ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Yes, that looks promising -- especially now that sonavor has confirmed that a transformer with a nominal power rating of 120 x 0.34 = 40.8VA is working just fine.
Don't worry too much about the nominal rating of 1.25A because it i just that, namely "nominal". Nominal values are based on international standards and norms and they are usually quite conservative, meaning there's quite some headroom left.
I do worry a bit more about the fact that the lower wattage may cause problems regarding interference between the 24V analog circuit and the 6V digital circuit....Here's what I would do in order to make up my mind: *) Measure the actual current on the 6V rail (AC measurement directly between the 10V winding and the bridge rectifier); not just a single measurement but a 15-30min measurement in normal operation. Your Fluke has a min/max/average function and that will help to assess the actual current drawn in normal operation. Let me know the average and max current you read there. And also the real AC output voltage under load...and the DC voltage at the emitter of 2TR6 under load! (The circuit diagram suggests a 6.7V DC output whereas the logic gate chips FCH131 and similar are spec'd with max 6.3V nominal supply voltage...and that makes me wonder...!)
*) Now do the same on the 24V winding at the AC side between coiland rectifier. I know that the current drawn on the 24V rail can go beyond 2A because of the solenoid and other power-hungry parts but that's only temporary and shouldn't affect the average load of the transformer - and that's what "nominal" power and current usually stand for in transformer specs.
Once we have those values we can make a reasonably safe decision on which way to go.
Craig: ... thing is I don't want to remove the voltage selector switch if I can avoid it.......
... thing is I don't want to remove the voltage selector switch if I can avoid it.......
What do you mean by that? You don't want to lose the 115V/230V selection option? Well fine, then get the 115V/230V version: https://uk.farnell.com/vigortronix/vtx-146-050-212/50va-toroidal-transformer-2x12v/dp/2817651
But that sets you back a twenty quid ... and it's on backorder...It's up to you, the decision is yours.
That transformer is 81 mm in diameter. I'm not sure it would fit.
-sonavor
Oops, sorry! That was the 50VA version. They also carry the 30VA transformer with 2x115V primaies:https://uk.farnell.com/vigortronix/vtx-146-030-212/30va-toroidal-transformer-2x12v/dp/2817644
And it's available ex stock...and costs 10% less...and yet I wouldn't blindly buy it without measuring the real currents on the 10V and 24V windings first. I'm still sticking to my "better safe than sorry" motto I guess.
Craig, I don't think it is worth trying to retain the multi-voltage selection if you go with an off-the-shelf transformer.To retain the full BG4000 functionality (meaning including the original type neon strobe lamp) you will have to have some available AC voltage that gets you to the 180V ignition voltage for the neon bulb.You won't have that with the 120 V option using those off-the-shelf transformers.That is one nice thing about the LED strobe replacement. It works off the 10 V secondary which is there for both 120 and 240.I would just choose the best replacement transformer options for 240 V and if the turntable eventually gets sold to someone in a country with 120 V then the transformer will have to be updated (as well as the strobe lamp...unless the new transformer also supports it).Otherwise you will have to likely have a custom transformer made the fits the available dimensions, has 120 and 240 volt primaries, has a 180-220 V secondary, a 24 V secondary and a 10 V secondary.
Decisions, decisions, decisions :-)
The transformer I was looking at was indeed the 30VA version VTX-146-030-112 with an output current of 1.25A. Its only a single primary voltage transformer with a diameter of 74mm, I will check this evening but I think it may just squeeze into the footprint of the existing unit. I don't want to retain the multiple input voltage selection...just the switch, removing the switch and fuse box leaves a hole in the bottom that will require blanking off somehow.......not a massive issue I know, but if I can avoid it I would like to do so.....I will perform the measurements Manfy has identified and base the decision on the findings.
Either way it looks like we have a cost effective way forward, thanks gents
Oh and I did contact Canterbury Windings yesterday...an elderly chap answered the phone and advised me he was indeed the man responsible for such work but at the age of 70 had decided to draw the stumps....another loss which most likely will never be recovered.
Just to recap on the secondary voltages required....the secondary AC output voltage to the bridge rectifier 0D1 under no load was almost 32vac for the 24vdc supply
The secondary AC output voltage to the bridge rectifier 2D5 under no load was almost 9.5 vac for the 6.0 vdc supply.....will 2X12 vac outputs be good for these requirements?......I dont see an issue for the 6vdc supply but I'm not sure about the 24 vdc supply?
Craig: I don't want to retain the multiple input voltage selection...just the switch, removing the switch and fuse box leaves a hole in the bottom that will require blanking off somehow.......not a massive issue I know, but if I can avoid it I would like to do so.....
