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Old 17th Sep 2011, 10:12 pm   #181
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Default Re: Restorers dream part 2 the chassis.

Hi,

Many thanks John. You've just jogged my memory and yes I have a small Mazda booklet "Data booklet 1972/1973" this covers Aerials-Picture tubes and Valves; the PY33 is included which I note is an half wave rectifier with an Int.Octal base.

I think this answers my previous question about bridging to replace the valve using a single rectifier diode as I didn't know the PY32 was an half wave rectifier; at least I'm thinking as I progress.

I'm not in a hurry and this morning I was actually looking at all the information you kindly supplied as I intend to work from it; also Jeffrey took the trouble to post a lot of detailed information.

I'll look forward to receiving the valve and knob and will take your advice not to run the chassis until the replacement valve is installed so I might go quiet for a short while and catch up with jobs around the bungalow.

Compared to the five valve vintage radios I've previously worked on there are a lot more components under this chassis to keep me occupied. As you've said earlier John this set warms up very quickly so checking after replacing each component sounds a good way to go.

I was just about to post the above then noticed the post from Dave. Many thanks Dave for taking the time to give such a detailed answer; I'll need to read it a few times for it to sink in; in fact whilst I await delivery of the valve I can spend time re-reading all the information so far supplied as there is a great deal of it to absorb.

Kind regards, Col.
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Old 17th Sep 2011, 10:37 pm   #182
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Default Re: Restorers dream part 2 the chassis.

Hello again Colin,
There are seven capacitors in the frame output stage that will require replacement. They will all be leaking causing the distorted display seen in your picture.
2 X .01uf. 2 X .1uf. 1 X .25uf 1 X .001uf 1 x .02uf. V13 on the circuit is the 30PL1 frame oscillator and output valve. It is a triode pentode or two valves within the same envelope.
T2 is the frame output transformer, the large black painted transformer with the metal cased [it was originally] .02uf mounted across it's tags. 30PL1 data attached. See if you can identify this with the circuit. Great fun! Regards, John.
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Old 18th Sep 2011, 2:31 am   #183
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Default Re: Restorers dream part 2 the chassis.

Hello Col,

I think you might find these books interesting and useful! They are a series of four BBC Engineering Training Manuals by S. W. Amos and D. C. Birkenshaw titled Television Engineering and published by Wireless World (Iliffe Books).

Volume 1. Fundamentals - Camera Tubes - Television Optics - Electron Optics. First published 1953.
Volume 2. Video-Frequency Amplification. First published 1956.
Volume 3. Waveform Generation. First Punblished 1957.
Volume 4. General Circuit Techniques. First published 1958.

They are still available (probably second-hand) from various sellers. I have all four and found them to be very useful. Volume 1 should do to begin with.

Regards,

Dave.
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Old 18th Sep 2011, 10:03 am   #184
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Default Re: Restorers dream part 2 the chassis.

Hi,

I was up early this morning with a plan of action. I was going to identify the area of the circuit diagram to work on and also to gather all the components required whilst I awaited delivery of the valve.

What can I say John, not only a top class guy but a mind reader as well. When I logged on there it was staring me in the face; thank you so much for taking such a great deal of trouble upon my behalf. I've printed the details off and even compared your circuit section against the full circuit diagram just to see where it fits in.

I believe I have already replaced the cap across the transformer and possibly some of the others highlighted but I'll take my time and work through the section but this time as I replace a cap I'll switch on to see what difference it makes.

Thank you Dave for the book details; I'll keep my eyes open for copies as they would make interesting reading during winter when I am frozen out of the workshop and garage.

With such comprehensive guidance I'm guaranteed success and there I was thinking I would be in for many months of frustrating work as I struggled through my first TV chassis; I'll never forget how long it took me to restore my first vintage radio working from scratch and not knowing forums existed. Although I am a total novice to TV work I think this could be unfair to what I would call a genuine TV novice starting from scratch. I already have decent background knowledge of most of the components and even rewind my own transformers so in reality I hit the ground running and although I don't fully understand everything I'm doing on this chassis I can grasp a lot of it.

