[Boatanchors] EF Johnson thunderbolt
Richard Knoppow
1oldlens1 at ix.netcom.com
Tue Aug 24 17:09:23 EDT 2021
FWIW, the rating on VR tubes is a "nominal" rating and the
actual voltage is slightly less on most of them. I don't remember
well enough to be definite but I think the 0B3 is considered the
most constant of the common regulators, only the 56V miniature
(forgot its number) which is intended as a reference tube, is
more accurate. The structure of the tube may interfere with the
visibility.
Many tube testers have means for testing VR tubes, usually by
means of a variable voltage controlled by the filament setting.
They can check the firing voltage and the range of regulation via
the meter. At least I can do that on both my TV-7 and Weston
testers. Will tell you if the tube is OK.
On 8/22/2021 9:12 AM, KA2PTE wrote:
> Wound up getting a GE brand 0B3 for my testing. It works, about
> 86V output,
> but strange thing is all the other VR type tubes light up white
> and you can see the glow from the top of the tube.
> On this GE, you have to really strain to see the white glow,
> nothing can be seen from the top - is that normal
> being its another manufacturer? The others I use are sylvania
> brand and you can see the white glow from the top.
>
> --
> Steve Hearns [ KA2PTE ]
> Technotronic Dimensions, VT [USA]
> WWW.TECHNOTRONIC-DIMENSIONS.COM
> E-Mail: Steve at Technotronic-Dimensions.com
>
> ----- Original Message ----- From: "D C _Mac_ Macdonald"
> <k2gkk at hotmail.com>
> To: "Boat Anchors List" <boatanchors at mailman.qth.net>; "KA2PTE"
> <ka2pte at 3950.net>
> Sent: Thursday, July 08, 2021 8:30 PM
> Subject: Re: [Boatanchors] EF Johnson thunderbolt
>
>
> VR octal tubes were:
>
> VR-75 = 0A3
> VR-90 = 0B3
> VR-105 = 0C3
> VR-150 = 0D3
>
> 7-pin miniatures were:
>
> 0A2
> 0B2
> 0C2
> 0D2
>
> IIRC
>
> 73 - Mac, K2GKK/5
> Since 30 Nov 1953
> Oklahoma City, OK
> USAF (Retired) 61-81
> FAA (Retired) 94-10
> ________________________________
> 0C3From: boatanchors-bounces at mailman.qth.net
> <boatanchors-bounces at mailman.qth.net> on behalf of KA2PTE
> <ka0CD2pte at 3950.net>
> Sent: Thursday, July 8, 2021 18:51
> To: Boat Anchors List <boatanchors at mailman.qth.net>
> Subject: Re: [Boatanchors] EF Johnson thunderbolt
>
> Ok got a line on some used chokes and will be ordering soon.
>
> Meanwhile I am trying to remember where I left off on this as
> far as the VR
> bias tubes go.
>
> The original setup was a VR75 neon type for the operating bias
> tube, and (2)
> VR150 plus (2) VR100
> in series totalling 550Vdc for the screen supply.
>
> At one point another guy who restored a Tbolt said you can try
> a VR100 for
> the bias tube, which I did, but did not get good results.
> I am not sure if I had left the screen tubes in the original
> config for that
> though.
>
> I did seem to get somewhat better results with all the screen
> tubes as VR150
> types, and also I think with the operating bias tube
> as a 150 as well, but at some point L8 gave out as its done 3
> times so far.
>
> I have the tube sheet, and I think for AB1 which the amps been
> modded for,
> using (2) 1K dropping resistors in series with the operating
> bias tube,
> I am told thats good, but I also read the more screen volts the
> better. the
> only reason I can think that the VR100 tube was not a good one
> for the bias
> are those dropping resistors? I am guessing there is a region I
> need to hit
> for the "sweet spot" on the bias for AB2 and 75 is the closest?
>
> --
> Steve Hearns
> KA2PTE
>
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--
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL
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