5u4g instead of gz34 ?

5u4g instead of gz34 ?

The only rectifier tube I have is 5u4g,
and it seems like a real over kill for a 18w project
I have in mind ( 2 x el84).

The heater current alone is 3 amp .. I take that is *peak*
current when b+ is drawing 350ma (max)? Is it safe to
assume running 100ma load will draw 1.5 heater current ?

Re: 5u4g instead of gz34 ?


"WB" <warbaby@ppp . com > wrote in message news:48094923$0$4058$bbae4d71@news.suddenlink . net ...
> The only rectifier tube I have is 5u4g,
> and it seems like a real over kill for a 18w project
> I have in mind ( 2 x el84).
>
> The heater current alone is 3 amp .. I take that is *peak*
> current when b+ is drawing 350ma (max)? Is it safe to
> assume running 100ma load will draw 1.5 heater current ?

No. The heater will draw 3 amps regardless of the current in
the cathode - anode circuit.

Fred

Re: 5u4g instead of gz34 ?

Fred wrote:
> "WB" <warbaby@ppp . com > wrote in message news:48094923$0$4058$bbae4d71@news.suddenlink . net ...
>> The only rectifier tube I have is 5u4g,
>> and it seems like a real over kill for a 18w project
>> I have in mind ( 2 x el84).
>>
>> The heater current alone is 3 amp .. I take that is *peak*
>> current when b+ is drawing 350ma (max)? Is it safe to
>> assume running 100ma load will draw 1.5 heater current ?
>
> No. The heater will draw 3 amps regardless of the current in
> the cathode - anode circuit.
>
> Fred
>
>
thx !

Re: 5u4g instead of gz34 ?

In article <48094923$0$4058$bbae4d71@news.suddenlink . net >,
WB <warbaby@ppp . com > wrote:

> The only rectifier tube I have is 5u4g,
> and it seems like a real over kill for a 18w project
> I have in mind ( 2 x el84).
>
> The heater current alone is 3 amp .. I take that is *peak*
> current when b+ is drawing 350ma (max)? Is it safe to
> assume running 100ma load will draw 1.5 heater current ?

No it is not safe to make that assumption, the 5U4G filament will draw 3
amps no matter what the load is, even 0 ma.


Regards,

John Byrns

--
Surf my web pages at, * fmamradios . com /

Re: 5u4g instead of gz34 ?



WB wrote:
>
> The only rectifier tube I have is 5u4g,
> and it seems like a real over kill for a 18w project
> I have in mind ( 2 x el84).
>
> The heater current alone is 3 amp .. I take that is *peak*
> current when b+ is drawing 350ma (max)? Is it safe to
> assume running 100ma load will draw 1.5 heater current ?

The cathode of the 5U4 will use 3A ac to heat it up no matter
what the Idc peak output from the cathode is to the reservoir capacitor
and amp load.

The flow of dc from any tube rectifier cathode or ss diode cathode is
not a steady flow, but a 120Hz series of
pulses to charge the reservoir cap, and the peak pulse current value is
maybe 2 or 3 times
the steady dc flow to the amp, depending on the amount of dc flow and
the value of reservoir cap.
The cap value MUST be kept to the maker's data recomendations of 40uF.
The dc is taken from one end of the cathode, so at this end, there is
slightly
more current in the cathode metal than the 3Arms of the heating power.
Even at maximum dc output, the tube is rated OK.

So you need 5Vrms at 3Arms (ac) with 100 Ma dc to your amp.

Put another way, you must apply 5.0Vrms to the 5U4 cathode, and then
you'd find
there was a 3A flow. Anything from 4.8V to 5.3V would be OK.

The 5V winding on the transformer must be intended for use with a
rectifier
and have suitable insulation from other windings.
This is because the the heater winding is at the B+ maximum potential
all of its life, maybe +350V, and adjacent windings could swing peak
voltages of
+/- 350V, so a working 700V voltage difference exists.



Patrick Turner.