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Old 29th Oct 2020, 12:01 pm   #61
Rich400
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Default Re: Adding a selectable line input to valve radiogram

Quote:
Originally Posted by Richardgr View Post
Quote:
Originally Posted by Rich400 View Post
. . . I will revisit the service manual and see if there are further issues to consider, but almost certainly there will be more load so the new T(m) transformer may have to be updated from its suggested 50 vA. I will post some photos of the tuner drawing shortly.
Thanks again
Snowman_al suggested 120VA, which is better than 50VA. Transformer prices don’t vary so much at that rating, and size should not be an issue. Your favourite auction site can be an option.
Thanks Richard
Its seems they do tend to go up a bit, i'd like to keep it small as much as possible to keep its physical size down so i can make it fit in on the chassis as much as possible.
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Old 29th Oct 2020, 12:08 pm   #62
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Default Re: Adding a selectable line input to valve radiogram

I am not sure how the resolution will work out but here’s a few shots of the additional tuner layout. Doing the grind of weekly shopping this morning so will get on this later any suggestions for total transformer rating welcomed
(last photo showing delivery of imperial 2pole 6way ABS spindle pot and panel RCA socket)
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Old 29th Oct 2020, 12:48 pm   #63
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Default Re: Adding a selectable line input to valve radiogram

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Originally Posted by Edward Huggins View Post
This Thead seems to have taken on a complete life of its own and, to me, seems to have created it's own complexities.......
The OP appears to have good understanding of what's going on here, so why not just add a rotary 2 way switch to the gram input socket, use 2 inline "Y" series 500V DC isolation caps, fit the switch to the rear card cover panel, ensure the mains neutral lead is connected to chassis and get going?!
Perhaps: 1: This is all too simple 2: I'm missing something here 3: I've lost the plot!
Hi Edward

Thanks for your sanity check.

No you haven't lost the plot, and what you suggest is what I had hoped I could implement on the outset.

This thread has been a real help to me and I am in a much better place than when i took delivery of this a week or so ago. In my career I have never seen this type of live chassis set up or lack of earthing arrangements so to implement my desire to input a 'line in' safely is requiring this journey for me.

A recent poster has identified that the 'common' line on the cartridge is chassis grounded and as such is live.

This is something I wish to resolve safely before I am able to achieve my goal. Although this may seem like the tail wagging the dog, until I remove the live element of the chassis I cannot perform my mod.

So all posts are entirely relevant, and very much appreciated.

Your suggestion of isolator caps is another education for me, I haven't fitted anything like this before, so will this give electrical isolation from a potential 240v fault on these lines?
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Old 29th Oct 2020, 1:11 pm   #64
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Default Re: Adding a selectable line input to valve radiogram

Re post #62 - What would help is any voltage or current data in the manual.
Also is there any information on the rear panel, it may have an indication of the total Wattage together with the voltage and mains frequency numbers for example?
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Old 29th Oct 2020, 1:43 pm   #65
Rich400
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Default Re: Adding a selectable line input to valve radiogram

Front page of manual attached 150w total consumption.
Apologies but there is nothing I can see that gives a further breakdown, perhaps the valve listing may give a better idea of the chassis load.
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Old 29th Oct 2020, 2:08 pm   #66
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Default Re: Adding a selectable line input to valve radiogram

Well that gives you the absolute minimum figure for an isolation transformer...
So it would need to be a 200VA (or 250VA) transformer to run everything comfortably.

Obviously under estimated the HT load previously. I will ponder over lunch.
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Old 29th Oct 2020, 2:23 pm   #67
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Default Re: Adding a selectable line input to valve radiogram

Hi Snowman
I’m not proposing an isolation transformer for the whole unit, just the portion of the chassis required as in post 47 to remove the live connections to the chassis. The only change to that is the extra load of the tuner.
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Old 29th Oct 2020, 3:56 pm   #68
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Default Re: Adding a selectable line input to valve radiogram

^^^ Understood.

A caveat before going any further with the separate HT transformer idea.
You have to make sure the transformer in the set is constructed as shown in the schematic and that disconnecting the chassis connection on the primary (mains) side does isolate the mains from the chassis. For example if the 2 secondary connections are internally connected to the primary for simplicity of construction.
You need to test this. Remove both primary connections from the transformer, then measure the resistance from the chassis to either of the transformer primary connectors. If you get open circuit (infinity) all is well. If you measure a/any resistance this scheme will not work. Let us know.

So a 'better' guesstimate of the HT requirement.
Look at the partial schematic in post #21 and R78 (270 ohms). That drops 20 volts so the current is 75mA and that feeds the majority of the set except for the ECL82 anodes. I have assumed they use 45mA each so they draw 180mA together. (That is from the ECL82 data sheet and the cathode voltages marked on the partial again.) Add them and you get 255mA, times the 240 volts gives you 61.2 watts. So again to be comfortable you need a 240 to 240 volt transformer in the 80 to 100VA range.

Note 1, if you go this route, you can easily change to full wave rectification (as David suggested in post #53) and that will actually reduce the 'stress' on the new transformer a little.

