We have just been watching "Repair Shop" which is a maker/fixers type of show here in the UK. One of the guests brings in a record-radio from the 70s and my wife then says, my mum has an old radio that's mine (essentially he mum would like to make space) but it doesn't work. Queue some searching of the images the mum sent and hey presto.
It's a Phillips H4X73A. A full tube radio and record player in a single cabinet: https://www.radiomuseum.org/r/philips_h4x73a.html
Needless to say - I'm very interested in getting my hands on it!
Has anyone worked on one?
It's a Phillips H4X73A. A full tube radio and record player in a single cabinet: https://www.radiomuseum.org/r/philips_h4x73a.html
Needless to say - I'm very interested in getting my hands on it!
Has anyone worked on one?
I now have the schematic from radio museum, although I won't post it here, the tubes are:
- ECH81 triode-heptode
- EF85
- ECC85
- EABC80 detector
- EM80 magic eye
- EZ80 rectifier
- EL84
If the Radiomuseum information is correct, it is a nice device. The speakers AD3700M and AD3700X are good dual-cone 7'' fullranges. I attach the data. The sound should be pleasant, expecially after disconnecting the treble-cut capacitor on the side tab of the volume potentiometer. The stylus rubber mount inside the piezo cartridge is probabily unusable, but the turntable arm does use a standard Philips quick change connector and the cartridge should be easy to replace with a later and somewhat better type, although it is quite far from Hi-Fi specifications.
Attachments
AD3700M is quite efficient, far more than today generic home speakers. But other parameters are worse. It may be damaged very easily by excessive power, as example.
My guess is a paper VC former, 30 ga or smaller wire, but still more than expected. 98 dB, 3%, I would have expected from their best ones. It’s not like the magnet will pin your hand to the refrigerator door like modern ones can.
So.. update.
checked mains 238V and power supply shows a 220V selectable so for long term it probably warrants a
Did an initial check on the caps for leakage, they read ok but would like to replace.
tubes check out great visually just dusty and probably the same initially installed.
Checked the wiring noted that the power and one of the antenna leads broken. Fixed.
Powered on and all ok, FM and AM sound very good. Only issue is record deck gets 110V power but the end limit switch is not passing any power to the motor plus the poor stylus is well dead I think. Next on the list to sort.
Only tube issue is the magic eye tube is very very weak and needs replacing.
checked mains 238V and power supply shows a 220V selectable so for long term it probably warrants a
Did an initial check on the caps for leakage, they read ok but would like to replace.
tubes check out great visually just dusty and probably the same initially installed.
Checked the wiring noted that the power and one of the antenna leads broken. Fixed.
Powered on and all ok, FM and AM sound very good. Only issue is record deck gets 110V power but the end limit switch is not passing any power to the motor plus the poor stylus is well dead I think. Next on the list to sort.
Only tube issue is the magic eye tube is very very weak and needs replacing.
So second update. The turn table works, the stylus does pickup but needs replacing. So after cleaning off the years of tobacco/nicotine it’s looking pretty good for a 64 year old piece of kit.
The tubes are philips made in holland branded. The only replacements needed are the very weak magic eye and the front panel bulb.
The tubes are philips made in holland branded. The only replacements needed are the very weak magic eye and the front panel bulb.
Reading up on the design, and more importantly on the caps, Phillips used overrated caps then encased them in pitch. Other restorations have found caps working 60 years later and the pieces used were 1300V rated! Others have taken to blanket replace with modern caps.
There’s a canned cap with two electrolytic which i will replace along with the heavily oxidised power cord and i couldn't see a fuse although on the schematic. Need to test the resistor values too later when i replace the magic eye and stylus.
An external EMI filter with 238/245Vac to 220Vac step down may prevent the system running a little hot. If i plug in at home that’s 11% over spec so the 6.3Vac heaters would be running over 7Vac.
There’s a canned cap with two electrolytic which i will replace along with the heavily oxidised power cord and i couldn't see a fuse although on the schematic. Need to test the resistor values too later when i replace the magic eye and stylus.
An external EMI filter with 238/245Vac to 220Vac step down may prevent the system running a little hot. If i plug in at home that’s 11% over spec so the 6.3Vac heaters would be running over 7Vac.
The fuse is the tiny bit of lead on a spring loaded holder on the side of the power transformer. Philips had this peculiar arrangement, the fuse also works as thermal fuse. There may be oxidation on the fuse holder contacts. It may be useful to add a conventional fuse in series, just in case. To avoid heawy modifications that will compromise the originality of the radio, a subminiature fuse with leads can be used. Philips capacitors of that era are mostly still on spec, sometimes even the canned main filter capacitor. I usually replace them anyway, when wiring and available space lend to a tidy and concealed work. To lower the mains voltage I usually install a 50W power resistor on an alluminium heat sink, when the wooden cabinet is big enough to place it in a concealed way. A bucking transformer can also be used. Don't forget to clean the rubber wheel inside the record player mechanism, othervise slippage and flutter may result. 6e1p is a close enough substitute for the EM80. The price of a true EM80 NOS tube is too high for this radio. You may need to adjust the resistor to lower the luminosity and prolong the magic eye life.
