Telefunken T6445GWK restoration - Printable Version
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RE: Telefunken T6445GWK restoration - RodB - 06-10-2023
Excellent Mike, that's awesome! So, for a permanent solution, do you have a proper step up transformer and space for it? My grandson wants to know if you're going to replace the dial lamps with color LEDs?
RE: Telefunken T6445GWK restoration - RadioSvit - 06-10-2023
Michael, I like the idea of replacing the single half-cycle rectifier on the UY-11 radio tube with a semiconductor bridge rectifier and feeding the filaments of the radio tubes from the 110 volt network through a small ballast resistor. Since one radio lamp with a voltage of 60 volts will be missing, then only three radio lamps with a total voltage of 90 volts will remain, and you will have to choose a ballast to neutralize only 20 extra volts. It seems to me that this is the optimal solution to the problem. And the bridge semiconductor rectifier will raise the anode voltage to at least 200 volts, which will be enough for good radio operation
RE: Telefunken T6445GWK restoration - RadioSvit - 06-10-2023
Quote: Mike;
From what I have read elsewhere those short metal tubes where called "stahl" or steel tubes, and were developed, and originally produced by Telefunken in 1938. The first time I saw some was in a war time set another collector had, they looked like oversized 6H6 tubes, and from what I can tell they carried on making them in Germany, and Poland well into the 1950s (or later), maybe some other Warsaw pact countries as well. Do they all have eight pin bases in that set? A really strange pinout, five on one side and three on the other, I would guess that the three pin side is for the tube heater plus the cathode, but since the base has a key why bother?
Arran, this type of German radio lamps has another slang name - "helmets". From the extraordinary similarity with the German helmets of the Second World War. And you would probably be very surprised if you saw the structure of the armature of these radio lamps - it is not placed vertically, but horizontally.
That is, the filament, cathode, grid and anode are in a horizontal position, not in a vertical position! As it was in radio lamps at the beginning of the 20s 
RE: Telefunken T6445GWK restoration - morzh - 06-10-2023
Peter
Yes, except instead of the ballast resistor I usually use a capacitor. This will turn the radio in the AC only set, but then I do not intend to use it with DC outlet. I converted a few radios this way.
This worked especially well on those radios that had the infamous "curtain-burner" power cord, with asbestos-insulated 3rd wire that was a ballast resistor and droped about 30W of power to feed filaments. When replacing it, it usually would take 6 to 8uF cap to drop the needed voltage, and without any power dissipation.
In this case this will work like this:
I need 100mA, so I need 1.2K total impedance.
Then the 1,200-squared is 1,440,000. That less 810,000 is 630,000 and the root of that is 794 Ohm.
This impedance gives us a cap of 3.35 uF.
I could make something like that or buy a single 3.3uF cap. Like this one.
https://www.tubesandmore.com/products/capacitor-audiophiler-400v-mkp-metallized-polypropylene
I have 3.3uF 100V cap. It needs to drop 80V (those who cannot make sense how 80V and 90V make for 120V, well, this is reactiove and active loads, so the actuall formula is the square root of the sum of their respective squares). And if it gets shorted, the voltage across the 90V-rated load will be 120V. Not catastrophic. Should do.
RE: Telefunken T6445GWK restoration - morzh - 06-10-2023
Rod
Sorry, did not mean to ignore you, but got distracted.
First of, there is no dial lamp. The dial is not lighted.
Therefore I am not going to replace it with anything, as there is nothing to replace.
If there were, I'd then leave it original, as this is the habit of mine, modify only when necessary.
Like, now I am intending to mod it to work with 120V. But this is necessary.
So the short answer, no. No color LEDs.
RE: Telefunken T6445GWK restoration - radiorich - 06-10-2023
hello Mike,
For sure a Dropping Capacitor is the way to go Did you ever visit ARF radio Forum if so do you remember Peter
RE: Telefunken T6445GWK restoration - morzh - 06-11-2023
Rich
I've been to ARF a few times, though I am not a regular there.
Which Peter?
RE: Telefunken T6445GWK restoration - morzh - 06-11-2023
Not too successful.
I changed the sch as follows:
1. The 700 Ohm resistor in series with filaments is replaced with 3.3uF cap.
2. The filament of the rectifier is simply shorted. (the short is clearly see in the next photo in the paragraph 3)
3. The rectifier bridge AC IN is connected between the AC lines with the 20 Ohms resistor being replaced by a 60 Ohm NTC thermistor (inrush control needed due to no warm up time). The thermistor is that black disk thingy.
