Big, stylish and Dutch. Initial look at this Philips Reverbeo B7X14A Stereo restoration - part 1

This project is the second on this style of Philips tube radio, but this time it's the big brother. Philips tend to follow a slightly different design and build philosophy to the German radios I usually work on. However, the quality of the design, incorporating stereo for the external source input, promises to deliver amazing sound quality.
It also has a reverb tank incorporated in it, hence the 'Reverbeo' in the name, so the effect should be interesting.
The condition of this radio is a little daunting, with a 'protective' coat of tar resulting from years around a smoker, but nothing that some TLC won't fix.
Hope you enjoy it.
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[@jassenjj]

Wow, what a radio! It has a transistor but a tube rectifier, my favorite tube EAA91 and a coil-driven FM tuning... It's a strange mix of technologies, can't wait for the whole project.

[@electronicsoldandnew]

👍

[@goodun2974]

The reverb tank is made by Gibbs/Accutronics, the same brand that was used in most (not all) guitar amps of the 1960s. The electrical input/output impedance of the tank would be chosen for the type of circuit it was to be used in; in a Fender amplifier with reverb, the tank was driven from a small (Champ !) output transformer and therefore had an input impedance of about 4 ohms; on the other hand, Ampeg and Magnatone often used tanks that were driven through a capacitor directly from the plate of a preamp tube, and so the impedance (not the same as DC resistance) was usually much higher. If you find a code on the tank that begins with a 4, like 4A, 4B or 4C you can look it up online and it will tell you the input and output impedances of the tank, as well as whether it was designed for horizontal or vertical mounting, and whether either or both of the input and output connectors (which appear to be missing) are grounded to the tank, or not. By the way, early reverb tanks often had a sticker on them that said "made by beautiful girls in climate controlled conditions in Wisconsin"! PS, the spring reverb system was actually a Hammond Organ invention and that's why they have a reference to a patent number on the tanks. And as an aside, Although we often associate Hammond organs and rotary Leslie speakers together, Hammond hated Don Leslie and his invention, and the company did their best to position their organ dealerships and their marketing so that the two different brands/products would never be used together; but in the end it turned out to be kind of like keeping peanut butter and chocolate, or peanut butter and jelly, apart. 🙂 ( I haven't watched the entire video yet but the parts covered in degraded foam that appeared to have fallen out of the reverb tank were probably some kind of locking mechanism to hold the springs from vibrating during shipment so that the little magnetized hooks that the reverb springs are attached to would not break off).

[@reynaldopichardo]

I grew up with one of these at home. It took a while for the sound to pop out at the selected volume level as you had to wait for the tubes to warm up enough to their ideal working temperature. The speakers were set at an angle,to project the sound in a way that each hit the sidewalls of the room, in order to meet at the center after bouncing to recreate the stereo effect. It was heavy as hell! We keep ours on its own high table. It had real wood (I think hardwood as ours was dark like mahogany) which made termites fall in love with it (they didn’t pretreat the wood back then). It was very loud! I guess the fact that it was solid, provided for the great deep base sound. You could fine tune the stations until you gained the best quality from the broadcasted signal. Mind you it was built to last. Only needed the casual burnt vacuum tube replacement if used too loud constantly for months. I was born in the 60’s and our radio was already at home with us. Saw the family expand till the last was born, then after that the grandkids… My dad had bought this radio, together with a black & white Philips TV and stereo console by Marantz to complete the entertainment needs. Back then they built things to last…

[@electronicsoldandnew]

They sure did. I’m always amazed how these things come back to life after a little work. Amazing.

[@ralphmans]

Looking at the Z1, I remember some German radios that used something similar. It was a high wattage, 7-10 watt resistor mounted vertically with a similar spring action connection. When the resistor would get too hot, the solder on top would melt and the “spring” would let loose and open the circuit. You repaired the problem, soldered the “spring” back on to the resistor and you’re back in business. Love your videos, keep ‘‘em coming.

[@electronicsoldandnew]

Those resistors got really hot. Yes, soldering it back is the correct way to solve it, but in this case you must do it with rose metal solder that melts at about 95 degrees Celsius.

