|
Alfred Pugliese
USA Articles: 36 Schem.: 0 Pict.: 5 23.Dec.07 00:29 |
Help with AJA radio Type 5842 mod 118068
You aren't logged in. (Guest)
1
Greetings all! I have changed all tubes, and a few caps. I have also cleaned all switches, and contacts. The radio plays and picks up stations on all dials....But, the volume is low, about 25%of what it should be ( even with volume control turned all the way up) What should I be looking for?? Anyone ever experience this?.........Thanks AL |
Dietmar Rudolph
D Articles: 462 Schem.: 168 Pict.: 148 23.Dec.07 20:02 |
Pick-up tested?
You aren't logged in. (Guest)
2
Probably the problem is in the audio part of the set. Can you please test the pick-up (PU or TA "Tonabnehmer"). If you insert here an audio signal, the audio part of the set can be tested. Even if you touch the PU pin with a screwdriver, a loud hum should be heard. 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 |
|
Alfred Pugliese
USA Articles: 36 Schem.: 0 Pict.: 5 24.Dec.07 15:34 |
You aren't logged in. (Guest)
3
Thanks for response Mr. Rudolph. Which tube is the output? I believe I get the hum, but it is not as loud as it should be. Something is suppressing our volume. I don't have schematic. I will check your question about ac/dc.....Merry Christmas! AL |
|
Alfred Pugliese
USA Articles: 36 Schem.: 0 Pict.: 5 26.Dec.07 05:47 |
You aren't logged in. (Guest)
4
Yes...It is AC Only....115volts. I will correct it under specs of this radio......AL |
|
Todd Stackhouse
USA Articles: 60 Schem.: 20 Pict.: 18 26.Dec.07 06:40 |
Audio tubes
You aren't logged in. (Guest)
5
...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.
|
Rolf Nickel
D Articles: 178 Schem.: 14 Pict.: 47 26.Dec.07 10:28 |
Negative feedback ?
You aren't logged in. (Guest)
6
Dear Alfred,
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 |
|
Alfred Pugliese
USA Articles: 36 Schem.: 0 Pict.: 5 27.Dec.07 01:04 |
You aren't logged in. (Guest)
7
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 |
Emilio Ciardiello
I Articles: 69 Schem.: 152 Pict.: 512 27.Dec.07 07:51 |
You aren't logged in. (Guest)
8
Dear Alfred, 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 |
|
Rolf Nickel
D Articles: 178 Schem.: 14 Pict.: 47 27.Dec.07 17:24 |
Application example
You aren't logged in. (Guest)
9
Dear all,
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 Attachments: |
|
Alfred Pugliese
USA Articles: 36 Schem.: 0 Pict.: 5 28.Dec.07 03:19 |
You aren't logged in. (Guest)
10
Thanks Emillo.....On the EL84 I am getting + 8.5 at cathode pin3......and pin 2 voltage moves from 0 to .9 and in between, never going over 1v....pin 9.. is 260v I will now try to examine points from the schematic Rolf just sent me.....AL |
|
Emilio Ciardiello
I Articles: 69 Schem.: 152 Pict.: 512 28.Dec.07 08:55 |
You aren't logged in. (Guest)
11
Dear Al, 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 |
|
Alfred Pugliese
USA Articles: 36 Schem.: 0 Pict.: 5 28.Dec.07 15:18 |
You aren't logged in. (Guest)
12
Hi Emilio......The control grid voltage was taken at full volume. I was not moving control knob. What value is 25nF .25? 2.5? Thanks AL |
|
Emilio Ciardiello
I Articles: 69 Schem.: 152 Pict.: 512 28.Dec.07 17:06 |
You aren't logged in. (Guest)
13
Dear Al, 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 |
|
Alfred Pugliese
USA Articles: 36 Schem.: 0 Pict.: 5 28.Dec.07 20:35 |
You aren't logged in. (Guest)
14
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 |
|
Alfred Pugliese
USA Articles: 36 Schem.: 0 Pict.: 5 29.Dec.07 17:24 |
You aren't logged in. (Guest)
15
Gentleman.....I checked the 10meg resistor to ground....and it measures 11meg ( probably in range) I hooked up cassette player to phono pick up.....same volume. I replaced 2 more caps....still the same....I checked all the resistors( not for actual value) and none are open. One note...when I first checked under the chassis, there was a 1 meg resistor connected to pin 9 of the eabc 80....and disconnected from other side...I found a solder line on the el84 pin 7...it made sense that thats where it should go. When connecting and disconnecting this resistor, it has no effect what so ever. aLSO...The bass switch has no effect on sound of radio...its as if it is not connected. The tremble works as it should. What are the tubular clear with 500v KF drp756214 marked on red label?? Thanks at wits end!!! AL |
