>
>>:Be sure to remove the wire between the bias contacts on the relay and
>>the 110VDC power supply. If you don't do this, a shorted tube can
>easily
>>:destroy the filament transformer.
>
>>In your opinion, would a series glitch resistor in the bias supply
>>prevent xmfr damage?
>
>:yes. 10k ohm, 2w to the bias contacts ought to limit the short circuit
>:current to a safe value.
>
>Then it would be a toss-up about doing the conventional "rewire mod" (as
>also described on Rich's web page) vs the install of one resistor.
The resistor is already there and wired to one of bias contacts. The mod
is to move one of the resistor's wires and remove the +110VDC from the
bias contacts on the relay.
>Ahhhh... the lazy man has choices to make...
>
>>Since the meters are near hens teeth to replace,
>
>:Harbach has them.
>
>Yes, but the last time I looked, they were not scaled/labeled for the SB
>220 or an exact fit. Seemed a shame to cut into the front face plate
>which I believe the Harbach meters might require.
>
The Harbach replacements are reportedly fairly ok.
>>I'd like to protect the movements if possible.
>
>A meter/shunt protection circuit is at Figure 2 on my Web site.
>
>It looks like a great circuit.
>In the past, I had a problem with the meter calibration changing too
>much.
That is why I use two 1N5408's in series across the 1A, 1-ohm plate
current meter shunt.
....
- Rich..., 805.386.3734, www.vcnet.com/measures.
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