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Old 11th Jul 2019, 8:39 pm   #1
RobertF
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Default Ultra 761. Actually a T671.

I have required an Ultra 761 radio which looks in great condition cosmetically.
There are all the usual leaky caps and a couple of scorched wire wound resisters.
Do any members with more experience than me know this machine. Is it a good set?. Were they popular? I cannot find any information about it on the internet.
Where can I acquire a schematic.
Any advice would be appreciated.
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Old 11th Jul 2019, 9:00 pm   #2
cathoderay57
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Default Re: Ultra 761

Hi Robert, are you sure you don't mean Ultra U7961? If not then a picture would be good. Cheers, Jerry
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Old 11th Jul 2019, 9:05 pm   #3
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Default Re: Ultra 761

Yes, Photos, valve line up, wavebands etc if it’s not the U7961
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Old 11th Jul 2019, 9:31 pm   #4
RobertF
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Default Re: Ultra 761

The markings on the label on the rear of the radio show T 761.
Most of the valve markings are illegible..
I will take some pictures of the chassis and the cabinet and post them tomorrow.
Thanks for the advise guys.
Robert
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Old 11th Jul 2019, 9:52 pm   #5
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Default Re: Ultra 761

Something described as an Ultra T761 Receiver appears in the results of the Sept 2017 BVWS auction. Interesting to see the photos when available.

Alan
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Old 12th Jul 2019, 9:10 am   #6
RobertF
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Default Re: Ultra 761

Apologies Lads,
When I took pictures of the radio and enlarged them, I realized it is a T671 and not a T761.
I have attached some pictures.
I don't have any information on this set.
Any advise would be greatly appreciated.
Regards

Robert
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Old 12th Jul 2019, 9:27 am   #7
cathoderay57
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Default Re: Ultra 761. Actually a T671.

Hi Robert, there are images and valve line-up on the RadioMuseum website here: https://www.radiomuseum.org/r/ultra_t671t_67.html but no service data. However, I found another website that says the T671 is similar to the Ultra Leader 51, for which Trader service sheet 1017 applies. If you click the Vintage Radio Service Data link at the top right of this Forum page, and put Leader 51 into the search box you'll find it. Good luck! Jerry
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Old 12th Jul 2019, 9:28 am   #8
Mike. Watterson
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Default Re: Ultra 761. Actually a T671.

https://www.radiomuseum.org/r/ultra_t671t_67.html
Look up the equivalents to the Mazda valves.
Any set with a similar lineup won't be much different.

I don't think it's in Trader sheets or R&TVS, though there may be a similar model. Check the index of service sheets here.

It's likely the first thing is to replace any paper dielectric capacitors (waxies, Hunts, Metalmite) before power is applied.
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Old 12th Jul 2019, 11:19 am   #9
RobertF
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Default Re: Ultra 761. Actually a T671.

I have downloaded the service information for the Leader 51 which looks like the same set.
I will start by changing the usual caps over the next few days before powering it up.
Thanks for pointing me in the right direction.
I will let you know how I get on. I may need further help down the road.
Regards

Robert
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Old 16th Jul 2019, 9:22 pm   #10
RobertF
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Default Re: Ultra 761. Actually a T671.

I know there are acceptable tolerances on resistors. Can anyone tell me what is acceptable.
I have some readings which I think are ok. Ie. 1.2k reading 1.3k and 100 ohm reading 114 ohm.
I have one I am not sure about ie. 18k reading 21.5k
Then one I think is unacceptable. ie. 68k reading 106k
Is there a % of the value you should use as a guide.
Any help would new appreciated.

Regards

Robert
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Old 16th Jul 2019, 9:32 pm   #11
crackle
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Default Re: Ultra 761. Actually a T671.

I would say that 10% is the normal tollerance for vintage radios.

Mike
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Old 16th Jul 2019, 9:40 pm   #12
Mike. Watterson
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Default Re: Ultra 761. Actually a T671.

20% often fitted and valve circuits can tolerate even 50%, except for cathode resistors or battery set HT- bias resistor, which indeed 10% is better.

