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Old 31st May 2016, 10:32 pm   #181
PJL
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Default Re: HMV 653 Broadcaster all wave.

Good to see you have solved the HT puzzle and the set is working well. Peter
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Old 1st Jun 2016, 6:36 am   #182
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Default Re: HMV 653 Broadcaster all wave.

Good morning, Lawrence and Peter.
Do you think I need to lower that HT any further to come in line with the quoted trader sheet valve readings? Or do you think my now only slight raised HT is due to I have a higher mains supply to start with compared to the lower one the trader sheet quotes when they took the valve readings?
Many thanks,
Dave.
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Old 1st Jun 2016, 6:41 am   #183
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Default Re: HMV 653 Broadcaster all wave.

The thing is that very often at that time were taken with a meter of low sensitivity which gave lower readings, even lower than an AVO would give so I should think your readings are fine. The meter used is not given in that case but it often was.
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Old 1st Jun 2016, 8:42 am   #184
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Default Re: HMV 653 Broadcaster all wave.

Quote:
Originally Posted by sobell1980 View Post
Do you think I need to lower that HT any further to come in line with the quoted trader sheet valve readings? Or do you think my now only slight raised HT is due to I have a higher mains supply to start with compared to the lower one the trader sheet quotes when they took the valve readings?
The voltage you have now looks fine, +-10% of the quoted voltages in the manual is usually ok.

Lawrence.
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Old 5th Jun 2016, 10:04 am   #185
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Default Re: HMV 653 Broadcaster all wave.

Thanks for the replies everyone. It was a week ago today that this set late on Sunday afternoon I heard an exciting interference hiss for the first time on this set. It then tuned into radio 4 loud and clear. I was so chuffed and excited. So many times I'd powered on just to be met with silence. Well, a week has passed and it will be the first time this week I've had chance to get back on the set. Today I will be tackling the front end tuning section wiring and caps etc as there is still a bit to do here. At least I can now power the set on in between each repair to make sure what I've done is good. Got to clean all the pots with servisol. I will let you all know how progress is going. Many thanks all.
Dave.
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Old 5th Jun 2016, 5:52 pm   #186
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Default Re: HMV 653 Broadcaster all wave.

Afternoon all.
I've removed the tuning section today to replace some more very dodgy looking caps and some more crumbled wiring. I have got to the point of replacing the oscillator tracking caps C7, C8 and C9. It was here I noticed there are two connected to L10 the LW tuning coil. C9 is correct, connecting between the lower end of C33 the tapping from L10 and to chassis ground. Then I see another cap connected directly in parallel across C33. So between the top end L10 and it's centre tapping, identically how C33 is connected. The caps look unmolested and all the same and original, so not as if it has been added in afterwards. They are large plastic black caps with no values on. So each tuning coil has a tracking cap but LW has two? Pictures to follow.
Many thanks.
Dave.
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Old 5th Jun 2016, 6:08 pm   #187
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Default Re: HMV 653 Broadcaster all wave.

Some pictures of the tuning block. The one I'm pointing to is the cap connected cross C33 which I believe is additional and not shown in either diagram.
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Old 5th Jun 2016, 6:12 pm   #188
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Default Re: HMV 653 Broadcaster all wave.

It is probable that those are micas and don't need replacing.
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Old 5th Jun 2016, 7:49 pm   #189
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Default Re: HMV 653 Broadcaster all wave.

I agree.

Manufactures extras in receivers but not on any schematic/manual is nothing new.

Lawrence.
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Old 5th Jun 2016, 9:00 pm   #190
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Default Re: HMV 653 Broadcaster all wave.

The coloured dots are likely to have some connection with the value, though some formats can be a bit "lost in the mists". Tracking caps often work out to funny values- sometimes manufacturers would have 3150pF (or whatever the maths said) made up for a run, but if a required value could be made up from in stock preferred values, that might have been the form here for LW. As said, they may well be fine- though any component could be problematic at this age. If LW seems to have good calibration/sensitivity/background noise all the way across the band after line-up, they're likely in good order.
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Old 5th Jun 2016, 9:26 pm   #191
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Default Re: HMV 653 Broadcaster all wave.

