Radiogram restoration or desecration?

It dates from 1953 and has a side cupboard for storing records. I fitted a new Sonotone 9TA cartridge and can play 78's and the new "micro-groove" LP's

A couple more pics.....

If you had not modded the amp you would not have used the the gram so a worthwhile improvement. Looks good.

Frank

Looks to me like you have done a very nice job reviving the gram! I wouldn't call the amp modification desecration, as by what you have said, there were already holes there waiting to be used, and if anyone in the future decides they want it back to original spec they can put it all back (then they will probably discover the naff sound quality, and realise why it had been modified in the first place!).

It's better that it gets used and enjoyed, I have a round Ekco that needs something doing to the output stage, as it sounds a bit unpleasant!

Regards,

Lloyd.

Thanks chaps,

To be honest such modification to a vintage item is not what I like to do but in this case, I thought it was necessary.

I have been looking at my old notes and I was convinced that the wrong mains transformer had been fitted since new. This is due to the fact that 5v instead of 6.3v was being supplied to the heater of the original EZ40 rectifier. (That 5v now supplies the GZ32 quite satisfactorily). Furthermore, the HT was way too high at approx. 365vdc at full load. The original smoothing electrolytics were rated at 350vdc and were replaced. I had found that with such values, about 48 mA were passing through each EL41 output valve as originally fitted. The maximum published rating for the EL41 is 36 mA anode current.

With the 6L6 modified output stage, the conditions are perfectly correct and has been running like this for about 10 years now. The mains transformer is barely luke warm after several hours of operation. I was and am certain that a mistake was made in production and like I said, the wrong type of mains transformer originally fitted. It looks undisturbed and fits the chassis perfectly with neatly soldered connections, so I doubt it was a replacement. The B8A base adaptors were riveted to the chassis and were original too. Cut-outs for octal bases were already there, so was simple to fit the octal's.

So there we are. One modified and now working radiogram. I will upload my circuit of the 6l6 output stage later. (In fact, I use 5881 (6l6wgb) as they were cheaper that the larger 6l6g valve types ! )

The ARG5000 was the first radiogram produced after RGD were taken over by Regentone; whilst this one just about passes muster as an RGD, subsequent models would never have the constructional standards of RGDs hitherto produced. It's astonishing that it ended up with the transformer that it did though.

You did the right thing in my opinion; short of locating a worm-eaten 5000 to raid for parts I can't see how else you could have got that back to anything approaching proper functionality, other than having the transformer rewound to provide the correct voltages.

I'm just wondering how much of a level difference there is between radio and gram, given you've got a Sonotone 9TA in the arm of the RC80 which, if I'm honest, bothers me somewhat; I know it's not the /HC version, but I'm not entirely convinced the cartridge is a good mechanical match to the arm.

Cathovisor said
The ARG5000 was the first radiogram produced after RGD were taken over by Regentone; whilst this one just about passes muster as an RGD, subsequent models would never have the constructional standards of RGDs hitherto produced. It's astonishing that it ended up with the transformer that it did though.

You did the right thing in my opinion; short of locating a worm-eaten 5000 to raid for parts I can't see how else you could have got that back to anything approaching proper functionality, other than having the transformer rewound to provide the correct voltages.

I'm just wondering how much of a level difference there is between radio and gram, given you've got a Sonotone 9TA in the arm of the RC80 which, if I'm honest, bothers me somewhat; I know it's not the /HC version, but I'm not entirely convinced the cartridge is a good mechanical match to the arm.  

The level is the same (there is an EBC41 pre-amp valve just for the phono stage), and the cartridge seems to work fine with stable tracking weight. As to a good match to the arm, you could well be right. At the time, it was the only cartridge I had to hand.

I agree with the build quality, radiograms such as the RGD 1046 are beautiful things.

Here is a scan of the output stage circuit, an ECC82 driving a pair of 6l6 or equivalent types.....

I heartily approve. You approached the task respectfully and with considerable forethought and insight, making it something that to be regularly enjoyed rather than occasionally tolerated. As found, it sounds (!) to have been something of an undeserving, even deceitful, sheep in wolf's clothing. It'll be possible to restore something like originality without scarring- should anyone want to. Most manufacturers, even the best, occasionally have a bad patch where the bean-counters and/or clever dicks got too much sway and this sounds like a case in point. I've long reckoned that once HT gets to over 300V or so, it's time for the EL84s, EL41s etc to get back home to their mammies and let the bigger boys get on with things.

