13th Dec 2016, 9:36 am | #121 |
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Re: Tandberg 64x after changing capacitors
I'm still no further forward understanding your voltage measurements, it would help if you posted them in the following format:
Q601 emitter (enter DC voltage) Q602 emitter (enter DC voltage) If you can only get to one of the emitter leads on the above transistors to do the measurement then enter the DC voltage for that transistor's emitter lead and for the other transistors emitter lead enter can't access. Q603 emitter (enter DC voltage) Q604 emitter (enter DC voltage) If you can only get to one of the emitter leads on the above transistors to do the measurement then enter the DC voltage for that transistor's emitter lead and for the other transistor's emitter lead enter can't access. Lawrence. |
13th Dec 2016, 6:28 pm | #122 |
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Re: Tandberg 64x after changing capacitors
Hi Lawrence,
I had access to all of the emitters as I have removed the metal panel from the back of the oscillator board. Each emitters has 3 pins. Q601 emitter (22 DC voltage) Q602 emitter (24 DC voltage) Q603 emitter (24 DC voltage) Q604 emitter (24~30 DC voltage) This is what I have measured yesterday. Thank you Levente |
13th Dec 2016, 7:08 pm | #123 |
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Re: Tandberg 64x after changing capacitors
I think you have some confusion going on with terminology.
The emitter is one of the three terminals of a transistor. On a wiring diagram, it is marked with an arrow; pointing outwards for an NPN transistor, or inwards for a PNP transistor.
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13th Dec 2016, 7:27 pm | #124 |
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Re: Tandberg 64x after changing capacitors
Yes, that's possible, having said that I did say to the OP earlier how to identify the emitters on the schematic, I then detailed which were the emitter leads for those transistors on the oscillator board layout shown in the last link I posted.
There are no voltages given for those transistors in the schematic, however the supply rail voltage for that board is given as 23.5 volts so I was expecting the voltage at the emitter connections to be about half that value. I also downloaded the full 6x manual as that is basically the same setup but again no voltages given for those bias output transistors. EDIT: Measuring the voltages on the transistor side of the bias preset capacitors (C602, C604) should confirm what's what. Note to anyone: The bias arrangements are cross-field. Lawrence. Last edited by ms660; 13th Dec 2016 at 7:35 pm. |
13th Dec 2016, 7:44 pm | #125 |
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Re: Tandberg 64x after changing capacitors
I am sorry guys....i am the one who is making a confusion here...as I am confused...sorry about that....
Its probably too complicated for me...all I have done is to find the "Q" points and measured the pins on them... Apologies Lawrence, I am not sure that I am following how to measure voltages on these emitters or transistors... Levente |
13th Dec 2016, 8:14 pm | #126 |
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Re: Tandberg 64x after changing capacitors
Ok, no worries...Let's try another way to measure the emitter voltages at the junction of the two emitters for both pairs of transistors...
Referring to the oscillator board again as posted in the last link, in that diagram at the bottom end of the board are two preset capacitors, the ones with the screw adjustment, C602 & C604, when you physically look toward the end of that board you should see two connecting legs from each capacitor going into the board for each preset capacitor... Still looking at the board from the same end, with C602 it's the left hand leg you want to measure the DC voltage on, that leg is connected by the printed circuit to the two emitters of one pair of transistors. With C604 it's the right hand leg you want to measure the DC voltage on, that leg is connected by the printed circuit to the two emitters of the other pair of transistors. Voltages measured with respect to HT-ve (chassis/ground) the same as you've measured all the voltages to date. Do not short out those capacitor connections to anything. Lawrence. |
14th Dec 2016, 7:14 am | #127 |
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Re: Tandberg 64x after changing capacitors
Hi Lawrence,
Thank you for this. C602 left hand leg measures 25VDC C604 right hand leg measures 26VDC Levente |
14th Dec 2016, 1:44 pm | #128 |
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Re: Tandberg 64x after changing capacitors
Not sure what to make of those voltages, they are almost equal as would normally be expected but I would have thought that both of them should be less, let's see what the other folks on the forum think.
