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HMV 2633 Revisited BRC 960 16" Portable

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Joined: Fri Aug 26, 2011 10:45 am
Location: Gateshead

HMV 2633 Revisited BRC 960 16" Portable

Post by Focus Diode » Sun Aug 14, 2016 8:31 pm

Following Andrew's superb efforts with his DER 980 16" portable I thought I'd give an update on the HMV 2633 16" dual standard portable dating from 1965.

Forum members will recall the work I did to the set back in 2013/14 on getting it from Chris. I got it working well yet the set suffered from reliability problems including the failiure of the EHT tray then the LOPT. The most serious fault was the failiure of the 4.33uF dropper capacitor which caused the heater volts to run abnormally high, the poor CRT heater resembled a 60W light bulb.... In retrospect I wish I changed the damn thing before first powering up the set, especially seeing suitable 4uF motor capacitors can be obtained with a 0.33uF mains filter type wired to the tags to make up the correct value. You live and learn...

Clearly in the hope more examples of these sets turning up it's essential this capacitor is replaced before powering up the set.

A 1400 LOPT was adapted to fit which has some connection differences to the original red one and a modified 980/1580 EHT tray got the set functioning again. The smaller tray as used in the other portables was necessary as a conventional tray would not fit in the limited space available.

The CRT is a Mazda CME 1601, not banded at all with the required Feinbridge guard sheet at the front.

The set is basically a Thorn 900/950 series electrically, the audio and frame timebase panels mounted on top and in wired form. The line timebase valves are similarly wired and are mounted horizontally, they retained the PL504 as the line output valve. The significant difference is in the power supply where one set of valves powers the other. When in good condition a blank raster first appears after a few seconds, then following another 45 seconds the picture slowly fades in. Another 15 seconds later the sound follows, the reverse to usual valve set practice in fact. Some examples reportedly took about half an hour to get going from cold! Later models featured a more conventional PSU. I considered it very important to keep the set as originally intended.

Some pictures of this fascinating set and off screen images. The test card is slightly enlarged at first but settles down. Will need to carry out further adjustments to the frame linearity as some cramping is now evident at the top.

All pictures taken on 405-lines.
2633 warm up 1.JPG
Initial raster looking a little dim as brightness pre-set. Plain blank raster with brtilliance advanced fully, then the picture will be too bright.
2633 warm up 1.JPG (67.4 KiB) Viewed 994 times
2633 warm up 2.JPG
First signs of a picture after 45 seconds....
2633 warm up 2.JPG (77.59 KiB) Viewed 994 times
2633 warm up 3.JPG
Some auto correction neccesarry!
2633 warm up 3.JPG (64.71 KiB) Viewed 994 times
2633 warm up 5.JPG
Nearly there
2633 warm up 5.JPG (68.06 KiB) Viewed 994 times
2633 warm up 6.JPG
Picture, but another 15 seconds before the sound fades in.
2633 warm up 6.JPG (70.09 KiB) Viewed 994 times
2633 3.JPG
On programme (The Prisoner break bumper, CH4 September 1983)
2633 1.JPG
The set
2633 2.JPG
Side view- UHF tuner top, VHF below
Last edited by Focus Diode on Sun Aug 14, 2016 9:00 pm, edited 3 times in total.

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Location: Chatteris, Cambs

Re: HMV 2633 Revisited BRC 960 16" Portable

Post by PYE625 » Sun Aug 14, 2016 8:39 pm

It's looking great Brian....well done :aad

Posts: 437
Joined: Fri Aug 26, 2011 10:45 am
Location: Gateshead

Re: HMV 2633 Revisited BRC 960 16" Portable

Post by Focus Diode » Sun Aug 14, 2016 9:49 pm

Thanks Andrew. One thing I also need to do is find a 160pF disc capacitor for the LOPT tags as required for the 1400 LOPT. I currently have a 180pF type which seems OK for 405-lines yet the width is excessive on 625.

With the original LOPT the set seemed to work better on 625-lines, the reverse applying with the adapted 1400 LOPT. The line whistle intensity is considerably reduced with the 1400 transformer too.


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