[@poormanselectronicsbench2021]

I will say that, your breakdown of schematic study, as well as documenting your progress through it, is second to none for anyone I have seen on any other channel. It looks like there was a direct connection of that bad rectifier tube and the thermal protection link being tripped on that transformer, so, that "cause and effect" part of the restoral should be considered solved. Great content, as usual! 👍

[@electronicsoldandnew]

Thanks

[@ry491]

Hi again . I have restored one of these for my own use . Same covering of nicotine ! Took ages to clean . Some points to bear in mind . Beware of the high voltage dial illumination panel . These are terrible and prone to burn out or even explode and crack the dial plate !! Yes really . Replace with normal bulbs run off the Lt supply . The speakers are 800 ohms and because the voice coil wire is so thin are liable to fail . Replacements are virtually impossible to find . One of mine had a normal speaker and a different opt fitted ... Not by me . Sounds ok so left well alone . The transistor is part of the reverb circuit . The caps and resistors are mostly good quality . I only replaced electrolitics and the Philips tar caps . Almost everything else checked out within spec . Alignment looked like a nightmare but it worked so well that I didn't disturb that . Sound quality is superb with very clean bass . Because it is biamp an MP3 or similar can be connected straight to the input without pot divider . The reverb gives fantastic realism to speech but not as effective on music I find . Good luck with it but DO watch out for that dial light panel . It is lethal . Even it yours works which is unlikely , disconnect it !! . I have used mine almost daily for the last 5 years and it has proved very reliable apart from replacing both EL 84s and magic eye at some stage . Enjoy the journey . Well worth the effort when working well . Best regards from Thomas in UK .

[@electronicsoldandnew]

Thanks for the info Thomas. Always appreciated.

[@michvod]

Hey, friend of mine actually had a go with an electroluminescent film that replaced the original. This was on similar radio, and the dial scale now looks stunning. It did cost him a bit and some experimentation. I think he got it from eBay, and he had to lower the current quite a bit as it was too bright. Btw, if his set was my set, I would probably machine a custom matte plexi plate to accept green LEDs and to disperse the light evenly. I would probably use a diffusor plate off a broken LED LCD screen as it is designed to diffuse the light evenly. Normal bulbs are okay, but once you see the EL backlighting it just blows you away

[@michvod]

Actually, found the right stuff. You can replace the electroluminescent panel with one that are selling by Conrad (at least here in continental Europe). Part number: 184057-62

[@electronicsoldandnew]

I’ve seen those screens before. Very rare nowadays.

[@electronicsoldandnew]

thanks

[@radio-ged4626]

Reverb on the common cathodes, very interesting. Clever bit of circuitry. Can't wait for the next episode.

[@electronicsoldandnew]

Actually, I got that wrong 😊 I’ve been corrected in the previous comments.

[@radio-ged4626]

@@electronicsoldandnew Ah, yes just seen Stefans comment about the pnp transistor. Will look at the circuit myself later. Hybrid circuits always catch me out.

[@electronicsoldandnew]

me too 😊

[@PatrickClutch]

One KZbinr taught me something important - when you start the equipment for the first time with the Variac, remove the rectifier tube and replace it temporary with a solid state rectifier diodes. thanks to this you will power the B + from the very bottom, without waiting for the rectifier tube to start conducting.

[@electronicsoldandnew]

Good point.

[@poormanselectronicsbench2021]

That is a good technique if you are trying to "reform" the existing electrolytic caps, as you can bring them up to voltage slowly instead of having the B+ "switch on" once the rectifier tube starts conducting at the higher secondary voltage. It probably wouldn't be as important to go solid state if you have replaced the caps (as Manuel has done) already, but with proper monitoring either SS or tube wouldn't hurt going with new caps.

[@goodun2974]

I do the same as you, temporarily replaced the tube rectifier with a plug in solid state rectifier, but, *Do not run the variac up to full line voltage while the unit is operating from a solid state rectifier*, Otherwise you will likely severely overvoltage the old capacitors and perhaps the tubes as well. Stop the variac at about 75 to 80%, so 90 to 100 volts maximum input AC for a 120 volt radio, and 180 to 200 volts input AC for a 220-240 volt radio.

