[Boatanchors] EF Johnson thunderbolt

[KA2PTE]

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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