I don't want to retain the multiple input voltage selection...just the switch, removing the switch and fuse box leaves a hole in the bottom that will require blanking off somehow.......not a massive issue I know, but if I can avoid it I would like to do so.....
Thanks, now I get it. It's a combined fusebox/selector switch. Yes, I would want to keep the switch too...just for the optical appearance from the outside.If I had to do the same thing, I'd probably first think of digging out my Dremel...
Craig: Oh and I did contact Canterbury Windings yesterday...an elderly chap answered the phone and advised me he was indeed the man responsible for such work but at the age of 70 had decided to draw the stumps....another loss which most likely will never be recovered.
Sad indeed, but fret not!What would you say to a custom toroid with 230V primary, 40VA, 1x9V/0.5A sec, 1x24V/1.5A sec, including thermofuse, magnetic and electrostatic shield, diameter 75mm, height 35mm, incl. mounting accessories and made in EU. ...and all that for my special Chinese New Year offer of only EUR49.?? GongXi GongXi!
I think that's an incredibly good offer and if I needed one, I'd order it right away! You can configure it any whatsoever way from this French supplier:
https://www.audiophonics.fr/en/toroidal-transformers/custom-toroidal-transformer-all-power-p-3675.html
And if you don't want to use a Dremel on the fusebox, you have an even better choice: Get a 30VA R-coil transformer 2x115V, 2x12V/1.25A incl. magnetic and electrostatic screen, size: 78x70x40mm for an incredible 25.- Euros! (In case you're unfamiliar with R-core, it's a squarish toroid with a number of benefits over simple toroids: less capacitive coupling, even less flux leakage due to rounded cross section, etc. ...some Audioholics even claim that it is the holy grail in the audio industry...
https://www.audiophonics.fr/en/r-core-transformers/r-core-transformer-30va-2x12v-p-8539.html
Manfy
The 30VR R Coil looks a very good option.....I have attempted to buy one from the audiophonics website, however it says I need a minimum order value of EU160....I have sent them an email asking if I can have just one
Craig: The secondary AC output voltage to the bridge rectifier 2D5 under no load was almost 9.5 vac for the 6.0 vdc supply.....will 2X12 vac outputs be good for these requirements?......I dont see an issue for the 6vdc supply but I'm not sure about the 24 vdc supply?
Don't worry about it. Sonavor has already confirmed that his custom-made toroid works fine with V0=24.1V and Vload=20.5V at 1.5A. And he's been running that Beogram for years now.
In fact I'd see such a high idle voltage as more problematic than helpful. At 32Vrms you'd see 45Vdc after the rectifier. That means that 0TR1 has to burn (45V - 24V) *2A = 42W at 2A load current and that's not good.In most transformer specs the nominal voltage is the voltage at nominal current, which in turn means that the idle voltage will always be a bit higher. Just pick 24Vrms as your nominal voltage when picking the transformer and it should be fine.
Another word to my previous post: please read my statement "made in EU" as "sold in EU". I just read some reviews on that site and it suggests that the toroids are made in China -- which is not surprising at that price. Additionally, one buyer complained that the actual size was different from the initially ordered size. That tells me, if you decide to order a custom-made toroid there, don't just do that online. Email them before placing order and make sure they understand your stringent size requirements. That'll help to avoid disappointments and unwanted costs.
Craig: Manfy The 30VR R Coil looks a very good option.....I have attempted to buy one from the audiophonics website, however it says I need a minimum order value of EU160....I have sent them an email asking if I can have just one
Sorry to hear that! ...damn Brexit! ...damn you, BoJo!
This also looks promising from RS....
0030P1-2-012 | Nuvotem Talema 230V ac, 2 x 12V ac Toroidal Transformer, 30VA 2 Output | RS Components (rs-online.com)
One other bit of information on the voltage selection switch.I kept the original multi-voltage selection switch on my Beogram 4000. It just doesn't switch anything now.-sonavor
How does this stack up for the voltage regulator?.....
L7806CV Stmicroelectronics, Linear Voltage Regulator, 7806, Fixed | Farnell
And I'm thinking these parts need to be replaced with the regulator?.....little guidance required here
Craig: Manfy How does this stack up for the voltage regulator?..... L7806CV Stmicroelectronics, Linear Voltage Regulator, 7806, Fixed | Farnell
Hmm...that's just a standard run-of the-mill voltage regulator. The dropout voltage is 2V at 1A...it might work...if you're lucky...