I am finding working on this chassis a lot different to working on a radio chassis as there are so many other sections and circuits involved but it is fascinating work. There are also more controls on a TV and I need to learn the function of each in relation to the circuit diagram; I can't believe all this started with a simple question.

Kind regards, Col.
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Old 18th Sep 2011, 2:39 pm   #185
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Default Re: Restorers dream part 2 the chassis.

Quote:
Originally Posted by Amraduk View Post
I think you might find these books interesting and useful! They are a series of four BBC Engineering Training Manuals by S. W. Amos and D. C. Birkenshaw titled Television Engineering and published by Wireless World (Iliffe Books).

Volume 1. Fundamentals - Camera Tubes - Television Optics - Electron Optics. First published 1953.
Volume 2. Video-Frequency Amplification. First published 1956.
Volume 3. Waveform Generation. First Punblished 1957.
Volume 4. General Circuit Techniques. First published 1958.

I have a set of these books. They were supplied, FOC, to BBC tv technical assistants during their training period in the late '50s and early '60s. Very good for the fundamentals of TV engineering but biased towards the broadcasting side of the industry. The explanations are very well done and not confusing. A good set of books.
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Old 19th Sep 2011, 4:46 am   #186
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Default Re: Restorers dream part 2 the chassis.

Hi Colin, I've also been following this thread with interest and have to say well done for coming this far and not giving up. Your jump into the world of vintage television was a big one and good on you for sticking at it this far. We never got TV here in New Zealand until the 1960's so as far as old TV sets go I've never seen anything like your TV in the flesh!
Keep up the good work, you're doing fine
Cheers!
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Old 19th Sep 2011, 8:55 pm   #187
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Default Re: Restorers dream part 2 the chassis.

Hi,

Thanks Dave and Brian regarding the books. I've just had a look through my "library" and have found two TV books to give me a start and these are;

Television explained by W.E.Miller Fourth edition published by Trader Publishing Co. Ltd.

The Mazda book of Pal Receiver Servicing by D. J. Seal.

For my purposes I believe the "Television Explained" book would be of more use as the Pal book covers colour TV.

I'm pleased you find the thread interesting Glen and many thanks for the encouragement. I seldom quit a project once I start unless it is through something beyond my control such as being quoted £150 to have a coil of resistance wire made when I was experimenting making my own potentiometer tracks and the track in question required three different resistance wires but I plan to go back to this later as I found the project most interesting and unusual.

I managed to squeeze an hour in the workshop this morning and changed the 500uF electrolytic which de-couples the cathode of V13B (30PL1). Oh my poor head!! This looked such an easy job on the circuit diagram; just two connections to play with so where did the other three come from that were connected to the tags? The cap tags were bridged with resistor which initially threw me until I realized that this was the 330R resistor conveniently soldered to the negative which also had another wire directly to chassis. I now had the wire to V13B; the 330R resistor and the chassis connections sorted but why is the big diode D3 connected directly to the neg of the cap? Again I then realized this was a convenient chassis connection so it all started to make sense until I had a good look at D3.

On the V13A end of D3 I think I've located both the 47K resistor and 330P cap (small black Hunts) but on the other end I couldn't locate a 0.01uF cap in series with the 47K resistor but at this point I had to pack in so more tracing for tomorrow. I was going to fit a 330uF 35V electrolytic but found a nice big 470uF 100V electrolytic that fitted perfectly into the chassis hole vacated by the original. I tested the new electrolytic before installing it. Before leaving the workshop I briefly switched power on and obtained a decent test card but still with only half screen height and left it at that. I took the opportunity to replace the 330R resistor using a new 2W item the original was well within spec which surprised me; I had snipped a lead but as I was replacing the cap anyway thought I might as well replace the resistor.

I took Bron out for some well deserved retail therapy so that took care of today.

In a situation such as this where the valve PY32 has been removed and a direct short added to retain heater chain continuity and the rectifier diode added I'm advised not to run the chassis too much. Is this because the rest of the heaters are receiving the voltage no longer being used by PY32; I've noticed the other heaters are well lit up. I've been thinking about this being awake again last night and ask the question if I would be able to run this chassis indefinitely by dropping the heater chain voltage by 29V in this case by the addition of a suitable series resistor? I note the heater is rated at 29V 0.3A (PY33).

