Ultra Model 50 (1937) Restoration
 

Good Afternoon,

Today I bought an Ultra Model 50; this will be my first pre-war radio!

It is in good external condition and looks to be intact. All of the valves and knobs are present. I have not looked under the chassis yet. It looks like a new mains lead was attached to part of the existing lead. I cut it off.

This looks to be a good radio. It has an RF amp and a three gang tuning capacitor!

I have a copy of the Trader Sheet and the manufacturers service data from the data CD.

Plan of Attack

Give the radio a gentle clean outside and out.
Clean any switches, potentiometers and valve bases.
Eventually, a new three core mains cable.

Cold checks:
Pots and switches.
Mains transformer primary and secondary resistances.
Audio output transformer primary and secondary resistances.
Check for HT shorts to the chassis.
Reform smoothing and reservoir capacitors.

If the above checks out OK I will remove all the valves bar the rectifier and check the smoothed and unsmoothed HT voltages. With my lamp limiter, of course!

That's all for the moment.

Re: Ultra Model 50 (1937) Restoration
 

Handy hint about sticky labels, smear with vaseline/margarine/butter (any fatty semi solid) and leave for a few days, then they lift off easily without the underlying varnish.

Re: Ultra Model 50 (1937) Restoration
 

It's an interesting sort of long short superhet. RF stage but no audio preamp stage.

The RF stage should improve its second channel rejection on shortwave a bit, though these days that's not very relevant.

Re: Ultra Model 50 (1937) Restoration
 

Thanks for the Vaseline tip, I have the stickers covered.

Here is the chassis. Top and bottom views.

The 8uf smoother looks to have been replaced with a 10uf plessey cap from 1974. It has a small bulge on its underside.

The mains transformer looks a bit stressed. Maybe it is just me?

Re: Ultra Model 50 (1937) Restoration
 

Does the mains transformer show any sign of waxy/bitumen drips on its underside?- it doesn't look bad in the pic but can never be sure from a distance! After decades of running, the topside insulation will look a bit dark, especially when inevitable fine airborne dust has been settled in place by sticky wax impregnation.

At some point in its life with a set this old, "that cap" and/or failing smoothers are likely to have bumped up HT consumption and transformer stress anyway, just keep fingers crossed that it didn't go on too long. Perhaps running the transformer without rectifier but with the other valves plugged in for a bit of heater loading and via a lamp limiter should be high on the list to check that there's nothing horrible wrong with it- resistance checks won't always show up shorted turns and it would be a shame to put too much work in before finding that the mains transformer was duff.

Re: Ultra Model 50 (1937) Restoration
 

Last year I restored an Ultra 49 which is the AC/D.C. version of the same set. It performed very well so I don't think you will be disappointed. The dial is a bit minimalist but the circular veneer insert on the front makes it look good. Do check out the energising coil (electromagnet) on the speaker because mine was open cicuit. Cheers, Jerry.

Re: Ultra Model 50 (1937) Restoration
 

I have just finished the cold checks of the mains transformer.

Primary is good and the heater windings are good. The HT secondary is open but I noticed bit of wire sticking out of the transformer. When this was clipped to its post the HT secondary measured 500 ohms. It looks like bad insulation caused a short between two points on the transformer. A lucky break!

I have attached a diagram.

What would be the best way to bridge these points? I have some thin kynar wire and some single core stuff.

cathoderay57, checks on the speaker and AOT will be done next.

Re: Ultra Model 50 (1937) Restoration
 

The audio output transformer and speaker coils all measure what they should.

The speaker was tested by connecting it to a 12w mini mono amplifier and it sounds good.

Re: Ultra Model 50 (1937) Restoration
 

Hi, it doesn't matter what wire you use for such a tiny length. It is carrying less than 100mA. So long as the thickness of wire looks approx the same as the stub end of transformer wire you will be OK. Be careful when you solder the extension wire to the stub end because the transformer wire might be enamelled so you might need to scrape the enamel off carefully to avoid breaking the wire again so that it will take solder. As the speaker worked on an external amplifier it sounds like it isn't an energised type which requires high voltage on the energizing coil to magnetise the speaker pole piece. Presumably then there are only 2 wires to the speaker? I haven't checked the service sheet.

Cheers, Jerry

Re: Ultra Model 50 (1937) Restoration
 

Nice radio, I hope you enjoy bringing it to life again!

