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Old 20th December 2012, 01:46 PM   #1011
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Location: Coffs Harbour
Hi Nigel
I was looking again at Semelab's range of power transistors and note that BDY56 & 58 are still in production. The problem is, does anyone distribute them in small quantities?

Magnatech certainly distribute a great range of Semelab's high power audio transistors for pro. audio in all popular case types (The MG633X/MG941X types even give Sankens some stiff competition for gain linearity and Ft). Profusion also sell a few of these types.

Yes, I have built a clone NAP140 using some very fast LAPT Sankens and drivers to suit but I can't say it sounded as good as I hoped. It ended up with MJ21193/4 outputs driven by the original MJE243/53 which I thought, resulted in better sound quality. I guess that's a personal view but I agree with your earlier statement that high Ft doesn't necessarily suit this design.
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Old 20th December 2012, 04:17 PM   #1012
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Hi Ian , This is the best I found .
http://www.cricklewoodelectronics.co...=search&page=1

I wonder if a small capacitor between base and collector on fast devices might help ? It might only be 22pF . Perhaps win / win ? Resemble the old device and might have slightly better measurements . Douglas Self says external capacitance is better than internal when talking about the voltage amplifier stage of a typical amp ( VAS ) . The VAS cap is the one that keep the amplifier stable . Could be the older transistors had slightly larger Cob ?
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Old 21st December 2012, 01:06 AM   #1013
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I haven't seriously messed with the VAS in NAP designs. The Ferranti/Zetex parts are such a fixture there that it seems pointless when their Cob is 30pF and way out line with current design trends. If you saw what NAP80 used for VAS transistors, you would surely blanch.

I have substituted BC639/40 and KSC3503/A1381 for a bit of fun but realised that the simple swaps then needed tidying up with more compensation. This led to a different "sound" which wasn't the object, unfortunately. Maybe it's worth a closer look now, in respect of your comments.

Thanks for the link. Cricklewood don't seem to offer quantity pricing but at least there is a credible source for BDY56/58, even if they don't disclose it. Strange, not to say anything about their products apart from a few words of very basic description.

Regarding the output stage; even on the CRO, in comparing 2 differently fitted output stages, you could see a different switching behaviour. I guess this characterised the crossover harmonics and hence the sound quality with some programme - I noticed it pretty easily on small classical ensemble recordings so given my mature earsight, it would be apparent to others too.
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Old 21st December 2012, 09:06 AM   #1014
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Hi all,
I started following this thread some time ago and I even bought the kit (from hifidiy.net). I now have some spare time and enthusiasm to start building it. Resistors have been soldered in and I would like to ask a question about capacitors. I want to use polystyrenes instead of the ones supplied but I don't have the exact values on hand.

Is it critical if I use slightly higher values than specified: e.g.

47pf instead of 39pf;
270pf instead of 220pf
560pf instead of 470pf.

Will such changes upset the networks they're used in or in any way affect stability, bias, sound, etc?

I ask because I'm not technical.

Thanks and happy Christmas holidays.
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Old 21st December 2012, 09:08 AM   #1015
Spuds is offline Spuds  South Africa
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Quote:
Originally Posted by sonata149 View Post
Hi all,
I started following this thread some time ago and I even bought the kit (from hifidiy.net). I now have some spare time and enthusiasm to start building it. Resistors have been soldered in and I would like to ask a question about capacitors. I want to use polystyrenes instead of the ones supplied but I don't have the exact values on hand.

Is it critical if I use slightly higher values than specified: e.g.

47pf instead of 39pf;
270pf instead of 220pf
560pf instead of 470pf.

Will such changes upset the networks they're used in or in any way affect stability, bias, sound, etc?

I ask because I'm not technical.

Thanks and happy Christmas holidays.
I would say go for it. I'm using only polystyrene in my 10 channel HT build.
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Old 21st December 2012, 09:11 AM   #1016
Spuds is offline Spuds  South Africa
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Bare boards:

Click the image to open in full size.

After spraying:

Click the image to open in full size.
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Old 21st December 2012, 10:02 AM   #1017
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Wow- large scale production!
Sonata 149, if you haven't used polystyrene foil caps before, just remember to be very quick soldering as the whole outer casing is polystrene too and they melt very easily. If the leads appear to move, you are doing damage.
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Last edited by Ian Finch; 21st December 2012 at 10:06 AM.
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Old 21st December 2012, 11:05 AM   #1018
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Location: Oxfordshire
Quote:
Originally Posted by sonata149 View Post
Hi all,
I started following this thread some time ago and I even bought the kit (from hifidiy.net). I now have some spare time and enthusiasm to start building it. Resistors have been soldered in and I would like to ask a question about capacitors. I want to use polystyrenes instead of the ones supplied but I don't have the exact values on hand.

Is it critical if I use slightly higher values than specified: e.g.

47pf instead of 39pf;
270pf instead of 220pf
560pf instead of 470pf.

Will such changes upset the networks they're used in or in any way affect stability, bias, sound, etc?

I ask because I'm not technical.

Thanks and happy Christmas holidays.
All good choices because they are cautious ones by going up a notch . Polystyrene fails when old due to foil to wire corrosion . Philips used lead foils to overcome this , now banned . COG ceramic are very good ( look in specs ) . Stability should be enhanced by what you have done . Some people go the other way , that is risky . Don't use non GOG( NPO ) ceramics . Mylar are OK .

Last edited by nigel pearson; 21st December 2012 at 11:08 AM.
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Old 21st December 2012, 11:43 AM   #1019
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Location: Malta, Europe
Thanks a lot, friends for your replies. I will check their value in place after soldering them.
So, in general there is no harm in using one notch up (or down?) in value.
Best wishes to all.
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Old 21st December 2012, 04:30 PM   #1020
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Quote:
Originally Posted by sonata149 View Post
Thanks a lot, friends for your replies. I will check their value in place after soldering them.
So, in general there is no harm in using one notch up (or down?) in value.
Best wishes to all.
Usually that is correct . In the old days components were to +/- 10 % so that almost says if going 10 % up it is the same but the cautious choice . - 10 % probably is OK if carefully checked with an oscilloscope . Problem with the clone kits is they sometimes are very far removed from the original design . The cautious approach seems best . Remember exact values can be made by parallel capacitors . I have a design that uses 6n8 , I find I have to use 4n7 + 2n2 as 6n8 in the quality I want is rare .

If high grade transistors are used go up rather than down . High grades often have very little Cob or intrinsic capacitance . For example a typical small transistor 6 pF , high grade 1.2 pF . Some respected types were more like 50 pF . These amps often have no apparent compensation . If going to a high grade replacement smoke from tweeters might result . A 47 pF added where none was before would almost certainly work . Upgrading amps is a bit of a minefield .
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