[@electronicsoldandnew]

👍

[@electronicsoldandnew]

👍

[@JacGoudsmit]

My high school in the Netherlands had an annual flea market where I bought some of my electronics in the days when I couldn't afford new hifi statement equipment. One of the things I bought was a Philips tube radio with stereo amplifier that (in my memory) looked just like this, but I know they made several variants. Unfortunately when I got it home, it didn't work. I threw it away (I know, I shouldn't have done that) but I kept the reverb. I found out that I could connect it to the headphone output and the microphone input of my sound mixer panel. Good times. Oh and I also remember it had some sort of fluorescent light that didn't work anymore either.

[@electronicsoldandnew]

I think all of us threw something away that we now regret 😊

[@dl7majstefan753]

Dear Manuel, what a big radio! I don´t understand the reverb circuit with transistor TS1 completely, but my opinion is that the reverb signal is fed out via the collector of TS1(R81) via C85. The emitter is the positive DC supply (for PNP) and filtered by C86/R83 and the cathode C84. Good success!

[@electronicsoldandnew]

That make sense. I first thought it was feeding through the cathode, but your explanation is more logical.

[@PatrickClutch]

These are the kind of videos I like - long, informative and interesting. Thank you :) And one more thing - this model is a white crow - there is nothing on the internet about it unlike the B7X43A

[@electronicsoldandnew]

I know. Very little info.

[@michvod]

Of course there isn't any info, as there is a typo in the title. The radio is actually B7X14A

[@electronicsoldandnew]

Corrected. Thanks 😊

[@nickk6109]

Nice - I've got the 1957 H4X73A (FM/AM receiver and record deck). Mono only. 220V only so needs a buck transformer for running at 245V to keep the heaters in spec. The Phillips black pitch caps were ok on mine but I may update them at a later date.

[@electronicsoldandnew]

👍

[@sincerelyyours7538]

Though I like your fuse add-on modification, I think there are situations where the current and temperature don't quite rise at the same rates so one should replace a current fuse with a current fuse and a thermal fuse with a thermal fuse whenever possible. A poor-man's solution that I have used on isolation and step-up transformers is to epoxy a NC furnace type thermal switch directly onto the transformer core. Those rated for 45 deg C will stay closed until the core temp reaches 45 deg, then open and stay open until the core drops 10 or 15 deg depending on hysteresis, then close and the cycle will repeat itself until the power is turned off and the fault isolated. Transformer cores take a while to cool down so depending on their physical size it could take an hour or more before the switch turns back on. I have probably saved myself from at least one shed fire with this modification. It's simple, cheap and reusable, though I admit maybe not that pretty inside a classic tube radio. Thanks for the clear and easily understood circuit description, BTW - always appreciated!

[@electronicsoldandnew]

👍

[@greengrayradio1394]

Nice project here, Manuel! I believe the cause of the thermo fuse melting was that shorted EZ81. Must have been an anode-to cathode short, the voltage was so low that the cathode could not heat and the tube not conduct in normal way. That fuse probably saved the power transformer. Regarding the transistor following the reverb tank, it seems to have its power feed from the cathodes of the EL84s. Nice way to get a low DC instead of using a big dropper resistor "oven" from 2-300V. Chassis cleaned up nice, this will be a show piece when done!

[@electronicsoldandnew]

👍

[@audioreparaciones8956]

This is going to be great! I restored a very similar model, so I am very interested in this work of yours, which is very good. Cheers, Manuel! I hope you enjoy this radio

[@electronicsoldandnew]

Thank you

[@dfddwm]

There is a later model that has a stereo tuning indicator which means it should be a stereo FM tuner. I see your model which you say is the earlier model doesn't have a stereo signal indicator so it's mono on radio. I think it's a fine sensitive tuner. Got mine from Holland in excellent cosmetic condition refurbished but needs attention now. I was told there are parts on this that just cannot be found anymore so I'm looking forward to the work you carry out. Many thanks for uploading.

[@electronicsoldandnew]

My pleasure. Good luck with yours

[@edwardhannigan6324]

Cool start to a new project..Love the walk thru, and fab description and info..Look forward to more videos..Learning so much all the time... Thanks for sharing your expert knowledge..!.. Ed UK...😁

[@electronicsoldandnew]

My pleasure

[@ronholder5844]

I remembered what is used in the overheating protection for the transformer. 'Rose's metal, Rose metal or Rose's alloy is a fusible alloy with a low melting point.'