Yet another question on the same subject of rectification; this particular valve is an half wave but I've noticed many? of my vintage radios employ a full wave rectifier valve; would it be possible for me to do a similar thing should a full wave rectifier valve expire? On this PY32 only a single rectifier diode has been installed and to be honest I've not checked the two pins Mike soldered it to but but thinking about it; bridging the cathode/anode? If so would two rectifier diodes connecting the cathode to two anodes of a full wave rectifier give the desired output?

I was aware a rectifier could be bridged but have never actually witnessed it being done until Mike did it on this chassis; I could of course ask Mike for clarification and he would be delighted to oblige but the answer would be lost for other novices hence I'm asking on the forum because if I'm asking I'm sure other novices too will be interested.

I've used solid state rectifiers previously whilst making PSU's and an alternative would have been to use four rectifier diodes but it's possible the applications are different?

Before I forget; the diode D3 is highlighted by John for replacement and I note the original which looks like a fat resistor with a couple of colour bands has tiny arrows pointing towards V12A; when I install the new diode am I correct in thinking that the direction of the arrows has now been replaced by a band around one end? It's ages since I did anything with rectifier diodes and I believe the direction can be checked easily with a DMM on resistance as it will only read one way? My thoughts are scrambled at the moment as it's been such an hectic day but I can't let go of this project as it has such a tight grip on me.

Tomorrow is another day and I have lots and lots of printed information already kindly supplied to work from. Once I can run the chassis for a decent period I'll try adjusting the picture height again but a quick attempt this morning failed.

Kind regards, Col.
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Old 19th Sep 2011, 9:49 pm   #188
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Default Re: Restorers dream part 2 the chassis.

If a suitable resistor is used to drop the voltage used by the PY32 heater it can be left out of circuit indefinitely. The required value is 97R (100R would be fine) and it would dissipate almost 9 watts. In other words it will get very hot. If you don't have a replacement PY32 and the heater of the old one is still intact you can disconnect the anode and cathode and just use the heater. The silicon rectifier and surge limiter resistor can then be bodged in under the chassis but NOT using the anode and cathode pins of the PY32 valveholder.

It isn't possible to use a fullwave rectifier. Well not easily. A few much later colour TVs did use a bridge rectifier directly from the mains. This has the unfortunate effect of leaving the chassis at half mains potential whichever way round the mains is connected. The T311 was designed for halfwave rectification so leave it that way.

Many DMMs will not give good results when testing diodes. This is because the voltage they apply is not sufficient to turn on the junction. Quite a few DMMs have a specific diode test range which can apply a higher voltage. The display then shows the forward voltage drop which is useful to distinguish between germanium (0.3 to 0.4V) and silicon (0.6 to 0.8V).
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Old 19th Sep 2011, 10:00 pm   #189
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Default Re: Restorers dream part 2 the chassis.

Hello Col,

Quote:
Originally Posted by Retired View Post
I've just had a look through my "library" and have found two TV books to give me a start...

For my purposes I believe the "Television Explained" book would be of more use as the Pal book covers colour TV.
I'm not familiar with either book but, yes, I would think 'Television Explained' would be more useful than the PAL book, although the basic principles are the same.

Quote:
On the V13A end of D3 I think I've located both the 47K resistor and 330P cap (small black Hunts) but on the other end I couldn't locate a 0.01uF cap in series with the 47K resistor but at this point I had to pack in so more tracing for tomorrow.
Although the circuit shows the capacitor connected to the diode, it's possible that the cap and resistor have been transposed, as they're in series, it makes no difference which way round they are!

Quote:
In a situation such as this where the valve PY32 has been removed and a direct short added to retain heater chain continuity and the rectifier diode added I'm advised not to run the chassis too much. Is this because the rest of the heaters are receiving the voltage no longer being used by PY32;
Yes, that is so.

