hw-101 troubles-hooting

[Multi-Volti Devices]

R6 and R7 were routinely replaced with a higher wattage resistor as soon
as one was put on the bench at Heath.

I would measure the voltage drop across R6 or R7 to get an idea what
current the tubes are running at...I don't know off the top of my head
what the current is, and actually I'm more concerned about what the
current is thru the resistor (same thing, but different interest on my
part). If the resistor is dissipating more than 1 watt I would look for
possible causes of excessive current thru the tube....improper bias for
starters.

You have a 1x3 call, (well, cc: to the list also) so you're probably
comfortable working with hv... I won't patronize you by telling you to
keep all body parts away from circuit under test.

While you're at it, check the audio output stage plate resistor (22k?),
same tendency to self-immolate, I think due to the 20 uF 350 V
electrolytic that overcooks and (we thought) draws excessive leakage
current thru that circuit. I never measured the leakage current, but
that was the conventional wisdom at Heath Service (B.H.) Use a 22 uF
350-450 V (because you can buy them easily). I think we used a 1W
replacement

I haven't looked at an HW-101 schematic in ..wow, 10 years? My rusty
memory thinks there might be another 20 uF 350 V 'lytic cap in the
carrier
oscillator plate bypass/decoupling circuit...it that's where R6, R7 is,
get it replaced.

Let me know if I've corrupted reality on the HW-101 schematic...is there
a 20 uF cap tied to the 'low' side of R6 or R7?

Murray


paul vickberg wrote:
>
> Hello to the group:
>
> I have a problem with an HW-101 which is driving me crazy. It started
> out with decreasing  drive  each time I transmitted until there was
> finally no drive or output. Upon checking, I found that R6 and R7 (33k
> ohms in the plates of V16) were increased in value to a couple of megs.
> I bridged these two resistors with 33 k's and got back my drive, but I
> also noticed that they were getting hot and would soon go the same way
> as the other two. After further checking, I found out that the resistors
>
> were getting hot in recieve mode: transmitting wasn't necessary. Upon
> further checking I discovered the following. Remember, this is all in
> recieve mode:
>
> When the mode switch is in LSB , there is no plate voltage on pin 1 and
> R7 heats up.When the mode switch is in USB or CW, there is no plate
> voltage on pin 6 and R6 heats up. To further complicate this, I can load
>
> up the transmitter to full power out on all bands, but if I continue for
>
> long, the resistors (depending on where the mode switch is set) will
> open up I substituted the 33 k's with two watters in the hopes that
> whatever was causing the problem would smoke and I could find it but so
> far nothing. This is really bugging me. Does anyone have any
> suggestions?.
>
> Paul, W0CPW
>
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