[Amps] New SB-200 owner

[Steve Thompson]

jeremy-ca wrote:
>>
>> Peter Chadwick wrote:
>>
>>> Steve said:
>>>
>>>> I think they can do better linearity than that - the amps I built have
>>>
>>>
>>> all done so at 250-300W/tube. The STC data sheet for 4CX250B gives IMD
>>> figures under the typical operating conditions. At 2kV, 325W pep output
>>> they give IMD3 -30dBc and IMD5 -50dBc.<
>>> They can do even better with some negative feedback. The KWS1 (which 
>>> didn't have feedback) claimed 35dB down, although they don't say if 
>>> that's relative to PEP or to tone. That's at 1kW input, which would 
>>> align with Steve's figures.
>>> But you need a screen supply, and from an economy viewpoint, that can 
>>> be a trouble.
>>
>> It needn't be. If you stay simple, a dropper from the anode supply with
>> an uncomplicated active shunt regulator costs about a pack of beer.
>> Regulation is more than adequate. I begrudge wasting 30W as heat, but it
>> saves a transformer.
>>
>> Steve
> 
> 
> 
> I wish Ian was back from holiday. He went thru this in much detail back 
> when he was designing his regulator boards.
> However, dropping thru any high impedence is far from ideal be it via 
> tubes, resistors, a 6 pack regulator or zeners.
> Im not going to get into this any further as Ive spent enough time when 
> I could be doing other more rewarding things already. Possibly the 
> archives have Ians notes.
OK. I'll ask Ian to correct me next time we share a beer. The way I see 
it, if the shunt regulator is doing its job right, then the dropper is 
of little importance. I'll also leave it at that.

Steve