R103A receiver, T1154B transmitter

[RedhillDave]

Hi all,
I am new to this forum, having just acquired an R103A receiver and T1154B transmitter from a relative (an ex amateur, now in his 90's but still sharp as ever).
I am a licensed amateur (M0WID) of about 6 years, and really am an amateur - electronics is not my profession so everything is a learning experience - which to me makes it more fun. I have some experience building things from kits or existing designs, but not in circuit design and especially not valve gear, even though my main rig is a Trio TS530S hybrid.

The receiver and transmitter have been stored in an outhouse for many years. The transmitter I think is as original but the receiver has been heavily modified. The relative owns up to modifying it to receive MW broadcasts.
I have Googled The R103A and found very little information about it, so if anyone does know anything that would be useful. It does not look very much like an R103. I will try and post a photo or two.

Never having attempted to bring something like this to life before, I am wondering:
A) - is it worth it? I think it is as I will learn a lot doing it. I will tackle the receiver first as I think getting the transmitter going should not be too difficult, other than sorting out some sort of power supply. It would be nice to show it working to the relative who kindly gave it to me.

B) Best way to go about it. Should I try and get the receiver working in the modified state, or return to original if any circuit diagrams etc are available (the inside of the case has a diagram showing the layout and part numbers, but no values or interconnecting wires)?

C) Things to definitely not do. For example the receiver case has some signs of light rust, but on the whole is not too bad. All the lettering seems intact apart from where an additional meter has been installed. My gut feel is to keep it as is rather than repaint.

D) One of the knobs on the transmitter (red RHS) appears stuck. All other controls seem good. Best way to go about sorting this?

E) Power supply. The front has two sockets, labelled mains and vibrator. The vibrator is missing and I think the power supply has been modified. I will need to work out the modified circuit diagram before doing anything.

F) Transformer for the R103A looks like it has taken a bash - see photo - skip the old transformer and install a new one or try to repair?

G) Test equipment - what is needed? I have a "spares or repair" oscilloscope that mainly works, an AVO and a digital multimeter. I can generate RF signals using a homebrew DDS and arduino device, and measure power up to about 80W using a homebrew Log amp type device, as well as the 'scope.

Due to work commitments this may be a very long term project indeed!

Dave

[HamishBoxer]

Welcome and no the R103 does not look like mine I must add. See what gives as is before returning to original.

The transformer Might be ok. The meters you have are fine, nothing else needed.

Try running the R103 up slowly via Variac or a lamp limiter, do not just plug in, maybe somewhere have a circuit.

[Sean Williams]

The R103 looks fairly good to me.

The socket on the front panel is to select which power supply the set uses - it is already set up for mains.

There are a couple of rectifier sticks in there that may prove to be a bit sick, but most likely will be OK.

I think the schematic is in Wireless for the Warrior - I will check my copies later, however two of my set are out on loan.

The modifications arent that severe by the looks of it - certainly the meter is doing no harm, and it appears that a couple of coils in the RF side of the set have been replaced with the Wearite P type coils.

Should be an easy set to get going

Sean
M1ECY

[Ed_Dinning]

Dave, you have a PM

Ed

[RedhillDave]

Many thanks for the replies everyone, much appreciated. If anyone can come up with a circuit diagram for the R103A that would be very handy. Even though I will have to trace out the modified circuit myself and try and work out what is going on, it would be good to have the original as a sanity check. As stated I know nothing about valve circuits - yet, so it is all a bit daunting at the moment.

Sean - you mention rectifier sticks - are these the long finned type devices? Is there a way of testing these easily before applying power? Do they tend to fail open or short circuit?

G8JET - I will ask if anyone at my club has a Variac I can borrow - good idea. Lamp limiter is presumably putting some sort of bulb in series to limit current? You see I really am new to this aspect of amateur radio!

Attached there should be some pictures of the T1154 as well. I opened this up today and it looks to me to be very good inside. Shame one of the plugs at the front is missing though - that could be hard to come by I guess. It is possible it may be attached to a supply that is hopefully still somewhere at the relatives house. He mentioned he thought there was one somewhere - a rotating device with a motor run off 12V dc and generator for the HT - that make any sense? If the plug doesn't turn up then I think it should be possible to make something that fits even if not identical in appearance - someone at the radio club has a small lathe.

First task though is to work out where to keep these things without upsetting the XYL too much (much bigger than even my boat anchor!), and then to trace out the receiver circuits. I will leave the T1154B and its very high voltages to one side for a while.

