From: Eric Webner 
Subject: Re: [drakelist] R4C xtal bank bad


Eric Webner  made an utterence to the drakelist gang
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Garey,
 
Several weeks ago when I discovered the play in one of the bandswitch
wafers, I set the wafer where it should be and used adhesive  on the inner
wafer and shaft. It appears to work very well, and with no binding. I
wouldn't recommend that for all the wafers, but just one seemed ok.
 
Regarding my low output, I may be ok. First of all, I was not loading it to
full power, since one of the errata sheets that Drake put out said to load
it for only 340 mA in order to avoid any spurious output. After reading
your latest message, I loaded 80 and 40 meters to full power, obtaining
135-140 watts measured on my Bird wattmeter. Loading it to full power ran
the plate current to 500 mA!
 
I also took your suggestion and checked a few components. R44, the 680 ohm
resistor, is good. The cathode resistors are good and very well balanced.
The screen resistors checked out as well. However, the resistor across the
meter measured 5.6 ohms. I disconnected one end from the circuit board and
the resistor snapped in half. I couldn't come up with another one, so I
hope to try a 2.2 ohm unit (measures around 2.6) so I can get on the air
this weekend.
 
Do you recommend that I vary the other resistor in order to achieve
accuracy on the meter, or can I play around with values on the shunt
resistor (the 3.3 ohm resistor)?
 
One other observation: my low power output could be attributed to this
meter shunt resistor being off, as that would cause me to back off on the
loading quite a bit. This is also why I didn't want to load it to full
power (500 ma???) for fear of melting a couple sweep tubes. It also makes
me wonder about my bias. Is there a voltage one should shoot for, or is
getting the bias (idling) current still the preferable approach? Do I need
to realign everything if I need to reset the bias?
 
OK, enough questions for now. Thanks for all the good responses!
 
73,
 
Eric KA8FAN


Garey Barrell  wrote:
Eric -

There isn't a "good" way to correct the wafer "play"
once it occurs, 
short of wafer replacement. I have seen some with very thin Teflon? 
tape wrapped around the shaft that seemed to work. I saw one where 
someone had cut small pieces of brass shim stock, carved out the hole, 
and epoxied them to the wafer. Inexpensive, but highly labor 
intensive! :-)

The Load control should be in the 2.5 - 4.5 range for a non-reactive 50 
ohm load. The Plate control should be in the 3 - 8 range. As long as 
a "dip" can be achieved, it doesn't really matter.

Your power output is very low. If you load for maximum output, you 
should get 130 plus watts out on 80 - 20 in Tune position, 150 -160 
watts in CW. Power that low is most likely from weak finals. With 
"new finals", you probably have an alignment problem. If you have done 
the alignment, check the 680 ohm resistor at R44, (located under T7, 
just at the end of the final feedthrough panel under the chassis,) 
especially if you did the alignment with a metal screwdriver. Shorting 
the alignment caps to the chassis, hard not to do with a metal 
screwdriver in those little holes, will damage this resistor. With 
regard to the plate current, this is most often a result of a meter 
shunt resistor that has gone up in value. This is a 3.3 ohm resistor on 
a small board under the chassis near the relay. The 'best" way to 
correct this is to replace it with a 1W (the original is 1/2W) carbon 
film resistor. At the same time, check the 15 ohm 1W cathode resistors 
for the final tubes. They should be close to 15 ohms, (+/- 5%) and 
closer to each other, (2%). Best replacements are Ohmite OY ceramic 
composition, although the carbon film types seem to work fine. If you 
haven't already, check the screen resistors for the finals as well.

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