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Type 106 Saga (Again)
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Hi all,
My type 106 was working fine until a few days ago when I had no more output at all on any output. Neither the High Amplitude nor the +/- Fast Rise. All voltages read perfectly fine, and I¡¯ve checked all I could (I think). Lastly I checked the ripple on all voltages, and found something very strange. Both the A supply voltage ripple, as well as the -150V ripple seem to be perfectly within specs. The +150V ripple is a bit higher, but seems within specs as well. They can be seen here. See the legends for more accurate descriptions. A and -150V ripple ¡ª> /g/TekScopes/photo/273030/3389525?p=Created%2C%2C%2C50%2C2%2C0%2C0 A and -150V ripple 2 ¡ª> /g/TekScopes/photo/273030/3389526?p=Created%2C%2C%2C50%2C2%2C0%2C0 +150V ripple ¡ª> /g/TekScopes/photo/273030/3389528?p=Created%2C%2C%2C50%2C2%2C0%2C0 -20V ripple ¡ª> /g/TekScopes/photo/273030/3389531?p=Created%2C%2C%2C50%2C2%2C0%2C0 and /g/TekScopes/photo/273030/3389532?p=Created%2C%2C%2C50%2C2%2C0%2C0 Now the last one (-20) is extremely weird as the square waves follow the frequency I set on the unit, but not the amplitude at all. It seems there is some ¡°crossover¡± somewhere. Also, the trigger output seems just fine. I¡¯ve replaced the filter cap C262, no improvement. All the el84 tubes check ok and very strong. I¡¯ve swapped some transistors, in the amplifier¡. Nothing. I put the originals back in. All this happened without any other signs of anything¡. One day is was working great, and the next¡ zilch¡ Any help appreciated. Thank you. |
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On Mon, Feb 28, 2022 at 07:38 PM, Stephen wrote:
Broken switch SW242A? In High Ampl mode you should measure R99 600R at the GR output plug. What would happen when R55 is open? Is the output 0V or some constant negative voltage? Now the last one (-20) is extremely weird as the square waves follow the frequency I set on the unit, but not the amplitude at all.I don't think this is weird. The -20 V on top of "A" supplies the grid and trigger circuits. The 4x output tubes anode currents flow in a separate circuit from GND to "A", regulated by anode-cathode voltage, not by grid amplitude. Albert |
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On Tue, Mar 1, 2022 at 05:55 PM, Albert Otten wrote:
Interleaved. Broken switch SW242A? In High Ampl mode you should measure R99 600R at the GRThanks Albert, Interesting¡. I didn¡¯t think of a broken switch. I check that out when I¡¯ll get beck home later. I¡¯ll check again, but from memory all of the outputs are pretty close to 0V. I¡¯ll check that again. I¡¯ll also check R55. I don't think this is weird. The -20 V on top of "A" supplies the grid andOk, but the 4 output tubes only supply the High Amplitude section, if I understood correctly. Why would all outputs be out? That must be caused by something they all share in common. Maybe the switch¡ Albert |
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In Fast Rise mode, the output tubes provide base drive to the Fast Rise circuit. See SW242A on the schematic.
SW242B bypasses the AMPLITUDE control in Fast Rise mode, jamming it to maximum. So don¡¯t leave it running for hours in Fast Rise mode unless you have lots of spare 7189A¡¯s. Dave Wise From: [email protected] <[email protected]> On Behalf Of Stephen via groups.io Sent: Tuesday, March 01, 2022 9:15 AM To: [email protected] Subject: Re: [TekScopes] Type 106 Saga (Again) On Tue, Mar 1, 2022 at 05:55 PM, Albert Otten wrote: Interleaved. Broken switch SW242A? In High Ampl mode you should measure R99 600R at the GRThanks Albert, Interesting¡. I didn¡¯t think of a broken switch. I check that out when I¡¯ll get beck home later. I¡¯ll check again, but from memory all of the outputs are pretty close to 0V. I¡¯ll check that again. I¡¯ll also check R55. I don't think this is weird. The -20 V on top of "A" supplies the grid andOk, but the 4 output tubes only supply the High Amplitude section, if I understood correctly. Why would all outputs be out? That must be caused by something they all share in common. Maybe the switch¡ Albert |
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On Tue, Mar 1, 2022 at 06:39 PM, Dave Wise wrote:
Hmmm. I have left it on a few times for quite a long time¡ Mine doesn¡¯t have 7189A¡¯s. It has old Philips EL84¡¯s which read very strong. But I¡¯ll check them again when I get back. I¡¯ll report back when I can get check all that tou guys suggested. And thanks for the tip regarding preserving the tube life. I¡¯ll certainly be more careful now¡. |
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To work with 6BQ5/7189, a minor wiring change is needed. Pins 1 and 6 are ¡°unspecified internal connection¡± while the corresponding 7189A pins are explicitly G1 and G2 respectively.
