Re: Hi does anyone have a stock or a source of B9D Valve bases please ?


"Ian Jackson" <ianREMOVETHISjackson@xxxxxxxxxxxxxxxxx> wrote in message
news:B84A8UAIFvGKFwwx@xxxxxxxxxxxxxxxxxxxx
In message <gvep5j$l5h$1@xxxxxxxxxxxxxxxxx>, Steve Terry
<gFOURwwk@xxxxxxxxx> writes
"Bill Borland" <bill@xxxxxxxxxxxxxxxxx> wrote in message
news:8F37PAA2SuGKFwEc@xxxxxxxxxxxxxxxxxxxx
In article <aqmi15ttdme8p0etvuj3c9ikel5opud7mr@xxxxxxx>, Jim
<jim@xxxxxxxxxxx> writes
On Sat, 23 May 2009 20:34:02 +0100, "Steve Terry" <gFOURwwk@xxxxxxxxx>
wrote:

A 5U4G you can replace with a couple of 1N4007 diodes
at a couple of pence each


Just to prevent any accidents -
There is quite a large voltage drop across a valve rectifier - I
expect you remember how hot they got. I can't remember figures, but
a drop of 50 volts at 500 mA would mean the thing is dissipating 25
watts. Solid-state diodes are much more efficient - they might drop
10 volts but no more. In other words, a straight replacement means
an increase of about 40 volts on the HT line. The electrolytics
and other components in the equipment *might* be able to cope with
this, but I wouldn't bank on it after all these years.
So - put resistors in series with the diodes to bring the HT line
back down to what the equipment expects. The only trouble is, these
resistors are then going to dissipate that 25 watts (well, 20 anyway)
and resistors of that rating are extremely large by present-day
standards, and probably expensive and hard to find. So it's not
quite as easy as it looks.
Bill Borland
(G3EFS)

OK if you get 10 volt drop with a IN4007 and you want 50 volt?
Put 5 IN4007 in series on each side of the full wave
(although 3 would probably be enough)

Using diodes in series isn't going to change the total watts dissipated.
And you're only going to get 0.6 to 0.7V drop across each one (not 10V).
For 50V drop, you're going to need a lot. You might just as well put
resistors in series (to spread the power out). However, diodes are
probably preferable, as the HT regulation will be better.
Ian


First I'd look to see if the transformer primary has any above 240v taps?
and if so, raise them to lower the output voltage.
Likewise any secondary taps to lower

Steve Terry




.

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