Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Oct Thu 18, 2018 5:39 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 28 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: Telefunken Gavotte 5253W - Diode question
PostPosted: Dec Wed 06, 2017 3:46 am 
Member

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 873
Location: Albion, CA, USA, 95410
Hi All,

EDIT: Changed this to a resto thread. See below for initial findings and questions.

Perhaps foolishly, I just bought a Telefunken Gavotte 5253W. Now that I have paid for it I started looking around for documentation. Maybe I should have done that first? Most of the sites I have found are full of big DOWNLOAD NOW buttons that actually want to install something. At radiomuseum I found a schematic but there is supposed to be an 8 page manual. Sams seems to have tons of other Telefunkens but not the 5253W. Anybody have a link or copy? Are there any other sources of information on this set? Not being a real radio repair guy like most of you I need all the documentation I can get.

Thanks! I'm gonna need all the help I can get on this one!


Last edited by madlabs on Dec Sun 17, 2017 8:33 pm, edited 2 times in total.

Top
 Profile  
 
 Post subject: Re: Telefunken Gavotte 5253W
PostPosted: Dec Wed 06, 2017 8:18 am 
Member
User avatar

Joined: Apr Sun 01, 2012 9:55 pm
Posts: 9335
Location: Seattle, WA
A couple pages...
http://oldtech.net/German.html

Maybe the same two pages... called a 5353W Gavotte:
http://www.nvhr.nl/gfgf/schema.asp?Merk ... mitted=yes

Which leads to an 8-page manual on RMorg:
https://www.radiomuseum.org/r/telefunke ... w5353.html

And a thread here indicating the 5253 and 5353 use the same chassis...
http://www.antiqueradios.com/forums/vie ... 4&t=323407

Hope that helps,
Rodney


Top
 Profile  
 
 Post subject: Re: Telefunken Gavotte 5253W
PostPosted: Dec Wed 06, 2017 4:39 pm 
Member

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 873
Location: Albion, CA, USA, 95410
Thanks so much!

So it looks like there was never a Sam's. Is there any other printed service info on these sets? I'm happy to buy if there is anything.

Now I'll go back to hoping the radio arrives intact. I've never bought a radio on ebay before. I did drop the seller a note and implored him to pack it well.


Top
 Profile  
 
 Post subject: Re: Telefunken Gavotte 5253W
PostPosted: Dec Thu 07, 2017 6:36 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 3556
Location: Advance, NC USA
I've got 5 Telefunken Radios:
-Gavotte 8
-Gavotte 9
-Gavotte 5253W
-Concertino 5384W
-Opus 7

They are all fine playing radios.
I think you have chosen well.


Top
 Profile  
 
 Post subject: Re: Telefunken Gavotte 5253W
PostPosted: Dec Fri 08, 2017 2:32 pm 
Member

Joined: Aug Sat 01, 2009 2:23 pm
Posts: 1548
I believe this may be one of the Gavotte radios that uses a printed circuit board. If so, be very careful as those boards are quite fragile.

_________________
John Stone
Antique Radio Club of Illinois


Top
 Profile  
 
 Post subject: Re: Telefunken Gavotte 5253W
PostPosted: Dec Fri 08, 2017 4:10 pm 
Member

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 873
Location: Albion, CA, USA, 95410
Thanks for the help!

Radio museum sends the doc in single pages. It'll take days to get the whole thing. If anyone has a complete PDF that would be great. Looking around I don't see any paper docs for sale, is it worth posting a want here?

It arrived intact! It was very well packed. I'll convert this thread to the resto thread.

Attachment:
gavotte2.jpg
gavotte2.jpg [ 131.1 KiB | Viewed 1403 times ]


The only thing that happened in transit was that the ferrite antenna had come out of its holder and had flopped over in front of the dial. Took me a minute to figure it all out.

Attachment:
20171207_184416_resized.jpg
20171207_184416_resized.jpg [ 125.76 KiB | Viewed 1403 times ]


You can see the thin bare wire up and over the speaker wires and down in front of the dial.