On all four sockets, move the G2 wire from pin 6 to pin 9. That is all. EL84 pins 1 and 6 are no-connect so this tube doesn¡¯t need the mod. The output tubes yank their plates toward their cathodes (which are being held at a negative voltage determined by the AMPLITUDE control), then release them and the load resistance pulls the line back up to ground. As the tubes wear out, two things happen. (1) Cathode emission decreases. This ultimately limits the maximum negative excursion. (2) Sometimes the cathode develops an ¡°interface layer¡± which acts like an RC time constant. Since only the positive corner¡¯s quality is specified in HI AMPLITUDE mode, this doesn¡¯t matter unless it becomes so bad that it compromises the negative output in FAST RISE mode. Dave Wise From: [email protected] <[email protected]> On Behalf Of Stephen via groups.io Sent: Tuesday, March 01, 2022 10:20 AM To: [email protected] Subject: Re: [TekScopes] Type 106 Saga (Again) On Tue, Mar 1, 2022 at 06:39 PM, Dave Wise wrote: Hmmm. I have left it on a few times for quite a long time¡ Mine doesn¡¯t have 7189A¡¯s. It has old Philips EL84¡¯s which read very strong. But I¡¯ll check them again when I get back. I¡¯ll report back when I can get check all that tou guys suggested. And thanks for the tip regarding preserving the tube life. I¡¯ll certainly be more careful now¡. |
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I¡¯ve rechecked all the tubes, and they still read very strong on my HealthKit tester. Since a I had a quad of EL84¡¯s laying around, I replaced all of them as precaution. They¡¯re not brand new, but they read very strong as well. That didn¡¯t make any change.
The DTPT switch seems to be ok. Although I can¡¯t seem to locate the B side on the schematic. I haven¡¯t checked R55 yet. David, are you suggesting that I rewire the tube sockets, even though everything was working properly before with EL84¡¯s? |
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Stephen, I mentioned the socket mod as a PSA. I wasn¡¯t exhorting you to do it.
From: [email protected] <[email protected]> On Behalf Of Stephen via groups.io Sent: Tuesday, March 01, 2022 1:02 PM To: [email protected] Subject: Re: [TekScopes] Type 106 Saga (Again) I¡¯ve rechecked all the tubes, and they still read very strong on my HealthKit tester. Since a I had a quad of EL84¡¯s laying around, I replaced all of them as precaution. They¡¯re not brand new, but they read very strong as well. That didn¡¯t make any change. The DTPT switch seems to be ok. Although I can¡¯t seem to locate the B side on the schematic. I haven¡¯t checked R55 yet. David, are you suggesting that I rewire the tube sockets, even though everything was working properly before with EL84¡¯s? |
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Stephen, the ripple sizes in your pictures are only a fraction of what I see in my working 106. Perhaps they are so small because the 4 tubes never conduct.
Even with almost exhausted tubes you should get some output square wave. I would measure the waveform at the grid line w.r.t. the DC cathode voltage(s). And then consult Ia-Vg characteristics of the EL84. Albert |
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On Tue, Mar 1, 2022 at 11:26 PM, Albert Otten wrote:
Albert, You¡¯re probably right. Hence the zero volt output measured on all 3. The question is why did they stop conducting all of a sudden, whereas the unit was working perfectly the day before, and had been for weeks. I¡¯m pretty sure it¡¯s not the tubes themselves. Had it been the tubes, changing them would¡¯ve solved the issue. It¡¯s kinda late in Europe, but tomorrow I¡¯ll check R55 and the voltages at the plates and grids. Will report back then. Thank you. |
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The EL84¡¯s should be getting plenty of drive on their control grids. Go back along the signal chain from there to the multivibrator. On my own instrument, after power-on, sometimes it doesn¡¯t start until I switch back and forth between HI AMPLITUDE and FAST RISE. Seems like the multi needs a kick.
