SB-200 Amp

[Multi-Volti]

Filament probably should be 6.3 not 6.0.

If 6.8 is without tubes installed that wouldn't surprise me.

If it's with tubes installed, that's a bit high - I can't remember but
thought those were directly heated cathodes, & I assume thoriated like other
large power grid tubes, and therefore probably subject to the rule of 5% max
overvoltage on filaments longevity. (6.3x 1.05 = 6.62 V). If this is
tubes-installed filament voltage, check your line voltage - may be high.

Not sure how much room there is, but homebrew nichrome resistor to drop some
filament voltage is what Rich Measures advised on SB-1000 which ran way too
hot on filament.

Murray


----- Original Message -----
From: Walter or Margaret Korab <wsmk at PTD.NET>
To: <HEATH at LISTSERV.TEMPE.GOV>
Sent: Monday, February 17, 2003 4:14 PM
Subject: SB-200 Amp


> Hello All,
>            I'm installing all the mods recomended for the SB-200 and I
wanted to check the
> input impedance at each of the input coils. One suggestion was to
temporarily install
> a resistor that matches the input cathode impedance, to each of the
cathodes to ground
> on the 572B. This is of course a check without powering up. I have an mfj
259b, but I can't
> make any sence out of what I'm finding.  The impedenace measurements are
all
> reactive, when Xc =Xl the frequencies are no where near the Fr should be
and R is no
> where near 50 ohms. I tried it with a cathode resistor of 50 ohms and
without, both
> measurements were the same. Tests were done with the tubes in place and
holding in the
> antenna relay. I know the accuracy is 2nd best without powering up, but if
I can just get
> close I could fine tune under power. Any Ideas?    Also, any ideas on the
best way to
> lower the filament voltage?  Should be 6.0V, I have 6.8V.
> Thanks,
> Walt,  w3fnz
>
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