Personally I'd reach for a real LDO, e.g. https://uk.farnell.com/rohm/ba06cc0fp-e2/ldo-fixed-6v-1a-to-252-3/dp/2342857?st=mktcpnslob2021It can take up to 25V input (and that's ok for 12V * sqrt(2) = approx 17V), delivers 1A, which is ok for our nominal 0.4A and has a droput voltage of 300mV.Unfortunately Farnell only has the DPAK version (SMT); the closest leaded TO220 they offer is a 7V version...We'd need to know the actual output voltage under load at the emitter of 2TR6 to be able to tell if that could work out.I do not know those antiquated logic gates FCH131++. The datasheet I have shows that they were made in 1967 and that's well before my time. I can't tell how they will behave when there are dips or surges in the supply voltage...and I fear that's what we may have to expect whenever the solenoids or motors draw a high inrush current.
And further to your second post, yes, those 3 components 2TR6, 2R22 and 2D4 need to be removed when a new 6V regulator is used.
Thanks for that Manfy....
Hopefully I will get some time to take some measurements to firm up the current and voltage levels under operating conditions...I'm happy to mount the voltage regulator off the circuit board so using a DPAK version will be fine if necessary, Dillen advocates moving 2TR6 off the board due to heat build up causing fluctuations in the 6v rail.......
Ok....first set of readings measuring between the 6v transformer output and the bridge rectifier 2D5.....MIN reading
MAX reading........
Average Reading.........
Lost the AVG reading.....no doubt it will turn up.
This reading is the Voltage measured at the output of the 6v transformer winding with no load....
Same measuring point with load.....
And now the 6v reading taken across OC2 which is essentially the emitter of 2TR6 under no load....
And finally the 6v measured across OC2 under load.......couple of the pics are awaiting moderator so may not be posted straight away
Ok.....bit of an issue getting pics posted, no problem these are the readings I have taken so far?
6v transformer output to rectifier
no load = 9.57vac
loaded= 8.61vac
6v transformer output to rectifier loaded
MIN = 0.001A (ac)
AVG = 0.236A (ac)
MAX = 0.257A (ac)
6v transformer output from rectifier
no load = 6.32vdc
loaded = 5.85vdc
24v transformer output to rectifier
no load = 32.27vac
loaded = 28.9vac
no load 0.07A (ac)
loaded 0.730A (ac)
It was unfortunate that I couldn't get a reading of the current when the solenoid energised on tone arm dropping, the first time I measured at this point the fuse in my fluke was blown.....its rated at 3A. Now this surge was so quick the fluke couldnt register it....I used my other fluke to make the same measurements as it is rated 10A and got the readings above.....I tried several times and couldnt get a MAX reading greater than 0.730A......looking at the solenoid operation it is very quick to operate the switch that drops the initial current down to the holding current.....i'm a little surprised its that quick!
Craig: .....I tried several times and couldnt get a MAX reading greater than 0.730A......looking at the solenoid operation it is very quick to operate the switch that drops the initial current down to the holding current.....i'm a little surprised its that quick!
.....I tried several times and couldnt get a MAX reading greater than 0.730A......looking at the solenoid operation it is very quick to operate the switch that drops the initial current down to the holding current.....i'm a little surprised its that quick!
I tjhink it's not surprising that you couldn't measure the initial surge current since the activated solenoid immediately switches off the direct connection of the soleneoid to ground. I guess this could happen in anywhere from 50-300msec and your min/max function on the Fluke789 isn't that quick. The manual for your meter doesn't provide any data but my Fluke 189, which came out shortly after, shows min 100msec for normal min/max and 250usec for transient detection in 'fast min/max' mode. But yours doesn't have 'fast min/max'.
It is a little bit surprising though that you see no difference between 'arm down' and 'arm lifted'! If I understand this correctly, the solenoid is ON whenever the arm is down and OFF when the arm is lifted, right? The holding current should be Vin/(Rsolenoid+7R1), ie. approx 30V/(9+8.2) = approx 1.7A... Is there any chance you could measure the solenoid current directly -- or at least the DC voltage from solenoid input to GND when it's activated? Or is that a mistake in the manual? An 8.2 ohm/ 1W resistor can take a maximum of 350mA before it starts going up in smoke...
============= edit: Oops, forget what I said! I completely overlooked the feedback from 7R1 to the base of 1TR10. This feedback loop controls the current through the solenoid transistor 0TR4, ie. as soon as that voltage goes >0.7V, 1TR10 and 1TR11 start throttling 0TR4.0.7V / 8.2 ohm = 85mA --> ergo, the holding current of the solenoid will be somewhere around 100mA...and that sounds fine for solenoid and 7R1!
