Yes, seemed strange to me because of it's sqaure shape, and also I have never seen how an oscillating amp looks like on the scope...
Wait, a Naim amp should not be cooled...? I saw here the small transistor thermally coupled to the heat sink, would that help? I noticed that during music playback the 14mV changes dramatically, hope that is OK. Also with warm output transistors and input shorted to ground I got readings way higher than cold, so after re-adjusting down to 14mV in warm state and cooled down it starts again with something as low as 7mV. All without a case, as shown in my photo, and with that old +/-32V bench power supply...
But it sounds, boy does it sound!!!!! And there is no noise or mains hum audible from the speaker
I found oscillations coming from the preamp I used to test music playback with the NAP250 board, but not looking sqare any more. Strange: even if nothing is connected to the preamp the scope shows these ~10MHz oscillations as soon as I put the probe on the preamps power rails. How can that be?
Just completed the second board: offset is -2.4mV, and bias is easier to adjust, and I have the feeling the output transistors get less warm... Question: my 39pF styerenes are vintage and have large inaccuracies (one is 29pF, the other one 40pF and so on), does this matter?
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I am trying to get the parts ready for another pair of amps and found Jeffs threads about BUV20s here and here. The BUV20s I received today look exactly like the ones shown here, even the packaging looks exactly as on those pictures. It seems there are still new old stock ones available, and I will be happy to supply a link, but first I would like to make sure they are genuine. I also got some small signal transistors from the same source and BDY58s. Here are some pictures:
BUV20 and BDY58 opened with my lathe. The BDY58 has 1mm pins and looks exactly like the ones I can see on these pictures of an old NAP250 I found online:
Here a closeup of the BDY58 I opened:
My BUV20 has 1.48~1.5mm thick pins. I scratched off the white protection from one die, it came easily off with the finger nails:
The die looks a bit damaged because I was not very careful when sratching off the white rubber-like stuff:
And the small transistors:
The ZTX108C looks old and has the typical flat shape shape, the other TO92s haave the normal shape. The MPSA56 looks like as if it was made by Philips. Both types of BC239Cs have the middle leg bent backwards. I was told that one was made by Philips and the other by Siemens. Here are my measurements I took with a small cheap device tester:
BDY58: HFE = 11, VBE = 0.57
BUV20: HFE = 22, VBE = 0.53
MPSA56: HFE = 204, VBE = 0.73
ZTX108C: HFE = 650, VBE = 0.79
BC239C (first picture: Siemens?): HFE = 460, BVE = 0.75
BC239C (second picture: Philips?): HFE = 676, VBE = 0.75
What do you think about my parts?
BUV20 and BDY58 opened with my lathe. The BDY58 has 1mm pins and looks exactly like the ones I can see on these pictures of an old NAP250 I found online:
Here a closeup of the BDY58 I opened:
My BUV20 has 1.48~1.5mm thick pins. I scratched off the white protection from one die, it came easily off with the finger nails:
The die looks a bit damaged because I was not very careful when sratching off the white rubber-like stuff:
And the small transistors:
The ZTX108C looks old and has the typical flat shape shape, the other TO92s haave the normal shape. The MPSA56 looks like as if it was made by Philips. Both types of BC239Cs have the middle leg bent backwards. I was told that one was made by Philips and the other by Siemens. Here are my measurements I took with a small cheap device tester:
BDY58: HFE = 11, VBE = 0.57
BUV20: HFE = 22, VBE = 0.53
MPSA56: HFE = 204, VBE = 0.73
ZTX108C: HFE = 650, VBE = 0.79
BC239C (first picture: Siemens?): HFE = 460, BVE = 0.75
BC239C (second picture: Philips?): HFE = 676, VBE = 0.75
What do you think about my parts?
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I'd be willing to bet the BDY58s and BUV20s are genuine.
The BUV20 is not particularly high-tech, and the example shows correctly-sized dies, pins and bonding wires, so there would be no savings for a counterfeiter.
The squashed case of the Zetex is known as an e-line case. The markings look like the ones I have from a known-good source.
I'll have to dig out my BC239s for a comparison later....
Great pics, BTW!
The BUV20 is not particularly high-tech, and the example shows correctly-sized dies, pins and bonding wires, so there would be no savings for a counterfeiter.
The squashed case of the Zetex is known as an e-line case. The markings look like the ones I have from a known-good source.
I'll have to dig out my BC239s for a comparison later....
Great pics, BTW!
Thanks Jeff, good news! But I am a bit concerned about the printing on the BUV20s coming off with aceton:
Also what do you think about the MPSA56? BTW with the BC239Cs I got from Langrex I get very different measurements. How can I test them to see if they are up to the specs?
