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Old 7th Sep 2016, 10:38 am   #41
paulsherwin
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Default Re: Hi From Cathy Lissen/Eveready Kenilworth??

It's all looking good so far. The o/c output transformer may be why the radio went out of use and there may not be any other actual faults, just age deterioration.

Examine the transformer carefully. They sometimes go o/c close to the solder tags and can be repaired quite easily.

If you need to replace, don't be overly concerned about the turns ratio as this is a lot less critical than is often assumed. There will be an ideal ratio depending on the ideal anode load impedence and the speaker impedence, but you can be as much as -50+100% out and still get reasonable performance. The only effect will be a reduction in maximum volume which may not even be audible.
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Old 7th Sep 2016, 10:49 am   #42
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Default Re: Hi From Cathy Lissen/Eveready Kenilworth??

Thanks for recent replies. Yes I have a mains 1kVA isolation transformer and various 'Variacs', so that I can gradually 'wind up' the voltage, after I have isolated the secondaries. I am surprised that the Trader Sheet doesn't quote AC secondary outputs. Always used to ask our 'trainees' How come you can get greater than 240 vac out of a Variac given that the input voltage is measured at 240v? Used to cause some head scratching that one, as they assumed it's just a simple potential divider (which it isn't) ! If I add power resistors to 'load' the output windings, then what is a realistic current to draw to give the Tx a 'bench soak' before proceeding any further ? Adding up the anode currents I was thinking 60 mA for the HT winding or is this too simplistic or excessive? I won't do anything without the blessing of you guys.

BTW my old pal Les, a radio amateur, who sadly passed away a couple of years back, and gave me that NOS audio Tx, used to call transistors 'three-legged-fuses'. He would have been in his element with this radio. He used to go into a shop on Hedon road in Hull as a boy to get his valves tested & in the '70's I remember a lady in that same shop still carried out valve testing as I gather her husband was no longer around.
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Old 7th Sep 2016, 10:56 am   #43
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Default Re: Hi From Cathy Lissen/Eveready Kenilworth??

Hi from Cathy ... told you he would 'warm' to this project . A big thank you to everyone on here for spurring him along. I got home last night at 10.45 to find him 'tinkering' ..just like my dear old dad used to do when I was small. Certainly brought back fond memories. Just can't wait for that characteristic smell of old hot valves, wood & dust !
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Old 7th Sep 2016, 11:07 am   #44
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Default Re: Hi From Cathy Lissen/Eveready Kenilworth??

Quote:
Originally Posted by cathy_vintage View Post
Thanks for recent replies. Yes I have a mains 1kVA isolation transformer and various 'Variacs', so that I can gradually 'wind up' the voltage, after I have isolated the secondaries. I am surprised that the Trader Sheet doesn't quote AC secondary outputs. Always used to ask our 'trainees' How come you can get greater than 240 vac out of a Variac given that the input voltage is measured at 240v? Used to cause some head scratching that one, as they assumed it's just a simple potential divider (which it isn't) ! If I add power resistors to 'load' the output windings, then what is a realistic current to draw to give the Tx a 'bench soak' before proceeding any further ? Adding up the anode currents I was thinking 60 mA for the HT winding or is this too simplistic or excessive? I won't do anything without the blessing of you guys.
The transformer's secondary voltages can be derived from the Trader sheet, the rectifier's anode voltages are given in the "Valve Analysis" section, they're are quoted as 264 volts AC per anode, that's 264-0-264 volts at the transformer's HT secondary connections, the unloaded voltage will be a bit higher.

The heater winding voltages can be derived from the heater voltages of the valve types used, here's one of the bibles for online valve data:

http://www.r-type.org/index.htm

EDIT: Here's the other bible:

http://www.shinjo.info/frank/

Lawrence.

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Old 7th Sep 2016, 11:56 am   #45
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Default Re: Hi From Cathy Lissen/Eveready Kenilworth??

Ash here... how critical are capacitance values in the smoothing cap block? When I used to build transistor amps in my youth the larger the capacitance value of the reservoir capacitor in the power supply the better. Or do you have to watch out for inrush if a larger value is used, on initial power up, with such a high voltage winding?
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Old 7th Sep 2016, 12:05 pm   #46
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Default Re: Hi From Cathy Lissen/Eveready Kenilworth??