Looking at the pics of the MW and LW osc coils and the size of the windings and also the resistance of those windings in the Trader sheet the LW coil seems to be screaming for that extra trimmer capacitance.

Lawrence.
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Old 29th Aug 2016, 8:51 pm   #192
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Default Re: HMV 653 Broadcaster all wave.

Good evening all.
This set has finally made it back on the bench after a couple of other repairs took my time up for a friend.

I have rebuilt the tuning block and have applied power .
All the valves have lit up and a healthy normal amount of hum from the loudspeaker on full volume. However no stations can be picked up on any waveband. Operating the wavechange switch causes no thud or click through the speaker. Because I've had the tuning block out and changed the caps i know it needs alignment so I set to it. Only a very faint tone could be heard. Barely audible. I thought this is not right. Best check if V1 is oscillating. Nope, nothing on any wave band. This was checked with my scope at c31 R2 and c6. The scope is working as I checked it with my sig gen at 465khz and had a good trace. So it seems as though none of the tuning coils are being powered up if this makes sense. I've checked my power to L11 through R4. All ok I have HT. No DC after c12 which I assume is correct? I haven't checked the grounding of C7,C8 and C9. I've either overlooked something again or omitted something on the tuning block. Any pointers gratefully received whilst I'm getting my head around this.
Dave.
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Old 4th Sep 2016, 6:22 pm   #193
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Default Re: HMV 653 Broadcaster all wave.

Good evening.
Progress made throughout the week and today.
The reason for no oscillation on any wave band when checked at c31 with my scope, was down to a poor connection of the wire to valve pin socket. This was g2 connection of valve one which is the oscillator anode wire, so no wonder I had no trace on my scope. I've resoldered this connection and now I have good oscillation but only MW and SW bands. I still have nothing for LW.
If I can take us back to post #186 and #187 you will remember I had a mystery cap in place across the LW osc tuning coil . The mystery cap was connected in parallel across C33. The cap was replaced as the leg going into the cap body was very weak and when I moved it broke flush because it was bent at a right angle to its body.
Now before this LW did work . For some reason I have replaced this cap with a 22pF cap, why I fitted this value I don't remember, perhaps I just about measured the old one on my meter and git a 22pF reading. So I'm assuming that this is the reason LW is not oscillating since I've changed this cap across C33. The old cap had no value stamped on it, just coloured dots that were hard to tell what colour they were. Please see previous photos in #186 and #187. I'm guessing that the cap I fitted is of insufficient value to make the circuit for LW oscillate.
Can anyone advise what value I could try to fit here across C33?
I had this problem once before but it was the cap type causing it not to oscillate not the value. It was the Q factor and I fitted a different cap type and it worked. But I'm sure this time it's the fact Ive fitted a 22pF.
If any one can advise or shed some light I would be most grateful.

On a separate note Ive also found out why my sig gen could only be faintly heard when I went to align the set.
Working back from the centre wiper contact of the volume pot R10 I found that I had a cracked tag on the tag strip board where C18 connects. Found this tracing back with my sig gen from R10 and when I wobbled the tag C18 connects to I could make the tone come and go. I have now rectified this and all is well. Receiving multiple stations on MW now. Just LW with no oscillation to solve and the set is finished. Really hope someone can offer some advice on the correct cap to fit. Many thanks,
Dave.
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Old 4th Sep 2016, 7:05 pm   #194
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Default Re: HMV 653 Broadcaster all wave.

Hard to say what value to try across C33, if it were me I'd try a 100pf or even a 200pf and see if the oscillator springs in to action.

Lawrence.
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Old 4th Sep 2016, 7:16 pm   #195
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Default Re: HMV 653 Broadcaster all wave.

