Hi,
I’m currently working on a quad 303, which has some issues. I have upgraded the quad 33 preamp with the dada recommendations. There are a lot of references to the downloadable dada literature for the 303. Unfortunately, the dada website does not work for the entire downloads section. I understand that dada has ceased trading. Does anyone have a copy of the 303 dada upgrade pdf. It was freely available from the site until recently.
I’m currently checking all the output transistors, although the amp powers up without lighting up a DBT, but one channel is very quiet, and as I increase the volume the louder channel under load starts to light the DBT, as I increase the Variac voltage.
The PSU outputs 74v instead of 67, and the trimmer has no effect. Will be investigating the trimmer and the transistors involved in regulation. With no speaker load I can use the variac to adjust down the 67v for now.
Many thanks in advance.
I’m currently working on a quad 303, which has some issues. I have upgraded the quad 33 preamp with the dada recommendations. There are a lot of references to the downloadable dada literature for the 303. Unfortunately, the dada website does not work for the entire downloads section. I understand that dada has ceased trading. Does anyone have a copy of the 303 dada upgrade pdf. It was freely available from the site until recently.
I’m currently checking all the output transistors, although the amp powers up without lighting up a DBT, but one channel is very quiet, and as I increase the volume the louder channel under load starts to light the DBT, as I increase the Variac voltage.
The PSU outputs 74v instead of 67, and the trimmer has no effect. Will be investigating the trimmer and the transistors involved in regulation. With no speaker load I can use the variac to adjust down the 67v for now.
Many thanks in advance.
Dada Electronics (Belgium) ceased trading last year. Dada Electronics Asia/Pacific and North America are still in business. The upgrade manual is available here, along with the Quad user manual and service manual and other goodies.
So Tr3 is short-circuit c/e, which you can easily test. Replace it with an M802.
No point. The 303 will run on the full voltage, but you need to get the regulator running first, as all the other 4 adjustments depend on the 67V rail voltage.
Esmond Pitt
Dada Electronics Australia
Thanks for the quick response and the pdf.
I had checked the resistors, which were in the right ball park, and the trimmer was high resistance, so I swapped for a multiturn 5K, set at 2.5K(middle). Slightly better, starting off at 68V, but rising slowly to 72V - I assume temperature related. I pulled TR200, which tested fine, and also TR201, which, on a component tester had a low hFE of 39 (with an Ie of 0.32mA, Vbe 600mV). I then read your response, and have subsequently tested TR3 - there is no short across CE. I pulled one leg of R207 (TR201 is still out) so I could diode test TR3 over 13, 14, 15 of the PSU pins and all tests fine. I had read somewhere that TR201 can fail when the temperature goes up.
I had checked the resistors, which were in the right ball park, and the trimmer was high resistance, so I swapped for a multiturn 5K, set at 2.5K(middle). Slightly better, starting off at 68V, but rising slowly to 72V - I assume temperature related. I pulled TR200, which tested fine, and also TR201, which, on a component tester had a low hFE of 39 (with an Ie of 0.32mA, Vbe 600mV). I then read your response, and have subsequently tested TR3 - there is no short across CE. I pulled one leg of R207 (TR201 is still out) so I could diode test TR3 over 13, 14, 15 of the PSU pins and all tests fine. I had read somewhere that TR201 can fail when the temperature goes up.
I took some voltages from Tr200 and Tr201, with the negative lead on point 14 (base of Tr3).
Tr200 PNP - collector 18.5V, base 20.3V, emitter 0.68 - so turned off (B>V).
Tr201 NPN - collector 6.8V, base 0.68V, emitter 0V - not sure what the source of 0.68V is on the base unless leaking from collector of Tr201 or from the collector of 'turned off' Tr200.
I have been reading this thread:
https://www.vintage-radio.net/forum/showthread.php?t=187383&page=2
So now have taken out Tr201 and get 56V on the collector pad and pin 13, and 33V on the base. This is different from the above thread as they got 0V on the base pad which pointed the finger at Tr201. They had already substituted Tr200 with a BC556, which I have done, which makes no difference. I still get 33V on the base.
I'm probably going down the BC441 route, then !
Still not sure why I have 33V on the base of Tr201 now.
Tr200 PNP - collector 18.5V, base 20.3V, emitter 0.68 - so turned off (B>V).