Quote:
I've noticed the other heaters are well lit up. I've been thinking about this being awake again last night and ask the question if I would be able to run this chassis indefinitely by dropping the heater chain voltage by 29V in this case by the addition of a suitable series resistor? I note the heater is rated at 29V 0.3A (PY33).
By all means, you can do that. You would need a resistor of 97 ohms, so the standard value of 100 ohms would do nicely. It would need to be rated at 8.7 watts, so I would use at least a 12 watt resistor.

Quote:
Yet another question on the same subject of rectification; this particular valve is an half wave but I've noticed many? of my vintage radios employ a full wave rectifier valve; would it be possible for me to do a similar thing should a full wave rectifier valve expire? On this PY32 only a single rectifier diode has been installed and to be honest I've not checked the two pins Mike soldered it to but but thinking about it; bridging the cathode/anode? If so would two rectifier diodes connecting the cathode to two anodes of a full wave rectifier give the desired output?
You could do that but the semiconductor diodes would give a somewhat higher supply voltage than the valve rectifier, which would need to be reduced to the correct value.

Quote:
Before I forget; the diode D3 is highlighted by John for replacement and I note the original which looks like a fat resistor with a couple of colour bands has tiny arrows pointing towards V12A; when I install the new diode am I correct in thinking that the direction of the arrows has now been replaced by a band around one end?
Yes, that's correct, the arrows point to, and the band indicates the cathode of the diode.

Quote:
It's ages since I did anything with rectifier diodes and I believe the direction can be checked easily with a DMM on resistance as it will only read one way?
Yes, you can. Connect the meter positive terminal the anode and the negative terminal to the cathode and you will get a low reading, about 500 ohms or so, swap them over and you should read infinity, or at least a very much higher reading!

Regards,

Dave.
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Old 19th Sep 2011, 10:05 pm   #190
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Default Re: Restorers dream part 2 the chassis.

Hello Jeffrey,

I see you beat me to it, replying to Col's post!

Quote:
Originally Posted by ppppenguin View Post
It isn't possible to use a fullwave rectifier.
If you re-read Col's post, I think you'll see that the full wave rectifier in question, is in some hypothetical piece of equipment that uses full wave rectification! The question was, can the same be done with a full wave valve rectifier (should it fail) as with a half wave rectifier valve but using two diodes as appropriate!

Regards,

Dave.
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Old 19th Sep 2011, 10:13 pm   #191
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Default Re: Restorers dream part 2 the chassis.

Quote:
Originally Posted by Retired View Post
Yet another question on the same subject of rectification; this particular valve is an half wave but I've noticed many? of my vintage radios employ a full wave rectifier valve; would it be possible for me to do a similar thing should a full wave rectifier valve expire? On this PY32 only a single rectifier diode has been installed and to be honest I've not checked the two pins Mike soldered it to but but thinking about it; bridging the cathode/anode? If so would two rectifier diodes connecting the cathode to two anodes of a full wave rectifier give the desired output?
Kind regards, Col.
I think Jeffrey has his wires crossed slightly on this second question, there are very few TV's of this era that would use a full wave rectifier, even my ferrantie set with mains transformer is still only half wave rectified. but if we are talking radios with mains tx and full wave rectifier then yes two diodes can be used to replace a full wave rectifier, just as you described. done it a number of times on sets where the correct rectifier valve was unobtainable. No resistor will be needed on the filament side as it's transformer fed but if it's a permanent fix then a serge limiting resistor should be fitted. otherwise you risk killing the smoothing caps.
Not really relevant to your excellent TV resto but you did ask.

keep up the good work and keep asking questions

Jay

Edit: looks like others have beet me to it.
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Old 19th Sep 2011, 10:46 pm   #192
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Default Re: Restorers dream part 2 the chassis.

I admit I may have misunderstood Col's point about fullwave rectification. It's nearly always possible to replace valve rectifiers with silicon. Usually all that's needed is a series resistor to limit the surge current and get the DC voltage about right. In a few cases the presence of HT before the valves have warmed up could be a problem.

Most AC only valve radios use biphase rectifiers. If only because it was cheaper and easier to have centre tapped transformer winding than an extra pair of valve rectifier diodes. AC/DC sets nearly always used half wave rectifiers. Soild state changed the rules as a bridge rectifier is cheap and easy.
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Old 20th Sep 2011, 9:01 am   #193
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Default Re: Restorers dream part 2 the chassis.