Not massively critical - as mentioned earlier, high value capacitors of this age have a huge tolerance, often as much as -50%/+100%. So take the value in the circuit diagram and pick then nearest available capacitor if you can't get the exact value.
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Old 7th Sep 2016, 12:30 pm   #47
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Default Re: Hi From Cathy Lissen/Eveready Kenilworth??

Don't go wild with the reservoir cap value, too big will over-stress the rectifier valve.
Smoother can be a good deal larger than the original, the choke or resistor will limit the charge current effectively. Older sets had small values because electrolytic caps were expensive, cheaper to tolerate a little hum!
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Old 7th Sep 2016, 12:33 pm   #48
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Default Re: Hi From Cathy Lissen/Eveready Kenilworth??

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Ash here... how critical are capacitance values in the smoothing cap block?
There is a limit imposed by the valve rectifier and varies with type. The rectifier in your radio has a stipulated maximum of 8uF but that value is no longer a standard value. I reckon (unless someone disagrees) that a 10uF will be ok but no higher. You could buy 3 off, use one for C38 and two in parallel (20uF) for C37.
Les

OOPS! Cross posted
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Old 7th Sep 2016, 1:30 pm   #49
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Default Re: Hi From Cathy Lissen/Eveready Kenilworth??

Hi from Ash... just ordered up all of the electrolytics in the set, went for best quality I could find in stock. I got three 10uF Vishay 'ATOM' 450v ones for rebuilding the smoothing block cap.
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Old 7th Sep 2016, 6:56 pm   #50
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Default Re: Hi From Cathy Lissen/Eveready Kenilworth??

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Originally Posted by cathy_vintage View Post
I took out all of the valves and checked out the heaters with Fluke DMM and then powered them from my bench DC supply and they all glowed nicely ......I kept the voltage around 3v as I wasn't sure on the heater voltages but sure it must be online somewhere. The scale illumination is marked as 5.5v and I think that runs off the same tranformer tapping as the valves except the rectifier one. The recifier runs off a different tapping so I kept that down to 2v . There are no secondary voltages given in the 8453 Trader sheet only winding DC resistances. There were no shorts (or any high resistance readings) on the valves from what I could see.
All of the five valve heaters are 4 Volts. Valves 1 - 4 are B7 7-pin bases, and V5 - the rectifier, is a B4 base. Both heater windings provide 4V AC for the heaters.

The reason that the rectifier valve has a separate heater winding is that if you look at the circuit, and the depiction of the rectifier's internal construction, you will see that the valve has a 'directly heated' cathode. This means that the rectifier heater and cathode are connected internally, and as well as there being 4 Volts DC from the transformer heater winding, you will see that the raw DC HT also appears on the heater winding, from whence it goes to the smoothing choke and the reservoir/smoothing capacitors.

Hopefully, the output transformer failed while there was still life left in the valves!

Great progress so far - good luck with further steps along the road of your 'voyage of discovery' Ash!
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Old 7th Sep 2016, 7:21 pm   #51
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Default Re: Hi From Cathy Lissen/Eveready Kenilworth??

Directly heated valves don't have a separate cathode structure, indirectly heated valves do.

Not sure how one would get 4 Volts DC from a transformer winding.

Lawrence.
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Old 7th Sep 2016, 7:58 pm   #52
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Default Re: Hi From Cathy Lissen/Eveready Kenilworth??

Well got home from work and removed the O/P Tx . Stripped off the outer frame and small lamination set and unwound the secondary , photoing each layer. managed to locate both ends of the sec. but still infinite resistance so guess it is BER.

Scoured the garage for the 'RS Components' transformer and it's a 'STANDARD OUTPUT TYPE'. I have photo'd it and annotated the picture with the DC resistances of the primary and found an old RS cat. page on it. Do you folks reckon it will be any good, at least to try out the chassis? Just love that little RS man, remind me of making my first Xtal set as a schoolboy. The secondaries seem OK too but I would need my TTi bench meter to measure such low DC resistances & it's at work.

Really getting into this now!
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Old 7th Sep 2016, 8:04 pm   #53
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Default Re: Hi From Cathy Lissen/Eveready Kenilworth??

It will certainly be OK as a stopgap. Some of these RS transformers had multiple taps so you could select the most appropriate turns ratio (I see from your pic that that one does).

Many forum members have boxes full of scavenged output transformers so somebody will probably be able to help you out if need be. Cross that bridge when you come to it though - let's get it working first.
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Old 7th Sep 2016, 8:07 pm   #54
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Default Re: Hi From Cathy Lissen/Eveready Kenilworth??

