Regentone A121 repair

[TrevorG3VLF]

This Regentone A121 was given to me by robbo1876 to look at.
Cabinet quite good but a little piece of veneer missing. Mains cable twin rubber with cloth covering. Both wires open circuit, one about 6in from the set. Mains switch open circuit - bypassed.
Mains 13A fuse replaced with 3A, then 1A.
Unsleeved Nettles pinned plug washed.
Tone switch rotates, wires broken, nut loose on the shaft.
Knobs very tight, one broken and glued with superglue.
The chassis was loose but would not come out. A hidden screw pulled up through the cabinet base, oh dear.
Three core mains lead fitted with grommet and cable clamp, chassis earthed.

[turretslug]

Good luck with this one, doesn't it seem to be the way that the apparently straightforward jobs turn out to be more tricky and involved.... To be fair, compensated by the ones where I've approached an overhaul task with a degree of trepidation only to find that the work was simpler and quicker than feared and successful to boot.

I've always quite liked sets with the "transitional" loctal and rimlock types- they make a change from IO and B7g/B9a models and, whereas the valves' presentation may have been short-lived, there were frequently good innards under the skin,

Colin.

[TonyDuell]

Good luck with this one, doesn't it seem to be the way that the apparently straightforward jobs turn out to be more tricky and involved.... To be fair, compensated by the ones where I've approached an overhaul task with a degree of trepidation only to find that the work was simpler and quicker than feared and successful to boot.

I've noticed that too. The repairs you worry about go smoothly, the jobs you think are going to be easy always have unseen snags.

I wonder if it's because you think about the former, work out what the problems are and then you know what to do when you come do do the job. Whereas with the latter you don't think about it in advance.

I am pretty sure I saw the radiogram version of this set many, many, years ago (no I don't have it). Same chassis at the top of a larger wooden cabinet. Drawer under it with the speaker at the front and a (Garrard?) autochanger inside.

[Robbo1876]

Trevor, I hadn't intended for you to have to perform major re-construction! You made a very generous offer and, if after examination, you think it is too much work, please use it as a supply of spares (if any are salvageable).

[Dave Moll]

Originally Posted by TonyDuell

I am pretty sure I saw the radiogram version of this set many, many, years ago (no I don't have it). Same chassis at the top of a larger wooden cabinet. Drawer under it with the speaker at the front and a (Garrard?) autochanger inside.

And I have a television (TR20) that has this same radio chassis bolted into the top of the cabinet (presumably to make the unit usable outside the limited TV broadcasting hours in the early 1950s) - so they seem to have repackaged it a fair bit!

[TrevorG3VLF]

I have a black chair, I have started so I will finish!

Chapter 2.

Has many Hunts wax capacitors but the 7C5 grid drive capacitor was a 10nF blue cylidrical RS capacitor so should be safe to light the blue touch paper.
40W series bulb
158V HT, 8V 7C5 cathode, ran for 30 min, then left for a couple of days.
One dial bulb replaced
100W series bulb
HT1 232V HT2 170V = 62mA
7C5 cathode 10V about right
11.8V across output transformer = 39mA
Checked the cathode voltage again 10V and the grid voltage. Woe, thrice woe. It is +11V.
Remove valve. 'grid' is now 28V. Grid (470k) resistor is 600k.
Looks as if I have a duff RS capacitor and a low emission valve.

To be continued.

[turretslug]

I wonder if the blue cylindrical RS capacitor is a mixed dielectric? Long ago, I acquired a lot of NOS in various values in a stores clearance. Checking them years later (they had always been in warm, dry storage both originally and post-acquisition), they were all markedly leaky and discarded. Lesson learned, and not forgotten. Once the 'net got into its stride, I found quite a bit of similar discontentment with "mixdees".

[TrevorG3VLF]

Chapter 3
Back for a little more punishment!
C15 replaced by 0.01 tropical fish
C10 replaced by 0.1 mustard
C13 (leaky) replaced by Vishay 630V
C18 replaced by 0.01 disc ceramic

Voltages about correct, voltages in brackets from diagram.
HT1 (290) 291
HT2 V4s, (230) 224
V4a (215) 212
V4k (10) 8.9
V1s, V2s (65) 71
V1tg -17V (MW)
V4g 39mV
V3a (80) 106
I do not see how V3a could be measured with an AVO 7 which has a resistance of 200k. The anode resistor is 220k.

No sound output other than some crackling and some wooshing. No sound generated by changing the waveband switch.

Will need to get a signal generator or scope on the job.

[Cobaltblue]

I do not see how V3a could be measured with an AVO 7 which has a resistance of 200k. The anode resistor is 220k.

The measurement you have is high because you're not using an AVO 7

The trader sheet shows the reading expected on working equipment with the test equipment specified not its real working conditions.

When I was at college we were taught to acknowledge the effect the measuring device would have on the readings.

That's why the trader sheet specifies what meter was used to take the readings and the range selected, although ISTR much later trader sheets just gave the Ohm/Volt rather than a particular model.

Cheers

Mike T

[TrevorG3VLF]

Chapter 4
Who repairs the repairer?
The set does work but is very insensitive, I used the outer of a co-ax cable connected to a four element Yagi in the roof space, this is normally gives plenty of signal.
I cannot shift the I.F. cores so I tried to see if the coils were resonant. I drove the primary with my Acton generator and looked at the secondary with a scope. The scope input lead had a capacitance of 83pF and the scope has a sticker "Do not use after 1987".
Drive L9, output L10 330kHz
Drive L10, output L9 340kHz
Drive L11, output L12 375kHz
Drive L12, output L11 320kHz
Swinging the generator shows that all the circuits have quite a nice resosnance.
I have purloined a knitting needle and filed the end to try to tune the I.F.s but the cores seem to be stuck and I do not want to force them.

I need a B8B Loctal socket to make an adaptor for my antique valve tester to check V1 and V2. Anyone got one, also an I.O. plug with all pins present. Will put a plea in the wanted thread.

I think I am stuck at the present. Any suggestions?

[TrevorG3VLF]

Chapter 5
Well, I was wrong (it does happen), the set was working but very insesitive. I missed a wax capacitor which was lurking under a resistor. This was C1, the aerial input cap. When I tried to disconnect it to measure it, it fell into two. Replaced by a 0.01 disc ceramic. Seems to work OK now.
Tone control put back in to the diagram.
Chassis dusted with a brush and put back into cabinet
To be collected by the owner tomorrow.
The set really needs a 250k log volume control with switch, quarter inch D shaft.

I hope this saga was of interest. I was asked to write it so here it is.
It now needs a good clean up.

[Robbo1876]

I would just like to express my grateful thanks to Trevor for bringing this 'firewood' back to life. It's fantastic and I'm currently using it to listen to the football commentary on Radio Five. Your hard work and perseverance is very much appreciated and the children will be enthralled when the radio makes an appearance at school on Monday.

[Pete_kaye]

Good work Trevor .What about a before and after set of photos? or from Robbo?

[TrevorG3VLF]

The set has gone. I repaired it, not restored it. The components used were mostly what I had in stock. There will be no difference between before and after except that I washed the knobs and the mains lead is modern.

The chassis view will show considerable dust and staining.