Old AM/FM receiver, amplifier problem
David Lo
I recently got an old Hitachi AM/FM receiver with amplifier, and when I
first turn it on, I hear a lot of static from the speakers. After a
while (1 minute or so), the front panel with the AM/FM frequency "bar"
will light up (a blue light). After it light up, then the static is
gone. Seems like the units need to warm up or something... (strange).
The receifier uses vacuum tubes inside, so it's probably a really old
unit.
Is that normal behavior (light up, then static gone), or is there
something wrong with it?
Thanks.
David
David Lo
This problem happens regardless of which mode (AM, FM or line-in) I turn
the receiver to.
And, it's a Hitachi SR-302.
Lareman
Larry
"David Lo" <dav...@bigfoot.com> wrote in message
news:3AA0A689...@bigfoot.com...
Thomas Abell
socket, it can be cleaned. You'll need to sub the tubes however, until you
find the one that's causing your problem.
"David Lo" <dav...@bigfoot.com> wrote in message
news:3AA0A15F...@bigfoot.com...
Asimov
--- on the topic of "Old AM/FM receiver, amplifier problem"
Most often sockets and tube pins get oxidized over time. Cleaning these
will often clear up most static when warming up problems. However, tubes
can develop intermittant internal connections. Once the amp is warmed up
use a plastic toothbrush handle to rap each tube lightly in turn until
you find the culprit. There's a lot more that can cause static, dry
filter capacitors and leaky interstage coupling capacitors will too, but
dirty sockets is a good start. .
DL> I recently got an old Hitachi AM/FM receiver with amplifier, and when
DL> I first turn it on, I hear a lot of static from the speakers. After a
DL> while (1 minute or so), the front panel with the AM/FM frequency "bar"
DL> will light up (a blue light). After it light up, then the static is
DL> gone. Seems like the units need to warm up or something...
DL> (strange).
DL> The receifier uses vacuum tubes inside, so it's probably a really old
DL> unit.
DL> Is that normal behavior (light up, then static gone), or is there
DL> something wrong with it?
... I remember the 6SN7...
Sofie
Vacuum tubes do require a time to "warm up" before there are operational.
Inside the tube is a filament that glows, that heats up a cathode element,
and that makes the tube work........so, as you can see, it is not "strange"
but rather the way things are when using vacuum tubes. Of course,
additional static, noise, etc can be caused by leaky or old paper capacitors
and electrolytics............age and heat are the enemy.
--
Best Regards,
Dan Sofie
Electronics Supply & Repair
==============================================
David Lo <dav...@bigfoot.com> wrote in message
news:3AA0A15F...@bigfoot.com...
Philip Nasadowski
shouldn't make any noise out the speakers until it's warmed up, and
unless you've got a lousey reciever, it shouldn't have much (if any)
noticeable "background" noise. I have a Fisher X-202 which you can't
tell it's on unless you stick your ear up to the speaker...
From your description, it sounds like the power amp section is a good
place to start looking. Try tapping gently on the tubes, and also look
at the voltages underneith. Do be aware that there are *high* (300+V)
voltages at pretty high currents going around in there. Also, if the
set has no power transformer, it's line conbected, so you'll *need* an
isolation transformer. If you're not used to servicing tube equipment,
a schematic with voltages is essentile, as the voltages are nothing like
solid state stuff. Also look for light blue flashes and haze (though a
dim, DEEP purple-violet is ok), and the dreaded glowing red plates,
which can spell doom for the output transformers. If there's a bias
adjustment, check the output tube bias and voltages to make sure they're
in spec - you'll need service info for that, unless it's listed on an
inside cover.
If it was a decently made unit, it should be capeable of surprsingly
good performance - BTW, what tubes are used in there?
--
To email me, remove the XXXX from my address, and replace it with "mail"
David Lo
upon close inspection, it doesn't have any vacuum tube inside (the person I
got it from told me otherwise).
Anybody know anything about this specific model? (as below, a Hitachi
SR-302).
hmm.... could be old components that are starting to fail.
David
Asimov
--- on the topic of "Re: Old AM/FM receiver (Hitachi SR-302), amplifier problem"
Aha!!!
Another intermittant 2SC828 from that bad lot they made in the mid 70's!
DL> Actually,
DL> upon close inspection, it doesn't have any vacuum tube inside (the
DL> person I got it from told me otherwise).
DL> Anybody know anything about this specific model? (as below, a Hitachi
DL> SR-302).
DL> hmm.... could be old components that are starting to fail.
... When I was your age, we carved transistors out of wood.
David Lo
Are you sure this unit has a 2SC828 inside? I can't seem to locate it.
David
Asimov
--- on the topic of "Re: Old AM/FM receiver (Hitachi SR-302), amplifier
problem"
The "bad lot of intermittant 2SC828's from the 70's" is a bit of a joke.
But *if* there is one in your radio it would be labeled simply C828
without the 2S prefix.
Notice that a dry electrolytic coupling capacitor can also make static
noises when 1st powering up.
DL> Hmm...
DL> Are you sure this unit has a 2SC828 inside? I can't seem to locate
DL> it.
DL> David
DL> Asimov wrote:
> "David Lo" wrote to "All" (07 Mar 01 02:41:37)
> --- on the topic of "Re: Old AM/FM receiver (Hitachi SR-302), amplifier
DL> problem" >
> Aha!!!
> Another intermittant 2SC828 from that bad lot they made in the mid 70's!
>
> DL> Actually,
>
> DL> upon close inspection, it doesn't have any vacuum tube inside (the
> DL> person I got it from told me otherwise).
>
> DL> Anybody know anything about this specific model? (as below, a Hitachi
> DL> SR-302).
>
> DL> hmm.... could be old components that are starting to fail.
... A stereo system is the altar to the god of music.
wozz
Maybe this is of some help,
I once owned the Model SR 502, the next model up from the '302'
and after many years of good service developed static across all inputs
except tape monitor, which bypassed the input selctor switch, and i also had
another tech check it out and he also suspected a fault selector switch, but
could not get
a replacement due to the age of the unit.
Try running some audio into the tape mon input and listen for any improvement.
regards
Warren...
David Lo
I don't think that's my case, since the static develop during start-up at any
inputs (I tried them all).
And, it goes away after a while (20 seconds now, it was about 1 minutes before).
And, I think the problem occurs in the power supply section, since the static is
linked to the front panel lighting. (When I hear static, the lighting looks like
it's trying to start-up, like a fluorescent light, but, of course it's a bulb, and
when the front panel finally lights up, the static goes away (after the 20 seconds
of waiting, at any speaker setting, and any input setting).
David
Lew
lights. Do the pilot lights thread into their sockets? It may be as simple as
tightening the bulbs in their sockets. Turn the amp on in a darkened room and
look for arcing connections in the power supply area etc. Give the PCB a good
visual going over.
Lew
Lew