Viking 2 low grid

[Detroit47]

Gentlemen
 I have a problem with my Viking 2. I have low grid current when I tune it up on any band. This cuts my output wattage down to about 50 watts.  I can adjust the oscillator and buffer for 8 mills of grid current with no hi voltage on plate. But as soon as I turn on the plate voltage the grid drops to about 2 mills. Is this a common problem? I just bought this as a basket case and I am bringing it back from dead. I have recapped it and replaced all the old resistors. I am thinking about getting rid of the 6al5 and building a solid state shunt regulator to hold grid voltage steady. The Viking is being driven with a 122 vfo I have tried a crystal with the same results.

73 Johnathan N8QPC

[WD8BIL]

Johnathan, try another set of 6146's and see ifn it still happens.

[K1ZJH]

If the grid current is varying with the plate tuning dip, check the neutralization.

Pete

[WQ9E]

Jonathan,

Pete is correct that incorrect neutralization can cause this issue and if neutralization is way off then do a rough adjustment on 20 meters before doing the final neutralization on a higher band.  If it is properly neutralized but the loading is excessive this will also cause drive problems.  Additionally:

How are the voltage readings on V5 and V6?  Have you tried substituting for these tubes?

With the plate switch off, temporarily de-tune the grid drive (to avoid damaging the 6146 finals) and check that R25 varies the screen voltage normally on V6.

Capacitor C25 (parallel mica caps) has been problematic in some rigs so you might suspect these if the previous steps don't clear the problem.

Be careful with the grid current, 3.5 mils per tube is the rated max and 6146 tubes do not take kindly to excess grid current.  Johnson added a notice to their Valiant manual about excessive grid current and the desired drive for three 6146's in Class C is 8 mils total.

Rodger WQ9E