PY33 posted yesterday. I would not suggest using a silicon diode in place of the slow heating rectifier. The H.T. will rise to a very high level until the line timebase becomes operative putting a strain on the smoothing block [as mentioned by Jay] and possibly the TV/radio switch.
I was going to mention the 500uf bias cap but thought this might confuse due to the fact that in some receivers, Ekco combined this with a 2uf H.T. decoupling capacitor.
You should receive the correct rectifier this morning Colin. Prolonged use with the heater shorted out will over run the valves and tube. This was a test situation only. It may be a little bit less 'lively' due to the correct heater chain current with the correct rectifier but this will sort itself out as you bring the receiver back to performance. Regards, John.
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Old 20th Sep 2011, 9:05 am   #194
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Default Re: Restorers dream part 2 the chassis.

When the BY100 appeared in the late 1960s, RS used to supply these in a packet with a 10 ohm 5 watt wirewound, and fitting instructions (!).

This was mainly for radio use, but often moving the dropper connections on a TV would get past overrunning the heater chain, but there's the instant warm-up problem, so not a good idea.

The BY100 was soon replaced by the BY127.
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Old 20th Sep 2011, 11:13 am   #195
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Default Re: Restorers dream part 2 the chassis.

Hi,

Thank you Jeffrey and I believe it was me who added the confusion as I have lots of bits of information flying around in my head rather like pieces of a jigsaw puzzle and I’m taking this excellent opportunity to connect a few up. Rectification plays such a huge part in this type of work and like me I’m sure other novices will appreciate it being discussed in great detail the way it is being discussed here.

Yes I was actually referring to my previous vintage radio work where I’ve encountered full wave rectifiers and tried to connect the method shown to me by Mike in by-passing the half wave rectifier on this chassis and wondering if the same method but using two diodes could by-pass a full wave rectifier as used on my radios.

You also make a very valid point Jeffrey about using a rectifier without emission but retaining continuity through its heater and leaving the valve in place allowing the heater chain to run as normal but then to disconnect the anode/cathode and bridge using a diode; I hadn’t thought of this but what a great bit of useful information and something so easily overlooked by a novice like me.

Regarding your information about using a DMM to check a diode being unreliable due to the very low voltage in the instrument would a very simple home made circuit comprising of a 9V battery; series resistor and led be better? Having just asked this question it leads to yet another question as a thought has occurred to me; would using a “led” in this situation work because a led is a diode and would something like a panel lamp be a better choice. It’s so easy to trip on even such a simple thing.

One thing I would like to clear up is that I stated Mike had made the connections to the pins of the valve which is a slip on my part in terminology as I should have stated the connections were made to the tags on the valve holder.

Thank you also Jeffrey for the extra information in your later post which I’ve duly noted.

Once again Dave many thanks for adding such a comprehensive reply and I’m delighted that I appear to be on track as I have a great deal yet to learn and to get the basics right is a huge step in the right direction.

In an earlier post; Jeffrey kindly added that it would possibly be better for me to concentrate on getting all the valve heaters working before connecting the HT up; as with my questions regarding rectification such a task as this would be easy to an experienced person and in this case Jeffrey explained how to go about it but otherwise I would have struggled; to me this is what makes having direct access to experts much better than spending many hours reading whilst trying to find the information then attempting to put the information to use.

Thanks Jay for your post and the kind words which are appreciated; yes I did ask and would prefer duplicated replies rather than no reply.

One thing I did ask Mike about was what is a Varite? It obviously looks like a resistor on the circuit diagrams but it’s not a normal resistor nor is it a pot. Mike explained that yes it is a resistor but a special kind that changes resistance due to its temperature rise in use making it in effect an automatic variable resistor. I’ve come across a similar thing on vintage radio with line cord droppers; this being where the supply cord works in the same way and at first I was quite alarmed by how heated the cord became. Yet another piece of the jigsaw in place. A Varite is usually very reliable.