Lawrence. |
14th Dec 2016, 2:14 pm | #129 |
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Re: Tandberg 64x after changing capacitors
I don't really do transistors, but those readings look all wrong to me. I'd expect to see half that. I'll try to post an annotated drawing of the Oscillator board later.
In the meantime it might be best to wait until the OP has a prerecorded tape to try.
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14th Dec 2016, 2:18 pm | #130 |
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Re: Tandberg 64x after changing capacitors
Yes, those were my thoughts too, I've posted the voltage question on another forum so I'll see what turns up.
I don't really do transistors either, used to back in the day but it's been a long time. Lawrence. |
14th Dec 2016, 7:12 pm | #131 |
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Re: Tandberg 64x after changing capacitors
Thanks Guys, i have rechecked again and I believe I am measuring at the correct place. Just out of curiosity I have measured both transistors three legs and if i reach the middle leg, the magic eye going wild as soon as I touch that pin...
I will get the tapes soon... Cheers |
14th Dec 2016, 10:51 pm | #132 |
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Re: Tandberg 64x after changing capacitors
If I 've got it right, the emitters are marked in red on the attachment.
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15th Dec 2016, 7:25 am | #133 |
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Re: Tandberg 64x after changing capacitors
Hi Graham,
Thanks for that. Yes, I am measuring exactly these points. I re did t his morning again, results are similar or even more what I have measured before: Q601 emitter pin 27 VDC Q602 emitter pin 26 VDC Q603 emitter pin 26 VDC Q604 emitter pin 25 VDC I am not sure this means good or bad, but I am sure that these voltages are there at those pins. Thank you |
15th Dec 2016, 9:53 am | #134 |
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Re: Tandberg 64x after changing capacitors
Had a word with someone else about those voltages, he also thinks they should be mid rail (1/2 B+ approx.) A high bias oscillator waveform at those emitter points might be fooling the DMM?
One way to prove the bias circuit would be to swop the feeds to the bias heads and see if the good channel turns to bad etc, not saying that should be done yet, best to check out the play back first with the pre recorded tape that's on its way. Lawrence. |
17th Dec 2016, 4:48 pm | #135 |
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Re: Tandberg 64x after changing capacitors
Hello guys..hope you are having a great weekend. I count not resist to look at the Tandberg again and something just always been bothering me at least of the look of it...
First is one of those Hunts coupling capacitor picture 1-3. It is cracked. The switch panel next to it cracked it. Should I replace this? The second also in the other corner...one resistor edge is chipped. Should I replace that too? Could this cause any issue? (picture 4) Three is I had a closer look of the oscilator board and found two miniprint caps hidden which I have not replaced when I did the others back in June. (pic 5) I have replaced that. Sound quality was increasing, but still having the same problem on recording.... Until my tape arrives, would you recommend me to replace all of the suspicious parts as above? Thank you |
17th Dec 2016, 5:09 pm | #136 |
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Re: Tandberg 64x after changing capacitors
I would replace those chipped components, making sure there's clearance between them and the switch mechanism.
Lawrence. |
17th Dec 2016, 6:13 pm | #137 |
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Re: Tandberg 64x after changing capacitors
Cheers Lawrence,
I have replaced the coupling cap....the weaker channel got better..and i have noticed if i tap the unit with a little force the channel gets a buzzed, specially the L one.... maybe ther/e is contact failure or some of the tubes responding to this tapping, a faulty one maybe? |
17th Dec 2016, 7:57 pm | #138 |
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Re: Tandberg 64x after changing capacitors
....quick follow up on my previous post.
Tubes V1 and V2-----> Contact failure possibly on the tube holders and microphony Tubes V3 and V4--------> contact failure at the rube holders. I will now change all the tube holders and get another set of brand new ecc83s |
17th Dec 2016, 8:28 pm | #139 |
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Re: Tandberg 64x after changing capacitors
Why waste money on a new set of ECC83's?
Once you've changed the valveholders you'll be able the check the voltages and see what state they're in.
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17th Dec 2016, 8:30 pm | #140 |
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Re: Tandberg 64x after changing capacitors
because of microphony? but i see your point...absolutely right Lawerence. Thanks.
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