John Parkins wrote:
> Hello Steve,
>
> Tuesday, September 20, 2005, 9:19:04 AM, you wrote:
>
>
> ST> You could see the same effect if the tank coil inductance is too low -
> ST> eg if part of it was shorted out when it should be in circuit.
>
> ST> Max load cap. gives you a high anode load resistance. The circuit might
> ST> like this if the ht was higher than intended, but I can't see runnning
> ST> 240V into a 220V input, for example, making enough difference. Tired
> ST> valves that don't have the emission to cope with a lower load resistance
> ST> might also do it.
>
> ST> What gain and output power are you getting, and how do they compare with
> ST> the spec. for the amp? Does the anode current dip - is the dip at max rf
> ST> output?
>
> ST> Steve
>
> I was wondering about the tank coil although I've not noticed a
> problem with it visually, perhaps adding a turn or two??
Can't see a problem with trying it as an experiment - I'd been thinking
along the lines of whether part of the coil was left shorted by the
bandswitch.
>
> The HT runs at 2100 off load and 1950 on load. As I've said in other
> replies I have a spare set of valves and switching them around hasn't
> helped.
I don't know the amp, but from what I read that looks about right.
>
> Gain and output seems to be OK, although I've seen that some say they
> get more output, on 80 & 40m 80w in gets around 625 - 650w out. As far
> as the anode current, dip it is deepest at max rf out.
>
I forgot to ask - what's the anode current / efficiency?
In the end, if it's all about right and output power and linearity are
ok, then you could do worse than leave it alone. In your place I
couldn't, but I spend much more time fiddling with equipment than
actually using it!
There's a good looking set of notes at mods.dk if you put in sb200 on
the article search.
Steve
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