I'm trying to restore a set named above, but there are some problems. My set is almost (I hope) complete, but there is probably one piece missing (coil, choke, LF transformer?) and one added (condenser) - this I could see by comparison with available in net photos. It's model 23L (without W or G) - I'm sure because there is a badge with such a sign and a paper sheet with the data of maker, controller and datums of this activities (22/24.11.1930). There is also (under the cabinet) a kind of dry battery and connections to it signed "gitterbaterie" - did anybody see such a solution? If anyone has any information, detailed photos or is an owner of such a set and could describe or measure details - everything could be helpful in restoration - I'll be grateful for any help. Compliments HP
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20.12.09 15:58
roehrenfreak
nicht registriert
20.12.09 15:58
roehrenfreak
nicht registriert
Re: Tefagon 23L - restoration
Hello spiga,
first of all: Welcome to our forum, feel free to browse and ask your questions. We´ll try to do our best to satisfy you with our answers.
A so called "Gitterbatterie", transl. "Grid (-Bias) Battery" provides the control-grid bias voltage for almost all tubes in the audio-section of those sets, where an automatic bias-circuitry was not implemented. A lot of battery-operated sets use this technique.
What is the bias good for? The purpose of the bias is to set the plate currant to a certain value almost in the mid area of the control curve - refer to the data sheet of the tube. This is to make sure that an input signal is amplified through the tube without to be distorted and to keep the tube in safe operating conditions.
Viewing the third photograph I see in the center aft area of the chassis a big capacitor, probably of the power supply filter chain, in very bad shape. May be caused by an internal short it got very hot and the rising pressure pinched the side walls out of the metal case.
I´ve got no circuit diagram of your set, but I think the circuitry is very similar to other audion-receivers of the ´30es. Could you please give us an idea of the types of tubes used in your set. This may help us for further trouble shooting as well as some more detailed photographs of the chassis.
Thank You roehrenfreak, it's very kind Literature says that the valves should be: REN1004, RE134, RGN1500 - in my set REN 904, RE134 and RE 134 (intentionally or mistaken used as a rectifier) are installed
About bias battery
Zitat:A so called "Gitterbatterie", transl. "Grid (-Bias) Battery" provides the control-grid bias voltage for almost all tubes in the audio-section of those sets, where an automatic bias-circuitry was not implemented. A lot of battery-operated sets use this technique.
I saw that solution in many battery sets, but mine is 110V AC feeded - it's simple to obtain appriopriate voltage using a divider for example. So, why use a battery? I'll make detailed photos and try to draw a schema - that could solve the problem Henryk
ya - nice to see your reply. To obtain the bias by some divider resistors is reasonable, of course. But I already saw even in few AC-operated receivers of the early 1950ies grid bias batteries. For what reason? I dont´t even know. Must have been a designer´s decision in - may be? - conjunction of the use of direct-heated tubes. As I stated - May be!
To draw a circuit diagram will not be such a great problem to you. Those sets were quite simple. I´m convinced, that you will make it easily. Do you have the connection diagrams of the tubes available?
The use of a RE134 as a rectifier confuses me a little, but the pre-owner may have changed the circuit. Did they abuse the grid as a plate??? However, such "modifications" were not unusual after WWII, where the people suffered insufficiency anyway - perhaps the original tube was not available at that time or what so ever. BTW: RGN1500? Are you sure? This type is not listed in my data-table, RGN1054 or RGN1064 are mentioned for full-wave rectifiers and were often used in comparable sets of that age.
roehrenfreak:Do you have the connection diagrams of the tubes available?
Yes I have
roehrenfreak:BTW: RGN1500? Are you sure? This type is not listed in my data-table, RGN1054 or RGN1064 are mentioned for full-wave rectifiers and were often used in comparable sets of that age.
A friend from Germany checked it in "Katalog Radio Zentrale Prohaska 1930/1931". A cold cathode rectifier RGN 1500 (http://www.hupse.eu/radio/tubes/RGN1500.htm) was also used for example in Nora K2 We, K3 Wd. Compliments
you´re revealing very, very interesting facts. I´ve never seen gas-filled rectifier tubes in "normal" radio receivers (for the plate power supply) but in early battery chargers like e.g. the "Koerting Lade-Gleichrichter BG", dated around 1928, which I introduced in this forum several months ago. But, as stated in the description, this type didn´t satisfy the expections and production was discontinued shortly after inauguration. So it will make it very difficult to find an adequate substitute. A more or less "direct" replacement by two silicon-diodes may be critical in this case because the initial plate-voltage may overshoot after power-turn-on and cause damage to the filter-capacitors. The "abuse" of a RE134 is in this case an absolute "No-Go" - now I´m hoping not to run out of ideas... Waiting for a detailed circuit diagram...excited...very excited...
Anmelden
Waiting for a detailed circuit diagram...excited...very excited...