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Old 12th March 2012, 06:37 PM   #761
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by danielwritesbac View Post
I am curious to know of what resistor and other values may change to optimize BC639 for Q5, Q6 (esp lower heat)
To do that, it would be necessary to reduce their bias current, but it is not a good idea, it would blunt needlessly the performances for no obvious benefit.
Quote:
and what is the maximum permissible rail voltage without overheating the BC639?
If we use a Pc max= 0.8W (depending on the manufacturer and conditions, it ranges from 0.6 to 1W), the theoretical maximum supply voltage is 60V.
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Old 12th March 2012, 07:27 PM   #762
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Quote:
Originally Posted by danielwritesbac View Post
to use for a small scale Circlophone.
It would be a darlington Circlophone also.. I found some genuine Philips BDV65B's. I think these gonna make sense for Dutch Circlophone . Mirroring current layout would be do most of job of darlington pcb imho.

Last edited by terranigma; 12th March 2012 at 07:32 PM.
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Old 12th March 2012, 07:31 PM   #763
Elvee is offline Elvee  Belgium
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Originally Posted by danielwritesbac View Post
Thanks to Elvee for saving me from counterfeit transistors!
Here's a photographic comparison of fake versus real 2SB649.
As a reference for others, here are some pics of the fakes in question.

Unlike other fakes I have already seen, these are not "best efforts" to imitate the real thing: they have been carefully and cynically designed to dupe the unwary amateur at the absolute minimum cost: nice and clean case molding, and all easily accessible parameters like Vceo or capacitance OK.

But when you dig deeper, you notice that the Ft is only 34MHz (instead of 140MHz), and a scanning shows that the die size is that of the smallest small signal transistors, roughly 1/10th of what it should be.

If such transistors were used in the Circlophone, they would broadly seem to work at first.
They would give relatively poor performances, because of the pseudo-2SD669 low Ft, but the amplifier would sing, and the servo would catch up with most deficiencies.
But as soon as the volume is pushed up, things would go seriously wrong: with drivers so desperately undersized, their SOA would immediately be exceeded, with catastrophic results for the OP transistors, and maybe the speaker connected to the amplifier.

Beware, be always on your guard!
Attached Images
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File Type: jpg 100_5179.JPG (249.1 KB, 359 views)
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Old 13th March 2012, 12:41 AM   #764
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Quote:
Originally Posted by Elvee View Post
Quote:
Originally Posted by danielwritesbac View Post
what is the maximum permissible rail voltage without overheating the BC639?
If we use a Pc max= 0.8W (depending on the manufacturer and conditions, it ranges from 0.6 to 1W), the theoretical maximum supply voltage is 60V.
That is well more than I hoped for.

If I understand correctly, a BC639 could work for at Q5, Q6 with the 25v rails of the Circlophone at Post 1?

The area of my chart that suggests Motorola/Onsemi MJE3055 (transistor and TO220 thermal pad, available in every shopping mall in the USA) is with "up to" ~22v rails, supports a wide variety of speaker loads and should be perfectly safe to use BC639 at Q5, Q6 with this smaller scale amplifier?

Reading this whole thread all again, suggests that R6, R7 can be 1K5 and I was asking what other non-disturbing way to lower dissipation at Q5, Q6 (or the entire board), even if the amount (per each step) happened to be very slight? The actual question is how to reduce the heat by any amount, at any location, without hindering performance.

My intended scale for "Miniature Circlophone" is with these transformers:
12+12vac (24vct), 13.5+13.5vac (27vct), 14+14vac (28vct), 15+15vac (30vct) for unregulated power.
For regulated power, one identical pair of 15vdc 90w laptop power packs that are double-insulated and have 2-conductor mains cords, are also usable, convenient, and low cost.

At this scale it seems that Philips ("PHI" gray case) Telefunken ("TFK") BD136, BD138 are usable for driver and their NOS market price of $5 is half as much as authentic Philips BD140, although new ST-BD140/HSB649/2SA1358/2SA968/2SA1930 all cost less than circa 1980's collectibles.

Before making up a schematic for "Miniature Circlophone" I'd like to know what value R21 and what single Zener for D8+D9 could work decently across a range of 15+15vdc rails to 20.5+20.5vdc rails? After the schematic, there is some possibility (probability) to generate a fairly orthodox miniature stereo Circlophone with NXP SMD parts for use with desktop/monitor speakers. It should be remarkable.

