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Old 6th Aug 2021, 7:33 pm   #81
Ed_Dinning
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Default Re: HMV 1920 made in 1960.

Hi David, in some early Meccano sets there were special radio parts that would allow you to build a crystal set. Has anyone got any of these?

Ed
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Old 13th Aug 2021, 10:32 pm   #82
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The 15watt lamp used to indicate the channel number was replaced last weekend. Now channel selection or switching the set off is no longer a hit or miss affair. With the electronic remote control it's now a simple matter of holding down the button until the TV channel or "off" position is found.
To switch the set on again just hold in the channel button on the control panel until the required channel is reached.

DFWB.
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Old 27th Dec 2021, 4:34 pm   #83
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Up to Christmas day the HMV 1920 was only used to display the test card. A Freeview receiver has been connected to the Aurora converter so that proper broadcast pictures can be displayed.
Those pictures are unwatchable. The CRT is really dim and yet looked not too bad when displaying the test card.
I'm tempted to give the tube a boost. Will go to the shop later today and collect the Muter CRT reactivator.

DFWB.
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Old 27th Dec 2021, 5:55 pm   #84
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Default Re: HMV 1920 made in 1960.

That tube looks good in your first picture David but of course these digital cameras tend to image intensify a poor quality display.

I can remember that Sylvania 23SP4 CRT. I would have been around 14 at the time working at D&B TV. The owner used to buy in receivers for overhaul and resale. These tubes would only have been around 2-3 years old at the time and we had quite a few that were completely flat. I don't think the RCA versions were much better.

It should boost. Bertha is fighting to get her base connector onto it but it's a long way to Newcastle. Regards, John.
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Old 27th Dec 2021, 8:31 pm   #85
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Default Re: HMV 1920 made in 1960.

The CRT reactivator has done the trick. The picture is really bright now. However, the bright picture has shown up short comings in the video circuits, the definition should be a lot better than it is.

DFWB.
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Old 27th Dec 2021, 8:33 pm   #86
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Default Re: HMV 1920 made in 1960.

Hi.
Ive cobbled together a "Bertha" from the PW article from 1957. I will be giving a really flat MW36-24 a go this week, I'll need to dig it out of the loft firstly though.
I did a comparison between the AW36-21 and the Russian 35M1 with only a slightly lower reading on the 64 year old Mullard out of the Bush TV62.
I think you need to make a "Bertha" David
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Old 27th Dec 2021, 9:04 pm   #87
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Default Re: HMV 1920 made in 1960.

"I think you need to make a "Bertha" David"
Hi Trevor,
I still use the Muter BMR90 CRT tester and reactivator.
Bought this instrument sometime in the 1980s. The firm which sold the Muter tube tester to me was Radio Supplies in Hartlepool. Ceased trading many years ago.
Readjusted the picture quality control to the "hard" position and adjusted the aspect radio for 4:3 displays.

DFWB.
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Old 27th Dec 2021, 9:33 pm   #88
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Default Re: HMV 1920 made in 1960.

I hoped I wouldn’t see another one of those, was the cause of a lot of rows between my parents, Mrs Bucket aka my mother was desperate for one…
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Old 27th Dec 2021, 9:55 pm   #89
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Quote:
Originally Posted by M0AFJ, Tim View Post
I hoped I wouldn’t see another one of those, was the cause of a lot of rows between my parents, Mrs Bucket aka my mother was desperate for one…
Now that really brings back memories of my mother and it really made me laugh.
V8 comes to mind!!!
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Old 27th Dec 2021, 10:42 pm   #90
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Default Re: HMV 1920 made in 1960.

Hi David glad the little tickle woke the CRT up
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Old 27th Dec 2021, 10:50 pm   #91
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Hi Bob,
the real test is to see what the picture looks like tomorrow.
Another recent job done to the set was refurbish those stubby legs.
This was done drilling out the centre of each leg and inserting a 12mm dowel piece. That done, the centre was drilled out again so that the long split pins attached to feet can be refitted securely.
This is a very heavy set, in fact it's heavier than a Philips G6 CTV!

