Message-ID: <D3D322E6591942ED804F9E86CF6928DE@gnat>
From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <162a4797468-1db9-bdf2@webjas-vae168.srv.aolmail.net> <1UQROqZht1.1c1VdzC0S69@optiplex980-pc> <f5cdf11c-819e-a83d-15cd-9590f7a07194@n1bug.com> <DM__180409110420_14031131174@smtp.eclipse.co.uk> <3a0c0669-018b-13a7-b56b-dd3f63fab464@n1bug.com> <197556217.20180409124931@gmail.com> <37574432-b72e-f2d1-0e85-af19dd970817@n1bug.com> <4D19B3707137430CBE04857FBA5C80B1@gnat> <E588340043AD4309B637D8ED22DE201D@DELL4>
Date: Mon, 9 Apr 2018 16:26:34 +0100
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Subject: Re: LF: W1VD amp help - more waveforms
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Hi Jay yes indeed but I think that the Vds(max) is quite high, and certainly 
not a prob at 12v, or even 28v.

Alan
----- Original Message ----- 
From: <jrusgrove@comcast.net>
To: <rsgb_lf_group@blacksheep.org>
Sent: Monday, April 09, 2018 4:02 PM
Subject: Re: LF: W1VD amp help - more waveforms


> Alan
>
> The main concern about the ringing is that the positive extreme stays 
> below the drain source breakdown voltage ... with some 'headroom'. 
> Otherwise ...
>
> Jay W1VD
>
>
> ----- Original Message ----- 
> From: "Alan Melia" <alan.melia@btinternet.com>
> To: <rsgb_lf_group@blacksheep.org>
> Sent: Monday, April 09, 2018 10:21 AM
> Subject: Re: LF: W1VD amp help - more waveforms
>
>
>> Paul
>> I think you need to step back from this a little. One point, design/cable 
>> routing at 137kHz is normally not that critical and it is unlikely it is 
>> having much effect. Many us have ''haywired'' PAs at these frequencies 
>> without major troubles....even using croc-leads!!
>>
>> You are unhappy about the drain waveforms.......why?? the ringing is on 
>> the ''off'' device and so doesnt really matter in terms of efficiency. 
>> Consider what is happening. The FET drive goes off and the drain current 
>> starts to drop inductance in the drain feed causes the voltage to rise to 
>> try to keep the current flowing. Then on top of this the other transistor 
>> switches on and the transformer connection for the off side sees a rising 
>> induced voltage out of the transformer. There is bound to be overshoot 
>> but it does not absorb much power. It may be the generous ''dead zone'' 
>> (whilst a good idea) that is producing this picture.
>>
>> The critical part is the the flat zero volt line when the FET is on. The 
>> current pulse rings a bit, but the current drops in the second half of 
>> the pulse.....why?? This, I think, is really the loss of power. Does 
>> Jay's show this? The point I am making is don't get drawn up blind alleys 
>> because a trace just does not look ''pretty''.
>>
>> I think we have mentioned this before but the transient performance of 
>> the power supply may be a factor. There should not be great changes in 
>> the current draw because you are switching the PSU load from one 
>> transistor to the other but there can be higher speed transients that can 
>> affect power supply regulators in unexpected ways.
>>
>> As Andy said efficiency at 12v is not very meaningful because of the high 
>> rds of these FETs. It is usefull to run up a PA at low volts say for 
>> safety when the antenna needs to be tuned.
>>
>> Finally the scope probes are placing an. albeit small, capacitance across 
>> the drains (I am assuming they are correctly trimmed) The waveform can 
>> often be affected by where the ground is picked up from.
>>
>> Stick with it because you are close to being ''there''
>>
>> Alan
>> G3NYK
>>
>>
>> ----- Original Message ----- 
>> From: "N1BUG" <paul@n1bug.com>
>> To: "Chris Wilson" <dead.fets@gmail.com>; "N1BUG" 
>> <rsgb_lf_group@blacksheep.org>
>> Sent: Monday, April 09, 2018 2:22 PM
>> Subject: Re: LF: W1VD amp help - more waveforms
>>
>>
>>> Hello Chris,
>>>
>>> There are plenty of possible causes here I think. When it comes
>>> right down to it, I'm not at all happy with the end result of my
>>> construction on this amp. If it ends up not working, it's because
>>> I'm not a good enough builder. Despite building for 35 years
>>> including many QRO tube amplifiers, I felt this pushed my skills to
>>> the limit... or beyond? It's not the fault of the design of course,
>>> it's me. This requires a very different skill set from what I've
>>> developed through the years.
