HoHo....That`s why I build around YC156/179 tubes....Lot`s of Head
room and at Legal limit they loaf along and are super clean....Of
course they are super expensive but will last a Lifetime..73
All,Jim..K7RDX..
On 8/13/21, Jim <jimw7ry@gmail.com> wrote:
> Do the math Joe....
>
> Watts dBm
> 500 = 57 dBm
> 600 = 57.8 dBm
> 700 = 58.5 dBm
> 1000 = 60 dBm
> 1500 = 61.8 dBm
>
> I run 1500 watts on RTTY because I can. BUT, now that I'm moving to a
> city lot from 13 acres, I'll concentrate on running 100 watts. Perhaps
> as much as 400600 watts with an SB220.
>
> A pair of 3500s is fairly marginal at 1500 watts output. (That is only
> 1000 watts of plate dissipation). Thats why I build my own amplifiers
> with an 8877 and 2ea 3CX800As. They both do an easy 1500 watts on RTTY
> with 25 to 40 watts drive, depending on which band.
>
> The 8877 is one of the best and easiest tubes to build a 1500 watt
> amateur linear amplifier ever made! And, their not that expensive.
> Although, the prices are going up... (because of the stupid
> Democrats)... :( (Have you checked the inflation rate lately)?
>
> Good luck in your SB220 endeavor.
>
>
> Thanks
> 73
> Jim W7RY
>
> On 8/12/2021 11:57 AM, Joe wrote:
>> Hopefully some of you here may remember my adventures with this SB220.
>>
>> I'm the one that ran RTTY at full power in a RTTY Contest and
>> literally melted down the HV transformer.
>> And in the process toasted a LOT of other stuff with it.
>>
>> So a complete rebuild and change of the HV section was needed.
>>
>> So after looking at what a Pair of 3500Z's can actually do, I decided
>> to try to get all I can from them.
>> Think like a Big Henry Amp.
>>
>> I looked at the Eimac data sheets. And found a suitable HV transformer.
>>
>> This amp now has 3800 volts at rest on the plates and at full load
>> 3600 to 3700 volts.
>>
>> Problem is, running this much higher voltage has changed the values of
>> the output network components needed to be to obtain a match now.
>>
>> It was discovered that on EVERY Band, until the amp is making 1400
>> watts or MORE the load control wants to be fully meshed, max amount of
>> "C" available.
>>
>> Once it gets above 1400 watts, then you can get a peak on output power
>> when adjusting it.
>> But it is still a very small less "C" like 5% less than maxed out.
>>
>> So a simple thought was add more "C" so added a nice variable in
>> parallel with the load cap.
>> This cap was about 1/2 the value of the main load cap, so thought this
>> should be plenty.
>>
>> I was amazed to see that if it made any change at all, it was very
>> minimal.
>>
>> So with discussions with many on this group and elsewhere, it was
>> decided that because of the higher voltage, this amp needs more "L".
>>
>> That is a major redo for sure so I set that on the side. So continued
>> to use the amp at 1400 watts or more.
>>
>> Thats been geez 2 years now? The AMP is still running great! But often
>> I did not need or want to run 1400+ watts, So I bit the bullet and
>> decided to try to add the More "L"
>>
>> Now I "CAN" just do a poke and not do anything Scientifically.
>>
>> Like on the 10/15 coil, just move the 10 meter tap 1 turn longer.
>> looking at the 80/40/20, coil, It actually looks like I can add in the
>> coil form up to 7 or 8 more turns! The grooves in the form are there.
>>
>> Give like 15 meters one more turn,
>>
>> 20 meters 1 turn
>> 40 2 turns
>> 80 3 turns
>>
>> And just see what happens?
>>
>> Or is anyone here great with all that math stuff that I probably
>> learned when I took my extra exam in 1980 or so, but have long forgot
>> how to do this kind of work to calculate the needed components.
>>
>> But thinking Ok here is a stock SB220 a pair of 3500Z's
>> Stock voltage is what? 2500 & 3000 volts
>>
>> With stock caps and the pair of 3500Z's How much "L" is needed on
>> each band.
>> I would assume that is how much "L" was designed in the Kit.
>>
>> Now raise the voltage to 3600 to 3800 volts.
>>
>> Now how much "L" is needed with the rest still stock?
>> for each band?
>>
>> and using the stock 1.75" coil form, how many turns should be the best
>> chance of working for each band segment?
>>
>> Anyone willing to try a gander at this?
>>
>> Joe WB9SBD
>>
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