DFWB.
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Old 27th Dec 2021, 10:59 pm   #92
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Hi how heavy would this set have been ? the legs looks very heavy duty for a 60s B&W set
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Old 27th Dec 2021, 11:17 pm   #93
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Hi Bob,
the cabinet is constructed with veneered 1/2" plywood, the full length doors from 5/8" plywood. Certainly weighs more than 100 pounds and the set's sheer bulk hinders any chance of carrying this console set with any ease.
Used to move G6s about but I'd baulk at carrying this one.
I reckon a 25" 2000 series CTV weighs the same.

DFWB.
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Old 28th Dec 2021, 1:05 pm   #94
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Today, the HMV continues to display a bright picture but there might be evidence the tube is already beginning to loose emission.
I'm still on the lookout for replacement tube.
This set would display better pictures if the DC component of the video supplied to the CRT cathode was properly referenced to to black level. As it is now the average brightness varies according to picture content.
The mean level vision AGC doesn't help matters.
The chassis is essentially the same as the model 1913, a 17" portable model.
A much better chassis for the model 1920 would be the high performance chassis fitted in the HMV 1912 and Ferguson 505T. This chassis has sync cancelled vision AGC and flywheel line sync.
But even in this chassis the output from the video amplifier is AC coupled to the CRT, so again the DC component is lost.
However, if the 505T chassis was installed, a separate FM radio 10.7mc/s IF amplifier will be required.

DFWB.
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Old 28th Dec 2021, 2:11 pm   #95
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Default Re: HMV 1920 made in 1960.

If you construct a 'Bertha' make sure you use an old metal rectifier rather than a modern silicon diode. It can be a bit clapped out but that does not matter. The more 'spongy' it is the better. I attempted a modernization many decades ago but she refused to work! I had to put her back to original birth. The only addition that might be useful is an amp meter in series with the tube heater supply. This would show up partially shorted heaters.

She loves colour tubes as well. Either croc clips or a switched base is fine. John.
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Old 31st Dec 2021, 12:14 pm   #96
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Four days after the CRT was boosted the picture is still bright.
However, the width of the picture is reduced, almost 1" at the left side.
The PL36 line output valve could be low emission or resistors in the width stabilising circuit are going high in value.
A reduction of width means that the EHT voltage will be lower.
First action, change the PL36.

DFWB.
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Old 5th Jan 2022, 1:51 pm   #97
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It's over a week since the CRT was boosted and so far it's it's still displaying a very bright picture.
However, the picture width fault wasn't so easy to fix. The usual suspects were changed, the PL36 and PY81 and the resistors R75 and R76 in the width control circuit. All these components were out of tolerance and replaced but the fault persisted.
More drastic action required.
The width control feedback system was taken out the circuit by disconnecting the lead from tag B on the line output transformer to the feedback capacitor C65 and also shorting out the VDR Z1.
See attached circuit diagram.
Switch the set on and be ready to switch-off if the the EHT is excessive. The result was an excess of picture width but not as much as expected, the castellations at the sides of the test card are just outside the screen area.
It's possible the characteristics of the VDR have altered which have caused a much higher negative voltage being applied to the PL36 grid.
In the meantime a bodge repair has been carried out by connecting a 820Kohm resistor across the VDR Z1. It's now possible to adjust width control so the the edges of the test card are inside the screen area.

DFWB.
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Old 5th Jan 2022, 1:57 pm   #98
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Default Re: HMV 1920 made in 1960.

Hi David,
Presume you checked the PL36 cathode current is still in spec?
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Old 5th Jan 2022, 2:12 pm   #99
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Hi Frank,
I haven't checked the PL36 cathode current. The HT voltage in the HMV is slightly higher than the figures in the service manual because a PY33 HT rectifier valve has replaced the original PY32.
The PL36 screen grid voltage is 180V and 165V in the circuit diagram.
The line output transformer remains cool even after many hours of use.
When I modified two Philips 21TG100U TVs to accept different line output transformers a 1ohm resistor was inserted between the PL81 cathode and chassis to measure the voltage and current during a 98uS picture line period.
The width stabilising VDR in the Ferguson 705T is the same type as in the HMV 1920.

DFWB.

Last edited by FERNSEH; 5th Jan 2022 at 2:26 pm.
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Old 5th Jan 2022, 2:48 pm   #100
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