[@electronicsoldandnew]

That’s the name I was looking for 😊

[@chrisclark6192]

Hi Manuel. Great stuff as always. I must confess that I have not come across a reverb tank in a radio before. Is this something that is unique to Philips radios?, as they always had a way of doing some things differently to most other manufacturers. I watched the part were you explained the theory of how it worked 2or3 times to grasp the idea and now I understand. This is looking like being a very interesting series. As always another enjoyable video of your great work. Cheers Chris.

[@electronicsoldandnew]

I’m not sure if any other brand used them. My explanation, while delivered with confidence, was … unfortunately incorrect 😊 Stefan explains why in the previous comments.

[@chicodosradios]

Parabéns por ter conseguido esta incrível peça de engenharia Holandesa. A julgar pelos meus que agora já são três vai ser um grande rádio no fim do restauro. Esse reverbeo é qualquer coisa de extraordinário. Continuação do excelente trabalho.

[@electronicsoldandnew]

Obrigado 😊

[@edmaster3147]

Great! Right now, i'm recapping a b5x42a for a friend, and putting in bluetooth, that one's stereo too. This one seems to have nothing much wrong with it, but hopefully that aren't the 'last famous words on that'. Anyhow, looking forward seeing your vids, thanks for sharing and all the effort involved!

[@electronicsoldandnew]

My pleasure

[@Michlag]

And another wonderful saga... Manuel, i was asking myself (more because I'm dwelling with this now) if you ever filmed a stereo multiplex alignment? This would be very interesting... Ok back to dutch :D

[@electronicsoldandnew]

Never did align one of those 😊 There’s always tomorrow 😊

[@garthwood5104]

As chance would have it, I'm working on a Philips B5X44A, ten tubes and six transistors (from circa 1964-65). It was DOA, so the first thing I suspected was the rectifier tube (an EZ81); sho 'nuff, it's dead, but it would be relatively easy to sub in a couple of diodes (you could probably replace them right into the sockets!). And like yours, mine's quite a large beast, with great honkin' speakers and a beautiful (although beat-up) real lacquered wooden case.

[@electronicsoldandnew]

Just be careful with the B+ that will result from the two diodes as it may be quite high. You may need to add a series resistor to drop it a bit. Those speakers should sound great.

[@garthwood5104]

Yeah, I've already been thinking about that -- the EZ81 can drop somewhere between 15 and 25V; fortunately, the schematic I've found for the radio specifies the B+ that's *supposed* to come off of the EZ81, so I can just adjust for that target. "New" EZ81's are around $20 USD per plus shipping and do not come with a guarantee, and I'm trying to get this working again for a buddy who doesn't want to burn money on this radio, so I'm looking to save wherever I can. And of course, there's a nice complicated dial cord setup inside it. I hate dial cords. ;-)

[@electronicsoldandnew]

There’s no problem with using the diodes and a resistor, except for the initial high voltage leak before current starts being drawn. Dial cords: A plague 😊

[@davidhollfelder9940]

M Caldeira into the big “caldera” of a big radio…

[@electronicsoldandnew]

😊 Just hope it’s not active. Crater lakes sometimes turn into volcanoes again. 😊 💨

[@nigelbrockwell6237]

This is one worth following. I guess Z1 is a thermal fuse and just tripped, because the solder sort of dried out over time. As for that re-verb spring unit it is the first time I've seen it in a radio. Many years ago I made a spring unit similar, to put a bit of an echo on a microphone. I hope later when you are testing that part it comes across on the video sound.

[@electronicsoldandnew]

I’m sure it will

[@michvod]

Z1 is a thermal fuse, and it is most likely of a low temp solder melt type (could be from 45 to 90 deg C.). It most likely tripped when the radio was turned on with the EZ81 shorted internally and the transformer got hot. The reason for the EZ81 failing could be leaky mains filter, too bad you didn't try to reform it as we would see if it draws excessive current. Also, I would re-set the fuse (remelt the existing solder), and put it back, and I would also keep the one you've put in, in series. David Tipton also repaired the same type of the fuse with the same low melt solder

[@donhall2759]

Looks like your original EZ81 rectifier short was the reason for the blown thermal fuse, IMO. I like your "real fuse" much better than the rose metal original. Looking forward to following the rest of the restoration!