Last edited by danielwritesbac; 13th March 2012 at 12:43 AM.
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Old 13th March 2012, 01:11 AM   #765
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Quote:
Originally Posted by danielwritesbac View Post
miniature stereo Circlophone with NXP SMD parts
This is exactly what was in my mind for a serious group buy project. That may be a very promising project to build a smd Circlophone with NXP transistors and MJL21194's at output.

Another thing is, Circlophone is very suitable concept for a very high quality mass production audio units.

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Old 13th March 2012, 01:19 AM   #766
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Wow, the fakes pictured in posts 756 and 763 are decorated much differently except for the glossy case, all square edges, same size and exactly the same collector plate. Do your samples also do HFE ~245 if checked with digital multimeter test port?

Is there some conveniently rudimentary/simple circuit that can be used for a current handling test so as to explode the fakes before installing them in an amplifier? For example a simple sort of current test that anything suitably sturdy will survive if given a heatsink but the pervasive fake devices do not pass?
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Old 13th March 2012, 02:21 AM   #767
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If D10 (anti-latchup) cannot turn off due to nonstop workload of saving the amp from destruction, that may cause the amplifier to act as if C3 is shorted. In this condition, Circlophone will amplify DC if there is DC at input. In any case, there is the "dancing offset." If the amplifier isn't busy trying to latch up, D10 will shut off. The means to turn this off is to stop the root cause of the error condition. The actual error isn't located in the area of D10. But the odd condition means that a broken part needs to be replaced. If you fix the amp (bad transistor?), the safeties like D10 will sleep.

Last edited by danielwritesbac; 13th March 2012 at 02:23 AM.
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Old 13th March 2012, 09:28 AM   #768
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by danielwritesbac View Post
That is well more than I hoped for.

If I understand correctly, a BC639 could work for at Q5, Q6 with the 25v rails of the Circlophone at Post 1?

The area of my chart that suggests Motorola/Onsemi MJE3055 (transistor and TO220 thermal pad, available in every shopping mall in the USA) is with "up to" ~22v rails, supports a wide variety of speaker loads and should be perfectly safe to use BC639 at Q5, Q6 with this smaller scale amplifier?
I am not very fond of BC639 as a VAS: depending on the manufacturer, there can be huge variations in the Ft and collector capacitance: it can reach up to 50pF, which is way too high.
You had found more modern and more suitable types if I remember correctly, BCP-something.

Quote:
Reading this whole thread all again, suggests that R6, R7 can be 1K5 and I was asking what other non-disturbing way to lower dissipation at Q5, Q6 (or the entire board), even if the amount (per each step) happened to be very slight? The actual question is how to reduce the heat by any amount, at any location, without hindering performance.
Modifying R6 7 will not change anything in the dissipation.
Anyway, trying fiddle a mW here and there is completely futile, since the basic philosophy underlying the Circlophone concept is to operate in warm class AB: that's what gives it its class A attributes, and every stage, VAS, drivers and OP dissipates significant amounts of quiescent power (and has to, to work properly and reliably).


Quote:
Before making up a schematic for "Miniature Circlophone" I'd like to know what value R21 and what single Zener for D8+D9 could work decently across a range of 15+15vdc rails to 20.5+20.5vdc rails?
Voltage of the zener ~= supply voltage, 500mW type suitable for up to 36V, 1.3W up to 100V

Quote:
Is there some conveniently rudimentary/simple circuit that can be used for a current handling test so as to explode the fakes before installing them in an amplifier? For example a simple sort of current test that anything suitably sturdy will survive if given a heatsink but the pervasive fake devices do not pass?
If they are used in a 50mA CCS operated at 100V (with a proper heatsink), the real ones should survive indefinitely, but the fakes will be pushed far outside their SOA: this should be enough to separate the wheat from the chaff.
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Old 13th March 2012, 06:55 PM   #769
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by danielwritesbac View Post
Do your samples also do HFE ~245 if checked with digital multimeter test port?
188 for the 2SD669
182 for the 2SB649
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Old 13th March 2012, 11:29 PM   #770
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Terranigma

If you havent made your PCB yet, there is a small change that might improve it. I notice that the feedback is not taken directly from the output and the output is not in the middle of the track between the two ouput transistors.

As was described in an earler post this makes a significant difference to the distortion and whilst it is by no means bad as it is, you might see an improvment if you get it exactly matched.

I have seen 6dB improvemnts in very low distortion amplifiers just by getting this symetrical and the feedback taken directly from the output.

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Andrew
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