[Hammarlund] HQ-110 hum modulation...

[Al Parker]

Hi Ken,
    This info is from a letter written by Frank Lesster, it's in the BAMA
files.  I hope it's some help.

HUM
from Svcs Notes -
=====
Excessive hum in the speaker is usually the result of excessively high
heater to cathode leakage on the part of the noise limiter tube type 6AL5
or the 6AV6 tube employed as the first audio and delayed AVC clamp.  If the
hum is only noticeable when the receiver is in the AM position, the chances
are that this is due to a bad 6BV8.  If the level of the hum varies as the
audio volume control is advanced, this more or less indicates that the hum
is due to a tube ahead of the audio gain control, such as the 6AL5 or the
6BV8.  If the hum level remains constant regardless of the setting of the
audio control, this means that the trouble is after or behind the audio
control and the 6AV6 or 6AQ5 output tube should be suspected.
THE HAMMARLUND MFG. CO., INC.
Frank I. Lester, W2AMJ
Sales Manager
=====
73,
Al, W8UT
New Bern, NC
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And remember; "-They don�t make tubes nowadays like they used to..."

----- Original Message -----
> I was given a nice HQ-110-C a while back. Even the clock works. I
> cleaned and aligned it. I was amazed at both the sensitivity (even
> on 6 meters) and the lack of frequency re-setability on 20 meters
> and above.
> However, when in the CW mode, with the BFO on, the note is hum-
> modulated. No hum with no signal. I have carefully checked the
> tubes and replaced those which seemed weak, to no avail.