Tr201 NPN - collector 6.8V, base 0.68V, emitter 0V - not sure what the source of 0.68V is on the base unless leaking from collector of Tr201 or from the collector of 'turned off' Tr200.
I have been reading this thread:
https://www.vintage-radio.net/forum/showthread.php?t=187383&page=2
So now have taken out Tr201 and get 56V on the collector pad and pin 13, and 33V on the base. This is different from the above thread as they got 0V on the base pad which pointed the finger at Tr201. They had already substituted Tr200 with a BC556, which I have done, which makes no difference. I still get 33V on the base.
I'm probably going down the BC441 route, then !
Still not sure why I have 33V on the base of Tr201 now.
Already checked and read 11.8v across it.
also checked all 5 power transistors on big heat sink at end, and they were fine (thankfully !)
will order the bc441 from Cricklewood in the uk. I have bd139/140 from a NAD 3020, which I could try, after adjusting the pinout (ECB from memory). Would that work - I think it is rated for 80v
also checked all 5 power transistors on big heat sink at end, and they were fine (thankfully !)
will order the bc441 from Cricklewood in the uk. I have bd139/140 from a NAD 3020, which I could try, after adjusting the pinout (ECB from memory). Would that work - I think it is rated for 80v
The emitter of Tr200 is connected to the zener, so either the emitter voltage was 11.8 or the Zener had 0.8v across it or the connection is faulty or there is something wrong with your readings. Which I think there is, as the collector of Tr200 can’t be more positive than the emitter. It should be one b/e drop above the negative rail. I think you have reported C and E back to front Above.
And the collector of Tr201 is connected to ground via R206, so it can't be positive. What are your voltages referred to? The thread you cited says to measure referred to pin 14, which is complete nonsense. You should measure referred to ground, e.g. pin 13.
During correct operation with no signal, the positive rail should be around 67V, and the negative rail should be around -24V, and adjusting the positive down shifts the negative down too, and vice versa.
Tr200:
E =~12V due to the Zener
B = E-0.6
C = B of Tr201 = 0.6V above the negative rail.
Tr201:
C slightly negative due to R206
B=0..6V above negative rail
E = negative rail
Please re-measure ref. ground and post some intelligible voltages.
During correct operation with no signal, the positive rail should be around 67V, and the negative rail should be around -24V, and adjusting the positive down shifts the negative down too, and vice versa.
Tr200:
E =~12V due to the Zener
B = E-0.6
C = B of Tr201 = 0.6V above the negative rail.
Tr201:
C slightly negative due to R206
B=0..6V above negative rail
E = negative rail
Please re-measure ref. ground and post some intelligible voltages.
Last edited:
Thanks for the advice.
Referenced to ground (pin 13)
Tr200:
E: 11.6V
B: 11.8V - so that's not right !
C: -5.6V
Tr201:
E: -6.33V
B: -5.66V
C: -0.09V
Negative rail i.e. pin 14 -7.05V
Positive rail i.e. pin 12 69V
I increased RV200 from 2K3 to 3K3 and retested.
Tr200:
E: 11.5V
B: 10.9V
C: -4.3V slowly drifting up to -3.3V
Tr201:
E: -4.2V - drifting up to -4.0V
B: -3.45V drifting up to -3.3V
C: -0.09V
+ve rail 71V
-ve rail -4.5V
I assume there is drift as Tr200 warms up.
I checked RV200 out of circuit and ensured it was set at max (4K9ohms), then powered up with the positive rail reading 74V, as I reduced the resistance in RV200 it came down to 68.8V, but would not budge any lower, there was still plenty of adjustment left in RV200.
What does MR200 do in the voltage divider to the base of Tr200 ?
Thanks for the help !
Referenced to ground (pin 13)
Tr200:
E: 11.6V
B: 11.8V - so that's not right !
C: -5.6V
Tr201:
E: -6.33V
B: -5.66V
C: -0.09V
Negative rail i.e. pin 14 -7.05V
Positive rail i.e. pin 12 69V
I increased RV200 from 2K3 to 3K3 and retested.
Tr200:
E: 11.5V
B: 10.9V
C: -4.3V slowly drifting up to -3.3V
Tr201:
E: -4.2V - drifting up to -4.0V
B: -3.45V drifting up to -3.3V
C: -0.09V
+ve rail 71V
-ve rail -4.5V
I assume there is drift as Tr200 warms up.
