Help with AJA radio Type 5842 mod 118068
Help with AJA radio Type 5842 mod 118068
To thank the Author because you find the post helpful or well done.
Pick-up tested?
On the model page http://www.radiomuseum.org/r/aja_5842.html the set is characterized as an AC-DC type. Regarding the tube line up, this is very unlikely. Be so kind and check the set for its voltage, and possibly correct this at the model.
Best regards,
Dietmar
To thank the Author because you find the post helpful or well done.
To thank the Author because you find the post helpful or well done.
To thank the Author because you find the post helpful or well done.
Audio tubes
...without a schematic, I can only make educated guesses here. The audio circuitry of your radio probably consists of part of the EABC 80 (triode section used as audio amp) and the EL 84 (output). If you have replaced the tubes, and you know the tubes are definitely good, start checking the capacitors around them. Look at capacitors at pin 7 (cathode bypass) and pin 8 (coupling) of the EABC 80, and pin 2 (coupling) and pin 3 (cathode bypass) of the EL 84. Pay special attention to that EL 84 cathode bypass, since it is most likely going to be an electrolytic; if it is open, it will cause a major loss of gain. Also, if any of these capacitors are paper types, it is a good idea to replace them as a matter of course. Like electrolytics, paper caps are notorious for not aging well and being a major source of performance problems in older radios.
To thank the Author because you find the post helpful or well done.
Negative feedback ?
I am afraid that Todd is right. Without a schematic this could become a bigger problem because of the possibility of a wrong negative feedback voltage from the output transformer. Please have a look at the schematic of this example !
This kind of circuitry and its dimensioning is comparatively simple regarding the (few) components but very complicated regarding the various influences of the two feedback windings from the output transformer and the bias of the EABC 80-Triode (in general with a 10MOhm resistor to ground). And did you ensure that all pins of the EABC 80 are properly connected with the socket jacks?
Kind regards
Rolf
To thank the Author because you find the post helpful or well done.
Hi...I dont see many capacitors involved with EABC 80 or EL84. The two that were there are the paper ( tar) type, and I changed those. However there are these clear caps? that have 300/20 500v imprinted on red paper....and Grey ( look like wire wound resistors) that have 10000 on them?? I am not familiar with these parts. Is there a voltage check I can do to head us in right direction? I would be willing to get reading of all tube pins if it will help. I assume they would all be on the DC scale. I cleaned and tightened all tube socket pins...still the same.
Thanks AL
To thank the Author because you find the post helpful or well done.
you should check the DC bias of the EL84. Assuming that a self-biasing circuit is used, you should find the following voltages on the output tube pins:
cathode, pin 3: -7.4 VDC approx.
control grid, pin2: 0
screen grid, pin 9: +250 VDC approx.
Any positive voltage value on the control grid would mean a leaky coupling capacitor from the plate of the triode section of EABC80.
Regards,
Emilio
To thank the Author because you find the post helpful or well done.
Application example
due to lack of the original schematic it could be helpful to dicuss our problems with an "application example" with an output-stage consisting of EABC 80 and EL 84. I made a reduction to the essential items and marked some critical components and values of voltages and currents. Please keep in mind that this is only an example and not the real schematic. Voltages and currents in red were estimated, see attached file.
Dear Alfred, the EL 84 voltages should be as Emilio told us. And then, please have a look at the critical 10 MegOhm resistor (if existing, recommendation : replacement !) for EABC 80 (triode) grid bias voltage and its grounding. Im my example you can see an "unusual" double grounding (in blue) at volume and bass controls. Do not try to measure the grid voltage of the triode. Instead of that you could perhaps check the plate current. It should be less than 1 mA and above 0,3 mA. I remember these values from my father's "Nordmende Fidelio".
Best regards
Rolf
To thank the Author because you find the post helpful or well done.
To thank the Author because you find the post helpful or well done.
check the high value resistors, as Rolf suggests, because often their value can be altered with the age and the moisture, even opened. Unfortunately, without the schematic diagram of this radio, you should check every component you see under the chassis around the two tubes.
However remember that the voltage on the control grid should never go positive. You measured from 0 to .9VDC, but you do not specify the conditions: if you have positive values moving the tone control knob (600K treble potentiometer in the diagram given by Rolf), you should assume that the coupling capacitor (25nF in the same diagram) is leaky.
Emilio
To thank the Author because you find the post helpful or well done.
To thank the Author because you find the post helpful or well done.
the 25nF capacitor, or 25000pf / 0.025uF, in the example is C64. Please, can you specify when the grid voltage of the EL84 is zero and when it raises to .9V. Is the value DC or AC? You should measure the DC bias condition and the DC grid voltage should be always zero, unless the coupling capacitor is leaky or the EL84 is gassy.
Emilio
To thank the Author because you find the post helpful or well done.
Thanks Emilio.....So those grey components marked 10000pf are .01? I tested the voltages on DC. Pin 1 and 2 of the EL84 are connected ( 0 ohms between them) is this correct? I will re check pin 2 and move the tremble control while I do it, and see if it changes. Also I should mention...the volume control has no stopper when turned to up volume...just keeps on turning....but does have stopper on decrese. I tried another volume control of 1 meg...without improvement. Is the color code of resistors the same as American sets? I will get busy tonite, and hopefully have this radio ready for the weekend...'Patients is a bitter cup.....where only the strong can drink'
Al
To thank the Author because you find the post helpful or well done.
To thank the Author because you find the post helpful or well done.
Clear parts
To thank the Author because you find the post helpful or well done.
To thank the Author because you find the post helpful or well done.
Capacitor value...
To thank the Author because you find the post helpful or well done.
To thank the Author because you find the post helpful or well done.
Hi all......While I refinish cabinete, I played radio through another speaker. It has a bit more output. The bass control, has no effect when used. Does anyone know what might be the cause?
Thanks AL
To thank the Author because you find the post helpful or well done.
Hi all....One question. The EM85 is the tuning tube. On American sets this tube has no effect on Audio. Is the same true on this set? I was reading article by Hani Knoll, and began to think so...
AL
To thank the Author because you find the post helpful or well done.
Hello Alfred-
You think right. EM85 is only a tuning indicator tube.
regards hans
To thank the Author because you find the post helpful or well done.
To thank the Author because you find the post helpful or well done.
Resistors
brown/black/blue/silver=10 megohm, 10%
red/black/yellow/silver=200k ohms, 10%
Both resistors in your radio are measuring much lower than they should.
To thank the Author because you find the post helpful or well done.
To thank the Author because you find the post helpful or well done.
To thank the Author because you find the post helpful or well done.