 The ARG5000 was an attempt by the new owners of RGD to create something like the old firm used to make. You can find the circuit diagram in the 1953/54 Radio and Television book.  Sure enough there are some design elements of the old RGD radiograms such as the separate radio tuner and amplifier chassis. Full marks there.  But looking at the circuit diagram it doesn't look as well engineered as an old RGD would be like, don't like that phase splitter arrangement with it's balance control.   I'd say your modifications to the amplifier are more like what the old RGD would have designed if the they had survived. By 1953 RGD would have given up with PX4 triode for the output stage, most likely they would have chosen the KT66 possibly triode connected like a Williamson amplifier. The 6L6 just as good anyway. Top quality Sowter output transformer, it doesn't get much better than that.   

I still haven't finished my RGD 1046G.  A Williamson output transformer replaces the original part, there just enough space on the chassis to accommodate the bulk of the thing. Triode connected KT66 tetrodes replace the PX4 triodes, the mains transformer has 4 and 6.3 volt windings so no separate heater transformer is required. The original 12" loudspeaker was missing and for the time being I've fitted a 10" unit of unknown make. Much better is the  Goodmans Axiom loudspeaker I have but the speech coil is OC.  Can this be repaired?

Till Eulenspiegel.

Unless it going to be a museum piece and never used, I have no problem with modifications to make something work correctly, or at least a lot better if the set had design problems. 

Apart from it being clean after 60 years it all looks very original, great job.

Frank

I would just like to add my own approval of a job well done Andrew, you've got yourself a good looking piece of usable kit there. Great stuff !

Marc,

Thanks everyone for the positive comments, I was a bit reluctant at first to post the above due to the rather drastic changes I made to the gram's amplifier.

I use it most weekends and really enjoy it, so for me it was worthwhile. I must get a decent AM outdoor antenna and listen to AM whilst we still have it. The Archers on Radio 4 longwave sound great, booming around the neighbourhood

I think the improvements you've made are brilliant!

To think some people would have turned it into a cocktail cabinet.

The infamous cocktail cabinet, had to strip a chassis out of many a console TV with doors for the cocktail cabinet that was never made. That was what was requested and in keeping with those times they were trying to recycle something rather than skip the whole item.

We can look at it now as unforgivable but it has to be viewed as make do and mend, recycle was the order of the day. We are just now getting back into recycling.

Frank

I have been reviewing my output stage alterations and although a GZ32 and 6L6's were used originally, I have found that a GZ30 (5Z4) rectifier and 6V6's are perfectly suitable too. The absolute maximum current draw from the HT is only 120mA with the radio operating and therefore within the spec of a 5Z4. The currents flowing through the 6V6's are ok too at just under 50mA per valve at maximum signal drive. 

It is pointless to use the more powerful valve set up just for the sake of it. Output power is just over 10 watts.... hardly a noticeable reduction from 12.5 watts as before, and still PLENTY loud enough !!

I've been playing around with the negative feedback arrangement too. Instead of having it going to the ECC82 pre-amp cathode as shown in the diagram above, I have applied it to the earthy end of the volume control via a 2k2 resistor and a 1k to ground. This way, there is a much more gentle increase of volume from zero whereas before, the volume was too loud with a small turn of the control. I had to reverse the polarity of the balanced drive of course, to maintain the feedback in the correct phase.

PYE625 said
I've been playing around with the negative feedback arrangement too. Instead of having it going to the ECC82 pre-amp cathode as shown in the diagram above, I have applied it to the earthy end of the volume control via a 2k2 resistor and a 1k to ground. This way, there is a much more gentle increase of volume from zero whereas before, the volume was too loud with a small turn of the control. I had to reverse the polarity of the balanced drive of course, to maintain the feedback in the correct phase. 

I've following alone, just fascinated by your project. The only 'mystery component' is the output transformer. Where did you source this and how important are those primary taps?

FordAnglia said

I've following alone, just fascinated by your project. The only 'mystery component' is the output transformer. Where did you source this and how important are those primary taps?

   

The output transformer came from Sowter and it is type U067 with a 9K primary with UL taps at 43%. It can handle up to 60mA per valve in the HT and has a 10 watt power rating. It is a well made transformer and requires very little negative feedback for low distortion, unlike a pentode connection only. Sowter specify it for use with UCL82 valves, but of course many other types can be used providing you keep within the spec limits.

Here is a link to Sowter, they still make the type I used. I bought it with the intention of using the EL41 valves as fitted, but changed the type as described previously.

http://www.sowter.co.uk/push-pull-output-transformers.php

The prices have gone up quite a bit since I bought my transformer, but the quality is unquestionable.

Here are a couple of snaps with the pair of 6V6 and 5Z4 fitted. I think they look better than the stubby 5881's lol

I have also installed an AM antenna which consists of a CB type rod aerial mounted on the side of the bungalow plus an earth rod pushed into the ground just outside as close as possible to where the radiogram is situated indoors. The results are pretty impressive and the earth connection reduces noise on longwave in particular. All main stations are very strong and listenable day and night without interference or heterodyne whistles. It was well worthwhile doing this, as before I used to hang a wire across the lounge and it was far from ideal.