The little general identified in 4 valve home constructed radio in my last post.
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Location: Kanahooka, NSW
Member since 18 November 2016
Member #: 2012
Postcount: 712
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I have rebuilt this to a 1947 circuit, except I used an 80 rectifier instead of the 6X5, the chassis originally had an 80 fitted so I retained it, being a good old valve.
However it is as dead as a door nail. This is what I wanted to use the 6B8G in place of the dud 6G8G in.
If I remove the top cap grid connection off the 6B8G I can get a healthy audio buzz from the speaker, so at least the audio end is healthy. I think I may have miss interpreted the pin connections on the 6J8G front end. I find the way it is drawn on the circuit confusing. The filament and cathode connections are obvious. The top cap G1 of hexode. I need to have a good look at my other connections. At least no expensive brown smells so all is not lost.
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Location: Kanahooka, NSW
Member since 18 November 2016
Member #: 2012
Postcount: 712
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Hi again from Jim.
In regards to the Little General.
Can anyone tell me what the dc resistance measured with a digital multimeter should be approximately for the secondary winding of the Aerial coil. I measure 3,7 ohms. I would have expected it to have been much higher.
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Location: Toongabbie, NSW
Member since 19 November 2015
Member #: 1828
Postcount: 1313
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Hi JimB, aerial, oscillator coils have 100 to 200 turns of solid or litz wire on the tuned secondary and measure low ohms, say under 10.
3.7 ohm sounds ok to me.
IF trannys have more turns say 500 and can measure typically 10 to 20 ohms.
These are the figures I measure when i'm checking or winding coils.
Fred.
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Location: Kanahooka, NSW
Member since 18 November 2016
Member #: 2012
Postcount: 712
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Thanks Fred.
It is now up and running quite well. Had a nasty front end problem and I thought I had made a wiring mistake. It was dead, checked with the cro and the oscillator was running could not get any response from the I. F. section. I suspected the Aerial coil and could not see anything obvious when I looked inside. Refitted it and it all worked after that. I basically used the 1947 circuit except I retained the 80 rectifier. The speaker cone is a bit stiff because large sections were missing and I used coffee filter paper glued in, it works ok at normal listening levels. The only other slight problem is at full volume on strong signal it motorboats, however I do not use it at these settings. I did wonder if I should have a shield on the 6J8G osc/mixer front end. I did shield the 6G8G valve.
In the case of this radio, could not find any noticeable difference between using a 6B8G or the correct 6G8G which at the time I did not have. I bought one from HRSA valve bank.
My next task is the cabinet, it is never going to look spectacular it is made from bits of ply tacked together however it will be in keeping with it's home made origin's.
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Location: Toongabbie, NSW
Member since 19 November 2015
Member #: 1828
Postcount: 1313
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Hi Jim, the motor boating is probably a lack of by passing on a HT line, maybe the electro's or the paper cap is low value/leaky/open circuit.
If you get to it just tack another electro or 0.5 μF across the HT line feeding the valves and see if that makes a difference.
Fred.
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Location: Kanahooka, NSW
Member since 18 November 2016
Member #: 2012
Postcount: 712
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Hi Fred.
Thank you for your reply. All the components are now new however I will have a play when I can.
Very great full Brad has managed to get the forum up and running again.
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Location: Kanahooka, NSW
Member since 18 November 2016
Member #: 2012
Postcount: 712
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Hi Fred.
I tried a few caps there was some improvement I settled on a 1 mfd on the ht line.
It is now completed and riding the air waves once more after being dormant for maybe decades.
Once Brad has the email sorted I will add a couple of photos. Still no oil painting but in keeping with the home made theme.
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Location: Toongabbie, NSW
Member since 19 November 2015
Member #: 1828
Postcount: 1313
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Hi Jim, looks like its all good enough electronically.
Make it the same with the cabinet, just make it secure with a bit of glue on any wobbly bit and put a clear coat over the lot?
Yes photos will be nice.
Fred.
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Location: Kanahooka, NSW
Member since 18 November 2016
Member #: 2012
Postcount: 712
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Thanks Fred.
I know I could have done better with the cabinet, I used what I had which is what would have probably occurred in the 1940's. I stained it rosewood however I used brown cloth for the speaker and brown knobs because that is what I had and it will be sitting on a shelf in the garage. It would have looked better with a red cloth and matching knobs. I use an AM transmitter to feed my radios because the local stations are either horse racing or ethnic. I have a generous down load capacity on NBN which I never use up so I feed the AM transmitter with an Telstra T Hub which was a tablet Telstra gave away to customers in the end because they were not very good and I use a radio app. On it via the T Hub into the transmitter. Not sure if we can now download our pictures.
I will give it a try.
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