Jim,
Great leads. Thank you. It sounds to the ear like the problem may be exactly
what you are suggesting. I’ve been sorting out a few issues with the rig and
only two remain – the whine, and my RIT is way off. I pulled DR7 last night
for access to the RIT alignment pot, and while I don’t yet have an extender
set, I took a few blind shots at getting the RIT at least into a useable range.
No luck. Seems to be out of range of the pot, suggesting a broader alignment
issue. I rarely use RIT, so this problem can be addressed later. The whine
is more of an issue. I really like the radio and have been enjoying 60 mtr.
QSO’s with my brother, Guy, in Memphis, WD5ACP; I’m near New Orleans. My
brother and I have been hamming since the late 70’s and my recent Drake
adventures have motivated him. He’s now awaiting receipt of a TR-7. Once
these minor issues are dealt with my rig will be 100%. The only real problem I
had
with the rig was transmitter instability, which cleared with a cleaning of the
ALC pot and a pot on the pre-driver board. I’ve been comparing the receive
performance to a Ten Tec Pegasus, known to have a great receiver. The TR7
holds its own. After this I’m moving on to get my TR4CW into top shape.
Thanks again.
________________________________
From: Jim Shorney <jshor...@inebraska.com>
To: "drakelist@zerobeat.net" <drakelist@zerobeat.net>
Sent: Monday, January 20, 2014 10:30 PM
Subject: Re: [Drakelist] TR7 high pitched wine in audio
The first thing I would look at is the filter cap on the DC-DC converter
("Power Supply") board in the front right corner of the radio. This capacitor
is IMO an "always replace" for any TR-7. Strange things can happen when it
starts to fail, and on a rig that old it most likely is. Replace with a part
specified for 105C temperature if possible.
There was also an engineering change to add a 470uF axial cap to the +10v rail.
This was added by Drake service to any radio that did not have it. Look for it
on the bottom side of the chassis, between pins 10 (+10V) and pin 3 (ground) of
the DC-DC coverter board connector.
73
-Jim
NU0C
On Mon, 20 Jan 2014 20:04:55 -0800 (PST), Leon Zebrick wrote:
>
>Picked up an early Sr# TR7. It's fine except for a high pitched noise in the
>audio. It's continuous and not affected by volume control. Not on transmit
>signal. It's not loud, but noticeable and annoying in headphones. Sounds
>like one of the oscillators is getting into the audio circuit. Any decoupling
>mods or improvements related to this? Sr no. Is in the 600 range. Wonder if
>this is something Drake eventually improved on. Or do I have a problem?
>Thanks.
--
“There’s something out of place – let’s go and poke it with a stick.” – The
Doctor, "Amy’s Choice"
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