I don't know if I'm in the right section, however I have an old Telefunken Domino that I'm trying to get my hands on. The main electrolytic filter caps may need to be replaced (actually I realized that the one connected to the rectifier valve has already been changed by a previous repairer).
I was wondering which ground connection is relative to the one encapsulated in the aluminum shield, is it the case itself? It is a 50+50uF. Thanks in advance
I was wondering which ground connection is relative to the one encapsulated in the aluminum shield, is it the case itself? It is a 50+50uF. Thanks in advance
Attachments
The case is ground for all sections of the can cap. It can be replaced by single caps for each section by cutting all the connections to the can and attaching them to separate caps. It’s cheaper and easier than finding a cap the first. Just hide them under the chassis. Make sure the voltages are correct in the new caps.
Ok thanks, it was as I suspected. I think I'll try with a pair of 47uF capacitors. I have seen in a network restoration that someone has emptied the capacitor and inserted an equivalent capacitor into the aluminum can. Maybe to keep the original aesthetics, but I'm only interested in a practical purpose 🙂
Does your schematics excerpt relate to your radio? Then be aware that it's got a transformerless power supply and a live chassis. Use an isolation transformer when working on it.
Best regards!
Best regards!
Kay Pirinha, I took the schematic from this italian site. The model I have is the R712 so for what I can see there's not an autotransformer:
https://elettronialtramonto.forumfree.it/?t=72979289
https://elettronialtramonto.forumfree.it/?t=72979289
I think your's is a R172, isn't it? Yes, that's no autoformer at all. The use of series heated tubes together with one parallel heated is quite unusual, though.
Best regards!
Best regards!
Smart idea is to replace the bridge rectifier along with that filter cap.
I've restored hundreds of those old german/european radios and by now they all need restoration.
The output tube coupling caps need replacing as well.
And further down the line there's usually a 4uf in there that should be replaced.
I've restored hundreds of those old german/european radios and by now they all need restoration.
The output tube coupling caps need replacing as well.
And further down the line there's usually a 4uf in there that should be replaced.
Well, I wanted to updated my trials on the Telefunken (that yes, it's a R712). After removing a lot o dust and dirt I used the WD spray to polish electrical contacts (tube socket, pot, etc.) and replaced the old capacitor with the new ones forementioned. At first glance also the old 1000-5000pF capacitors seemed in good shape, except one that at one end is about to crumble. I tested all tubes just as heater's continuity but not at work (a,k,g1,g2,etc.), so I can't say if some tube is broken or not.
Anyway I decided carefully to power up the and il took life, let's say apparently because I couldn't hear anything but in FM and almost at max volume. Tuning in this range works (it's not distorted), and I can pick up the radio stations.
Given that I know little or nothing about radio, I wonder why in OM I don't hear absolutely anything while the volume is very low in FM. Any valves in the previous stage broken? Problems with the oscillator, or something else? I don't want to embark on something that I don't know, but if there are some basic tests, maybe I can try them and see
Anyway I decided carefully to power up the and il took life, let's say apparently because I couldn't hear anything but in FM and almost at max volume. Tuning in this range works (it's not distorted), and I can pick up the radio stations.
Given that I know little or nothing about radio, I wonder why in OM I don't hear absolutely anything while the volume is very low in FM. Any valves in the previous stage broken? Problems with the oscillator, or something else? I don't want to embark on something that I don't know, but if there are some basic tests, maybe I can try them and see
HI indaco,
your link in #6 shows up nine different Telefunken Domino models. None of them is assigned R712. So, which schematics correlates with your radio?
Best regards!
your link in #6 shows up nine different Telefunken Domino models. None of them is assigned R712. So, which schematics correlates with your radio?
Best regards!
The first test in encouranging, but a lot more work needs to be done. It may be worth it because this radio does have a good (but small) 2-3W fullrange speaker and phono input, so it can be connected to modern audio sources. The weak point of your radio are the piano key contacts. Mechanical action is sometimes needed to remove the thick oxidation layer on the contact working surfaces. Then, you must replace ALL the paper and electrolytic capacitors because they are leaky, expecially so in a Italian built budget radio made in the '50. This is not a Telefunken german radio - they were sold as premium "export" models and they had german text on the back cover. The series connected tube string was very popular because those tubes had a lower cost in Italy back then. A cheaper power trasformer is also needed because the filament supply is derived from the HT winding. This was a cheap-ish radio, so the expensive selenium rectifier was not fitted - they used a single vacuum diode. Some background hum is to be expected even after the restoration. To my experience, ECC85, UL84 and UABC80 tubes are often weak and must be replaced. You have FM reception, so the ECC85 may still be good. The UY85 rectifier may also be weak, but it does happens less frequently.
