Viking II cap/resistor changes: Going Further?

[KC4HGH]

Thanks for answers to previous replies to my posts...just thinking, however, & looking for opinions: would it do any good to replace bypass disc caps and resistors biasing tubes & in power supply areas, et. al.?  I think I'll go ahead & change ALL electrolytic caps anyway, but would discs, mylars, etc. go bad after half a century?

Also, are there any cap changes from one value to another that would better the audio or lessen stress in critical areas?

If I can get this ol' darlin' sounding as good as many of you fellers out there, I'll be happy!

Thanks, de Bud KC4HGH

[KB2WIG]

Check out the AM Window site... there are some audio mods to consider.... generally, fatten up the audio couplin' caps a little, helps a bit... do a few things at a time so if you screw up like I do, you wont have so many things to look/worry at/about......     klc

[KC4HGH]

Didn't see anything in AM Window other than what I've gotten already.  I don't want to do any major refitting, like different tube additions/tube changes.  I was just looking for simple upgrades, for my simple mind.... ;-)

[ve6pg]

...BUD..TIM IN TORONTO...I WOULD REPLACE ALL CAPS,AND RESISTORS IN THE VIKER..REMOVE THE CAP ACROSS THE 807s,REPLACE THOSE 100ohm RESISTORS,AS WELL...YOU WILL NOTICE,C52,AND R26 ON THE DRAWING...AT THE MIKE INPUT..REMOVE THESE AS WELL...THE CAPS MAY,OR MAY NOT REQUIRE REPLACING,BUT AS BOB,W2ZM TOLD ME,IF YOU ARE ALREADY WORKING ON THE RIG,MIGHT AS WELL REPLACE THEM...I'M USING AN OUTBOARD MIKE PROCESSOR/EQUALIZER...GOT IT CHEAP OFF OF E-PAY,AND I USE A HIGH IMPEDANCE DYNAMIC MICROPHONE..I DID NOTICE,THAT ALL CAPS HAD SOME LEAKAGE,AND ABOUT 80 PERCENT OF THE RESISTORS HAD CHANGED THEIR VALUE,DUE TO HEAT,AND AGE....IT WILL SOUND FB,IN NO TIME...TIM....SK...

[WD8BIL]

Hi Bud.... This is Bud !!!

Particularlly, change the resistors in the bias supply string. Both my Viking 1 and 2 had bias problems do to these resistors going high.

WD8BIL

[KC4HGH]

Thanks, Bud!  Anything to make sure this darlin' runs right when I finally do fire it up.

[Tim WA1HnyLR]

Hi Bud There are a number of improvements that can be done to the Viking II besides the usual cap  changes. Change the second audio stage to a triode connected 6AQ5. Use same value cathode resistor but 2 watt dissipation to be safe. Solid state the power supplies. Change the low voltage suckply to choke inpoot. Use 200 MFD of filtering . the outpoot voltage should be about 260V series up the unused 5V rectifier phillament windings . Put a bridge rectifier around them use about3--5000 mfd of philter condensity. This becomes a 12V suckply for PTT relay control . Use at least a 4pole DT relay. One set of contacts is used for RX muting  or control of a larger RF amplifier the other contacts are used to apply screen voltage to the modulator. The 20K bleeder that they use for screen voltage and goose tube screen voltage is a very poor means of screen voltage source.  It is common knowledge that voltage regulation of screen and bias  voltages is VERY important.With 260-270v on the 8O7 screens a bias of -22----24V is required. I used a string of Radio shack 5 and6volt 1watt zeners with a  paralleled 250Mfd 50V cap clamping the bias to the modulator.By making theses changes to the modulator you will have more available CLEANER audio . RF bypass caps at bottom of RF choke are .01 caps . These should be changed to .001 3Kv dics The first audio stage 6AU6 should have plate coupling cap of .01-.05 the screen bypass should be at least.2--.5 mfd. The cathode bypass be 50-100 mfd@10 volts. The grid resistor should be at least 10Meg ohms.witha 100Pf bypass and 10K series resitor for RF supression. The audio gain in the viking II is not much . Maybe try a 6AH6 for the first stage. aD10-4 may have enough snot to make full modulation with gain turned all the way   up. You may wind up using a good microphonium and processor  ahead of the transmitter to get good modulation level and audio quality.