On Tue, 2 Mar 1999 23:05:13 EST KA2YKC@aol.com writes:
>In a message dated 3/2/99 10:13:54 PM Eastern Standard Time,
>km1h@juno.com
>writes:
>
><< >
> >I have changed tubes between three different amps and three
>different
> >sets of 3-500Z's and it happens with all tubes. I am sure the
>problem
> >is in the amp. In addition, I have checked the shunt resistors in
>the
> >grid circuit, and they all check good.
>
> What shunt resistors?? In an un -voodooed TL-922 there are no
>resistors,
> just a pair of grid chokes plus 220pf caps per pin. Those original
> chokes are too big, current and low resistance wise. I suggest
>replacing
> with something in the 750uh to 1.5mH 160ma and 25 Ohms DC resistance
> range...as used in the SB-220. If there are some strange parts in
>the
> amp, it might be best to throw them away and follow the original
>design.
>
> >>
>?????
>
>In a factory-stock TL922A there is a 470 ohm resistor in parallel with
>the
>grid choke -actually the resistor is wrapped & soldered to the leads
>of the
>choke. A real pain in the ass to measure each individually during
>troubleshooting.
>
>Eric
>KK2ED
Eric,
I forgot about that resistor since it does not appear to serve any useful
function. Maybe it is designed to stabilize the ckt in case of a open
choke. Anyway the value is 4.7K according to the manual.
I have a TL-922 in here now so going to have to experiment a bit.
73 Carl KM1H
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