Roberts RT1 which has been dropped

['LIVEWIRE?']

Amongst other things (I have a thread on Golborne VR about this radio)the Volume control is this radio was seized solid. Never come across that before. Fortunately I had an almost identical NOS 5k log pot. with which to replace said control. Now to sort out the other issues, including the tuning gang, broken handle, etc.

['LIVEWIRE?']

Further to the above, I've now rectified the faults mentioned (see my thread in the 'Success stories' section) but am wondering if Roberts ever fitted a car Aerial Socket to the RT1. (Btw this example is a Harrods one) There is a coil in the centre of the ferrite rod for this purpose, and a car aerial socket has been fitted, along with another socket, both visible in the picture, which had been wired in parallel to the speaker. Neither looks factory fitted, and it is surely not good practice to simply connect a second speaker in parallel to the exsisting one, so I've removed that connection

[mike g3zii]

Hello there. I have a Roberts RT1 and there are only the two aerial coils on the rod. No small car aerial coupling coil. There are no sockets for aerial or ext speaker either. so maybe yours has been 'improved'
Serial no of mine is 9799 and it still has the original envelope inside with the instruction leaflet. radio bought november 1958 written on it.
the only problem is that the handle was broken so I put something non original from a different set. I don't suppose they are obtainable now.
apart from that the set works well and gets regular use.

['LIVEWIRE?']

The one I've been working on has the serial no. T8718, and a Harrod's plate with the number 8034 stamped on it, so I'm guessing it's quite an early version. AFAIK the ferrite rod and coils are original, but, as can be seen from the photos, the sockets were definitely 'retrofitted'. Regarding the Handles, they must, as you say, be unobtainable from anywhere by now. My idea is to get a modern 'Revival' handle from Roberts. I know one will fit the RT1 as I borrowed one from a RD60. They are available in Apple Green for about £12 including P&P from Roberts.

[poppydog]

Hello Livewire

Your post in Success Stories says "have also replaced the original main smoother (100uf, 6v) with a modern 470uf 16v electrolytic." can you tell me the reason why you did this?

Regards
Poppydog

[AD360 Rob]

some RT1s did indeed have an a car aerial socket from new, it was fitted in the upper right hand side of the rear door. I'm sure one of mine has it but can't get at any of my sets at the moment to photograph.

['LIVEWIRE?']

Poppydog - I was simply using components I had to hand, and a modern 470uf is, as you know, no bigger than a 60 year old 100uf electrolytic, besides which, being almost 5 times the capacitance of the original, and thus having 1/5 of the impedance at any given frequency, provides better smoothing. I'm not into restuffing old capacitors, and in any case the 100uf is too small to make this practical. Besides all that, the owner of the RT1 asked me to get it working as well as possible again and restore the cabinet and other externally visible parts to as near original appearance as possible. They had no objection to my using modern electronic components in repairing the set.

[poppydog]

It was nothing to do with modern replacements, I just wondered why you increased the capacitance. A bit disappointed with my rt1 as it has no bass, sounds very shrill. Just wondered if that is why you put the 470uf in.
Regards poppydog

['LIVEWIRE?']

Sorry if I sounded a bit harsh, Poppydog, but one of my bugbears on this forum is the fact that some members sem to feel that, because a radio is old, the internal and/or under chassis appearance must look exactly the same as before it was repaired i.e. no modern components visible anywhere, whereas i approach things with my service engineer's 'hat' on, i.e. replace with a later component as would have been done in the trade at the time. I would only go down the 'restuffing & concealing' route if I was working on a very rare set. As noted, the reason I fitted a 470uf was simply that it was what i had to hand, though increased capacitance should improve smoothing, and, in the case of a battery set, should help an aging battery last a little longer, though I've no proof of this. I doubt that increasing the capacitance of the smoother (C21 in Trader sheet 1357, available from 'up top' if you don't have it, would make the radio sound less shrill. If yours is an early version, c12, C24 (0.1 & 0.02uf respectively) may not be fitted, and R13 may be 4k7 instead of 1k5. The omission of C24 in particular, may affect the frequency response, but only on LW, as it is out of circuit on MW in those sets where it is present.

[GeoffK]

The larger 470uF C25 capacitor across R17 the emitter resistor of the driver transistor will decouple the feedback (which would otherwise reduce the gain of the driver transistor if the AC signal was being developed across this resistor in phase with the input signal without being decoupled) at a lower frequencies, meaning the driver transistor will amplify at lower frequencies than a 100uF capacitor across R17, though the audio affect will be hardly noticeable due to the limitations of the speaker and the inductance value of both the driver and output transformer limiting the lower frequencies. The input stage capacitor C23 of the driver can also determine the range of the lower frequency. The speaker should also be checked for free cone movement, and correct location of the speech coil so it is not biased forwards or backwards on its suspension which could affect the sound quality. Though it is not this radio being discussed so apologies for any confusion.

['LIVEWIRE?']

Good points, Geoff. though it wasn't C25 I replaced, but C21.

[GeoffK]

Yes I should have read you success story first. I agree with what you say about component replacement.

['LIVEWIRE?']

Good points, Geoff. though it wasn't C25 I replaced, but C21.

[julie_m]

On the subject of replacing electrolytic capacitors, the one between the midpoint of the output stage and the loudspeaker can usually be increased and will result in improved low-frequency response, giving a fuller sound (at least, to the extent the speaker is capable of). However, some amplifiers can become unstable unless you also increase the power supply capacitor. (A battery-powered set might only show problems when the battery is getting low.)

[GeoffK]

Originally Posted by julie_m

On the subject of replacing electrolytic capacitors, the one between the midpoint of the output stage and the loudspeaker

This radio has driver and output transformers as do most earlier transistor radios. Capacitor coupling tended to come along in the seventies.

[poppydog]

Originally Posted by 'LIVEWIRE?'

Sorry if I sounded a bit harsh, Poppydog

No need to apologise, as if I had worded my question a bit clearer you would have known why I was asking. I also assumed/incorrectly read that C25 was the one you replaced. Apologies for hijacking your thread.

Regards
Poppydog

['LIVEWIRE?']

Electronically, despite the misfortune that befell it, the RT1 is working very well, but I've found that the wood at the hinged side of the back has split, as a result of which the hinge cannot be secured, so I'll either have to fit a new lengthe of wood to that side or rotate the back through 180 degrees, fitting the hinge to the 'clasp' side, and the clasp to the former 'hinge side. Because a previous owner had drilled two holes in the cabinet back for added sockets, these holes will now be at the bottom. Ideally a replacement back is needed, but I'm very unlikely to be able to obtain one (nothing on ebay other than a complete RT1. I may put a request in the 'Sets & Parts wanted' section, more in hope than expectation!! Pictures of the cabinet are in the 'Success Stories' section, btw.