>>>
>>> The driver board you see is my fourth attempt yet I'm still very
>>> unhappy with my layout and on-board routing of connections.
>>>
>>> I probably made a huge error in design and mounting of the driver
>>> board. Everyone seems to agree my gate leads are too long. This may
>>> take a while. If I'm starting over I'll have a few more goes at
>>> trying to come up with a more sensible layout and on-board routing.
>>> I'll probably have to design the new board so it can be soldered to
>>> the ground plane for mounting. The only other way I can think of
>>> would involve complete deconstruction of the amp to drill and tap
>>> new holes in the heat sink for relocated board mounting standoffs.
>>>
>>> I literally spent two weeks and likely 50 attempts at winding the
>>> output transformer, still not happy with it. I'm not sure the
>>> primary winding is acceptably tight.
>>>
>>> Today I'll try swapping out the cables connecting amp to LPF and LPF
>>> to dummy load. No reason to suspect bad cables, but I've seen
>>> strange stuff happen. The cable between amp and LPF is a bit long at
>>> 4 feet, maybe it doesn't like that. I'll have a look on the PSU side
>>> of that choke with the scope too. Good idea. Could be some RF there
>>> causing the PSU to go insane.
>>>
>>> I haven't added bypass caps on the driver board yet. I'm out of .1
>>> uf caps. I have some 1 uf ceramic but that may be a bit much? I'd
>>> probably get shorter leads by tacking them on the back side of the
>>> board. Bear in mind I'm testing at 13V which gives about 65W output
>>> so there's not massive amounts of RF around yet.
>>>
>>> Still puzzling over why my gate waveforms look OK (I think?) but
>>> drains don't. To my usually wrong way of thinking that suggests the
>>> ringing problem is caused by some defect in the drain circuit or
>>> outside the amp (cables, LPF). I think I'd like to try and eliminate
>>> those possibilities before I go back and completely redesign the
>>> driver board and mounting to shorten gate leads. No doubt it'll
>>> still come to that but I can hope not a bit longer. :)
>>>
>>> Paul
>>>
>>>
>>> On 04/09/2018 07:49 AM, Chris Wilson wrote:
>>>>
>>>>
>>>> Hello Paul,
>>>>
>>>> If my similar amp exhibits ringing on the drains (which I monitor in
>>>> real time), it means an antenna mismatch or a dicky connection (PL
>>>> type plugs were the cause, cheap junk off Ebay, a change to branded N
>>>> types fixed that issue). So if the output transformers are the right
>>>> material and wound right, the snubber resistors and caps are correct,
>>>> and the gate driver wires are really short, and you are looking into a
>>>> decent dummy load, well, it's a mystery! You have put decoupling caps
>>>> on all the Vcc pins? If you have a nice PCB and don't want to make
>>>> new, and the IC's are socketed you could solder the decoupling caps
>>>> direct to the IC pins for a test. Or even if they aren't socketed I
>>>> guess :) Without them my amp suffered with RF getting back into stuff
>>>> and  "funny  things"  happened. You should also have a `scope about on
>>>> the PSU side of the choke.
>>>>
>>>> Monday, April 9, 2018, 12:29:18 PM, you wrote:
>>>>
>>>>> Thanks Hugh and everyone else who commented and provided tips on my
>>>>> earlier post about this amplifier.
>>>>
>>>>> I will wait for Jay to have a chance to comment but I *think* I'm OK
>>>>> on timing of the phase transitions. However, something is causing
>>>>> major ringing (is that the correct term?) on the drains. I believe I
>>>>> need to find the cause and do something about that but I have no
>>>>> idea what to look at.
>>>>
>>>>> I've been building and even designing QRO amplifiers for 35 years
>>>>> but I'm a vacuum tube HF/VHF/UHF guy! This FET class D/E stuff is
>>>>> all new to me and I don't learn new tricks as easily as I once did. :)
>>>>
>>>>> Paul
>>>
>>
>>
>
>