[@electronicsoldandnew]

👍

[@geirendre]

Rose's metal consists of 50% bismuth, 25-28% lead and 22-25% tin. Its melting point is between 94 and 98 °C (201 and 208 °F). Philips used this type of themperature fuses in many of their transformers back then. I use to harvest rose's metal from old transformers and other items as it's dificult to buy it.

[@electronicsoldandnew]

👍

[@goodun2974]

It sounds like this Rose's Metal is similar to "chip quick", a special low temperature solder with a wide temperature range for its liquid or plastic state, which is used to make it easy to remove microprocessors that have many dozens or hundreds of small tiny connections. The stuff is rather expensive.

[@kevkabluebird1032]

I recently got a similar big grundig for free. Just the electronic and base, no chassis. This will be my first radio with my very own... wooden radio chassis :D Sadly i dont have such nice speakers like your Philips. This Grundig is also some sort of hybrid with transistors, tubes and relays too. Never had a tube radio with big relays to be honest. I dont have a part number for my grundig, its all gone sadly. The faceplate does not tell the model either. It also has some "moduls" with additional tubes and you connect these "moduls" with their own PCB into some of the empty tube sockets. Its like connectors with a tube base. All the PCBs are royal blue in colour, very interesting. Oh and its the first radio i own with... 4 transformers. A very big on and 3 smaller ones. Also very odd but okay.

[@electronicsoldandnew]

That sounds like a really unique Grundig. Have fun restoring it.

[@kevkabluebird1032]

@@electronicsoldandnew In the end it will be more about building a case from scratch. Never did any big wood work and stuff.

[@garthwood5104]

As I've dug around further in my B5X44A, I've run into exactly the same problem that you have -- a thermal fuse buried in the primary windings that's blown. I'm not sure of how I want to proceed, but I think I would like to do a closer visual inspection of the high-current-draw components and see if anything's dark or burnt-looking; perhaps one of them was drawing excess current and caused the transformer to heat up to the point the fuse melted. My EZ81 rectifier's "getter" is almost black, which makes me suspect I might have a problem like yours (but unlike you, I don't happen to have any other EZ81s to swap in!). The other possibility is that the layers of caked-on dust etc. caused a "partial short" (low impedance path) somewhere, perhaps due to absorbing humidity and then being energized (it was stored in a relatively humid basement for a number of years). I'm quite wary of replacing the fuse and powering it up, since I'd like to know the reason the fuse blew. I've also found evidence of others having been monkeying around inside the case -- some solder joints to newer components/wires are badly corroded, which makes me suspect plumber's flux might have been used. To my surprise, all of the interior pilot lamps are still working, but their current draw is considerable; if I proceed with repairs, they're all getting swapped out for appropriate LEDs (single lamp or strip!). This is not going to be the quick fix I'd hoped. :-/

[@electronicsoldandnew]

These philips sets are almost never quick fixes 😊

[@hanske4106]

Nice! Another Bi Ampli project! A look at the scale learns this radio was probarly sold in Germany. I have seen many Bi Ampli's in my life but never saw the 800 ohm speakers or the special connectors they would use. Not very practical those high impedance outputs. Good luck!

[@electronicsoldandnew]

👍

[@tkcs8872]

Cool, I have one of the same type. It came from Switzerland with Italian inscriptions. Yours seems to be in German (except for the balance control which seems to be Dutch). So I can use your videos when I do the restoration of mine. There is a sheet of asbestos between mains transformer and amplifier tubes. Was it already removed on your radio?

[@electronicsoldandnew]

Yes, that sheet was something I was on the lookout for, but it’s not here.

[@p_mouse8676]

Interesting to see that one little transistor in there lol On so many levels makes you wonder, why they didn't use those as current sources and such etc etc...? When you said that Philips always does things a little different, that made me really laugh. Also so my experience, I came across quite some schematics that just don't correlate with the actual circuit. I have never succeeded to empty a Philips B+ capacitor can. They all seem to be totally stuck in there unfortunately :(

[@electronicsoldandnew]

Use a heat gun or hairdryer to heat the can. It then comes out easily.