Attachment:
gavotte1.jpg
gavotte1.jpg [ 151.26 KiB | Viewed 1403 times ]


Luckily the 30 gauge or so wire had only broken in one spot and so I wound it back on the ferrite, a little tape and solder the break and it is back in action.

Attachment:
20171208_061920_resized.jpg
20171208_061920_resized.jpg [ 128.9 KiB | Viewed 1403 times ]


The seller said it played, so I fired it up with a variac and ammeter. It is drawing 420mA or so, less than the docs say it should. The eletrolytics in the PSU are running cool as is the transformer. It works GREAT on FM and quite well on AM. Haven't really tried it on SW yet. And before someone says it, I will immediately replace the 'lytics and paper caps. I just had to see what it could do.

The only physical thing I see so far is that one of the tuning pulleys on the AM dial is very warped. It still works but for how long?

Attachment:
20171207_193318_resized.jpg
20171207_193318_resized.jpg [ 148.62 KiB | Viewed 1403 times ]


It does have PCB's so I will be careful of them. In what regard are they fragile? Does the board break or traces come of easily? Is it best to hook and loop replacement parts?

Are there any other parts that should be replaced out of hand? The rectifier diodes or anything?

I have some more questions but I am going to try to get a complete schematic and docs and do some more poking around first.

I am really liking the look and performance of this radio. It is gonna look great next to the Predicta!


Top
 Profile  
 
 Post subject: Re: Telefunken Gavotte 5253W - Starting work
PostPosted: Dec Sat 09, 2017 3:36 pm 
Member

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 873
Location: Albion, CA, USA, 95410
Working on a parts list.

I assume that 2.2uF should be fine for a 2uF and that 47uF should be fine for a 50uF?

I assume that all caps over about 800pF are paper?

I also only have one dial light but the schematic says two. Where would the other one be?


Top
 Profile  
 
 Post subject: Re: Telefunken Gavotte 5253W - Starting work
PostPosted: Dec Sun 17, 2017 8:30 pm 
Member

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 873
Location: Albion, CA, USA, 95410
Hi All,

Well, got a cap order in and a paper schematic for the 5353 chassis which is supposed to be the same as the 5253 and comparing the schematics it appears so.

Went to start on the power supply and quickly got confused. It took me a while to figure out that a can I assumed was a cap is the FWB rectifier diodes. These are listed as selenium. They get just barely warm if the set is in operation for 1/2 hour. Should these be replaced?

Of course I didn't get all the caps I needed but I should at least be able to get the power supply done. With the holidays coming up and the set playing so well as is I would like to do what needs to be done to make it safe to use first and use it a bit over the holidays and then come back in January and complete the job. What other caps need to go to prevent catastrophic meltdowns?

I'm sorry but I can't seem to resize the schematic and keep it legible. I'll work on that.


Top
 Profile  
 
 Post subject: Re: Telefunken Gavotte 5253W - Diode question
PostPosted: Dec Sun 17, 2017 8:57 pm 
Member

Joined: Jan Mon 16, 2012 4:15 pm
Posts: 4645
Location: Near Brandon, Iowa
The black can is an AEG selenium bridge rectifier. If it doesn't get excessively hot to the touch after an hour of operation AND if B+ voltage doesn't sag by 15V or more over that time period, you can postpone replacing it. For selenium rectifiers, these units last an amazingly long time in my experience with them.

The critical caps (IMO) to replace are: both 50 uF filter electrolytics; any bypass caps hanging off the B+ bus; the coupling cap linking the first audio amp tube plate to the grid of the audio output tube; and (if present) a bypass cap between the plate of the output tube and ground. If any of these caps short out it will cause expensive collateral damage to the set. Other caps may prevent the set from performing to its full potential but won't really damage it if they fail shorted.

