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Ultra V815

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6.3volts
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Where to start!

Ok, I'm 14 years old and walking home with the chassis of a tv set donated by my school on the understanding that I make it go away. Of such stuff are life-changing moments made! My Dad and I always had a wide interest in things technical and scientific but this was a whole new avenue. From this sprang my lifetime interest in such things and hence my eventual presence on this forum and in the home of one of our members.

At this point I would like to praise our member, Rich, known as "slidertogrid " for his generous spirit in allowing his Ultra tv set to pass into my care having fully understood my 45 year long hope that I would have the chance to own another example of this uncommon set. The chassis I had as a lad was long ago sent, in my absence, to landfill and I apologize to you all if this thread is looking a bit romantic. I fully intend to get technical from now on.

So down to business! Having picked up the set from Peterborough yesterday my thoughts today have turned to the fact that I am now the owner of a very old Mazda CRT. Now having gotten this far I dive right in this morning with a heater test which shows 0.3amps at 12.6 volts and a nice glow so maybe the heater is ok and the tube is not full of air. Next I apply a dc voltage between cathode and g1 and am rewarded with 45 microamps at 5.8 volts so far so good. I'll leave it soaking for a few hours now and have already noticed the current starting to creep up. It's looking good and I hope to add some pics later to show the set full of dust and untouched except for the U801 having been replaced with a pair of PY82 rectifiers. Not sure if this is a past repair or a factory mod.

 
Posted : 31/03/2013 2:31 pm
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Katie Bush
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...untouched except for the U801 having been replaced with a pair of PY82 rectifiers. Not sure if this is a past repair or a factory mod.

Very possibly an "in service repair".. I can remember my granddad making similar mods to sets, back in the 1960's.. Sometimes, it was cheaper than replacing the single valve, and sometimes, the owner wanted the set back in time for the "big match" or whatever, with only PY82s available.

I could imagine the U801 being a bit hard to find these days? You could always "retro fit" a PY33, or 32 (coke bottle) if you wanted something closer to the original.

Marion

 
Posted : 31/03/2013 4:23 pm
slidertogrid
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So the first signs are good?

It was a pleasure to meet you, Jonathan,I am sure we could have talked " old tellys" all day! I'm so pleased the Ultra has gone to such a good home! I shall follow your progress with great interest.

Regards, Rich.

 
Posted : 01/04/2013 12:22 am
6.3volts
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First of all thank you Katie I bought the U801!.
Some slight progress and a few pics to start the process of restoration. At this stage I can't decide whether to fully restore the wormy cabinet or just tidy up the scratches and leave it more or less original. Similarly the space I was expecting a U801 to be taking has a pair of PY82s in it and although not as per trader spec the two valve bases look to have been riveted in to factory standard even though some repair work to the dropper resistors has clearly not. I'm open to advice on this one as I have not decided yet what to do and will include visuals at the end. This looks to be a later set as it has the cutouts for the band3 tuner and I wonder if Ultra had moved away from the slightly iffy U801 to a more reliable set up.
The CRT looks as if it is not one of Mazda's best efforts. The internal silvering at the screen end has a lot of what look like watermarks / old staining under it as if the glass was not properly clean when deposited. Also a few spots of silver have dropped of and are presumably loose inside the envelope. Hopefully they will keep out of the way ! Speaking of standards I have counted 9 air bubbles in the screen glass is this a record? Answers on a postcard----or should that be a testcard?
So far I have air-blown the chassis----interesting note here; I am used to the smell of old telly and radio dust but this is the only example which smells very strongly of coal smoke/soot! I am guessing it was sited next to a smoky open fire. Reminds me of Boxing Day sat in Aunty Polly's front room praying no more coal smoke would chuff out of the fireplace into a room already full of adults smoking pipes and cigars.
Anyway back to the set. Pretty much original apart from a few wire wounds and the mod to the rectifier circuit. I will investigate what the heater chain looks like now as two PY82s do not replace an 80volt 0.2 amp valve.
The CRT is out and safe so I can look underneath and everything is as it should be so I will start with the ht supply and work on from there.
Jonathan.

 
Posted : 02/04/2013 12:58 pm
6.3volts
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A bit of advice please. The first thing that looks well wrong here is a mod to the line output valve wiring. The G2 feed of 10k has been removed and replaced with a wire link then a lash-up of 2.7k wirewounds has been taken to the G2 pin. The emission of the 20P4 is up there with the best so I'm left wondering if the repairer was very confused or he knows something I don't. Is this a way of boosting performance? It looks to have been in use for a while before the set was laid up. Can any of you shed any light on this before I put it back to the correct state. The scan shows exactly what should be on the left and what actually is on the right.
Jonathan

 
Posted : 03/04/2013 11:49 am
mark pirate
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Wow, that really is full of soot

My Bush TV24 was in a similar state inside, in fact the left side of the cabinet was slightly scorched, so must have been right next to an open fireplace in it's younger days, once the layer of soot was removed, the chassis was in surprisingly good shape.