[@ricardoaliasdelatorre6836]

Manuel, I assume that Ts1 works as an impedance transformer from Hi Z (delay-spring line) to Low Z cathode. Did you check Ts1 for leakage, aging affects this manner. Only as a caution 😉😉.

[@electronicsoldandnew]

Not done that part yet

[@greggaieck4808]

Phips shortwave receiver is cool

[@electronicsoldandnew]

👍

[@lennartbenschop656]

This one has a faceplate with German inscriptions and the AM bands marked in kHz/MHz. There's probably also a version with combined Dutch/French inscriptions on the faceplate and the AM bands marked in meters,, as Philips sets for the Dutch and Belgian markets typically had. 800 Ohm speakers were originally designed for output-transformerless sets, using a special output stage using two tubes, with an exceptionally low output impedance (for a tube stage that is) and 800 Ohms was probably as high as they could get the impedance of non-electrostatic speakers. The built-in speakers appear to be the same impedance as the external connections. But this set does have output transformers. Apparently they found it too costly to have the OTL circuit twice for a stereo amp. It also has the Bi-ampli logo on the faceplate, another Philips invention. Originally they had dedicated amplifiers and speakers for bass and treble, but when stereo records came along, they used identical amplifiers/speakers and when the radio was used for mono. they would feed bass to the left channel, treble to the right channel. This reverb spring makes an interesting sound effect that is mainly good for demonstration purposes. This one uses conventional dial lamps, but some versions of this radio have an electroluminescent screen that emits green light. That will not work after all those years and it real electroluminescent screens are impossible to get.

[@electronicsoldandnew]

Great feedback. thanks

[@goodun2974]

Some late model Magnatone guitar amps used electroluminescent backlighting, and as of a decade ago a suitable replacement tape was available. You might be able to use some kind of kind of Cob or gel phosphor LED tape nowadays.

[@goodun2974]

Here in the States, my brother had an early Sixties Dodge or Plymouth convertible that used a reverb tank for the speaker in the rear of car! I have also seen a few old Magnovox or Motorola stereo consoles, both tube and solid state, with a reverb tank built-in. Fisher used to make an add-on spring reverb system for some of their tube type stereo equipment.

[@electronicsoldandnew]

👍

[@tobi8496]

The original reason of the Reverbeo is that the AM bands sounds a little bit more like FM stereo. I have the stereo version of this radio it sounds great with the Reverbeo.

[@electronicsoldandnew]

I’m looking forward to trying it out.

[@EsotericArctos]

I'll be watching this for the bluetooth add on ideas this time. As much as I love the radio itself as well, I have a little project of my own I need ideas for. I have an old Grundig that has a stereo input, but is mono for the radio side. I'd be interested in looking at ideas on how to possibly use a bluetooth option. I saw you put a fuse to replace that little heat sensitive device on the transformer. Not a bad idea. Was the original device also detecting temperature of the transformer to kill the power if it get too hot, or was it purely an absolute value current limiter?

[@electronicsoldandnew]

I believe it melted when the transformer got too hot. Since that happens when the current gets too high, I decided the fuse could do the same thing.

[@EsotericArctos]

@@electronicsoldandnew Sounds like a good solution. That little device may have saved the power transformer in this set.

[@goodun2974]