The tuning cap plastic wheel is very deformed but you don't have much of an alternative to using it. There are no new reproductions for it. Even distorted as it is, it should work OK; if it breaks you can only replace it with a like part from a junked set. This isn't a rare set so junkers should be able to be found.

You dodged a bullet with the loose ferrite antenna rod. These OFTEN break loose when unaware shippers fail to secure them before packing. More often than not when they do break free, they batter the glass dial plate while the set is in transit, breaking it. When the glass dial breaks, the set is reduced from a nice collectible to a parts set.


Top
 Profile  
 
 Post subject: Re: Telefunken Gavotte 5253W - Diode question
PostPosted: Dec Mon 18, 2017 12:33 am 
Member

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 873
Location: Albion, CA, USA, 95410
In the no good deed goes unpunished department...

I replaced the two 50uF/450V caps, as well as C701 and C702, which are both located on the PSU section. Since I had to take board "A" off to get the power section out, I replaced C703 and C704. For my efforts I see to have been rewarded with lower signal reception and distortion on FM, which was playing wonderfully for a half hour or so and then had a little distortion creeping in. I cleaned all the connectors as well. I have double checked part values and solder joints. Any ideas what I screwed up?

As to the rectifiers, the do actually get pretty hot, although the voltage only sags by a few volts. I can only comfortable hod on to the rectifier can for 3-4 seconds. Should they go? And do I need to add a dropping resistor with silicon diodes?

EDIT: Forgot to mention, I have the chassis half in and half out of the cabinet, so lead dress may be different and the PSU is not in the usual place. Could this be causing the lower reception/distortion?


Top
 Profile  
 
 Post subject: Re: Telefunken Gavotte 5253W - Diode question
PostPosted: Dec Mon 18, 2017 1:15 am 
Member

Joined: Jan Mon 16, 2012 4:15 pm
Posts: 4645
Location: Near Brandon, Iowa
If the rectifier can gets warm, that's OK. Hot is not. Recommend that you replace the bridge rectifier with a
1000PIV silicon bridge. You can pick these up on eBay for a few bucks. Or roll your own with four 1N4007 axial-leaded diodes.

A dropping resistor is optional. Most people need to add dropping resistors when converting tube rectifiers to silicon, since the forward V drop across a vacuum tube is from 20 to 40 volts depending on tube type. It is less than a volt for a silicon diode. However, the forward V drop for a selenium bridge is much less than that of a tube rectifier so use of a dropping resistor is optional. You probably should measure what you have B+ voltage wise after the conversion to silicon and then decide if a resistor is needed.


Top
 Profile  
 
 Post subject: Re: Telefunken Gavotte 5253W - Diode question
PostPosted: Dec Mon 18, 2017 7:36 pm 
Member

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 873
Location: Albion, CA, USA, 95410
OK, since hot and warm are a little difficult to distinguish over the internet, I think I'll go ahead and replace the selenium diodes. I have plenty of 1N4007's in the junk box. What is the max allowable voltage 10% above stated B+? And I am using a Fluke 117 to measure voltage with so it will read a little higher, right?

I'm really bothered by the lower signal strength and added distortion. I'm going to replace the diodes while I have it apart and hope that the distortion and weaker signal return to normal when all is back in place. I have noticed that this set is sensitive to a human being near it, it does change the reception a little. I sure hope I didn't screw this set up already! If anyone has tips as to what I might have done with please let me know!


Top
 Profile  
 
 Post subject: Re: Telefunken Gavotte 5253W - Diode question
PostPosted: Dec Mon 18, 2017 8:29 pm 
Member

Joined: Jan Mon 16, 2012 4:15 pm
Posts: 4645
Location: Near Brandon, Iowa
Quote:
madlabs wrote:
OK, since hot and warm are a little difficult to distinguish over the internet, I think I'll go ahead and replace the selenium diodes. I have plenty of 1N4007's in the junk box. What is the max allowable voltage 10% above stated B+? And I am using a Fluke 117 to measure voltage with so it will read a little higher, right?