Ok Lawrence. Thanks as ever for your valued response.
I know it has to be this. LW worked before repairing the tuning block. Everything else MW AND SW spot on now.
Really pleased I found the two faults of the C18 cracked tag causing loss of signal and the zero oscillation due to poor joint to oscillator anode on v1.
Dave.
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Old 4th Sep 2016, 7:42 pm   #196
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Default Re: HMV 653 Broadcaster all wave.

I assume C9 is as it should be?

Lawrence.
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Old 20th Sep 2016, 9:22 pm   #197
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Default Re: HMV 653 Broadcaster all wave.

Hi all. I've been on and off this set for brief periods over tge last few weeks.
I discovered the problem with LW. Bear in min that things on this set have varied wildly from the service data. Such as the connections on the tag strip to the speaker magnetising coil were different and different to those on the radio museum and the service data.The output transformer was different with an extra pair of secondaries . An extra trimming cap on LW fitted but not shown on the diagram. The sets been severely got at and the simplest solution was a complete re wire .
Another strange thing i found why I was getting nothing on LW. I actually found from using the waveband switch diagram that the LW switch contacts are being made when the wavechange switch according to the knob is in the SW position and the SW switch contacts are being made in the LW indicated position on the selection knob.
The knob looks original. It's almost like this set was an early prototype or some test set! Nothing I tackle is straightforward. I can confirm this switching issue by confirming continuity across which coils are being switched with the wave change switch. So I now have LW oscillation all be it in the SW indicated position. I have now attempted an alignment. MW all working great. Switch to LW and I've done the alignment but I cannot get radio 4 at 1500 metres. I can catch faint stations at the extreme end of tuning mirrored from MW. Im sure it's to do with this extra trimming cap that is not on the diagram across in parallel to c33. I measured just about the old one which was damaged at 22pF with my meter. However this may not have been it's original value. Please see from post #186 onwards. At the moment this extra cap is omitted as per the diagram. Could some one help me with working out what my scope is reading at 1500metres to see what I'm getting on the scope is correct to what the set should be tuned into? Hope all this makes sense. So close now. Many thanks.
Dave.
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Old 20th Sep 2016, 10:23 pm   #198
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Default Re: HMV 653 Broadcaster all wave.

Receiving MW stations when the set is switched to LW is generally a sign that the local oscillator hasn't switched from MW to LW.
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Old 20th Sep 2016, 10:28 pm   #199
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Default Re: HMV 653 Broadcaster all wave.

Quote:
Originally Posted by sobell1980 View Post
Could some one help me with working out what my scope is reading at 1500metres to see what I'm getting on the scope is correct to what the set should be tuned into? Hope all this makes sense.
Regarding measurements ('scope)

According to the Trader sheet the IF is 465 kHz:

IF = 465 kHz

Fs (signal frequency) = 200 kHz (1,500 meters wavelength)

Fo (oscillator frequency) = Fs + IF

Therefore if the receiver is tuned to 200 kHz (Fs) the oscillator frequency should be 200 kHz + 465 kHz which = 665 kHz if all's well.

The time period (t) in microseconds = 1/F(mHz) which is 1/0.665 which equals 1.5037 microseconds (near as damn it) that is what it should measure on your 'scope if all's well when tuned to 1500 meters on the receivers tuning scale.....(timebase variable control set to Cal. and timebase Mag. set to X1)

If the time period you measure is different from the above then do this calc....... 1/t (time period in microseconds) to get the oscillators frequency in mHz then subtract 0.465 (IF in mHz) from that to give the signal frequency in mHz.

This post might cross.

EDIT: Fs (signal frequency) = the frequency the RF tuned circuit is tuned to.

Lawrence.

Last edited by ms660; 20th Sep 2016 at 10:46 pm. Reason: Addition
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Old 20th Sep 2016, 11:08 pm   #200
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Default Re: HMV 653 Broadcaster all wave.

Re: Post#199, 'scope at the oscillators anode (G2) 'scope set to AC coupling, failing that the oscillators grid (G1) you might have to make allowances for any probe loading but it should get you in the ball park.

Lawrence.
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