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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 26th Jul 2019, 5:19 pm   #1
Avid_Nerdlinger
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Default ITT CCR300 Cassette hum

Got a ITT CCR300 Cassette for £28.44 (!) a few weeks ago off ebay - I wanted a radio alarm clock with an uncrap LW radio and this is the closest I could find on ebay at that time. It worked OK except for a barely audible but annoying mains hum. The hum was only there when the audio came on using sleep or alarm, if you then switched the Auto/Off/On to On the hum went away. I tried a few things, replaced a few electrolytics, then focussed on R167, R168 and C181 (R168 goes on to the input of the audio amplifier). First I replaced the 10uF cap C181, no change, then I tried lifting one leg of R167 - hum gone. Not sure what that hum path was there for because everything else still works.

I don't think I need to think any further on this now but I can't see anything other than a design fault, I wonder how many were sold and are still being used if that is so. Anyway might be of use to somebody.
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Old 29th Jul 2019, 9:41 pm   #2
kevinaston1
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Default Re: ITT CCR300 Cassette hum

Could the 50Hz have been used on the alarm?

I seem to remember a lot of early electronic alarm clocks had a lot of 50Hz in their alarm beep tone.


Kevin
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Old 30th Jul 2019, 8:01 am   #3
crackle
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Default Re: ITT CCR300 Cassette hum

I just checked my one of this model and the same faint hum.
Does your snooze button still turn the radio off again when on auto.

Both my ITT SCR200 stereo alarm clock radios have no hum at all.
Later I will try and compare the circuits.

Mike
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Old 31st Jul 2019, 10:05 am   #4
Avid_Nerdlinger
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Default Re: ITT CCR300 Cassette hum

Quote:
Originally Posted by kevinaston1 View Post
Could the 50Hz have been used on the alarm?
Kevin
Maybe. The alarm is higher pitched and goes beep-beep, it is a bit weak - distorted and quiet, I never tested it before my bodge mod. That would explain why that path exists better than sharing an electrolytic for a LP filter.
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Old 31st Jul 2019, 10:13 am   #5
Avid_Nerdlinger
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Default Re: ITT CCR300 Cassette hum

Quote:
Originally Posted by crackle View Post
I just checked my one of this model and the same faint hum.

- Interesting...

Does your snooze button still turn the radio off again when on auto.
Mike
Yes. The Sellotape and foam rubber parts of that switch have deteriorated so now it seems to operate like an electrostatic switch. I had tried disconnecting this at the PSU/LED PCB but the hum persisted.

Interesting that yours has the same problem, maybe it is a design fault, likely more of a case of being prone to this when multiple components drift in value with age.
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