[Johnson] Johnson Viking II repair
Bill Cromwell
wrcromwell at gmail.com
Fri Apr 21 21:26:21 EDT 2017
Hi Rodger,
I have Johnson Ranger and that is where the drive pot wore out. It's the
same part used in the Heathkits. I have a pair of MatchBoxes, in-line
low pass filter, and electronic T-R switch - all Johnson. There is no
concern about mixing the finals. It's a single 6146#. My double barrel
6146 rigs are Kenwood T599, DX-100, and Apache. The Kenwood was dead on
arrival at a friend's shack and I bought it from him. The least of it's
problems was a 2001 and 6146 (no last name) final. It mostly worked
after the other repairs - but every once in a while. I am not even sure
that matching the flavors fixed it. Maybe I bumped something else while
I was swapping tubes. I had to redo the neutralization and maybe *that*
fixed it.
73,
Bill KU8H
On 04/21/2017 01:57 PM, Rodger Singley wrote:
>
> Bill,
>
> Thanks for posting the information about the drive pot replacement and
> I believe the part you found is at Digikey, at least I couldn’t find
> it at Mouser. That looks like a winner! Several years ago I ordered
> some pots from Digikey when they weren’t stocking these 5 watt pots
> from CTS and what they carried then were 4 watt pots with some sort of
> resistance material plated on ceramic that had a ridiculous
> temperature rating that caused the wattage rating to drop quickly with
> increased ambient temperature. At 110F the pots were de-rated to 1.5
> watts but what you found are true wire wound types that will work very
> well. I am going to order a few soon just in case they disappear from
> production.
>
> I agree with your advice about not mixing tube types within the final
> although you can probably get away with it most of the time. I bought
> a perfectly operating Valiant 2 that came with one 6146 and two 6146B
> in its parallel three tube final and it worked OK on all bands.
>
> There is no need to perfectly match tubes in these parallel tube
> finals; the biggest concern is if one tube has greater gain it is
> going to tend to hog the current possibly causing it to exceed its
> ratings. In push/pull service (like the modulator) mismatch can
> impact distortion however some people purposely put a “hotter” tube in
> the positive going side in an attempt to increase audio without
> driving the final to cutoff on the negative going peaks. However even
> if you match a set of tubes now they aren’t going to age equally and
> tubes that are matched for equal idle current probably won’t be
> matched at peak current. The best designed “sweep tube” linear I have
> seen is a Kenwood TL-911 I picked up at a hamfest a few years ago. It
> uses five 6LQ6 tubes in parallel with a meter that can be switched to
> read total cathode current along with individual cathode current for
> each tube. The screen voltage is adjustable individually for each
> tube to equalize idle current and a capacitor adjustment in each grid
> circuit allows setting each tube for equal peak current. An
> electronic current sense circuit puts the amplifier in standby
> instantly if safe peak total cathode current is exceeded and also goes
> into standby if average current/duty cycle is too high even if the
> peaks are safe. It shows what a company can do when amplifiers using
> sweep tubes were designed to be good instead of just cheap 😊
>
> And the Viking 1 and 2 are probably the most rugged pieces of gear
> made by Johnson. I have most of their stuff from the small Adventurer
> and Navigator through a Viking 500, Desk KW, Invader 2000,
> Thunderbolt, and 6N2 Thunderbolt but the component and construction
> quality of this early Johnson design is very nice. They certainly
> weren’t designed with cheap as the priority.
>
> Rodger WQ9E
>
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> Windows 10
>
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