[ARC5] Marconi R1155: Replacing the VR103 Eye Tube

[David Stinson]

Marconi R1155: Replacing the VR103 Eye Tube

If one can find it, a replacement for the
"tuning eye" valve/tube, VR103 has gotten
expensive. I hear that many which have been
purchased from places like India arrive in
NOS boxes, but are in fact used-up duds.
Good luck with that refund.

The easily-found 12V filament 1629 is a
pin-for-pin replacement, save that the R1155's
filament buss is 6V.

If your 1629 is NOS, one can simply plug it in
and get an acceptable brightness at half filament
voltage. If one's VR103 is very dim, as is mine,
this is "better than it was."
This photo shows the 1629 at 6V filament:
https://photos.app.goo.gl/wjNg7Y4frWi3eWox8

However, if one wants full brilliance, there
are inexpensive, small DC-DC "boost" converters
which, when provided with a single-diode half-wave
rectified input from the 6-Volt filament buss
will provide 12.6 VDC for the 1629.
Here is one like that I used, sourced from Ebay
several years ago:
https://www.ebay.com/itm/383731706019

I bought many of these little boards
years ago and have found them very useful.
One trade-off there is the possibility
of RFI "Birdies" and some of the designs
are bad about it.
I haven't found an objectionable birdie
from the AM Broadcast Band and up with a
quick scan using this board, but I was
not through.
If a birdy does happen to land right on
your favourite frequency, a change in input
voltage will move it. Add a second series
diode or a small resistance.  The board
will work down to 3.5V input, so we
have a lot of "wiggle room."
There are several "newer" designs available
since I bought these. At the tiny price,
I think I'll buy several and see how they
compare for RFI. Make sure it is a "boost"
version, not a "buck," which only lowers the
output voltage from the original buss.
Here is the brightness at full filament:
(150V B+):
https://photos.app.goo.gl/xvnauCNUrhkYmnbh7

I unsoldered the wire to pin 2 on the eye tube
and connected a single diode from the wire to
a power diode, and the diode to the "IN +"
connection. This board already has an acceptable
filter cap on the input. The "IN -" is connected
pin 7, which is Ground/Earth.  "OUT +" goes to
pin 2 on the socket.  Here is the "clipped in"
check to confirm it works.  Board is generating
regulated 12.6 VDC under load. Yeah, I know
my R1155 needs some paint:
https://photos.app.goo.gl/16xKwxmAyUgTXFt27

I wrapped the little module in tape and soldered
it in behind the eye tube socket.  I'll probably
velcro it down:
https://photos.app.goo.gl/pup8Q6m4oNieJ2Ck7
(No; I have not removed all the DF stuff.
  I took out the two VR99s and the VR102 to save
on filament current until I'm ready to work with
the DF meter supplied by one of our members,
who is kinder to me than I deserve.)

NOTE: These inexpensive DC-DC converters are
not isolated; the "IN -" and "OUT -" are a
common point, so be sure to connect that side
to pin 7 or other Ground/Earth.

Nice to have the "eye" tube working again.
https://photos.app.goo.gl/VrppFTKoBgwyEZ399

GL OM ES 73 DE Dave AB5S


-- 
This email has been checked for viruses by Avast antivirus software.
www.avast.com