Hmmm, nevertheless.... you still should see a different current on the 24Vac winding on arm up and arm down! I think you should redo that measurement, but this time forget about the min/max average mode, just measure it in normal AC current measurement and give me the mAac values for tonearm up and tonearm down. Thanks!
Ok.......took three measurements this afternoon:
Unit switched on, measuring between the transformer 24vac output and rectifier, carriage moving to drop point for 33rpm = 420mAac
carriage stopped and solenoid energised = 740mA ac
Tone arm lifted and solenoid deenergised = 370mAac
Excellent! That settles it!Those values make sense and we can assume an average current of 0.75A at the 24V coil during normal opetration and 0.25A at the 9Vrms winding (or 12V in case of the 2x12V replacement trafo). Thus we get 0.75Ax24V+0.25Ax12V = approx 21VA at normal continuous operation. By choosing a 30VA transformer we therefore have 50% headroom for surges caused by solenoid, relay, motor inrush currents and other unknown factors/variations.Your measurements in max mode show that we don't have to anticipate lengthy repetitive high current events during nornal operation.
Therefore I'm happy to sign off on your request for an off-the-shelf toroid with only 30VA nominal power and 2x12V secondary windings. I'm 95-98% confident that this won't cause any trouble in the future in terms of overload or overheating of the transformer.
Regarding the 6V supply I still stick with a fixed 6V LDO rated at 0.8-1A. A leaded TO220 would be best because you could add a 50 Cent clip-on heatsink if needed, but an SMD version is fine if kept away from external heat sources.You may want to order some 0.2A slow blow fuses as a replacement for the existing T0.25A versions. 30VA/230V = 0.13A nominal primary current, so 200mA fuses seem more appropriate.
Congratz! Now I have a good feeling about the 30VA transformer and the whole fix of ths transfrmer issue.
That's quality........I have a 30va transformer on order, its 70mm dia some im confident it will fit into the footprint of the original, I dont have a problem mounting the voltage regulator off the PCB2, It's a very congested board and as I said Dillen advocates removing 2TR6 to avoid excess heat....I will order this BA06CC0FP-E2 Rohm, Fixed LDO Voltage Regulator, 4V to 25V, 300mV Dropout | Farnell and mount it on a board and wire onto the PCB2....
Cheers Manfy.........appreciate your help
Craig: ....I will order this BA06CC0FP-E2 Rohm, Fixed LDO Voltage Regulator, 4V to 25V, 300mV Dropout | Farnell and mount it on a board and wire onto the PCB2....
....I will order this BA06CC0FP-E2 Rohm, Fixed LDO Voltage Regulator, 4V to 25V, 300mV Dropout | Farnell and mount it on a board and wire onto the PCB2....
Don't forget to order the stabilizing caps! They are to be mounted close to the input and output pins of the regulator.Your datasheet recommends >330nF at input and shows a 22uF cap at the output (specifically defined as tantalum and low ESR). Since you'r not running the LDO at its limit I think that 10uF tantalum on input and output should be fine (or any value from 1-10uF).
Impressive team work between the 2 of you, Craigs perseverance and Manfys technical knowledge coming together in perfect harmony, I cant wait to see the end of this, standing applause to both of you
Collecting Vintage B&O is not a hobby, its a lifestyle.
thanks Soren.....always a comfort to know your looking on.....
First pass at connecting the voltage regulator off the PCB....the unwanted components removed
Well...a further twist in the saga of the missing BG4000.....Justin has sent me this from his other BG4000 which is not in as good condition cosmetically as the missing unit...I will install this transformer into the missing deck, test it over the weekend then ship it back to Justin in the armoured enclosure......following which Justin will forward the donner deck and I will install the power supply mod and toroidal transformer into that one.
Got the doner transformer fitted yesterday........went in well enough
Plays well.......the transformer gets lukewarm after around 40mins playing, considerably cooler than the original, I will leave it on test for a day
Good news Craig! Just beautiful.
You know, my Beogram 4000 has been permanently plugged for 10 years now. Still works great.
Jacques
Ok......that chapter closed I have started to look to the transformer mod prior to receiving the donner unit......I wanted to hook up the various components and see what transpired.... small piece of circuit board and a bridge rectifier that I wont need to install in the final fit.
The TO252-3 package isnt the most friendly configuration in my view........difficult to connect to a circuit board in the conventional manner...this is due to the FIN being used as the ground.
An uncomfortably ugly spot of solder to attach a pin worked, I was worried about using too much heat to achieve this resulting in damage to the package.
The circuit board will be cut down to suit the final mounting location when chosen....
Hooked up my variac and measuring across one of the transformer 12v secondary windings to the rectifier measured 14.4v...a little higher than I was expecting but not an issue.....