Thanks for the suggestion pcan, I remember you are from my country and maybe from what I see you know well about the popularity and the type of vintage radios. I've read also that for my kind of problem - a part the forementionend tubes and capacitors to replace - one should check the intregrity of an old component called "lares" oftentimes tending to degrade, and the alteration of value of tube cathode resistor (especially to the final tube).
When I have some time possibly I try and put my hands on
When I have some time possibly I try and put my hands on
This radio is pretty basic. It should be easy to repair. The first 3 steps on my routine are: clean the contacts, replace the paper and electrolytic capacitors, check basic electrical safety. The last step is important, because old devices may be unsafe: check fuse rating or replace it - remove or replace the "death capacitor" - maybe replace power cord with a new one with ground - rearrange wire location on the primary side of the power transformer and add spaghetti tubing if needed. You can then test it again and fix any further faults such as weak tubes and drifted resistors.
To the benefit of forum members outside Italy that may have been scratching their heads about the "lares" thing you mentioned, LARES was a local manufacturer of resistor/capacitor pre-built blocks. To my knowledge they were originally developed and widely adopted by USA radio/tv manufacturers such as Motorola, but this cost-saving feature never became popular in Germany.
If I correctly remember, there is no built-in ferrite antenna on your Domino radio: AM reception absolutely needs a long wire connected to the antenna input, and during the day you will be able to receive indoor only one or maybe two AM radio stations above the static from switched mode power supplies, LED lamps etc.
Avoid moving or relocating components and wires on the radio frequency section. They may look messy, but this is done on purpose. If you move them, the alignement on intermediate frequency transformers may be lost and the radio becomes insensitive. Unfortunately, sometimes the original owner attempted a fix by moving the tuning adjustements on those coils. A restoration to factory specifications then requires some instrumentation, but it is rarely worth the effort.
To the benefit of forum members outside Italy that may have been scratching their heads about the "lares" thing you mentioned, LARES was a local manufacturer of resistor/capacitor pre-built blocks. To my knowledge they were originally developed and widely adopted by USA radio/tv manufacturers such as Motorola, but this cost-saving feature never became popular in Germany.
If I correctly remember, there is no built-in ferrite antenna on your Domino radio: AM reception absolutely needs a long wire connected to the antenna input, and during the day you will be able to receive indoor only one or maybe two AM radio stations above the static from switched mode power supplies, LED lamps etc.
Avoid moving or relocating components and wires on the radio frequency section. They may look messy, but this is done on purpose. If you move them, the alignement on intermediate frequency transformers may be lost and the radio becomes insensitive. Unfortunately, sometimes the original owner attempted a fix by moving the tuning adjustements on those coils. A restoration to factory specifications then requires some instrumentation, but it is rarely worth the effort.
Hi,
I wanted to update the Telefunken setup ... well, replaced the main electrolytics and a couple of bypass caps I took care of the dial tuning cord. Since the original one was totally lost, I used a silk "haberdashery" thread that seems to me to have fulfilled its task quite well.
Given my lack of skills about vintage radios I think the result is good, now I just have to ask my carpenter friend for advice on how to clean and polish the wooden outer cover (veneered?).
Furthermore, if I also find the original "Domino" writing plate, I think I will add it to it.
Below is a short video of the radio at work in FM (not yet tested in AM)
I wanted to update the Telefunken setup ... well, replaced the main electrolytics and a couple of bypass caps I took care of the dial tuning cord. Since the original one was totally lost, I used a silk "haberdashery" thread that seems to me to have fulfilled its task quite well.
Given my lack of skills about vintage radios I think the result is good, now I just have to ask my carpenter friend for advice on how to clean and polish the wooden outer cover (veneered?).
Furthermore, if I also find the original "Domino" writing plate, I think I will add it to it.
Below is a short video of the radio at work in FM (not yet tested in AM)