Managed to find time to get setup without pets in the vicinity with the front off to check the EM80. Weak but also not really showing any open/closure which could point at a weak beat detector. However pin access to the triode/twin diode EABC80 is convoluted being shielded tube and box shielded on the underside of the socket. So that will have to wait.
I did note a missing cap (it has the 3.2uF but not the large cap that i could see.
Oscillator seems tight enough in AM.
Switching band seems a little ragged at the top and bottom of the waveform.
I did note a missing cap (it has the 3.2uF but not the large cap that i could see.
Oscillator seems tight enough in AM.
Switching band seems a little ragged at the top and bottom of the waveform.
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I spent this evening tracing and measuring each resistor against the schematic - happy to say theyre within their marked tolerance and match the schematic. I still have the record preamp section todo but theres only w few resistors. All the ceramic dogbone capacitors are blocking, as to are all the black pitch caps and the main AC filter cap.
So it seems my list of fixes are:
I also found this site suggeston these radio was sold under different models: https://www.doctsf.com/radiola-ra-498-a-am-fm/f2891?PHPSESSID=1fedcbec22395a39394a363799fbc044 This alsohas a schematic.
Lastly it has some flaking paint so i may stabilise that then consider if a wood matched touch up is in order.
I doubt I need to touch the
So it seems my list of fixes are:
- chassis mount resistor to drop 245Vac to 220Vac
- install small fuse
- replace blacklight bulb
- replace em80 magic eye.
- check FM sweep given the display doesnt sweep fullscale.
- find replacement stylus - the original arm has a M/N types. Tonar seem to have a replacement model but this needs further investigation
I also found this site suggeston these radio was sold under different models: https://www.doctsf.com/radiola-ra-498-a-am-fm/f2891?PHPSESSID=1fedcbec22395a39394a363799fbc044 This alsohas a schematic.
Lastly it has some flaking paint so i may stabilise that then consider if a wood matched touch up is in order.
I doubt I need to touch the
Auto transformer using a small creatively wired 240v 24v transformer would be my preferred way of dropping the mains rather than a resistor.
Yes, I'd prefer a transformer also, but 12 Vac instead of 24 Vac. Wired as an autoformer, a 4 VA type will do for a radio with a power consumption up to 70 VA.
After 60+ decades, all magic eyes indicator tubes of similar construction do fade. Most recently I bought this EM 80 tube. It was labelled RSD, which isn't a tube manufacturer, but was a reputed rebrander. Well, € 20 plus S/H might exceed the realistic value of your radio, but if you intend to keep it, why not? After all, any other source in Germany wants more money.
Best regards!
After 60+ decades, all magic eyes indicator tubes of similar construction do fade. Most recently I bought this EM 80 tube. It was labelled RSD, which isn't a tube manufacturer, but was a reputed rebrander. Well, € 20 plus S/H might exceed the realistic value of your radio, but if you intend to keep it, why not? After all, any other source in Germany wants more money.
Best regards!
I did think an autotransformer would work better as i can reuse across any 220Vac devices assuming power handling/current limits.
I agree I think it’s worth getting back to a working state but it’s mono.
I agree I think it’s worth getting back to a working state but it’s mono.
Update - I went down the route of a bucking transformer using a Hammond 30VA 230V-12.6V 2.5A piece. I can also reuse this as a heater transformer 😀
This morning the line voltage is down to 240Vac. So the resulting bucking is giving me ~226Vac. The little transformer seems to have no problem with the load of the receiver and after removing power it's cool to touch.
So even with the regular 245Vac line voltage I'll only be getting 231Vac which is neat.
This morning the line voltage is down to 240Vac. So the resulting bucking is giving me ~226Vac. The little transformer seems to have no problem with the load of the receiver and after removing power it's cool to touch.
So even with the regular 245Vac line voltage I'll only be getting 231Vac which is neat.
Been a while busy with other priorities but the Mrs wants this fixed 😀
Plan:
1. Fit the EI buck transformer and replace the power line. I was going to use the 12.6V for a heater supply for the new amp but that will be replaced by a toroid 😀
2. Replace the black pitch caps - given the sizes I'm tempted to replace with film caps. The size on the caps and they're 20% tolerance at about 100V-400V so I'll replace but I think the modern moderate priced caps will be fine for this purpose. I'm using Mouser as this will come in the same free delivery as the new amp hence the limited selection of components. I'm sticking to lowest cost caps of the brands I know:
C27 - 100K (0.1uF) topside will be replaced by WIMA MKS4 0.1uF 400V 10%
C39 - 1K (1nF) will be replaced by WIMA FKP2 1000pF 400V
C42 - 8.2K (8.2nF) will be replaced by Panasonic ECQ 8200pF 10%
C45 - 220K (0.22uF) will be replaced Panasonic ECW 0.22uF 400V
C46 - 470K (0.47uF) will be replaced by Panasonic ECW 0.47uF 630V 10%
C48 - 3.3K (3.3nF) will be replaced by WIMA FKP2 3300pF 630V 5%
The EM80 I think I may leave for now. If I need to replace the tubes I'll batch that in with the order.