I’m sure you will all understand when I say this kind of work does not come naturally to me and that I have to work extremely hard to achieve any kind of success. I have my own personal life; trying to get to grips with restoring a wreck of a TV and also trying my best to string coherent sentences and questions together to add to the forum with everything whizzing around in my head at once; it’s a wonder I don’t explode and to compound all this I’m awake in the middle of the night trying to keep up and resolve problems that are bugging me. I could very easily take the soft option and become merely a robot with all you experts pushing my buttons saying do this; do that but it would be grossly unfair on you and idle of me and by doing so I would not be able to give a bit back by way of thanks to everyone who has put themselves out on my behalf.

It takes me a lot of time to add my story to the forum; I’m writing about a subject I know very little of; coming to terms with TV “language” doing the restoration in real time and just to cheer me up I’m doing this in front of the world acutely aware of my ignorance and inexperience of the subject. Each time before posting I always run the grammar/spell check and re-read what I have written in the hope that at least it makes sense to me.

I did a similar thing whilst restoring the cabinet but at least with the cabinet I had some good basic experience to fall back upon even though the cabinet looked beyond restoration. The cabinet was worse to do because I was on my own covering work few have done previously but I won through and it gave me immense joy to stand back and see it completed; not just a restoration but a totally customized cabinet veneered to my liking.

I would say to all novices I’m just like you and face exactly the same problems as I tackle something new; long ago I left my own personal comfort zone and now enjoy walking on the wild side as my projects become increasingly impossible at first sight but I find if I tackle them bit by bit just nibbling away and asking all the questions on this excellent forum somehow with a great deal of patience I succeed so please have a go; you too can do exactly the same thing as me and what pleasure and joy there is to be had.

We have a hospital appointment later today so hopefully I can get into the workshop tomorrow; I find it difficult to pop into the workshop and pick up where I left off as it takes me a little while to settle in and even longer to wade through the pages of excellent advice I’ve been given. At this point I feel more confident of success than failure with this chassis.

As I've been typing and finally pasted onto the forum I'd like to say a huge thank you to John and look forward to receiving the valve hopefully today and to thank both John and Mike for the information they have given.

Once I realized the valves were being over run by noticing how brightly the heaters were glowing I've only briefly run it up on power in fact yesterday I only switched on just to check the new 500uF cap was installed correctly and this also was my reason for enquiring about adding a series resistor in the heater chain to drop the voltage. Working on this chassis I've learned a great deal in a very short time and even become much more informed about rectification; won't it be something to see this set fully completed and working?

Kind regards, Col.
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Old 20th Sep 2011, 2:33 pm   #196
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Default Re: Restorers dream part 2 the chassis.

Quote:
Originally Posted by Amraduk View Post

The question was, can the same be done with a full wave valve rectifier (should it fail) as with a half wave rectifier valve but using two diodes as appropriate!

Regards,

Dave.
I don't see why not as long as there is something like 100 ohms in series with each diode to limit surge current.

Cheers
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Old 20th Sep 2011, 2:38 pm   #197
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Default Re: Restorers dream part 2 the chassis.

Hi,

Firstly; John I'm in your debt; thank you so much for your generosity; the valve and knob arrived safely just a short while ago and the valve is now installed and working. I didn't forget to remove the short or diode so I'm back in business once again.

I need to go out shortly but wanted to let you know before I set off. I've tried just about every permutation in twiddling the controls and the double picture is about as good as it gets full screen with the rear height adjustment on maximum.

I've also included a couple of pictures of the LOPT area; as it was and as it is now.

Kind regards, Col.
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Old 20th Sep 2011, 4:35 pm   #198
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Default Re: Restorers dream part 2 the chassis.

Rather than a resistor how about a thermistor in series with the diode. Wouldn't this stop the instant switch on high voltage business?
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Old 20th Sep 2011, 4:38 pm   #199
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Default Re: Restorers dream part 2 the chassis.

No. It will limit the surge but the reservoir cap will charge to 1.4x230V until the valves start to take current.
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Old 20th Sep 2011, 5:46 pm   #200
Boom
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Default Re: Restorers dream part 2 the chassis.

How come? Surely the thermistor would be almost o/c until the HT rail starts taking current.
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