4. The bridge DC OUT is connected between the Rect tube Cathode (1st filter cap Positive) and the 1st filter cap Negative.
5. The filament string side that went to the fused AC line (the Negative of the rectifier) is disconnected and together goes to the Bridge AC IN (one of the bridge's inputs already mentioned in #3).
6. A green Soviet-made large wire-wound resistor, of 70 Ohm, for whatever reason added in front of both 700 ohm and 20 Ohm (perhaps due to poor power control in that part of the former USSR, where it is known to go to 250VAC) was removed.
Also the 2K filter resistor was 3.3K, so it was replaced.
The result is, the radio playes but is very hummy.
Also the DC 220V at the rectifier output was about 145V. So the full bridge diode rectifier does not compensate for the lower input AC by much larger margin than I was hoping for (I was hoping the Half-bridge lowers the voltage but the DC level was 225V DC with the 220V AC in. 165VDC to 120VAC is much better ratio but still not enough).
So I increased the input filter cap to 330uF (vs 16uF). The DC rose to 165V DC. But hum, though smaller, is still very pronounced. I wonder if this is due to the fact that the filaments were connected to the Negative before, and now they are not. I might try inserting a small cap between the fused input and the Negative, but I doubt it will help much.
RE: Telefunken T6445GWK restoration - morzh - 06-11-2023
I could possibly use a doubler rectifier circuit
https://electricalacademia.com/electronics/half-wave-full-wave-voltage-doubler-working-circuit-diagram/
This does allow for a common tied to the AC line.
RE: Telefunken T6445GWK restoration - Ron Ramirez - 06-11-2023
Mike
I'm not sure but I think Richard may be referring to the late Peter Balazsy (RIP).
RE: Telefunken T6445GWK restoration - RodB - 06-11-2023
Mike, would a safety cap across the line cut the hum?
RE: Telefunken T6445GWK restoration - morzh - 06-11-2023
Ron
Got it. I was not sure what this reference was in the context of the postings, but maybe Richard could explain, if maybe he meant Peter made something simialr.
Rod,
Well, I thought about it and then it probably would not. I did not try as I decided that there was a reason for referencing the filaments to the Rect negative.
So. What I've done is this:
I created (and it is a simpler, actually, solution to implement) a half-wave doubler. It brings up the voltage up quite a bit, the radio consumtion is OK to not droop it too much, and it allows one of the AC INs to be the common negative.
With this (two diodes, two caps) I turned the radio on and I have:
258V instead of 220VDC as the rect. output (good), 202V or so in place of 180VDC as the filtered voltage output.
The filaments at 117VAC are exactly at 90V, so 3.3uF is perfect.
Now, the circuit is as such:
My C1 is 22uF and the output cap C2 is 16uF. During the charging the voltage distributes itself across these two as serialized. Therefore, I think, by decreasing the C1 I could adjust the output voltage down a bit. Which is what I am about to to.
This said, the radio works fine now.
The concoction looks like this:
The rect tube is still there for looks with shorted filament.
Now, here's a video.
[Video: https://www.youtube.com/watch?v=AicnFfNcjFY]
Also, I decreased C1 cap to 10uF. My voltages now, when the radio warms up, are exactly where they should be:
225V first cap (220V in the schematic) and 178V filtered (180V in the sch).
Now to alignment. Tomorrow possibly.
RE: Telefunken T6445GWK restoration - radiorich - 06-11-2023
Hello Ron,
exactly Peter Balazsy he really did some amazing restorations and his write-ups and photos were amazing .
Nice Job Mike See Peter was a fan for the dropping capacitor too and this restoradio reminded me of his work .
Sincerely Richard
RE: Telefunken T6445GWK restoration - morzh - 06-11-2023
Rich
It is a popular technique altogether, especially, as I noted before, when replacing "curtain-burner" 3-wire ballast power cord.
This of course will stop the radio working from DC. But then who today needs a radio to work from 110VDC?
I always have some caps specifically for this purpose, they range from 2uF to 6uF, when I want to remove a ballast resistor.
RE: Telefunken T6445GWK restoration - radiorich - 06-12-2023
Hello Mike,
I have a Philco I think is a model 59c that also uses a ballast it will be a winter project .
Sincerely Richard