@@electronicsoldandnew i recommend replacing the thermal fuse (that's what it is, subject to going "open" from heat and not from current) with another of similar or same temperature rating. It isn't there to protect the transformer really, *it's there to prevent your house from burning down if the radio is accidentally left on overnight or while you are away*. If a fault elsewhere in the radio causes the transformer to run too hot, or for that matter if some windings short inside the transformer and it overheats, the thermal fuse will shut it down before it can set fire to the radio and, by extension, your house. Remember that these transformers were designed for intermittent use and not continuous or commercial service where they would be on 24/7. You will find similar devices inside modern coffee pots and Keurigs and so on. If the thermal fuse has a number on it, you might be able to look up the spec, otherwise, Take a guess at the maximum safe temperature of the transformer, or measure the transformer temperature when the radio is in operation, and select a thermal fuse that is just very slightly higher than that. Be sure to locate the replacement thermal fuse right up against the transformer windings ( with some transistor-heatsink grease). Many modern solid state receivers and amplifiers and so on have the thermal fuse actually tucked into the windings tightly, but sometimes visible and typically with the connections brought to the outside frame of the transformer onto a terminal strip, so that you can test the thermal fuse if the transformer stops operating. Sometimes we can put a drop of silicone lubricant spray on the dead thermal fuse and grab it with pliers and pull it out, and tuck a replacement device in between the windings, but oftentimes the best you can do is bypass it with a new thermal fuse, pushed up against the windings and coated with transistor-heatsink grease. A few years back I worked on a direct drive turntable that died after accidentally being left on all night. The electromagnet coil was wrapped in rubber or heatshrink tubing and had a dead thermal fuse tucked against the coil. I cut away the rubber and replaced the dead thermal fuse, and the platter started spinning again ----- at over 100 rpm ! I found a shorted driver transistor on the power supply board; I am guessing that the transistor failed first and caused the turntable to run at excessive speed for a few hours night until the thermal fuse blew before the direct-drive motor coil could get hot enough to catch fire.

[@electronicsoldandnew]

👍

[@goodun2974]

Update: I just watched a little more of the video including the close up of that thermal fuse device. This is a very early version of the modern thermal fuse devices I am familiar with , which are usually little torpedo shaped metal cylinders, about the size of a 1/2 W resistor. The device you hold in your hands was apparently made with a low temperature solder (similar to Chip-Quick"?), and instead of having a filament or wire that melts and breaks the connection, the solder would melt and then the contacts would spring apart. Pretty ingenious for those days but I would suggest you get a modern thermal fuse and use that as a replacement. And since I mentioned chip-quick, it is a special low temperature solder with a wide range of temperature at which it remains liquid and plastic, used to more easily remove/unsolder microprocessors with multiple, closely spaced pins that are almost impossible to individually desolder.

[@alfredneumann4692]

Someone hast used the two switches, to replace the inner loadspeaker with externals, which are to heavy. So boom, the temperature-fuse and EZ81 blows. Am i right?

[@electronicsoldandnew]

Probably what happened. Those switches were definitely a hack.

[@mackfisher4487]

Had a weird thought during this episode, it would be fun, but probably not practical to add a digital FM circuit (or analog) for stereo FM as you have the two audio output amplifiers. However that could lead to a revolt amongst Phillips radio community.

[@electronicsoldandnew]

definitely would cause a revolt 😊

[@geirendre]

I don't totally agree with your analysis of the Reverb circuit I'm afraid. As the Cathode of the EL84's have a 160uF capasitor and C87 (54uF) in parallell to ground, basically shorting all audio to ground. So I don't think there's much of a audio signal there. That's just DC supply to TS1. I rather think that the signal goes from collector of TS1 trough C85, trough Switch 12 and to the grid (pin 2) of the ECC83. So it modulates the right channel with reverbed audio from the left channel it looks like. When it comes time for those beloved IF cans (yes you know who I mean... LOL), I found that on mine Philips it worked great to heat them gently with an airgun at a low temperature (150 C or so), just to soften the wax inside them. Without heat they where stuck and impossible to move. After heating the cans, and waiting a few moments to let the heat get into the core then they moved quite easely.

[@electronicsoldandnew]

You’re absolutely correct about the reverb circuit. I just didn’t give it enough thought when I first looked at it. Stefan raised the same subject. I’m already dreading those IF cans 😊 I’ll definitely go that route when I get to them.

[@tubeDude48]

*TRIPLE THUMBS-UP* If I could!!

[@electronicsoldandnew]

😊

[@jutukka]

I don't understand how that reverb transistor would modulate EL84 cathodes which are bypassed by a large capacitor. I think the reverb signal goes out amplified by the transistor from collector through c85. And the pnp transistor just takes its 7V power supply voltage from the cathode voltage of EL84s. Even tremolo oscillators cannot modulate hi value capacitor bypassed power tube cathodes, they always modulate high imp. signal path.

[@electronicsoldandnew]

I’ve had a closer look at the circuit, and I believe you’re right.

