Tom
Transformers provide power measured in watts. 300 VCT at 250 MA means
about 75 watts, plus 250V at 280 mA means another 70 watts. So, in
continuous commercial service, it put out about 145W plus the power in
the filaments, maybe another 30W. In intermittent Amateur service...and
not caring too much if the thing burns up, maybe you can double the
power...(145 + 30) x 2 = 350W input to the 811's. The marked current
ratings only apply if the secondary windings use the centertap...this
application will use a bridge and float the center tap.
Let's consider how to connect the windings. A full wave bridge on the
300-0-300 winding yeilds about 800V. Full wave on the 250-0-250 winding
yeilds about 700, in series on the DC side yeilds about 1500V at 350W
means 233 mA plate current. Alternatively, put the 600V and 500V
windings in series for 1100 VAC, multiply by 1.4 for capacitor input and
get about 1550V out..dropping significantly under load. This application
doesn't need voltage doubling.
The transformer may not survive floating the secondaries this way. They
get a lot more voltage relative to the core or AC line than designed so
the insulation may break down.
So, this transformer runs a single 811A ok but seems way overloaded
trying to run two tubes...but what the heck...it didn't cost anything
and maybe the original designers put in some extra sauce. Suggest using
a separate filament transformer to get the most power from the plate
transformer.
jeff, wa1hco
Tom Bowman wrote:
>I'm looking for parts to build an inexpensive amp.
>I'm thinking about using a pair of 811 tubes because the price is right.
>Now the transformer problem:
>I have an unused TV transformer and would like your opinions on whenther or
>not it would work for SSB service using the pair of 811s.
>Transformer has two plate windings, 300-0-300 volts at 250 madc and
>250-0-250 volts at 280-0-280 madc, plus the usual 5 and 6.3 volt windings.
>I figured with a full-wave voltage doubler I would be close to 1700 volts.
>But would the transformer rated 250 ma be sufficient for SSB service???
>
>73,
>Tom WA3REY
>
>_______________________________________________
>Amps mailing list
>Amps@contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
>
>
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|