Note 2, even though I suggested the transformer idea, if this were my project, I would still go the Bluetooth or as you said opto-isolator way (yes plenty fast enough). They give you the protection you want via isolation and would be smaller and cheaper in the end.

Alan

PS I wonder what others think, please chime in.
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Old 29th Oct 2020, 4:05 pm   #69
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Default Re: Adding a selectable line input to valve radiogram

Re: chassis isolation transformer sizing

the two items to draw load on this gram are the chassis and the deck of course.

I would guess 15w for the deck so that would leave 135w for the rest (Chassis).
So deducting the heater load as its covered by the T3 autotransformer would leave the loading I have to cover to perform this mod to remove the live from the chassis.

The trouble is I have researched the valve loads and I'm not confidant my calculations are reliable, so unless anyone else has a better suggestion I will size my new isolation transformer at 135w (or the closest i can find) which will give me the headroom of the load that is being performed by the heater autotransformer.

I would like the smallest physical dimensions to enable a neat fit for the mod.

I am not sure if there are preferred suppliers regarding cost/quality, but recommendations are again welcomed.
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Old 29th Oct 2020, 4:14 pm   #70
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Default Re: Adding a selectable line input to valve radiogram

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^^^ Understood.
So again to be comfortable you need a 240 to 240 volt transformer in the 80 to 100VA range.
Hi Alan
Sorry I was writing my last post as you issued yours.

I am much happier to use your calculations and defer to your experience with these valves. I have none!

Also the cost and physical size of the 80-100VA range will suit me much better. (I am thinking RS 123-4140)

I appreciate your suggestion re: bluetooth being the cheaper option, but It would still (for me) leave the issue of the live pots potentially exposed/lamp mounts and now the 240v from the chassis at the cartridge common.

And as this chassis will need a lot of attention when it comes to being serviced, I am happy to put the effort in. And its a nice journey to take for a newbie like myself.

Genuinely blown away with the effort put in there to help me with this.

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Old 29th Oct 2020, 4:53 pm   #71
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Default Re: Adding a selectable line input to valve radiogram

I think the metal work of the deck is, or should be, connected via an isolating capacitor. It maybe under the deck and I can't see it on any of the drawings. I owned a 300 model with the same chassis and you could feel a slight tingle from the metalwork with the mains wrongly connected.
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Old 29th Oct 2020, 9:33 pm   #72
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Default Re: Adding a selectable line input to valve radiogram

Vidjoman returns to the sort of thing I was meaning [in post 39*] and I would certainly doubt my own ability as a Pat Tester. I sympathise with what Edward said [at P60*] but fatigue seems inevitable, given the complexities of a modern regulatory framework, as it also often includes individual choices needing to be made Unfortunately perhaps, Richards RG does seem to have an unusual circuitry to grapple with as well. It's interesting to note that that there now appears to be three Radiograms related to this general area on the Forum ie there's also Hayerjoe's thread about adding aux-in to a valve Radiogram and the recent enquiry by Greg Simons about Pat Testing a Ferranti 355 RG All potentially complex areas it seems.

Dave W

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Old 29th Oct 2020, 11:48 pm   #73
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Default Re: Adding a selectable line input to valve radiogram

Hi Dave, I think the factor that is missed is that although this equipment complied with safety regs when it was built, it is now 50-60 years old, so the electrical components can no longer be assumed to totally reliable. Transformers can short circuit, capacitors break down, resistors drift. Therefore some of the safety considerations are to protect the user from issues that were not foreseen when the equipment was designed. In my opinion an earth is vital, and it is not so difficult to fit one really.
Rgds, Richard
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Old 30th Oct 2020, 12:19 am   #74
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Default Re: Adding a selectable line input to valve radiogram

Well that's fair enough Richard and thanks for responding. Actually I broadly agree with your point but it's a matter of degree. I'm the opposite of a professional or an an expert but I would not go to all the lengths involved [particularly with more complex equipment] to change everything in situ That's the way that those running this site do HAVE to think [for very obvious reasons] being in the public domain.

Privately, it's possible to overthink everything, in which case buy something [allegedly] safer in the first place. I'm sure that I take a lot more care over domestic wiring, for example, than someone on his way to the next job! The best example I can quote is a chap on the Forum [miles from anybody] who spent a fortune on a discrete dream workshop in his large garden] and then felt obliged to tell the Local Authority. [Remember when your Conservatory had to be 75% transparent or else?]. He then had then to demolish his dream workshop and said "I suppose you were right Dave I was very sorry for him.

It's the same with vintage equipment, just apply common sense! I once said to my doctor [here in the South] everything you advise Dr G is the opposite of Dr K in the North. He said "Well David- put two Doctors in a room and you get at least, three opinions

Dave
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Old 30th Oct 2020, 10:03 am   #75
Rich400
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Default Re: Adding a selectable line input to valve radiogram

Hi Dave and Richard

A healthy debate there!

I am here for the kind assistance with regard to technical goals I have for this gram, but as my posts have prompted your comments I would like to give my view before we return to the job in hand!