Dave Wise From: [email protected] <[email protected]> On Behalf Of Stephen via groups.io Sent: Tuesday, March 01, 2022 3:20 PM To: [email protected] Subject: Re: [TekScopes] Type 106 Saga (Again) On Tue, Mar 1, 2022 at 11:26 PM, Albert Otten wrote: Albert, You¡¯re probably right. Hence the zero volt output measured on all 3. The question is why did they stop conducting all of a sudden, whereas the unit was working perfectly the day before, and had been for weeks. I¡¯m pretty sure it¡¯s not the tubes themselves. Had it been the tubes, changing them would¡¯ve solved the issue. It¡¯s kinda late in Europe, but tomorrow I¡¯ll check R55 and the voltages at the plates and grids. Will report back then. Thank you. |
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On Wed, Mar 2, 2022 at 12:43 AM, Dave Wise wrote:
On my own instrument, after power-on, sometimes it doesn¡¯t start until IDavid, I noticed the same in my 106. Stephen, just for comparison: Setting 10 kHz, "A" = Vk = -40 V, output in 50R is 2 Vpp . Then Vgk is almost square wave between -1.5 V and -15 V. Albert |
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David, Albert,
I will make some more measurements later on. My unit never had that issue you both experienced. It started up right away when it was working. I remember measuring between R55 and R56, and from memory I didn¡¯t have the proper -145V, but something like +15V (I think). I have to review my notes when I get back home. BTW, R55 reads dead on. I¡¯ll also check R56. Thank you both again for your time and inputs. I¡¯ll report back as soon as I can. |
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Today¡¯s measurements:
1- Both 6EW6 measure good and strong. 2- Pin 6: +3V 3- Pin 7: +1.6V 4- Pin 8: -4.7V instead of -145V 5- Between Pin 2 and R55: +3V instead of -151V I would say that it¡¯s very, very wrong¡. I didn¡¯t locate V56 (10¦¸) in the unit yet. Also, since I can¡¯t locate SW242B on the schematic, I¡¯m not sure my readings are what they should be. Meaning that I see that both sides (B side) are always connected no matter the position of the switch. As if the switch was just there for nothing¡. I doubt this is normal, otherwise why even have them go through a switch in the first place¡. Just connect them directly¡ |
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Check Q54, does it have base drive? And does it conduct when turned on? Sounds like NO to at least one of those questions. Which is consistent with the multivibrator not running. Scope it and see.
As clearly shown in the parts list, R56 was only used on serial number 200 through 634 and then deleted. SW242B is on the power supply schematic, towards the upper right corner. It forces AMPLITUDE to maximum in the FAST RISE position. If you see no change in the switch potentials when it¡¯s flipped, maybe the switch is bad. That usually gives the handle a characteristic ¡°feel¡± which unfortunately I can¡¯t describe in words but it¡¯s drastically different from a working one. Dave Wise From: [email protected] <[email protected]> On Behalf Of Stephen via groups.io Sent: Wednesday, March 02, 2022 11:46 AM To: [email protected] Subject: Re: [TekScopes] Type 106 Saga (Again) Today¡¯s measurements: 1- Both 6EW6 measure good and strong. 2- Pin 6: +3V 3- Pin 7: +1.6V 4- Pin 8: -4.7V instead of -145V 5- Between Pin 2 and R55: +3V instead of -151V I would say that it¡¯s very, very wrong¡. I didn¡¯t locate V56 (10¦¸) in the unit yet. Also, since I can¡¯t locate SW242B on the schematic, I¡¯m not sure my readings are what they should be. Meaning that I see that both sides (B side) are always connected no matter the position of the switch. As if the switch was just there for nothing¡. I doubt this is normal, otherwise why even have them go through a switch in the first place¡. Just connect them directly¡ |
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On Wed, Mar 2, 2022 at 08:46 PM, Stephen wrote:
Today¡¯s measurements:Stephen, I suppose you misread pin 3 as pin 8 (cathode, "A") in the schematic. That -145 V is measured with Amplitude at maximum. Did you perhaps set Amplitude here to minimum? (But I still would expect pins 6 and 7 to be slightly negative then, not positive). Albert |
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David, Albert,
I rechecked the voltages, this time with the correct settings, and they are still exactly the same. I also checked all the waveforms to be expected on the ¡°GENERATOR¡± schematic. All waveforms are perfect until I get to R99 (600¦¸). From this point and everything beyond (to the right), zilch. Flat as a pancake. Which was to be expected since there is no output. Q54 is fine. For good measure I replaced it temporarily. Same results. Although the TP voltages are all fine, I¡¯m seriously considering recapping the power supply¡ again. At this point, I don¡¯t know what else to do. What do you think? |
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