The 68K reading 106K may or not matter depending where it is. If it's the Local Oscillator HT feed, then indeed it's too high. It doesn't much matter for a grid resistor.

Older resistors
No band = 20%
Silver = 10%
Gold = 5%

Newer resistors
green = 5%
red = 2%
brown = 1% (there is usually an extra value band, so Red, Yellow, Black, Orange, Brown = 270K 1%)
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Old 17th Jul 2019, 9:24 am   #13
RobertF
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Default Re: Ultra 761. Actually a T671.

Hi Mike,
The 68k resistor is the osc. anode feed.
I think I will go ahead and replace it.

regards

Robert
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Old 17th Jul 2019, 9:37 am   #14
Mike. Watterson
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Default Re: Ultra 761. Actually a T671.

I thought it might. A notorious place for high resistors. Often results in reception stopping at one end of a band, or if mains low (or batteries low).
If you have only 1/4W resistors you can put a pair of 33K in series. That's only 3% out and modern resistors are 2% or 1%. Twist the middle connection and cut short. Cut out existing one close to body and use pointy pliers to make hooks for new resistor wires. Unless the existing tags easy to solder.

An actual value of to 55K to 82K will likely be fine. It may even "work" at 106K, but that is 56% out and the oscillator might not start at any lower Q part of band, or band if the radio turned on.
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Old 17th Jul 2019, 6:46 pm   #15
RobertF
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Default Re: Ultra 761. Actually a T671.

Thanks for the advise Mike. I will swap it out and if i come across any others over 20% out I will replace them also..

Regards

Robert
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Old 17th Jul 2019, 7:01 pm   #16
Mike. Watterson
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Default Re: Ultra 761. Actually a T671.

I'd not worry even at 30% unless a cathode to ground (0V) / chassis.
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Old 25th Jul 2019, 9:26 pm   #17
RobertF
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Default Re: Ultra 761. Actually a T671.

I have replaced the usual wax caps and a few resistors which were way out.
I have powered it up using a lamp limiter. The bulb is just giving a faint glow with full power.
I am only getting 160v at the rectifier (Mazda UU9) . If I remove the rectifier the voltage goes up to 200v. The schematic says it should be 240v. The heater voltage is 4v.
Does this mean the transformer is faulty , or should I be looking elsewhere..

Any advise appreciated.

Robert
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Old 25th Jul 2019, 9:57 pm   #18
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Default Re: Ultra 761. Actually a T671.

Lamp "limiter" ?

Lawrence.
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Old 26th Jul 2019, 8:36 am   #19
cathoderay57
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Default Re: Ultra 761. Actually a T671.

Quote:
Originally Posted by RobertF View Post
I am only getting 160v at the rectifier (Mazda UU9) . If I remove the rectifier the voltage goes up to 200v. The schematic says it should be 240v.
Hi Robert, where are you measuring the voltage, and are you quoting a dc or ac measurement? UU9 pins 2 and 6 are the anodes so they should each measure 240v ac with the negative meter probe connected to chassis. That should not change with the rectifier in or out unless for example the rectifier has an internal short or the HT reservoir capacitor has gone very leaky and the rectifier is drawing a massive current. The cathode pin 7 should be measuring anything from 280v dc downwards depending on the condition of the rectifier valve. I doubt that the transformer is at fault but if you clarify the measurements in the light of the above it would be easier to diagnose the fault. The most common suspect is that the rectifier has gone low emission and its dc output is dropping when on-load. Cheers, Jerry
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Old 26th Jul 2019, 10:26 am   #20
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Default Re: Ultra 761. Actually a T671.

Quote:
Originally Posted by Mike. Watterson View Post

Newer resistors
green = 5%
red = 2%
brown = 1% (there is usually an extra value band, so Red, Yellow, Black, Orange, Brown = 270K 1%)
Never seen a green band for 5% tolerance, it's still gold.

Apparently green is used for 0.5% though.

More confusing can be five or more band codes with a third digit band and maybe a sixth for tempco! Resistors in E48 or higher series are specced to three figures in value.
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