Dave M0WID

[M0FYA Andy]

David, can you clarify which is the 'missing plug' - if it is the single pin EHT Jones connector they are indeed relatively hard to find.
Andy

[RedhillDave]

Hi Andy - yes it is the single pin HT plug that is missing.

Dave M0WID

[RedhillDave]

Spent some time trying to work out what has been done to the R103A.

It seems as though the band select switch has been changed and now has 4 positions rather than the original two. So it looks as though there are the original coils on the front end, and also two new ones for the additional bands. The arrangement seems a bit strange but I will leave as is and see how it works in practice.

The 6V secondary on the mains transformer for the valve heaters is open circuit, which confused me for a while when trying to trace the circuits through. The other secondary seems OK. I have removed the valves and applied 5vDc from a USB supply and all seems fine, so no idea what caused it to fail. Am I better off making a DC supply or finding a suitable 6V transformer and keeping the heaters on AC?

When removing the valves one had some sort of carbon or paper inserted over the valve. This disintegrates on handling - see photo. Is this important and if so what can I replace it with?

One of the valves is loose on its base, another has been glued with what looks like araldite or similar. What is the best glue to use to repair the loose one?

Many thanks

Dave M0WID

[AC/HL]

That disintegrated "carbon" looks like the coating from a metallised valve, not needed with a shield can.

[G6Tanuki]

Where the glass envelope of Octal valves have come unbonded from the bakelite base, my preferred way to re-attach them is to use a short length of large-bore heatshrink tubing.

You only need about an inch.

Unlike the sometimes-suggested Araldite or superglue fed into the joint, heatshrink gives a small degree of flexibility to the joint, minimising the risk of cracking the valve-envelope.

This method was used as standard practice by the MoD and their refurbishers in the late-1960s: I've got a bunch of "KTW6x"-style valves from a CR100 receiver I bought as an ex-WD disposal in 1971 that have all been heatshrunk.

[RedhillDave]

G6Tanuki - I like the idea of the heat shrink tubing. The heatshrink tube I can see available at suitable diameter has a max. temp rating of 125C - just how does the base of a valve run and will 125C rating for the tube be OK or will it just go soft or even start to burn? Actually maybe it doesn't matter if it goes soft as when warm the valve is not being moved around and is supported to some extent by its metal shield can.
I suppose the temperature will also depend on whether or not is a power application or not - here the valve concerned is an IF Amp.

Dave M0WID

[G6Tanuki]

Here's a shot of a couple of my WWII-era "VR100" valves [military-spec version of the KTW62 - used extensively in receivers like the CR100].

One's been fitted with heatshrink sleeve by the MoD before it came into my ownership sometime in the 1970s. The other I've dribbled black cellulose-lacquer into the bulb-to-base gap.

For signal-frequency valves where there's not significant power dissipation heatshrink used to reattach bulb to base won't be heated in-service to the sorts of temperatures where the heatshrink will soften.

I wouldn't suggest using heatshrink to reattach a base on power-rectifiers or output-valves like 6F6 6V6 or 6L6 though!

[RedhillDave]

Having replaced all the large value waxed paper caps, and the mains lead, last night I powered up the set, via a lamp limiter, with the valves removed. I have not replaced any of the small value caps yet, or opened up the IF transformer cans to see what may lurk inside.

Initially the mains current was high so I turned it off and found another waxed paper cap that I had missed. After replacing that things were a lot better, but with just the transformer connected, no connections to the secondaries, it was drawing 30mA from the mains with the limiting lamp bypassed.
The 6.3V secondary for the heaters is definitely open circuit.

Turning on the plate supply, with the lamp in series, the current increased, and I got a fairly sensible value on the HT DC, with no bangs and nothing getting noticeably warm. The DC volts gradually increased over time, so then I tried briefly bypassing the lamp - no bangs, current 70mA from the mains supply, about 240V on the HT DC - which seems perhaps a bit high but then there is no load.
Should I worry about the 30mA just taken by the mains transformer by itself, or just carry on, sort out 6V supply for the heaters, fit the valves back in and see what happens?

[Herald1360]

Originally Posted by RedhillDave

Should I worry about the 30mA just taken by the mains transformer by itself, or just carry on, sort out 6V supply for the heaters, fit the valves back in and see what happens?

No. It's just the magnetizing current determined by the primary inductance and the mains voltage/frequency.

If the transformer doesn't overheat after an hour or so, apart from the 6V secondary problem it's fine. The 6V secondary problem is odd- it's unusual for relatively heavy windings with few turns to go open circuit.