[Amps] 10 KW CCS ON 6M...USING THE 3CX-6000A7... PART 12

Thu Nov 24 17:59:45 EST 2022

The person posting all of the links to this mystery project is not the 
same as the builder.

Not sure why the poster is doing all of the posting?

73, Jim W7RY

On 11/24/2022 4:35 PM, Steve Thompson wrote:
> For sure the stub (looking like a short to even harmonics) works best 
> when combined with some series inductance to work against. Hopefully 
> the load cap is already a low impedance to harmonics so the short 
> circuit of stub won't do so much when added across it - but it 
> shouldn't do any harm either, and appeals to my laziness compared with 
> having to manufacture a nice choke like you did.
>
> Nice job on your build, and yes, the ASI amps are just gorgeous.
>
> 73, Steve G8GSQ
>
> On 24/11/2022 14:32, jim.thom jim.thom at telus.net wrote:
>> I designed the entire RF deck. That was my original plan, to use a 
>> 1/4 wave
>> shorted stub.... and provide a DC short, + kill even harmonics. That
>> SDT-600 teflon coax has a .70 VF.  The issue is, it has to be wired 
>> to the
>> vac load cap / NO contact of the pair of vac relays.   It can't be 
>> wired to
>> the output connector.   Works out to 3.38' in length (51 mhz).
>>
>> The story I got from K9YC is..... IF it's a PI-L network, the 1/4 
>> wave stub
>> is usually installed at the output connector...(on outside of amp).  IF
>> it's a PI network, the 1/4 wave stub is ineffective as an even
>> harmonic trap.  For PI networks, the 1/4 wave stub has to be located an
>> electrical 1/8 wave on 51 mhz... downstream from the load cap itself.
>> Since the load cap is mounted to sub front panel, and vac relays a 1/2"
>> away.... we have to factor in the length of SFT-600  from load cap...to
>> rear panel.... then some more  required on outside of amp  to make up 
>> the
>> electrical 1/8 wavelength on 51 mhz.   1/8 wave on 51 mhz =  1/4 wave on
>> 102 mhz ( 2nd harmonic).  THEN the T connector installed, with 1/4 wave
>> shorted stub hanging off the T connector.
>>
>> So we went to a conventional safety choke.  The end user can always 
>> install
>> the T connector + shorted 1/4 wave stub if he thinks it's required.
>> Another method is to use a series harmonic trap, tuned to the 2nd
>> harmonic.  ( L in series with a NPO cap).  High L, low C provides for 
>> the
>> deepest notch.  But that only takes out the 2nd harmonic.   A 2nd trap
>> could be used for the 3rd harmonic.
>>
>> K9YC's rationale was based on exhaustive testing.   Turns out it's 
>> based on
>> whether the last component is a coil (PI-L)   OR a cap (load cap) in 
>> a PI.
>>
>> Now I have some ham in indonesia who wants me to build him a monoband 
>> 20 kw
>> pep out amp for 7.1 mhz .  He has the new  3x10 tube, and also the
>> fil xfmr..and also the completed   B+ supply. .  Complicated a bit, 
>> since
>> he has 400 vac 3 phase power and 230 vac from phase to grnd...and  50 
>> hz.
>> 60 hz rated blowers run a lot slower on 50 hz.   Bear-el in Japan no 
>> longer
>> builds tube amps..and charlie asamoto ( ASI) is now retired..and 
>> moved to
>> Ore.  Nobody left that builds custom one off amplifiers. Charlie 
>> built the
>> last big 6M amp, using a 4x10, with screen V..and cathode 
>> driven...like a
>> 30S1 on steroids.  He still has his ASI  website up....the pix are
>> fabulous.  http://www.ampsystems.com/
>>
>> Jim   VE7RF
>>
>> On Thu, Nov 24, 2022 at 4:14 AM Steve Thompson <g8gsq at gmx.com> wrote:
>>
>>> You could also try a shorted quarterwave line across the output, gives
>>> you a solid dc short and helps with harmonics.
>>>
>>> Steve G8GSQ
>>>
>>> On 23/11/2022 22:34, jim.thom jim.thom at telus.net wrote:
>>>> Here, the 15 uh safety choke is installed across the ceramic vac 
>>>> load cap
>>>> on the output side.  This DC grounds the entire PI output tank 
>>>> circuit at
>>>> all times.  IF any of the 4 x plate block caps ever failed shorted, or
>>> semi
>>>> shorted, you don't want 5.5 kv getting onto the tune + load caps, 
>>>> vac TR
>>>> relay's, coax between TR relay's and output connector, nor going up 
>>>> the
>>>> coax to the ant array.  You want the entire tank DC grounded 
>>>> anyway, so
>>> the
>>>> plate block caps act like plate block caps...IE: they will still 
>>>> have a
>>>> tiny leakage due to high internal leakage resistance.
>>>>
>>>> 18 ga magnet wire used for the safety choke, wound on 1" solid Teflon
>>> rod.
>>>> Mounted to sidewall with a 1/4-20 screw. Cold end of choke is 
>>>> bonded to
>>> the
>>>> sidewall.  Teflon wire used to wire hot side of safety choke...to 
>>>> the NO
>>>> contact of the vac output relay assy.  The NO of the output relay is
>>>> directly bonded to the vac load cap.
>>>>
>>>> I see in a lot of  HF / 6m  amplifiers, both commercially built, 
>>>> and also
>>>> HB, they will use a pie-wound safety choke...like a 2.5 mh type.  The
>>>> problem with that is....  the DC resistance of the choke is typ 25-40
>>>> ohms.  IF the plate block cap assy fails shorted, the pie-wound safety
>>>> choke will not handle the entire fault current...and simply 
>>>> explodes.  I
>>>> have seen them blown to bits  a few times over the years.
>>>>
>>>> The safety choke is installed at the 50 ohm end of the tank 
>>>> circuit. It's
>>>> XL does not have to be high.  50 uh is ample on any 160-10m amp.  
>>>> 10-15
>>> uh
>>>> is ample on a 6M amp.
>>>>
>>>> This latest video also shows the coax wiring to the input ceramic vac
>>>> relay, which also includes the bypass leg, and also the input going 
>>>> back
>>>> towards the SO-239 input coax connector.
>>>>
>>>> https://www.youtube.com/watch?v=r_jxiYM7bcs
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>>
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-- 
Thanks and 73, Jim W7RY