[ARC5] Marconi R1155: Replacing the VR103 Eye Tube

[Scott Robinson]

Hi David,

There's a no-birdy way to get 12V from a 6V AC source: a voltage 
doubler. Uses two diodes and two electrolytics and works entirely at the 
mains frequency.

Happy listening!

/Scott Robinson

On 3/2/23 3:18 AM, David Stinson wrote:
> 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
> 
>