ULTRA portable tube radios

[6AL5W-Martin]

if you see anywhere a offer, I need one oft this ULTRA logos, one my raadios need one.
It may be possible to rebuild that, but it`s a very long time job to get a respectable result.

And now I see 2 pcs. R906 in the british ebay, to they are not so extremly rare to you.
The radios are nice, but there is no UKW, fm. A fine way to use them may be a little receiver for internet + Fm , with remote. This can find a place in the batterie box, without manipulating the original parts of the radio.

I am not shure about the names / types of the original tubes inside . In the set what is actually at first in restoration, I found the typical battery tubes DK9x (92 or 96), 1S5, 3V4

I have no application.
The filant voltage is given to 7,5V.
Adding all little filaments in series (the DL94, 3V4 have 2 of them and is to use as 3volt) = 1,5+1,5+1,5+3 = 7,5V. Battery can be 5x AA 1,5V (6pack holder with one missing)
The negative g1 voltage can be made from the series filament, the little 3V4 need the own -1,5V minus -4,5V from extern source what can be the 3 other tubes in serie, so my theory.
The german akkord sets use the filaments parallel to 1,5V , the -4,5V comes from the anode battery what decount the anode batte from 90 to 84V
Ultra seems to go another way there. Also the have written a battery of 85V, not 90V. What is a 85V battery ? I have never seen one.

greetings
Martin

[Paul_RK]

Originally Posted by 6AL5W-Martin

Also the have written a battery of 85V, not 90V. What is a 85V battery ? I have never seen one.

The B129 was an 85V (actually 85.5V) HT battery - just three fewer cells than usual - and there was also a B127 combination HT/LT battery, 85 + 7.5V. Quite adequate for a fairly basic portable, but rarely used - small sets using the B101 67.5V HT battery were much more numerous.

Practically all UK-made dry battery-only sets used parallel valve filaments, while most, though not all, mains/battery sets had filaments in series which meant, for standard four-valve models, 7.5V LT.

Would be interesting to know, now that you have the Ultra sets, whether the cabinets appear to be from the same source as that of the Offenbach 55, or it's just an instance of one manufacturer copying the style of another.

Paul

[6AL5W-Martin]

hello Paul
thank you for helping me.

This question is very hot, what`s the matter with the cabinet design of them, or who have gotten the idea ...

Here you see the size comparement of the both.
They are both made 1955.
please remember: you are inches, I am metric. they fit.

[6AL5W-Martin]

what is this for a part please ?

[Paul_RK]

The white ceramic item is just a high wattage resistor - sold in quantity by Radiospares back in the day, mainly to replace failed sections in TV mains droppers. The design would allow them to be stacked on a rod to replace the entire tapped dropper, but more often one or two were used to replace open-circuit sections, and hung from the original component - it looks as though that may have happened here.

[Nickthedentist]

Yes, it's a power resistor, connected across part of the original dropper resistor assembly which has presumably failed.

Not pretty, but a cheap way of getting a radio working again, especially an older set for which original spare parts were no longer available.

Often colloquially referred to as a "Polo mint" in the UK because they look a bit like the popular sweets: https://keyassets.timeincuk.net/inspirewp/live/wp-content/uploads/sites/8/2023/04/FATD66-scaled.jpg

[6AL5W-Martin]

thank you.
I have seen it is NOT solded, only handwired.
A comparement to another R906 if there is also one, I think not. So the green resistor can be RIP = test now.

[6AL5W-Martin]

the eletrolytic 50+50µF in the R906

64+66µF looks good.

the 1420 Ohm where this R was handwired parallel ist allready working.

I found our standard tubes, DL94 , not the on the case written Mazda Tubes = 1p11 what is the same.

DL94 is checked to 7,1mA = good or better. (Neuberger tube tester)

[6AL5W-Martin]

I have found the following problems in the first set:

1.) this Polo Resistor handwired in parallel to the 1k42 resistor, why ? 1k42 is still OK.
2.) safety: Fuse not found anywhere
3.) There was a power cable, 3wire ! , soldered parallel to the ac plug, and later cuttet. Bec. this set is a 2 wires without AC transformer it`s not possible to understand what they have done there. The Power switch open/close contact between the Powerline and chassis, here in germany where you can turn the AC plug this can do as result a radical shorting between power and ground, without any fuse.

4.) On the front of the R906 case scala (not identical to 786 coronation twin) you find the word LIGHT. I found no light anywhere, also no socket for any bulb, or any switch for light on/off in this radio.

I have no application from this set, but a 4 valves radio can be repaired also without the papers

greetings
Martin

[Simon Gittins]

Originally Posted by 6AL5W-Martin

4.) On the front of the R906 case scala (not identical to 786 coronation twin) you find the word LIGHT. I found no light anywhere, also no socket for any bulb, or any switch for light on/off in this radio.

I'll answer the easy question. The word LIGHT refers to the LIGHT programe as in "light" music or popular music. The other two main stations were HOME (mainly speech) and THIRD (classical music).

[Nickthedentist]

“Light” refers to the BBC Light Programme:
https://en.m.wikipedia.org/wiki/BBC_Light_Programme

Crossed with Simon

[Nickthedentist]

Lack of a fuse was normal in British radios of this era, unfortunately.

There would have been a 5A fuse in the house fuse box to offer a degree of protection, or a 3A fuse in the mains plug with the more modern design of plug which was introduced in the late 1940s but not universal until about 1980 or thereabouts.

[Nickthedentist]

And the 3-core mains cable sound like the work of an amateur with a dangerous lack of knowledge! Probably done by someone when the original mains connector was lost.

[6AL5W-Martin]

There is a missing spring, the plug have a internal switch for swapping line / battery by plug in the cable.

pictures coming

[6AL5W-Martin]

pictures again.

[Simon Gittins]

That 3-core lead uses the old UK colours red, black, green so it was either added before the mid 1970s or done using old cable. People have been making mistakes for a long time.

[Nickthedentist]

Bizarrely, it looks neatly implemented though!

[6AL5W-Martin]

powered up slowly by the adjustable isolation transformer. (Grundig RT5A)
I have solded a Fuse behind the plug bec. here is much more then 5A on the table.

pictures: fuse, and the C behind the rectifier is a furnace, see IR

greetings
Martin

[Simon Gittins]

That's a better view of the mains lead and it looks as though it has 4 wires now, very strange.

[6AL5W-Martin]

a bad news: I think the primary coil of the output transformer is interrupted.

The 100nF will be changed to another one.