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Post by Deleted on Mar 7, 2017 9:20:48 GMT
Web pages not complete but Alan is getting done I love my photo in about us Cheers Mate  EWA |
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Post by MartinT on Mar 7, 2017 10:25:46 GMT
Hah - placeholders or permanent? I never knew you were so good looking, Colin!
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Post by Slinger on Mar 7, 2017 11:12:34 GMT
Blimey, I though I had a decent beard, but Colin's leaves mine standing.  |
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Post by Deleted on Mar 7, 2017 12:18:12 GMT
It is all the drugs the quacks have me on, and the voice is fun also, I could sing Mud Mud and Old Man River in sub sonic bass. But I must say I do look well at last. |
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Post by John on Mar 8, 2017 5:35:47 GMT
Nice looking gear Colin I wish you the best with this
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Post by MartinT on Nov 14, 2017 3:04:23 GMT
I see there is a nice review of the EWA Q-20 preamp and power amp in the HiFiAnswers site here. |
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Post by Deleted on Nov 29, 2017 21:22:54 GMT
Well history always comes back and bites you. I have been asked now to upgrade A.C.Magnum kit including a few designs borrowed wrongly by Mr.Relph including a design meant for for another UK company (Magnum A Class Inter). So my question to you all do I do it or say no you should have bought other kit or send it back to Magnum, as it is my design my babies, do I dabble? help HELP  ? I am in a tortured mind here.  |
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Post by ChrisB on Nov 29, 2017 21:37:34 GMT
I don't know the ins and outs of the relationship Colin, and I was in business with someone who I would rather now forget about too, so I think I understand a little of how you feel.
I'd like to think that if I were in your shoes, I'd try to think about the owners of the amps rather than your old business partners. No-one else is in a position to do the job justice as you are.
If you don't take on the work, will that decision make any difference good or bad to the other guy? I doubt it. I expect it'll make a big difference to the music lover who gets his pride and joy working again though.
Your old designs have a following because of you and the work you did, not these other people. That following (and your superb reputation) can only improve if you help kit owners out, I'd think.
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Post by MartinT on Nov 30, 2017 8:35:32 GMT
I would agree with Chris in that the amp's owner just wants an upgrade by the person who knows and is not directly involved in its previous politics. If you do the work I should imagine you would receive tremendous gratitude and you still have lost none of your principles in doing so.
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Post by Slinger on Nov 30, 2017 10:55:15 GMT
What Chris and Martin said. You'd be cheering up a longtime fan rather than lining the pockets of the ignorant sods who screwed you over.
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Post by Deleted on Nov 30, 2017 13:56:38 GMT
Yeh nice to see the original Engineers servicing the old amp. I only realised a while back that Nytech were back offering full services for the original kit. im capable of servicing all my own Vintage Equipment but a hell of a lot are not.
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Post by Deleted on Dec 20, 2017 11:58:48 GMT
I have just found my old Germanium Transistor amp all of 10W Mono, it sounds bloody good, all hard wire no PCB EI transformer and just 2,700uF 35V cap and not DC coupled. OC28 with OC72 and AD161? driver and cap coupled to the speaker with 1,000UuF 25V, I made it in 1968. With a ceramic cartridge input stage, and a huge wire wound volume control. I will now reverse engineer it and give up this circuit for you all to play with, but with modern caps and resistors but you have to find the transistors he he    |
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Post by MartinT on Dec 20, 2017 12:45:09 GMT
Gosh, I remember playing with those OC range germanium transistors when I was a young lad. Did they deserve their fragile reputation?
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Post by Deleted on Dec 20, 2017 18:24:38 GMT
I have just found my old Germanium Transistor amp all of 10W Mono, it sounds bloody good, all hard wire no PCB EI transformer and just 2,700uF 35V cap and not DC coupled. OC28 with OC72 and AD161? driver and cap coupled to the speaker with 1,000UuF 25V, I made it in 1968. With a ceramic cartridge input stage, and a huge wire wound volume control. Hi Colin I used to have an old 60's Trio 'TK150' intergrated & an original Brown faced 'KA2000', Both were pretty much the same thing but the '150' was Germanium, sounded better to me apart from it eventually self destructing. Same with the old Armstrong '421' i preferred that to the later Silicone '521' |
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Post by Deleted on Dec 20, 2017 21:03:04 GMT
Yes I found if the Si transistors do not get close to saturation the Miller effect plays hell with the speed so I tend to over drive the base current i.e. HFE 10 so I feed the base current 2.5A Peak for a 10A peak in the output. And I use a driver transistor with a much wider Ft than the output drvice i.e. 2MHz monster with a 140MHz driver. now I get control with speed.
Fun fun FUN
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Post by MartinT on Dec 21, 2017 6:52:55 GMT
Is Miller worse in a germanium transistor?
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Post by Deleted on Dec 21, 2017 10:41:16 GMT
Is Miller worse in a germanium transistor? No better due to sat volts 0.3V approx and base emitter volts 0.3 ish . Bad in FET Gate volts about 10V sat RdsOn 50mOhms so at 10 Amp Vsat is 50mV And most Si device VBe 0.6V a Vsat 0.4-1.2V So if the Vsat gets below V on drive the Miller suck the current away cause the worse parrot sick oscillation possible (yes I no it is not spelt that way)  Hey the same thing happens in Hifi News another Miller effect maybe  At high speed you can use a Baker Clamp but these are NOT very linear. Now the stored energy in the drive capacitance bad on FET's now has to be switched off fast so I tend to suck it fast with a transistor with a very fast On time 30nS or faster, so we tend to use a Totem Pole Drive stage i.e. On Fast of Faster if possible, reducing heat as the FET's in there Off and On cycle FET's run in linear mode not saturated lots of heat. and smoke and bangs whoops and in a 150KW SMPSU that can be expensive. Well it was I did it whoops but only once it works now see your Xray Machines. |
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Post by MartinT on Dec 21, 2017 10:50:04 GMT
Thanks! Yes, I know Miller is bad in FETs and MOSFETs, I still remember the Hitachi application note. I think that's why some early MOSFET amps based on the Hitachi circuit sounded so poor. They also used a lot of NFB.
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Post by Deleted on Dec 21, 2017 14:46:26 GMT
Thanks! Yes, I know Miller is bad in FETs and MOSFETs, I still remember the Hitachi application note. I think that's why some early MOSFET amps based on the Hitachi circuit sounded so poor. They also used a lot of NFB. Yes I started the Claymore design using the Hitachi design and found it wanting the drive transistor with large value gate resistor was wrong so I changed them to low value 27R resistors and used a driver pair that had a huge BW and high peak current the BD139/140 then on to a NTE ?? series at 3A , it worked well and sounded much better, then I drove the drive cct with +10 on +VCC and -10V -Vcc this enabled me to drive the FET's hard and have less losses in the FET's at high power peaks. i.e. +45V -45V with no High drive and +35V -35V with drive. this also with the same 200VA transformer gave me a little more current. Since the output pair was Source followers design only 1 transistor in the cct had a gain of more than 1 and this was a BD139 also, high BW HFE about 40. I have since learnt more and would not use this design again but hey how they did sound lovely.  |
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Post by MartinT on Dec 21, 2017 15:17:43 GMT
So that's why the Claymore sounded so good! I remember puzzling over those high gate resistor values thinking that perhaps there is no Miller effect in MOSFETs. Hah!
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