Re: Ultra Model 50 (1937) Restoration
 

I'm just starting work on the same set but mine has experienced some dodgy repairs in the dim and distant past. The cabinet is in beautiful condition so I'll work hard to get the chassis working and up to standard.

Re: Ultra Model 50 (1937) Restoration
 

The transformer was patched up with some thin kynar wire. I believe that the speaker is HT energised.

Thanks for the well wishes, astral highway!

I'll start conducting some power supply tests soon.

Re: Ultra Model 50 (1937) Restoration
 

Hello DoubleWound, I missed your post. The chassis looks a bit rough. It looks to have had a replacement 8uf smoothing capacitor, just like mine. Good luck!

Part designations refer to the Trader Sheet 236.

Power Supply and Voltage Testing

These tests have been done with a lamp limiter and a RCD. Safety goggles on!
All transformer (mains and audio) windings ohm out correctly.

No HT shorts.
Electrolytic capacitors tested with Hunts CRB3 tester.
C22 (original, 8uf) leaky at 20v-100v.
C22 (Plessey replacement, 10uf) leaky at 200v-300v.
C23 (32uf) leaky at 100v-200v.

V5 anode to anode (no rectifier): 700VAC
V5 each anode (rectifier installed): 310VAC
Rectifier heater: 3.8VAC
Lamp and heater winding: 4.5VAC

The power supply was tested with its original smoothing capacitors but they acted more like resistors lowering the HT to 60v. Replacing C22 with its Plessey replacement helped things a bit as it reformed. I noticed it getting hot so it was removed. C23 seemed to reform somewhat. Later I noticed that it was leaking electrolyte and getting hot.

Modern replacements have been temporarily clipped in for testing.

Both smoothed and unsmoothed HT measures about 360v with limiting on. It rises to over 400v with direct mains. I was concerned about too high HT but I assume that this will come down when all the valves are fitted.

Is C17 the grid coupling capacitor for this radio? I have never seen one before the volume control.

Here are some photos of the radio while it is under test.

Re: Ultra Model 50 (1937) Restoration
 

More photos.

Re: Ultra Model 50 (1937) Restoration
 

Yes it is, so far as I can make out it's in that circuit position to prevent the detector diode from being cut off at anytime due to the cathode bias voltage.

Lawrence.

Re: Ultra Model 50 (1937) Restoration
 

The anode cap on V2 was loose so I desoldered it. What would be the best adhesive to reglue the metal cap to the glass envelope? I was going to use 'No More Nails' until I remembered how useless it is. I also have some Evostick Impact but it is very old and has gone off.

Thanks for confirming C17, ms660.

Re: Ultra Model 50 (1937) Restoration
 

Re: Ultra Model 50 (1937) Restoration
 

Thanks for the feedback OldTechFan96.

You're a few days ahead of me and it'll be interesting to exchange notes in the coming weeks but my set has passed the lamp limiter test so far.

In addition to the 8uF electrolytic you may have noticed non standard mains and output transformers.

So, I will not be aiming for authenticity and I'll change all the paper and electrolytic capacitors and then seek optimum performance.

My first simple job will be to fit a three core mains cable and earth the chassis as I don't trust the insulation on anything in a set of this age.

Let me know if you need the 32uF electrolytic as I'm replacing it even if my Wayne Kerr says it's good.

Re: Ultra Model 50 (1937) Restoration
 

The anode cap was stuck on with Unibond repair power epoxy as it looked to be the best stuff available at the the local B&Q. It sets in one minute and claims to be heat resistant up to 150c.

I let the cap set for 24 hour before resoldering. The heat from my soldering iron did cause the glue to break down but it quickly set again. The cap is now firmly held in place.

It will be enjoyable to exchange notes, DoubleWound. Your mention of transformer insulation makes me wish that my 500v Wee Megger worked.

I always told myself that if I bought a pre-war set I would try and restuff all of the capacitors I could, except the smoothing cans.

Next I will check all of the paper capacitors for leakage with the Hunts tester.

Re: Ultra Model 50 (1937) Restoration
 

You're making more progress than me.:thumbsup:

I started checking coils and the aerial coupling coil (L1 on Trader Sheet 236) was open circuit. The can came off easily and the lead outs were seen to be burnt - not that clear in the image below:

An extremely knowledgeable member of this forum has given me guidance to rewind the coil but I'll check all Coil Unit 2, Coil Unit 3 and both IFTs first. If I find any more this fine set may be sold for spares.8-o