[Amps] Tank tweaking - plate choke

[2]

>    A question, ¿is 225 uH inductance enough for the plate choke at 160? 
>(taking in care 3200 ohms plate load..)

**  A means of analyzing a HV-RFC is to calculate the RF circulating 
current through the choke at the lowest frequency of operation, and see 
if the total current burden on the choke seems reasonable.    For 
example, 225uH has 2544-ohms of reactance at 1.8MHz.  The RF-Vrms across 
the choke is roughly 2/3 of the HV anode supply V.  If the HV were 
6000Vdc, the choke would see c. 4000Vrms.  The resultant current would be 
4000V.rms/2544-ohms = 1.57A.rms.  If the choke's wire is capable of 
handling this plus the DC anode current, and the RF-bypass caps can 
handle 1.5Arms, all should be well provided the choke does not have any 
resonances within c. 6% of an operating freq.
- - [notes -- typical HV disc ceramic bypass caps get warm at c. 1A.rms, 
so multi-cap bypassing is not a bad idea. /  All HV-RFCs need a coat of 
gloss urethane varnish to prevent wire-rattling during modulation.  Info 
on building no-surprises HV-RFCs is on my Web site].
>
cheers
>Bill Coleman escribió:
>
>> Thanks for all the ideas.  I've had a few requests for a couple bits of 
>data...
>>
>> On 160 the target Q is 12, Plate load is 3200 ohms.
>>
>> I have tried changing the plate blocking cap from 800 pF (it was 4 200 pF 
>HT57's) to 1000 pf and 2000 pF using some HH58's. This appears to have 
>helped, but it's still way down on efficiency (<50%) compared to any of 
>the other bands (even 10M - 60%).
>>
>> I tried changing the physical layout of the coil stock relative to the 
>10/15/20 meter coils. Thinking (?) there was some wierd 
>cancelling/coupling.  No change.
>>
>> Next experiment will be to tune the input circuit on 160.  I didn't bother 
>tuning either 160 or 80.
>>
>> Right now the only band that is troublesome is 160.
>>
>> Thanks all.   73, Bill  N2BC
>> ~~~~~~~~~~~~~~~~
>
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-  R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K, 
www.vcnet.com/measures.  
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