W8JI Johnson Auido mods opinions?

[W3NP]

do  c99 and c100 have to be a polarized capacitor or can it be a unpolarized cap.I noticed a black line on either cap on one end.I bought a couple replacment caps from allied elec. Both illinois capacitor  630 wvdc metalized polyester .1 uf and a .47 uf.Both unpolarized.

Not polarized. Older caps had the black line to denote the outerside of the foil for shielding purposes and that usually went to ground or the less positive side of the circuit.

[scottdarling1221]

Is it a wise thing for me to have removed the clipper circuit for am use or should i have left it in and bypassed the anode to cathode diode section that limits negative positive peaks with a .02 ceramic disc capacitor.I did the audio mod on the site i listed before in this tread and the radio sounds really good.My freind says i should have left the clipper circuit in im not sure what to do. any advice

[Steve - WB3HUZ]

You are far better bypassing the clipper and the filter following it. They do nothing but restrict the audio and create distortion.

[W3NP]

Is it a wise thing for me to have removed the clipper circuit for am use or should i have left it in and bypassed the anode to cathode diode section that limits negative positive peaks with a .02 ceramic disc capacitor.I did the audio mod on the site i listed before in this tread and the radio sounds really good.My freind says i should have left the clipper circuit in im not sure what to do. any advice

Most get rid of the entire clipper circuit. That is my recommendation. I did.

[scottdarling1221]

Hello again,Im trying to set my johnson viking valiant static modulator current by the book but am a little confused.When i went to set it i set the radio at 3.5 mc 80 meters and tuned it like it said to but my meter under mod selection is showing me a little over 150 and when i tried to lower it with the resistor adjustment on the side the lowest it would go was 100 so i put it back to where it was.Am i doing somthing wrong am i reading the meter wrong

grid set to 8
loaded to 330 ma
i adjusted r61
keyed on am no audio

any help would be greatly apreciated would hate to burn up the new modulator tubes

[WQ9E]

Scott,

Have you replaced the filter caps in the bias section (C93A and B)?  These are generally bad if they are original and will lower the bias voltage too far so you cannot bring the resting modulator current to where it should be via the resistor screen voltage adjustment.  If you do replace these, you will also need to reset the VFO keyer control.

The current standard value of 22 uf (use either 350 or 450 volt rated with positive terminal to ground since this is a negative bias supply) will work fine to replace the old 15 uf units.  While you are in there, make sure that the wiring from the LV transformer to the 866A cathodes is proper HV rated wire.  Early units were built with regular hookup wire which tends to short to the chassis taking out the LV transformer in the process.

With the clipper circuit control turned full CLOCKWISE, the clipping is set to zero.  The Valiant is a medium power transmitter and depending upon your antenna and band conditions there are times when a little clipping is better than hifi audio; with the clipper circuit intact you can make that decision.

Rodger WQ9E

[WQ9E]

Additional info:

I am not sure what audio mods you have done so far but if the cathode bypass caps are original in the low level audio stages also replace those.  As these begin dropping in capacity, low frequency response and overall audio gain suffer.

Rodger WQ9E

[scottdarling1221]

thanks for the response.c93a and b have already been changed to sprague atom 30uf 450 volt caps pos sides are wired to ground. I was able to set the bias voltage for the output trio but cannot get the modulator static current right.Is there anything else i can try.The radio works i see 150 on the mod scale but i dont want to use it if its not set right.I replaced all of the coupling caps and decoupling caps in the audio stages along with all filter caps.Im going to hook the clipper back up and  bypass one side of the 6al5 cathode to plate that limits NEGATIVE RF peaks.I changed the original 6146 tubes to 6146b tubes i dont know if that could be part of the problem.Any other ideas thanks

[WQ9E]

If the resting modulator current is really 150 mils you definitely don't want to use it as you could quickly damage the tubes and the mod transformer with this high of a resting current.  Be careful resting the Valiant upside down as this generally causes the coupler in the VFO drive to break and they are not a standard item (different sized input and output shafts).  I generally loosen the set screws in the coupler whenever I have to do any significant work on a Valiant.  The problem is that the Valiant is very heavy and the coupler tries to hold the front panel perpendicular to the chassis when it is upside down and the coupler will berak.

It would be useful to make some voltage measurements at this point but be EXTREMELY careful if you are not used to working around high voltage since the voltages in the Valiant can easily prove fatal.

To safely measure the voltages, turn the Valiant off and unplug it.  After a few minutes short the plate supply to ground (if you don't have a shorting stick then a large screwdriver with a good plastic handle will work).  Make sure the HV is dead before you proceed.  If you have 2 meters available, hook one to measure the DC voltage on the screens of the 6146 modulator tubes (pin 3).   Hook your second meter to read the grid bias (pin 5).  If you don't have two meters then I suggest making the measurements in two steps being sure to go through unplugging and killing the plate voltage before setting up for the second measurement.  You should measure around 220 volts on the screen (pin 3) and -46 volts on the control grid (pin 5) with the Valiant loaded to its normal 330 mils of final plate current and with grid drive set at around 8 mils.

The 6146B tubes will work fine in the modulator (or the final except make sure all 3 are the same type in the final).  It is possible your audio mod could have led to oscillation in the audio stages and if you have a scope you can look at the grids of the modulator tubes and see if this is the case.  Johnson metering shunts are often inaccurate but I doubt that is the case here.  You should be able to adjust the modulators down to near zero resting current (not that you would want to) if the bias is set correctly.

Rodger WQ9E

[N2DTS]

To get slightly off topic, I DID do mods on my 32V3 to run the mic amp filiments on DC.
I had quite a lot of hum otherwise.
A high gain stage with a 5 meg input impedance is prone to hum, even when the tube is close to the mic jack like it is on the 32V3.

What I did was easy, just half wave rectify the filiment with one diode, put an electrolytic cap to ground, the size of the cap sets the voltage, more capacitance, higher voltage, I got it at 6 volts with something like 100 UF.

Its interesting to note that it does not have to be well filtered at all, nasty pulsing dc is fine, no audible hum as long as its not actual AC.

The 32V3 has been working that way for the last 10 years without any problems....
 
 Brett
N2DTS

[scottdarling1221]

what do you guys think about removing the caps and coils on the accesory plug and just bypassing it.I dont ever plan on externaly modulating it ever.

[WA1HZK]

I tried every trick in the book when I was doing mine. In my opinion just go through the transmitter to get the cleanest audio you can and use a good processor/limiter outside of the radio. You can make about 90% with the stock transmitter iron and a ton of mods but it's never going to be perfect. The best sounding Valients use external modulators with Hi-Fi amps and reverse connected audio output transformers with Heising modulation hook ups. That makes nice peaks but will expose the coarse loading switch problem. That switch will burn up after shorting out with 140% external audio.
Check my notes & others notes on the transmitter & modifications sections of this site.
Keith
WA1HZK