I'm really bothered by the lower signal strength and added distortion. I'm going to replace the diodes while I have it apart and hope that the distortion and weaker signal return to normal when all is back in place. I have noticed that this set is sensitive to a human being near it, it does change the reception a little. I sure hope I didn't screw this set up already! If anyone has tips as to what I might have done with please let me know!

10% over the schematic spec is OK. Above that voltage you should consider installing a dropping resistor between the + output of the diode array and the first electrolytic filter cap.

Even if the original schematic voltages were determined using a relatively low-input-impedance meter, a modern high-impedance voltmeter shouldn't read much different- the output of the bridge is low impedance so the voltmeter load, be it low or high, is irrelevant.

The set being sensitive to a body being near it (presumably on FM) sounds like an antenna issue. You might try unplugging the internal FM antenna and plugging in a old TV-style dipole antenna. The external dipole can then be oriented for best signal. There is a length of twinlead that links the FM antenna socket on the rear of the set to the FM tuner module. You might examine the ends to see if one got broken loose. That would have an effect similar to a poor antenna.


Top
 Profile  
 
 Post subject: Re: Telefunken Gavotte 5253W - Diode question
PostPosted: Dec Thu 21, 2017 4:40 pm 
Member

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 873
Location: Albion, CA, USA, 95410
Lorenz, thanks so much for the help. Just got back from my 48 hour shift and am back on the radio today.

I had already made an antenna out of 300 ohm twin lead and it works well. The reception/distortion issues mentioned above are with both antennas but the signal is stronger with the external, of course. I'll check all the connections as recommended.

As to the rectifier, I am trying to figure out a good way to make one that is also mechanically strong and allows me to add a dropping resistor. I could cut the can and dangle it all but that just seems too vulnerable. It's too packed above the can. Even removing the can will be a pain. Any ideas?

Attachment:
20171221_072609_resized.jpg
20171221_072609_resized.jpg [ 77.68 KiB | Viewed 1165 times ]


Edit: What is the likely increase in voltage when changing selenium rectifiers for silicon? I'd like to calculate the dropping resistor I'll need. This set will be used on grid where the voltage can swing high.


Top
 Profile  
 
 Post subject: Re: Telefunken Gavotte 5253W - Diode question
PostPosted: Dec Thu 21, 2017 6:22 pm 
Member

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 873
Location: Albion, CA, USA, 95410
OK, so I decided to cut apart the rectifier can. I also decided to bread board up my rectifier circuit to test resistor values. I'm glad I did! I started with a 50 ohm resistor, ramped up the voltage and boy was that too low! I ended up with a 300 ohm, 10 watt resistor. The current is 120mA and the voltage drop is 19.2V which is 2.3 watts. However, I feel like I must be doing something wrong as the 10 watt resistor is pretty hot. I'd think a 10 watt with 2.3 watts going through it would be warm but not hot. Am I calculating that correctly or am I missing something?


Top
 Profile  
 
 Post subject: Re: Telefunken Gavotte 5253W - Diode question
PostPosted: Dec Thu 21, 2017 7:14 pm 
Member

Joined: Jan Mon 16, 2012 4:15 pm
Posts: 4645
Location: Near Brandon, Iowa
OK, excuse me if I haven't been following the entire thread but if you haven't replaced the filter and bypass caps, you are wasting your time trying to calculate a dropping resistor value- the aforementioned caps can be leaky and causing the B+ bus to draw an excessive amount of current. Before replacing the AEG bridge rectifier, replace (at least) the B+ filter caps and any bypass caps to ground that are hanging on the B+ bus.

I would replace the selenium bridge with a potted silicon bridge rather than using discrete 1N4007 diodes. Easier
to mount and the cost differential is piddling.


Top
 Profile  
 
 Post subject: Re: Telefunken Gavotte 5253W - Diode question
PostPosted: Dec Thu 21, 2017 8:33 pm 
Member

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 873
Location: Albion, CA, USA, 95410
Filter caps have been replaced. Still working on figuring out which caps are the bypass caps. I will replace those next.