[@jutukka]

@@electronicsoldandnew And because transistors don't need 200VDC power supply, the very easy way to get that around 7V is from that EL84 cathode voltage. Because the collector side of the PNP transistor is at ground level side, that positive emitter voltage gives excactly the negative power supply voltage to collector, which neg. voltage is needed because that transistor is a PNP.

[@electronicsoldandnew]

👍

[@Mrdibzahab]

You don't see Hilversum and Bayreuth often on the same dial plate :)

[@electronicsoldandnew]

😊

[@goodun2974]

Explanation?🤔

[@jdmccorful]

A different but interesting "cat". Thanks for the look and education.

[@electronicsoldandnew]

👍

[@paulbennell3313]

Philips weirdness. Keeps it interesting!

[@electronicsoldandnew]

Sure does !

[@FrancisoDoncona]

I have this

[@renowden2010]

so now you know why the fuze was blown.

[@electronicsoldandnew]

👍

[@danielsaturnino5715]

Hmmm I dont like the aesthetics to be honest. But it sure looks like a great reciever and audio platform.

[@electronicsoldandnew]

I actually like it 😊

[@danielsaturnino5715]

Even better then :)

[@andrewagner2035]

Nicotine infused radio, power up with a series light bulb.

[@electronicsoldandnew]

I always do. The dim bulb tester

[@jutukka]

That reverb in an a radio seemed to be a very short-lived gimmicky fashion phenomenon, and no wonder, because it really isn't very useful in radio listening, and is very far from true principles of hi-fi. For example a separate 6.3V heater winding for only rectifier tube would have been a sensible investment, to make that radio more reliable. But perhaps useless gimmick features sold better than reliability then, as they probably sell nowadays better as well.

[@electronicsoldandnew]

The power of marketing 😊

[@jutukka]

@@electronicsoldandnew In guitar amps however spring reverb tanks still are great sounding and very usable effect devices. Especially original made in USA Accutronics tanks sound great and last forever if not mishandled.

[@electronicsoldandnew]

👍

[@DavidTipton101]

Hi Manuel, the low melting point solder is called Roses's or Rose metal, I have some (a lot 😒) I'd be happy to send you some but the fuse will do a similar job as you know. The electro cap worked well, it looked like it hadn't been touched and the chassis is cleaning up so well, I'm very jealous. I assume the speakers are 800 Ohm, I haven't had a set with them yet so I am curious as to why they jumped from under 20 Ohm to 800. Thanks Manuel. en.wikipedia.org/wiki/Rose%27s_metal

[@electronicsoldandnew]

I remembered that you had a rose metal encounter in one of your projects. The speakers are in fact high impedance ones, so can’t test it with my usual bench speakers. Must remember that 😊

[@kerronjohnstone5789]

I am working on restoring a similar unit - a South African-designed and manufactured Philips F4VZ 25A/R from the '60s, a radiogram unit which I want to convert into a desktop similar to the B7X14A. I looked around a lot and eventually found an original Philips document explaining the reverbeo concept - the "electro acoustical reverberation unit gives considerable depth and spaciousness to sound stemming from radio broadcasts or gramophone records and appears to expand the dimension of a conventional room to those of a concert hall" - see www.vintage-radio.com/download/reverbo-leaflet1.gif There was no schematic available, so I had to trace out the whole circuit. In short, when on the reverbeo setting, both audio channels are directed to the left channel, and the left channel speaker output drives the reverb tank. The output of the reverb tank is amplified by a transistor and fed to the right channel, which puts out an "echoing" version of the L+R signal. So the result is one clean channel and one reverberating version, giving the effect of being in an echoing room. It makes mono radio signal sort of sound live, but is pretty pointless if you have stereo music in. The reverb transistor amp is fed by B+ divided down appropriately. The reverb amp in the B7X14A is indeed powered off the cathodes as suggested in other replies - see www.vintage-radio.com/recent-repairs/philips-reverbeo.html If interested, my threads on the F4VZ 25A/R are on www.avforums.co.za/index.php/topic,79108.0.html and www.avforums.co.za/index.php/topic,94042.msg1054307.html. Ironically, I am stuck with exactly the same tuning slug problem you had earlier.

[@electronicsoldandnew]

I had no idea they actually made these radios in SA. I should know - I grew up there 😊 Thanks for all the reference links. It’ll make interesting reading.