UK Vintage Radio Repair and Restoration Discussion Forum

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-   -   Vintage Radio and Phonograph cutter schematic (https://www.vintage-radio.net/forum/showthread.php?t=159989)

Levente 9th Nov 2019 8:21 pm

Re: Vintage Radio and Phonograph cutter schematic
 
Quote:

Originally Posted by ms660 (Post 1190291)
Just looking back at Post#41, only slight hum was reported, I would check everything done since then and also determine whether the hum is 50Hz (mains, heaters etc) or 100Hz (HT ripple)

Lawrence.

I believe that the hum is 50 cycle. Will re check again, might change the first 8A electrolytic cap too and will test this in another room further away from any other appliances.

Levente 10th Nov 2019 10:38 am

Re: Vintage Radio and Phonograph cutter schematic
 
2 Attachment(s)
Quote:

Originally Posted by Levente (Post 1190295)
Quote:

Originally Posted by ms660 (Post 1190291)
Just looking back at Post#41, only slight hum was reported, I would check everything done since then and also determine whether the hum is 50Hz (mains, heaters etc) or 100Hz (HT ripple)

Lawrence.

I believe that the hum is 50 cycle. Will re check again, might change the first 8A electrolytic cap too and will test this in another room further away from any other appliances.

CORRECTION:

I think is 100Hz hum. Now I did change the 8A cap also. Now the filter and reservoir cap is the same. Made a small rail for that as It was easier to tie several leads to the rain instead of directly to the cap.

Now, volume down no hum. Volume up massive 100Hz hum.

I think these capacitors I have are not suitable for this.

Shame I only have 275VDC and 350VDC rated one and not 450V.

Would need to order a proper filter and reservoir cap....

ms660 10th Nov 2019 1:05 pm

Re: Vintage Radio and Phonograph cutter schematic
 
No hum with the volume control turned down and massive hum with volume turned up suggests 50Hz hum, sometimes caused by a screened lead that has lost it's ground connection or a control grid that's floating, ie: no or extremely high resistance to ground, other causes could be heater/cathode leakage in a valve.

Hum problems can be difficult to diagnose via the internet.....Is the hum level the same on Radio and Pickup?

Lawrence.

Levente 10th Nov 2019 2:11 pm

Re: Vintage Radio and Phonograph cutter schematic
 
Quote:

Originally Posted by ms660 (Post 1190454)
No hum with the volume control turned down and massive hum with volume turned up suggests 50Hz hum, sometimes caused by a screened lead that has lost it's ground connection or a control grid that's floating, ie: no or extremely high resistance to ground, other causes could be heater/cathode leakage in a valve.

Hum problems can be difficult to diagnose via the internet.....Is the hum level the same on Radio and Pickup?

Lawrence.

Thanks Lawrence. I just googled a 100Hz hum and compared it and it is the same by the sound. Now I disconnected the two electrolytic 8A and 8B. Will order two new can ones.

Until that will arrive can not do anything further sadly. I thank you so much for your help Lawrence. I am learning so much from you here seriously, I owe you one.

Have a great weekend and will post here again when the cap's are her.

Ordering from hificollective UK proper filter cap's.

and forgot to answer your question, hum level is the same except the external speaker position on the switch.


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