Also what do you think about the MPSA56? BTW with the BC239Cs I got from Langrex I get very different measurements. How can I test them to see if they are up to the specs?
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As one corner of the die of the opened BDY58 was a bit damaged I opened one more BDY58 and BUV20 and also let the VBE break through lit up the die (just for fun, see attached pictures). The BUV20 looked identical to the first one I opened apart from the slightly different looking white covering stuff. The second BDY58 had the same damage to the die corner, but the die itself looked different and also had a different wiring. So it seems these are rejects, I will probably return them. I have noticed that BUV21 and BUV22 are still available, would they suit the Naim clone?
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Some progress: I made PSU boards and tested the amp with my transformers:
Also I made some speakers for the amps:
I am getting a bit high voltages from my PSU, does the regulator board cope with 58~60V instead of the usual 56V? Also I have a bit weak diodes in my rectifier with only 5A per diode:
I use this schematic with a 500VA transformer. The transformer has two center tapped windings. Do I need to worry about the diodes?
I compared the inverted regulator with an original Naim regulator board: the inverted sounded cleaner and more natural, the Naim had a punchier bass. So both are good!
Also I made some speakers for the amps:
I am getting a bit high voltages from my PSU, does the regulator board cope with 58~60V instead of the usual 56V? Also I have a bit weak diodes in my rectifier with only 5A per diode:
I use this schematic with a 500VA transformer. The transformer has two center tapped windings. Do I need to worry about the diodes?
I compared the inverted regulator with an original Naim regulator board: the inverted sounded cleaner and more natural, the Naim had a punchier bass. So both are good!
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Yeah, I think it makes sense that the inverted sounds more transparent. The Naim had BDY58s on it. BTW here are the links for the vintage transistors:
ZTX108C
BC239C (they also have ZTX108, BUV20s and MPSA56s but not listed)
Jeff, did you already try your BUV20s? Also have you seen this post about clipping on BUV20s?
ZTX108C
BC239C (they also have ZTX108, BUV20s and MPSA56s but not listed)
Jeff, did you already try your BUV20s? Also have you seen this post about clipping on BUV20s?
I fired up the boards with BUV20s on them and what can I say: I have clipping on one channel... But it's my fault: I accidently wired one regulator board wrong to the PSU 
and connected the negative supply to the positive input and vice versa. It was only for 5 seconds powered but the 1N5621s on the amp board (D4/D5) and one MPSA06 on the inverted regulator board (TR7) went up in smoke.
Stupid me: because I often confuse right with left, numbers, and all kind of things I controlled carefully my wiring, but I knew this would happen one day, and most certainly it will happen again.
I replaced the 1N5621s on the amp board. On the inverted regulator board step by step I replaced all MPSAs, the driver MJEs and the 10uF caps. But the clipping is still there, especially in the bass lines I hear strong distortion which disappears at low volume.
The BUV20s on the regulator board show normal values on my two small and cheap component testers (I tested them in situ when the drivers were removed). Do I have to replace them as well? What else can be done?
BTW the BUV20s sound better than both the BDY58s and the MJ15003s!
and connected the negative supply to the positive input and vice versa. It was only for 5 seconds powered but the 1N5621s on the amp board (D4/D5) and one MPSA06 on the inverted regulator board (TR7) went up in smoke.Stupid me: because I often confuse right with left, numbers, and all kind of things I controlled carefully my wiring, but I knew this would happen one day, and most certainly it will happen again.
I replaced the 1N5621s on the amp board. On the inverted regulator board step by step I replaced all MPSAs, the driver MJEs and the 10uF caps. But the clipping is still there, especially in the bass lines I hear strong distortion which disappears at low volume.
The BUV20s on the regulator board show normal values on my two small and cheap component testers (I tested them in situ when the drivers were removed). Do I have to replace them as well? What else can be done?
BTW the BUV20s sound better than both the BDY58s and the MJ15003s!
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Update: reverted the BUV20s in the clipping channel back to MJ15003s. After some more testing I found clipping on the healthy channel too.
So it seems the BUV20s indeed clip. Pity, because the BUV20s sounded so much better than the MJs...
BTW if I probe the amps output with my scope the sound changes drastically and looses the heights: do I need to probe through a resistor or the like?
So it seems the BUV20s indeed clip. Pity, because the BUV20s sounded so much better than the MJs...
BTW if I probe the amps output with my scope the sound changes drastically and looses the heights: do I need to probe through a resistor or the like?
Regarding the BC239s: I can't get the Siemens, Philips, Langrex devices to work well, only the Onsemis deliver HFE>500 and can be matched to give low DC offset. I found some schematics of newer Naim amps, see attached files, which state SMD devices in the LTP: how about the BCM847DS?