Don't worry about the bubbles in the glass, my 1950 Ferguson is just as bad, it really worried me when I had to remove the tube, I was much happier to have it back in place behind the implosion shield!

The picture on the set is really good despite the bubbles, one of which is visible at the bottom of the screen.
Just handle with great care.

 
Posted : 03/04/2013 11:49 am
Anonymous
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A bit of advice please. The first thing that looks well wrong here is a mod to the line output valve wiring. The G2 feed of 10k has been removed and replaced with a wire link then a lash-up of 2.7k wirewounds has been taken to the G2 pin. The emission of the 20P4 is up there with the best so I'm left wondering if the repairer was very confused or he knows something I don't. Is this a way of boosting performance? It looks to have been in use for a while before the set was laid up. Can any of you shed any light on this before I put it back to the correct state. The scan shows exactly what should be on the left and what actually is on the right.

The left is correct. There is no advantage and lots of disadvantage to the right. The decoupler is essentially doing nothing on the right and also the gain will reduce at peaks of g1 volts with the version on the right*. A grid series resistor without decoupling is only used on a signal grid to try and reduce parasitic oscillation due to layout (grid stopper).

[* Gain is related to g2 volts. At low anode voltages the g2 current increases and thus g2 volts decrease. Hence g2 decoupler is usually low impedance at operating frequency so the g2 volts is constant and also g2 to Anode has gain, so you want additional decoupling at g2 pin to avoid injecting supply noise. If the anode load is a transformer then the effect of g2 volts vs g1 drive is more complex. Unless you are doing an exotic tetrode oscillator a series resistor on g2 without decoupling, like on the right, is not a good idea. The other things you can do with g2 is use it for DC gain control or feed part of the anode signal (via resistor or transformer tap) which gives negative feedback and thus so called "Ultralinear" operation. Feed too much Anode signal and the output impedance drops, eventually with 100% (g2 and anode connected or low value resistance) you get a Triode characteristic and 20% to 50% more peak power, but more distortion.]

 
Posted : 03/04/2013 12:14 pm
Katie Bush
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From what I can see in the photos, I'm convinced that your set has always had that pair of PY82's.. It certainly looks like factory fitted.

I know that Bush also made changes to production specs, and I even have circuit diagram for the TV53 which shows a single PY33, and then a later diagram shown two PY82s in parallel.. Then, as I've already said, my granddad modified a few sets from single PY32/3 to parallel PY82s.

Marion

 
Posted : 03/04/2013 10:52 pm
6.3volts
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Katie. I have found reference to a later manufacturers mod with two rectifiers in place of the U801. The heater chain is also modified as these are in series with the efficiency diode as per manufacturers spec.

The mod to the G2 of line output 20P4 is very crudely done so is definitely not original. I could not see how it was possible for this circuit to operate properly in spite of being a well used repair hence my question in case I am not as well informed as I'd like to think.

I have reformed the major electrolytics and hope to move on to the individual components tomorrow.
Jonathan

 
Posted : 03/04/2013 11:28 pm
slidertogrid
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The layer of soot could mean that the set lived near a railway, I had to replace the ceiling upstairs in my shop back in the early eighties, the shop was in a row of houses that had been railway workers houses for many years, there was more than 2 inches of soot on top of the old ceiling which I was told had built up over the years from the railway about 500 yards behind the shop.
I don't know if this would get into the houses so maybe this set spent some time stored in a loft.
I will see if the friend I bought it from can find out any more.
That Mazda bomb.. full of air bubbles! scary!
:eek:
Rich.

 
Posted : 04/04/2013 12:15 am
Refugee
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The layer of soot could mean that the set lived near a railway, I had to replace the ceiling upstairs in my shop back in the early eighties, the shop was in a row of houses that had been railway workers houses for many years, there was more than 2 inches of soot on top of the old ceiling which I was told had built up over the years from the railway about 500 yards behind the shop.
I don't know if this would get into the houses so maybe this set spent some time stored in a loft.
I will see if the friend I bought it from can find out any more.
That Mazda bomb.. full of air bubbles! scary!

Rich.

That soot collected in the lofts of all houses that were down wind of big cities due to the making of steel, pottery and coal gas.
I removed several cubic meters of dust in order to get loft insulation to fit in my house.