I checked RV200 out of circuit and ensured it was set at max (4K9ohms), then powered up with the positive rail reading 74V, as I reduced the resistance in RV200 it came down to 68.8V, but would not budge any lower, there was still plenty of adjustment left in RV200.
What does MR200 do in the voltage divider to the base of Tr200 ?
Thanks for the help !
RV200 should be a 5k pot, set somewhere around its mid-value. If you have any negative voltage at all, the regulator is probably basically working. You just don’t have enough resistance in the bias chain to let Tr200 turn on and bring the top rail down. I would investigate R202 and R205.
MR200 is just there to start the regulator.
MR200 is just there to start the regulator.
Thanks - R202 is 8K1 and R203 is 2K2
VR is a 5K multiturn pot set to 2K5.
At that setting there is 68.4V at to top end of R202, 25.3V at bottom of R202/RV200, 11.92V on the base of Tr200, with the DMM neg on pin 13.
Tr200 emitter is at 11.7V
Adjusting RV200 to increase resistance:
Tr200 (BC556B) Vb😛in12 - 11.5V:67.9V 11.3V:67.9V 11.1V:67.8V 11.0V:67.8V - it bottoms out there, despite having a few turns left on MR.
With the original U17229 in Tr200:
Vb😛in12 11.56V:68.8V 11.37V:68.9V 11.08V:68.9V 11.00V:70.3 10.9V: 73V then pin12 stays at 73V with RV at max resistance 5K.
All made slightly more difficult by the voltages drifting.
I'm not sure why the voltage goes up with increasing MR200 for the original Tr200, versus the BC556B.
The BC556B seemed like it was getting a bit nearer and responding as expected. I think I will put it back in.
VR is a 5K multiturn pot set to 2K5.
At that setting there is 68.4V at to top end of R202, 25.3V at bottom of R202/RV200, 11.92V on the base of Tr200, with the DMM neg on pin 13.
Tr200 emitter is at 11.7V
Adjusting RV200 to increase resistance:
Tr200 (BC556B) Vb😛in12 - 11.5V:67.9V 11.3V:67.9V 11.1V:67.8V 11.0V:67.8V - it bottoms out there, despite having a few turns left on MR.
With the original U17229 in Tr200:
Vb😛in12 11.56V:68.8V 11.37V:68.9V 11.08V:68.9V 11.00V:70.3 10.9V: 73V then pin12 stays at 73V with RV at max resistance 5K.
All made slightly more difficult by the voltages drifting.
I'm not sure why the voltage goes up with increasing MR200 for the original Tr200, versus the BC556B.
The BC556B seemed like it was getting a bit nearer and responding as expected. I think I will put it back in.
Sorry - it put in the emoticon for the ":" followed by the "p" for pin. It gives the opposite sense of my emotion at this point !
Tried a different zener 12V zener (salvaged from Quad33) - 12.5-13.0V across it, but then the base voltage was higher on Tr200. Also the more I increase RV200, the less negative pin 15 gets, so effectively getting less regulation.
So the voltage divider R202, RV200, R203 seems to work, being most effective in the middle as expected.
As RV200 is a multiturn pot, the only way I can roughly put it back in the centre is to get the voltage drop at about 12.5V as 5mA is passing through it.
There is quite a variation in the voltages I get every time I check, which makes me think a transistor is causing a variation and the problems. The passive components seem ok. I am hoping Tr201 replacement may we the solution.
So the voltage divider R202, RV200, R203 seems to work, being most effective in the middle as expected.
As RV200 is a multiturn pot, the only way I can roughly put it back in the centre is to get the voltage drop at about 12.5V as 5mA is passing through it.
There is quite a variation in the voltages I get every time I check, which makes me think a transistor is causing a variation and the problems. The passive components seem ok. I am hoping Tr201 replacement may we the solution.
Update:
Got a replacement for Tr201, and now I have a perfect 67V.
As above the original Tr201 tested fine on the component tester. But I have had that issue before. I have a kit to make a curve tracer, but not got around to making it yet or sourcing the transformer.
Now for the amplifier boards........
Will post on a new thread for those, if I have any issues.
Got a replacement for Tr201, and now I have a perfect 67V.
As above the original Tr201 tested fine on the component tester. But I have had that issue before. I have a kit to make a curve tracer, but not got around to making it yet or sourcing the transformer.
Now for the amplifier boards........
Will post on a new thread for those, if I have any issues.