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Title: Valiant II Modulator Bias Pot Mods Post by: WA4JK on October 13, 2013, 04:43:09 PM I'm attempting to get a Valiant II going and I have run across an issue. Apparently the Mod Bais pot crapped out, and a mod was partially put in place. It is incomplete and I am trying to return the circuit back to normal. Anyone have a R61 in a carcus they want to sell??? I'm going to have to rip out the mod and restore it back so I can see what else is not working. I'm backing this thing up mod by mod until I get it working and then I'll see where I take it from there. Thanks
Title: Re: Valiant II Modulator Bias Pot Mods Post by: DMOD on October 15, 2013, 09:46:43 PM Sorry, I don't have one but if you have to order one on line there are at least two choices:
http://www.jameco.com/1/1/816-rv4naysd502a-rv4-potentiometer-53c35k-5k-ohm-2-watt-10.html http://www.mcmelectronics.com/product/501-0009&scode=GS401&CAWELAID=220552017?catargetid=1545764029&cagpspn=pla&gclid=CI2alLOdmroCFfBaMgodnE4AIQ Phil - AC0OB Title: Re: Valiant II Modulator Bias Pot Mods Post by: WA4JK on October 17, 2013, 06:59:24 AM Thanks Phil, I need to do a little more reading up on these to determine if they are wire wound. For this service that would be a must.
Title: Re: Valiant II Modulator Bias Pot Mods Post by: WD5JKO on October 17, 2013, 07:25:24 AM There is an Ebay seller that makes Drive pot modules for the Ranger. He also sells a 300V regulator for the LV B+. You might contact him concerning the Viking II. I attach an image showing a completed listing for the Drive Pot module. He has a current listing for the 300V regulator. Jim WD5JKO Title: Re: Valiant II Modulator Bias Pot Mods Post by: WQ9E on October 17, 2013, 09:01:09 AM Although it isn't quite as easy to adjust you could use a regular adjustable tapped wire-wound resistor to replace R62. Two watts is a very minimal rating for this piece. If you used the Johnson 6N2 transmitter with the earlier production Valiant it required you to modify the bias system so that the modulator bias was independent of final grid drive and the factory modification was a duplicate of what you find in your Valiant 2 except they specified a 10 watt resistor for R-62. You could easily end up dissipating about 2.2 watts across R-62 with a slightly higher than average line voltage (it also forms part of the bias bleeder network) and it sees this continuously since the bias supply is always active.
The original Valiant adjusted modulator (and SSB final standing bias) through adjusting the screen voltage via taps on the HV bleeder. Adjusting the bias instead is more convenient. Title: Re: Valiant II Modulator Bias Pot Mods Post by: WA4JK on October 17, 2013, 01:30:43 PM I don't need the drive pot all of that entire audio section was bulldosed and a Audio transformer installed. The Final bias and modulator Bias circuits have been modified and they do not work. So I'm trying to put it back to the original design to get it working and then go from there.. I could go with a higher wattage pot if the size is the same or smaller AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
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