>Hi Bob: I do not have a specific idea about where your problem lies but
>thought you, or others, might be interested in my experience in fixing a
>77DX which was inop when I got it.
> 1. The chain drive for the input and output bandswitches was not
>indexed properly. On some bands the input switch was between contacts
>when the output sw was indexed. Loosening the sprockets , resetting
>them, and the idler tension adjustment fixed that.
> 2. The input reed switch was cracked and worked intermittently. I
> 3. The HV bridge rectifier blew each time I turned it on. This was the
>tough one to find. The bleeder resistors are under the chassis in the
>rear. The pos HV lead was routed near the ground end of the resistors
>and was arcing to the resistor terminal.
> 4. I seemed to be able to get proper output only when the grid current
>meter read about 100ma. This really worried me so I put a post on Amps
>about it. Several people told me that the 500ma f.s. meter was actually
>set at the factory to be 250ma f.s. Apparently the deflection when
>tuning on a 500ma scale is too small to see.
Why would one need to tune for grid-current ? Minimal grid current does
not give a correct tune. Maximal grid-current does not give a correct
tune. A correct tune is max out with the drive needed to produce 1A of
anode current per 8877 -- which coincidentally results in c. 100mA
grid-current per grid, which could be seen on a 0-500 scale. However,
there is no need to measure grid-current on a cathode-driven amp.
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,