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 GEC BC 7445 turntable issues.
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 Return to top of page · Post #: 1 · Written at 7:36:43 AM on 15 July 2018.
Muzzery's Gravatar
 Location: Maleny, QLD
 Member since 28 February 2018
 Member #: 2218
 Postcount: 88

Hi all.
I have just revived this nice little unit. However, it has had its turntable swapped out for a “laboratory series AT6” turntable. The pickup was not connected to the radio circuit when I received the unit. This is a stereo turntable, in a single speaker unit.
I connected both left and right into the pickup together. It works, but with a very low volume., using a new stylus/ needle head, from my Kriesler multisonic. Same turntable.
1. Should I try to find the correct turntable? It should be a Garrard RC110 .
2. Should I leave it as is, Can it be done with left/right joined into one mono channel?
Cheers
Murray


 
 Return to top of page · Post #: 2 · Written at 10:26:15 AM on 15 July 2018.
Gandhn's Gravatar
 Location: Windella, NSW
 Member since 5 November 2010
 Member #: 770
 Postcount: 319

I encountered a similar effect with a stereo cartridge into a mono radio and realised that the phase of each channel were cancelling out. I reversed the connections on one channel and all was good.
I did put a resistor (10K?) in series with each channel so that there was some isolation, not simply tying the 2 cartridge outputs together.
Harold


 
 Return to top of page · Post #: 3 · Written at 9:49:11 PM on 16 July 2018.
Muzzery's Gravatar
 Location: Maleny, QLD
 Member since 28 February 2018
 Member #: 2218
 Postcount: 88

Thanks Harold.
I tried this tonight, with no improvement. I think I probably need to go through the turntable with a fine tooth comb. I have to say that isn’t something I cherish the thought of..
There is some serious feedback style “hum” whenever my hand goes within about 4 inches of the cartridge end. I’ve cleaned any contacts, including the audio lockout device up underneath.
Murray


 
 Return to top of page · Post #: 4 · Written at 10:42:27 PM on 17 July 2018.
Muzzery's Gravatar
 Location: Maleny, QLD
 Member since 28 February 2018
 Member #: 2218
 Postcount: 88

Sorted! There’s a cutout device underneath that isolates all the audio signal when the auto changer works. (I think) Someone had put those tiny wires from the tone arm all in the wrong places. That must be marcc’s monkeys 😁 I don’t actually know how it got any signal at all, as nothing was connected to the negative side. Those little wires are terrible to solder!
She is singing like a canary now!


 
 Return to top of page · Post #: 5 · Written at 2:07:43 AM on 18 July 2018.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5262

Those little wires are terrible to solder!

Yep, but worse is trying to solder the wires in flexible telephone cables. Easier to nail jelly to a wall.

She is singing like a canary now!

Good job. Patient and logical signal tracing usually pays dividends.


 
 Return to top of page · Post #: 6 · Written at 9:30:03 AM on 21 July 2018.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 3698

Something worth noting: Haemostats come in a few different sizes and are "Magic'. They can act as a heat sink and in cases like here, hold wires of varying sizes, preventing big fingers getting burnt whilst leaving room for the soldering iron tip. They can also be used as an aid to getting hot components out & getting new ones in.

I use these pretty much every time I repair a radio. Two can get parts in and out of some really tight spaces. They also clamp. Most of mine came by accident... got small pair this time.


 
 Return to top of page · Post #: 7 · Written at 6:33:58 AM on 23 July 2018.
Muzzery's Gravatar
 Location: Maleny, QLD
 Member since 28 February 2018
 Member #: 2218
 Postcount: 88

Yes, I agree. I have a handful of haemostats as well, I found them especially useful as a heat sink.
Murray


 
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