|
Title: Valiant Problems Post by: k5kab on May 19, 2010, 10:01:26 AM Good out put 100w, hard to tune according to the manual.
1. Turn drive to 3, use exciter to bring grid to 8 mil. The drive has to be turned to its maximum in order to obtain 6 mil. 2. Plate voltage is very squirrely at best it’s all over the map, the unit should put out about 150w, with all new 6146m, it takes a lot to get 100w. What dictates the grid in comparison to the drive? Title: Re: Valiant Problems Post by: W1ATR on May 19, 2010, 11:05:09 AM Test or replace the 5763 driver tube. If the plate current dances around and the carrier holds steady on an external meter, then try cleaning the meter selector switch. Start with the easy stuff first.
Title: Re: Valiant Problems Post by: k5kab on May 19, 2010, 11:15:55 AM Are you talking about plate VOLTAGE or CURRENT?
Plate CURRENT is what I was Refereeing to sorry. Title: Re: Valiant Problems Post by: k5kab on May 19, 2010, 12:42:25 PM Yes that was me, I have all 6146m new matched.
Title: Re: Valiant Problems Post by: Pete, WA2CWA on May 19, 2010, 01:55:18 PM It's always helpful (more info is good) to know what bands (160, 40, 15, all of them, etc.) you are having issues with the transmitter.
6146W tubes manufactured after 1964 have internal characteristics that are almost identical to the 6146B tubes. The big difference is that the "B" can handle more plate dissipation then the "W". I've been using three 6146B's in my Valiant for years. Title: Re: Valiant Problems Post by: Pete, WA2CWA on May 19, 2010, 03:30:47 PM ;D The old RCA tube manual said the 6146B was interchangeable with 6146A, but it didn't mean it was direct replacement. It's possible that if he did use the W's and they are the GE's from Nebraska Surplus what you just said is exactly what’s happening. I wish I had a dollar for every Kenwood TS-520S I repaired back in the 1970's because someone made that very mistake and they smoked the resistors on the PCB. I'd be a rich man today ;D The TS-520S used a pair of S-2001A tubes which were interchangeable with 6146B tubes. My Kenwood 599D transmitter (transmitter section almost identical to the 520 series) currently has a pair of 6146B's in it. At one point, back many years ago, one of the S-2001A tubes failed (open filament) in the T599D and I just replaced the bad one with a 6146B, so for several years, the final had one S2001A and one 6146B. Worked well right up into 10 meters. Title: Re: Valiant Problems Post by: WQ9E on May 19, 2010, 04:09:50 PM Although you might lose a small amount of efficiency at 6 mils of grid drive the effect is going to be very minor. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
Some things that should be done if you haven't already: 1. Replacement of filter caps: LV, HV, and especially bias. 2. Replace dropping resistor for the VR tube in the VFO. 3. Check/set bias for final and modulator tubes. 4. Check/adjust clamp control. 5. Check/adjust neutralization. If it is way off, first set it roughly on 20 meters and then do the final setting as per manual. 6. Make sure the loading is not too heavy; you may have bad capacitors on the coarse loading control. Too heavy loading results in low grid drive, high plate current, and low output. 7. Also try a crystal to rule out problems with the VFO. I have 2 original Valiants and a Valiant 2 and between them I have probably used every iteration of the 6146 family in the final and modulator positions. The neutralizing circuit will handle any of the 6146 family but I wouldn't advise mixing types in the final. |