I am going with the 1N4007's because I have 'em in hand. I wound up doing this:

Attachment:
20171221_111809_resized.jpg
20171221_111809_resized.jpg [ 149.61 KiB | Viewed 1148 times ]


I know that is pretty sloppy by most standards around here and will require an extra screw hole in the cabinet. However, it will be mechanically and electrically sound and I will be able to replace the dropping resistor if I find it needs a higher wattage. Speaking of which, is there a flaw in my math above? With 19.2 volts across the resistor and 120mA, shouldn't that be 2.3 watts? Because that resistor feels hotter than that to me. The transformer is running cooler now though, so that is a plus.

Also, the set is playing fine again. Whew! I was worried I had messed something up. I have two more electrolytics in the FM section to replace and then I'll figure out which caps are the bypass.


Top
 Profile  
 
 Post subject: Re: Telefunken Gavotte 5253W - Diode question
PostPosted: Dec Thu 21, 2017 9:18 pm 
Member

Joined: Jan Mon 16, 2012 4:15 pm
Posts: 4645
Location: Near Brandon, Iowa
madlabs wrote:
Filter caps have been replaced. Still working on figuring out which caps are the bypass caps. I will replace those next.

I am going with the 1N4007's because I have 'em in hand. I wound up doing this:

Attachment:
20171221_111809_resized.jpg


I know that is pretty sloppy by most standards around here and will require an extra screw hole in the cabinet. However, it will be mechanically and electrically sound and I will be able to replace the dropping resistor if I find it needs a higher wattage. Speaking of which, is there a flaw in my math above? With 19.2 volts across the resistor and 120mA, shouldn't that be 2.3 watts? Because that resistor feels hotter than that to me. The transformer is running cooler now though, so that is a plus.

Also, the set is playing fine again. Whew! I was worried I had messed something up. I have two more electrolytics in the FM section to replace and then I'll figure out which caps are the bypass.

Your math is correct. But fingers are notorious for being inaccurate temp sensors, especially at higher temps. Two watts dissipation will heat up a resistor to the point where it is painful to the touch. One guideline is that for each calculated power dissipation, the physical resistor should be derated by 70%. So if you expect to dissipate 2.3W, use a greater than 3.3W resistor (i.e., 5W). The resistor will still get hot, but it won't burn open.


Top
 Profile  
 
 Post subject: Re: Telefunken Gavotte 5253W - Diode question
PostPosted: Dec Thu 21, 2017 9:42 pm 
Member

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 873
Location: Albion, CA, USA, 95410
Thanks for the math confirmation. Hot is indeed subjective.

OK, I just replaced C313, a 50uF/15V electrolytic cap and have been rewarded with hum in the speaker. I used a 47uF/25. Now if I touch the transformer it quiets the hum mostly, but not entirely. I cut the old cap too short and can't get it back in. I tried a different cap and it is the same.

Attachment:
TFGC313.gif
TFGC313.gif [ 17.08 KiB | Viewed 1146 times ]


I see this cap does go to ground.


Top
 Profile  
 
 Post subject: Re: Telefunken Gavotte 5253W - Diode question
PostPosted: Dec Fri 22, 2017 12:27 am 
Member

Joined: Jan Mon 16, 2012 4:15 pm
Posts: 4645
Location: Near Brandon, Iowa
That cap is the output tube cathode AC bypass. It can't cause hum by itself regardless of its value, or even if it is entirely missing. Did you change (lengthen/reroute) the wires in this section or accidentally cause a pin-to-pin solder short on the output tube socket?


Top
 Profile  
 
Post New Topic Post Reply  [ 28 posts ]  Moderators: Marcc, Norm Leal Go to page 1, 2  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: Cwebs and 9 guests



Search for:
Jump to:  
























Privacy Policy :: Powered by phpBB