That transformer should do, somewhere on this forum there might be a full spec sheet for it, I'm sure I saw it the other day. Haven't got time to look right now but someone else might.

EDIT: Post crossed.

Lawrence.
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Old 7th Sep 2016, 8:44 pm   #55
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Default Re: Hi From Cathy Lissen/Eveready Kenilworth??

Attached is the current universal transformer sold by RS. The terminal annotations are the same but not necessarily correct for your transformer but a good bet that they are. For an 8k Load for the A70D into a 3 Ohm speaker suggests using tags 1 and 3 for the primary and tags D and C for the speaker.

Looking at the circuit, I suggest you change all capacitors that see the HT, the three I have in mind are C12, C27 (both 100nF 400V) and C34 2.2uF 450V.
This assumes you have already replaced the MUST DO THAT capacitor C35 47nF 400V.

The Mica capacitors will probably be OK so don't change them just yet as alignment may be upset.

Good Luck with this one, it looks a great set to recon.
Les
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Old 8th Sep 2016, 12:04 am   #56
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Default Re: Hi From Cathy Lissen/Eveready Kenilworth??

Bear in mind that the RS output transformer is only rated at 40mA primary dc. Luckily the A70D output valve normally runs at 36mA anode current, so all is fine. It needs an 8K optimum load which will certainly be close enough to one of the RS transformer ratios.
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Old 8th Sep 2016, 8:21 am   #57
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Default Re: Hi From Cathy Lissen/Eveready Kenilworth??

Cathy here... feeling ever so slightly guilty, as I have got him totally obsessed with getting my radio working. I guess the challenge from you guys that he was 'biting off more than he can chew' is spurring him on. His posts are all gobbledygook to me but I am over the moon that he is using a part in it given to him by our sadly departed friend Les Miles.

Whist he is working on the gubbins inside I feel I should be cleaning up the cabinet. Any pointers please, like best stuff to sympathetically remove 70+ years of grime. Also the speaker front grille woven 'fabric' needs sprucing up ...any ideas here please. Same goes for the tuning scale & pointer.

I would also like to source some material for the missing rear cover. Ash says he remembers a compressed board, something like hardboard but slightly different painted black on one side. We have still not found an image of another identical radio. Ash says he took Les once to a National Museum in Bradford which he remembered having vintage sets but Googling that, there appears to be removal of exhibits from there to the V&A. What is the best place/museum to see vintage sets at, which is open to the public please?
x Cathy
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Old 8th Sep 2016, 9:23 am   #58
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Default Re: Hi From Cathy Lissen/Eveready Kenilworth??

A lot of Radio backs are made of a material like Millboard.

If you know of a local vintage car restorer you may be able to get some there or you can buy larger pieces here
http://www.woolies-trim.co.uk.

You will need to make some ventilation slots.

There are several threads on this forum about reproducing backs.

Cheers

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Old 8th Sep 2016, 10:00 am   #59
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Default Re: Hi From Cathy Lissen/Eveready Kenilworth??

Some 1930s sets had a plywood back (with slots or mesh cloth covered windows for ventilation), so that might be an option. Otherwise hardboard with holes in it - known as pegboard is a common substitute for the proper back panel.

Effectively you just need something that'll let air flow in and out, but keep fingers and pets out.

Be really careful cleaning the tuning scale - it's very likely that the dirt is the only thing holding the letters and numbers on My 1930's Invicta appears to have a gold plated tuning needle which is immaculate. The dial it moves over is some sort of cream plastic and has a cellulose based clear plastic window, which has gone yellow and shrunk a bit after 80 years or so. I chose to just use a soft cloth and plain water to gently lift the dust from those.
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Old 8th Sep 2016, 10:30 am   #60
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Default Re: Hi From Cathy Lissen/Eveready Kenilworth??

Great work so far.

As Rich said, be ever so careful with the tuning dial. Personally, I would remove it, clean the front with a rag lightly moistened with foaming cleanser, and do nothing to the screenprinted reverse except lightly dust it with a very soft brush.

Some people replace the speaker fabric with new, but unless it's too bad, you're probably best leaving it as-is, keeping the set nice and authentic.

Where to go to see old radios? Definitely the late Gerry Well's wireless museum in Dulwich, London. Have a look at the "Virtual Tour" here: http://bvwm.org.uk/
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