|
Todd Stackhouse
USA Articles: 60 Schem.: 20 Pict.: 18 29.Dec.07 20:15 |
Clear parts
You aren't logged in. (Guest)
16
...those are probably polystyrene ('Styrol') capacitors. These were used primarily in the RF and IF circuits (if any of these are in the audio section, they are most likely part of a tone control circuit, probably a treble control) and were generally quite stable and not prone to failure. In the example you previously mentioned, marked '300/20 500V', the markings probably refer to the value (300 pF), tolerance (20%), and working voltage (500V). Values of capacitors of this type only ranged to perhaps .01-.022 uF. |
|
Alfred Pugliese
USA Articles: 36 Schem.: 0 Pict.: 5 04.Jan.08 03:59 |
You aren't logged in. (Guest)
17
hI ALL...I hope everyone's New Year celebration was grand! As for me, I got back to work on this radio. I decided to take it out of cabinete ( we all know how much fun that is) I gave the push button connections good cleaning, and cleaned all contacts. Took off dial glass and made it pristeen. I found a bad looking 'tar' cap on Output transformer ( buldging a bit ) It reads 5000pf. My math is horrible, would this be .005? I also started to strip the cabinete, and found beautiful wood grain, under the black crackling finish. This will be a wonderful work of art....I just hope I can get it working 100%........Thanks AL |
|
Todd Stackhouse
USA Articles: 60 Schem.: 20 Pict.: 18 04.Jan.08 06:39 |
Capacitor value...
You aren't logged in. (Guest)
18
...you are correct; 5000pF=5nF=.005uF. You should be able to use a .0047uF cap there with no difficulty. |
|
Alfred Pugliese
USA Articles: 36 Schem.: 0 Pict.: 5 04.Jan.08 20:12 |
You aren't logged in. (Guest)
19
Thanks...When I put everything back together....I will let all know outcome....AL |
|
Alfred Pugliese
USA Articles: 36 Schem.: 0 Pict.: 5 06.Jan.08 05:05 |
You aren't logged in. (Guest)
20
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 |
|
Alfred Pugliese
USA Articles: 36 Schem.: 0 Pict.: 5 07.Jan.08 21:27 |
You aren't logged in. (Guest)
21
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 This article was edited 07.Jan.08 22:27 by Alfred Pugliese . |
Hans M. Knoll
D Articles: 1286 Schem.: 137 Pict.: 59 07.Jan.08 22:37 |
You aren't logged in. (Guest)
22
Hello Alfred-
You think right. EM85 is only a tuning indicator tube.
regards hans |
|
Alfred Pugliese
USA Articles: 36 Schem.: 0 Pict.: 5 23.Feb.08 20:06 |
You aren't logged in. (Guest)
23
Hello all...Still trying to get this one going strong. A helpful radio friend has the same radio,( in working order ) and took a photo of the underside. I noticed 2 resistors in series going to the EL84 pin 7 . The colors were different on his ( mine were replaced by someone) The correct colors should be black/brown/blue--silver going to pin 7 in series with red/black/yellow---silver. My resistors measure 1 meg and 220 ohms...do these correspond to the correct colors? I am looking for anything that might be supressing my audio. Thanks AL |
|
Todd Stackhouse
USA Articles: 60 Schem.: 20 Pict.: 18 24.Feb.08 07:25 |
Resistors
You aren't logged in. (Guest)
24
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. |
|
Alfred Pugliese
USA Articles: 36 Schem.: 0 Pict.: 5 24.Feb.08 17:42 |
You aren't logged in. (Guest)
25
Thanks Todd.....I will make the change and hopefully she will work better....Thanks AL |
|
Alfred Pugliese
USA Articles: 36 Schem.: 0 Pict.: 5 25.Feb.08 15:42 |
You aren't logged in. (Guest)
26
I have good news! AJA Is fixed! On pin 8 of the EF89, voltage was way out of range. Found a resistor measuring 200k, when it should be 47k. Thanks for every ones help, especially Dennis Daley who guided me through the diagnostic exam............All the best AL |
| rmXorg-09 |
|
09JanX |