For me I try to keep it simple, and its about choices really.

For example before I started in engineering my main priority was not the earth wire, it was the two that made things go (phase and neutral of course). My choice was to make something work.
When I was trained the opposite was the priority, you get the safety right first then worry about the function. You make it safe.

Why I say its about choices, for me it was related to my knowledge level.
When I didn't appreciate how electricity could harm you, and I didn't understand how you protect yourself from it, I wasn't concerned.
But once you do know, its a choice that for me is simple. I either make it safe to todays standard, or I don't have it in the house.

I have invested a bit of time refurbishing the cabinet and will now start on the record deck today, while our healthy debate reaches a conclusion about how technically I am going to make this safe, and add a line input.

At the end of it, I have decided to do the safety mods, although I could have chosen to dump it, another choice.

As I am not paid to perform these works (the gram is for my households use), I have a certain freedom that may not be available to a professional audio repairer, in that to perform this mod correctly will require updating associated drawings, and completing revised on board signage etc etc. This of course is required so that if someone is asked to repair it, knows exactly how it deviates from its original specification, they can repair it safely, this will also be lawfully compliant.

This process is often too time consuming and expensive to perform when being employed to do a simple repair. And I have no issue with the view that once you change it from its original specification, if you don't spend a lot of time on it, you could put your self at risk of litigation. Another choice, although driven by economics.

I could see a possibility with this gram where my tiny grandaughter would find it plugged in. It is also possible that she would fiddle with the volume knob and pull it off and grab the exposed live pot.
This is a possibility I do not accept, and will eliminate this and also the 240v mains in the record cartridge with the kind assistance of all the very professional help from this site.

I hope at least some can see my point here.

Regards Richard

Last edited by Rich400; 30th Oct 2020 at 10:11 am.
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Old 30th Oct 2020, 12:55 pm   #76
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Default Re: Adding a selectable line input to valve radiogram

Oh I think we've always been able to see what your concerns are Richard and there's clearly no reason to get overheated in a healthy debate. I suppose there is always a level of concern about possible live conditions [when it can only be discussed remotely] but that's what the Forum is for and you must do what you think best in terms of your domestic situation. Regardless of all the various comments, it will be very interesting to see how you get on with this relatively unusual model. Maybe a photo of the finished renovation

Dave

I note a few previous threads re the 600 and that member Josh Ward received advice re his deck in 2010!

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Old 30th Oct 2020, 2:29 pm   #77
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Default Re: Adding a selectable line input to valve radiogram

Hi Richard, Earthing aside, did you mention what type of source you were hoping to use with the line input? You are aiming for something at line level, 1vRMS? So CD players, blue tooth receivers etc?
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Old 30th Oct 2020, 3:26 pm   #78
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Default Re: Adding a selectable line input to valve radiogram

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Oh I think we've always been able to see what your concerns are Richard and there's clearly no reason to get overheated in a healthy debate. I suppose there is always a level of concern about possible live conditions [when it can only be discussed remotely] but that's what the Forum is for and you must do what you think best in terms of your domestic situation. Regardless of all the various comments, it will be very interesting to see how you get on with this relatively unusual model. Maybe a photo of the finished renovation
Hi Dave
Yes of course will be more than happy to pass on photos as things progress, the YouTube tutorials are a must for a first time french polisher and next will be the Garrard 121 Mk2 (which currently does not move at all!)

Hopefully by that time I have finished this I will have arrived at a solution with help of the good people on here like yourself.

Thanks again

Richard
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Old 30th Oct 2020, 3:42 pm   #79
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Default Re: Adding a selectable line input to valve radiogram

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Hi Richard, Earthing aside, did you mention what type of source you were hoping to use with the line input? You are aiming for something at line level, 1vRMS? So CD players, blue tooth receivers etc?
Hi Richard
Firstly, I have to say brilliant work supporting my quest on here, thanks are definitely due.

I have an innuous HIFI server that stores all my music and films, and via wifi distributes these wherever there is coverage around the house. We currently have several Yamaha Musicast enabled devices that link to this server and we find these to be excellent. These sync to each other so can all play the same thing at the same time, or individually separate choices -Marvellous!

One of these is a Yamaha WXAD10 which enables all Musicast functions to be realised at an older HIFI amp enabling it to select via iPad or iphone all music from the server.

The intention is to connect another WXAD10 to the gram to see what a hifi signal sounds like through a valve amplifier, and of course to open it up to all our favourite music. We have several 40's 78's and some early 50's/60's 45's so it is important to have the deck operational too.

Hopefully a black Friday deal may be in order for the Yamaha.

I hope I haven't gone on too much with this explanation!
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Old 30th Oct 2020, 4:50 pm   #80
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Default Re: Adding a selectable line input to valve radiogram

Without wishing to add to the complexity of this continually evolving thread, there is going to be some difference in signal voltages at your planned line selector switch.
The output from the WXAD10 is liable to be much more than the 250mV (or probably less) from whatever stereo cartridge you use in the yet-to-be-fixed Garrard. This might mean some attenuation may be needed for the new device.
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