RX tubes in HW-101

[Ed Lambert]

An interesting point...

The schematic for the HW-101 that I have does show the V10 and V11 as
6HS6, BUT in the area where the filament string is shown, V10 and V11 are
listed as 6AU6.

The set uses a specially balanced filament string so that it can run six
volt tubes from 12 volts.  This means the current through each half must
(should) be identical.

Both of these are sharp cutoff pentodes with the same (7BK) basing.  The
6HS6 appears to have a higher transconductance.

The 6HS6 requires 450 milliamperes of filament current but the 6AU6 only
requires 300.  This does make a difference in the filament balancing.

The 6EV5 is a sharp cutoff Tetrode, not a pentode and the basing is
different (7EW).  Besides the filament current only requiring 200
milliamperes, I see there are two connections to the cathode, pins 2 and
7, while the other two have the cathode only on pin 7.  Pin 6 is the
connection to the screen grid.  I can understand if pin 2 were cut, but
not pin 6.

While they are all used as RF amplifiers, I don't know why one would
select one over the other for this application.

Ed
K1ZOK

On Mon, 23 Jun 2003 23:26:05 -0500 Marten T Beels <martentb at GOSHEN.EDU>
writes:
> Hello all, this is my first post to the list, so I guess it will do
> double duty
> as an introduction.  I have been using a HW-101 as my first HF
> transciever
> since 1999 and only recently began having trouble with it.  First
> off, I think
> that I blew the finals, only 5 watts RF out.  But that is easy
> enough to
> replace.  The hard part is deciding 6146, 6146A, 6146B, 6146W, or
> 6293.  But
> there is a lot of discussion in the archives that I can look
> through.
>
> My main question is this: V10 and V11 are listed as being 6HS6
> tubes, and
> looking through the archives, there is much discussion of replacing
> them with
> 6AU6 tubes.  However, I found 6EV5 tubes installed.  Furthermore,
> pin 6 has
> been cutoff from each tube.
>
> I wonder if my HW-101 has been modified to use the 6EV5 tubes or is
> it a direct
> replacement?  (sans removing a pin)  How similar are the 6EV5 and
> 6HS6 tubes?
>
> Marten
>
>

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