ordered replacements from Maplins for R7, R3 ,R17,R18 and R19. They are rated at 0.6 watts, will this be sufficient for these resistors application? There is no mention of what wattage resistors are in either service data. Also R5 has previously been replaced with two very large resistors in parallel and twisted together. They are the largest resistors in the set. Again no wattage recommended but they look like they would consume a lot of power unless someone before has gone in overkill as that's all they had? I would like to replace R5 for a singular resistor but am concerned what wattage to buy? It supplies the screen grid HT for valves 1 and 2 . For reference purposes I'm using the Marconi sheet as I'm finding it much easier to read the diagram. So my resistor references are from the Marconi sheet. Please see photo of R5. Many thanks.
Dave.
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