HQ-150 S meter

[W9BHI]

I have a Hammarlund HQ-150 that has been recapped and aligned.
It works great on all bands BUT the S meter won't hold a zero adjustment.
You set the zero according to the manual and check it 10 minutes later its either way below zero or reading an S5.
I haven't swapped any of the IF tubes yet.
Any thoughts?
Thanks,
Don W9BHI

[Todd, KA1KAQ]

It's possible that you still have a defective cap, even if new. But not likely. That leaves a tube or some thermal issue. Tubes would be the sensible place to look since they haven't been tested or swapped out.

Might be a good idea to let the receiver stabilize for a few hours before calibrating the S-meter, too.

[WQ9E]

Very common due to a tube that is gassy or suffers from secondary emission as it gets hot.  A decent tube checker will catch the former but most not the latter unless it is extreme. 

Try subbing another 6BA6 in the V5 and then V6 positions.

[w5rkl]

There's a simple means of measuring whether a tube is gassy or not by simply measure the voltage on both leads of the grid resistor. A gassy tube
will have a more positive (less negative) voltage on the grid side of the grid resistor than on the opposite lead of the grid resistor.

73s
Mike

[W9BHI]

I have some NOS 6BA6's on the way.
We'll see what happens.
Thanks for the replies guys.

Don W9BHI

[KM1H]

The HQ-150 will have several very drifty resistors, even low values as were in the one I shipped 2 months ago. It also had flaky sockets that needed a lot of insertions after a tiny drop of DeOxit. And it also had a flaky 6BA6 first IF that would crackle at times. I decided to change that with a 6BZ6 to boost the overall gain a bit as well as changing a few resistors to get the "typical" operating voltages per the tube manual. Id already went to a 6GM6 in the RF as 10M was doggy and the customer particularly wanted that to be good.
Besides that the crystal needed cleaning and one of the filter micas was way out of tolerance.

I could have done 2-3 129/140's in the time the 150 took! And with several 150's under my belt I can safely say the 140X and 140XA are far superior except for the lack of a notch filter.

Carl

[W9BHI]

Changed the 6BA6's and now the meter is holding the zero adjustment.
Thanks,
Don W9BHI