 
Posted : 04/04/2013 1:33 am
6.3volts
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Just a quickie to say that following a cap replacement exercise and a few other bits of remedial work I have sound from the speaker when a modulated signal is injected at the aerial socket. (Can't wait to get my Aurora back from loan to the Ideal Home Show).
I'm now moving on to look at the LOPT which is covered in a thick layer of carbon muck that pervaded the whole set. I quite fancy cleaning the worst of this off before giving it chance to arc and carbonize the insulation. Also I will test the 'Visconol' smoothing cap before trying to operate this part of the set. Hopefully I will post some pics tomorrow.
Jonathan.

 
Posted : 05/04/2013 12:02 am
6.3volts
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Here are more details of the set. One pic shows some of the new caps in the IF area and a few more of the LOPT before cleaning it. The Visconol eht cap claims to be a dead short at high voltage so I will try a nos one before deciding what to do next about that. As you can see it is built in to the lopt assembly. So far I have remade the connection to LOP valve by replacing the green-corroded red wire. All windings seem to be intact and I hope to have some life out of it as soon as time allows.

 
Posted : 06/04/2013 12:39 pm
mark pirate
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The Visconol eht cap claims to be a dead short at high voltage so I will try a nos one before deciding what to do next about that

I would not bother trying a NOS Visconal, as it is likely to be faulty, or will fail after a few hours, there is a seller on ebay that does HV caps at two for a fiver including postage, I used one to re-stuff the old Visconal on my 1948 Baird set.

 
Posted : 06/04/2013 8:25 pm
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Next I apply a dc voltage between cathode and g1 and am rewarded with 45 microamps at 5.8 volts ----- so far so good. I'll leave it soaking for a few hours now and have already noticed the current starting to creep up

How much current should a good tube pass when tested like this? I have gone to 5mA but suspect that might be OTT.

 
Posted : 06/04/2013 9:52 pm
6.3volts
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Back in the workshop after a break to catch up with the world outside!
I have cleaned the LOPT as best I can with white spirit and taken a chance with my NOS Visconol.
Early results are a bit mixed with full boost ht of 400 odd volts but my home made eht meter showing only 6kv. with a bright rectifier heater. Interestingly the overwind is running stone cold as is the entire lopt winding.
I suspect the time is right to mount up the CRM141 and look for first light.
I now have my trusty Aurora back from the Ideal Home Show so hopefully I can move on a bit.
Pics to follow.
Jonathan.

 
Posted : 15/04/2013 1:20 pm
6.3volts
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Sorting out the frame circuit first. Several caps are almost perfect shorts and some very high resistors. Thought I would see to this before connecting everything back as the frame oscillator works from boosted HT.
Jonathan.

 
Posted : 16/04/2013 9:44 am
6.3volts
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First Light at last.
After sorting a few more caps etc I set the tube in place and lit the fuse. I was rewarded with a raster and nothing bad happened. After the usual fiddling with ion traps and centering the picture things were looking quite good so the next shot shows the first picture on this crt for many years. A couple of tweeks and I have a pretty good circle on my test card but a weak and slightly fuzzy resolution. I am asking for advice here as the EHT is running at about 4Kv intead of 10Kv and the boost HT is 380 instead of 410. Could this be a short in the overwind? Running at the wrong frequency I have had as much as 6KV and 500v HT out of it. I thought it would have improved with a new LOP valve and Eff Diode but remains the same. Would I have a linear scan if there were shorted turns in the LOPT? All advice welcome. Thinking back I wonder if the bodge on the LOP valve G2 was an attempt to boost the system.
Jonathan.

 
Posted : 21/04/2013 1:25 pm
slidertogrid
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Hi Jonathan,

It's looking good! The tube looks like a goodun as well. I would be suprised if there wasn't a lack of width and signs of heating in the transformer if it had shorted turns, but I confess I am not speaking from experience here.
Certainly on later dual standard sets a short in the overwind affects linearity and pulls the width in severly, worse on 625 usually.

I don't know if it would affect an earlier circuit differently as the tranformers construction is different?
How stable is the EHT ? I would expect poor regulation and a underrun EHT rectifier heater possibly .
Great to see a picture on the set, and so soon!

The world is certainly a very different place now to when this old set last reported! It might be a good idea not to show it modern programmes, the shock might kill it...

Regards, Rich.

 
Posted : 21/04/2013 2:03 pm
6.3volts
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Hi, Rich, The EHT is dead stable as is the boost HT. It has me fooled at the moment hence my request for advice.
Regards Jonathan.

 
Posted : 21/04/2013 3:24 pm
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