[Boatanchors] Heath audio question

[Bill Henderson]

Let's see...

You've checked the pot - how about the solder connections?

 - Bill H. / va3hwa



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08/09/19,
01:03:37 PM

On Fri, Aug 9, 2019 at 11:24 AM RAY FRIESS <rayfrijr at msn.com> wrote:

> Working on an SB300 and I suspect I have a bad tube, but I'm still
> puzzled.  I'm still digging through the junk box to find a replacement to
> verify it one way or another.   V10 is the first and second audio amp with
> the volume control feeding audio to the grid of the first audio section of
> the 6HF8.  The tube also contains the second audio or audio output
> section.  From there it goes to the speaker and headphone jacks.
> First, I notice the receiver seems more sensitive to speaker and headphone
> impedances than most other receivers I've had.  Specs call for an 8 ohm
> speaker, which I use with the SB600 speaker.  However, when I plug in a 16
> ohm speaker in the headphone jack , I notice a decrease of 50% or more of
> audio availability and have to turn the volume control clear up and even
> then it's not real loud.   I've never noticed such a thing with other
> receivers.  I know we should match the speaker impedance with the audio
> output impedance, but I've never noticed such a dramatic cut when there has
> been a mismatch.
>
> SECONDLY and more important, the volume control at minimum volume is not
> cutting off all volume.  The volume level does go down, but remains at
> about 25% (even with the correct speaker plugged in.)
> So, I'm wondering if maybe the 6HF8 somehow is taking even the lowest
> level audio going into it and somehow still jacking it up?  At the lowest
> setting, the tube should not have enough, if any, signal to amplify, but
> somehow some signal is getting past the volume control and the tube is
> amplifying it.  At minimum, incoming audio should be going to ground
> through the pot.
> YES, I have checked the pot ... it doesnt appear to be the problem.  It's
> not even scratchy, indicating a dirty pot.
> Ray
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