The original dial bulb is powered off the heater line. The 8024N/778 6.3V 300mA but mouser only has a 6.3V 150mA bayonet bulb and bypass and parallel with a 42ohm resistor so the heater rails are kept in close to. The bulb is 20,000h at 4.15lm. I could replace the resistor with a second bulb.
I'm trying to think what todo with the record deck. It's phono stage is designed for the high output cart so I can't replace with a MM or MC. One option is to replace with a bluetooth board for the modern use..
Plan:
1. Fit the EI buck transformer and replace the power line. I was going to use the 12.6V for a heater supply for the new amp but that will be replaced by a toroid 😀
2. Replace the black pitch caps - given the sizes I'm tempted to replace with film caps. The size on the caps and they're 20% tolerance at about 100V-400V so I'll replace but I think the modern moderate priced caps will be fine for this purpose. I'm using Mouser as this will come in the same free delivery as the new amp hence the limited selection of components. I'm sticking to lowest cost caps of the brands I know:
C27 - 100K (0.1uF) topside will be replaced by WIMA MKS4 0.1uF 400V 10%
C39 - 1K (1nF) will be replaced by WIMA FKP2 1000pF 400V
C42 - 8.2K (8.2nF) will be replaced by Panasonic ECQ 8200pF 10%
C45 - 220K (0.22uF) will be replaced Panasonic ECW 0.22uF 400V
C46 - 470K (0.47uF) will be replaced by Panasonic ECW 0.47uF 630V 10%
C48 - 3.3K (3.3nF) will be replaced by WIMA FKP2 3300pF 630V 5%
The EM80 I think I may leave for now. If I need to replace the tubes I'll batch that in with the order.
The original dial bulb is powered off the heater line. The 8024N/778 6.3V 300mA but mouser only has a 6.3V 150mA bayonet bulb and bypass and parallel with a 42ohm resistor so the heater rails are kept in close to. The bulb is 20,000h at 4.15lm. I could replace the resistor with a second bulb.
I'm trying to think what todo with the record deck. It's phono stage is designed for the high output cart so I can't replace with a MM or MC. One option is to replace with a bluetooth board for the modern use..
One tiny chip can be a fine phono preamp. Nobody needs to know.
I've been working through the Phillips design, and some design history, and came across this: https://www.maximus-randd.com/eq40-and-eq80.html excellent history of Phillips as they started with the EQ80 and then ended up in 1951 with a 5 valve reference design (fig 13 down the page). That design is exceptionally close to the design of the H4X73A.
I made an assumption that the design used a shared RF FM amp stage/phono stage. In fact I was wrong - the design has 6 switches that work together but make it an absolute pain to trace the signal path. Additionally one switch simply goes to a weird plug symbol and the FM RF amp starts with a switched centre tap transformer (to antenna or ground) or two open contacts. This now makes sense as the external antenna connection rather than the stylus.
I wanted to understand the design before I start replacing the caps. One black cap is a filter for the FM so I may find the FM behaviour change. The rest is all audio or the main power cap.
I can now see the Foster-Seeley FM frequency discriminator configuration, although this has a centre tap in the IF can compared to the straight FS circuit. The C39 1K cap is part of the input filter for this.
Before this something was not making sense (ie surely you'd have a switch for RIAA compensation if the FM and phono preamp where shared). Turns out there is no RIAA compensation and the ceramic stylus high output of 100mV is fed straight into the EABC80 triode as the audio preamp/driver. The difference in reference to this design is the use of a EL84 on the output audio amp!
I made an assumption that the design used a shared RF FM amp stage/phono stage. In fact I was wrong - the design has 6 switches that work together but make it an absolute pain to trace the signal path. Additionally one switch simply goes to a weird plug symbol and the FM RF amp starts with a switched centre tap transformer (to antenna or ground) or two open contacts. This now makes sense as the external antenna connection rather than the stylus.
I wanted to understand the design before I start replacing the caps. One black cap is a filter for the FM so I may find the FM behaviour change. The rest is all audio or the main power cap.
I can now see the Foster-Seeley FM frequency discriminator configuration, although this has a centre tap in the IF can compared to the straight FS circuit. The C39 1K cap is part of the input filter for this.
Before this something was not making sense (ie surely you'd have a switch for RIAA compensation if the FM and phono preamp where shared). Turns out there is no RIAA compensation and the ceramic stylus high output of 100mV is fed straight into the EABC80 triode as the audio preamp/driver. The difference in reference to this design is the use of a EL84 on the output audio amp!