Re: Vintage Radio and Phonograph cutter schematic
 

Thanks a million for this explanation. I did not know these at all. :thumbsup:

Re: Vintage Radio and Phonograph cutter schematic
 

Hello again !

I did go through again all of the components, capacitors and again a full on voltage readings.

I also put one new old stock 6v6GT in.

Sadly there is still a massive mains hum in there and some blue light appears on the 6v6 tube. Attached some pictures of all the tubes in place.

...anything I tap on this player, the side the top, all the tubes if I tap them I can hear it in the speaker and in the headphone. Just like a massive microphonic effect.. If I switch on the motor, I can hear the motor noise also in the headphone and the speaker too.

What could be wrong here? this hum is really loud and disturbing. ???

and now as soon as I switch it on, a fast popping sound is heard in a fast repetitive pattern and slowing down ...on the top of that massive hum :(.... and now is squealing like crazy when I turn the volume up !

Re: Vintage Radio and Phonograph cutter schematic
 

Is the loud hum there when the volume controls are turned to minimum ?

Lawrence.

Re: Vintage Radio and Phonograph cutter schematic
 

Both... popping sound and hum is there when the volume control is down, but when I start to turn up the hum gets even higher and louder and then a massive squealing starts...

I have several 6v6s and tried a few, all are having the same effect


I do not have another 6SC7 I am unsure on that

the 6SJ7s i have one extra so started swap them one by one, no change and I have none of the rest of the 6SA or 6SF tubes..

I was reading the robribinette site for trouble shooting but with these sounds, and those repeating popping (is that the osculation?) and squealing can be anything...

I am also really suspicious of the on/off switch pot.. the pot responds weirdly...

thinking of where should I start...

cleaning the tube sockets
check again the soldering? poking around with a chopstick?
ground connections... on the chassis counted 5 ground points in total
getting better filter caps?


Thanks Lawrence

Re: Vintage Radio and Phonograph cutter schematic
 

For instability and hum I would check the HT filter capacitor (electrolytic)

If no joy then short the control grids of V5 to chassis, that's pin 3 and 4 of the 6SC7 to chassis and note any difference.

Lawrence.

Re: Vintage Radio and Phonograph cutter schematic
 

Flipped the chassis up and started to poke around. Before that checked in the dark, no spark I saw.

Then just as you said Lawrence, the second filter electrolytic cap which +ve has 3 leads connected to..now as soon as started to move thos leads or poked on that cap it is definitely something there.

For some reason now up side down it does not squealing. But the hum is there.

I only have a very small size new electrolytic cap.. would be that OK to try? It is not a massive can capacitor but rated 22uF 450V and designed for low profile PSUs (modern ones) ?

If this is OK will try this first then shorting the pins on the 6SC7 or shall i just do it anyway? Thanks a lot Lawrence.

Re: Vintage Radio and Phonograph cutter schematic
 

I did tie the pin 3 and 4 together to chassis. Unfortunately no sound is coming through the speaker or no sound on the external speaker plug either.

Hum is reduced and no any other issues but the sound has gone...

Re: Vintage Radio and Phonograph cutter schematic
 

It will kill the sound, that's part of the test, if shorting those grids to chassis has got rid of the loud hum you had with the volume controls turned down then remove the short from one grid and see if the hum gets loud again (volume controls still turned down) if it doesn't then remove the short from the other grid, that should tell you which grid the loud hum is coming in on, let us know which grid it is, ie: pin 3 or pin 4.

Lawrence

Re: Vintage Radio and Phonograph cutter schematic
 

Aaaa okay.

With the volume pot down, now there is not much hum like before (when the other capacitor was in place) I did change the 8B cap.

If I turn up slightly the volume, then I can hear the hum and with the volume control the hum increasing and decreasing.

If I ground pin 4 the hum has gone. If I remove the short hum comes back.

If I ground pin 3 does not seem to change anything at all. Same results grounded or not grounded.

Thanks for helping me on this.

Re: Vintage Radio and Phonograph cutter schematic
 

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.

Re: Vintage Radio and Phonograph cutter schematic
 

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.

Re: Vintage Radio and Phonograph cutter schematic
 

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....

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.

Re: Vintage Radio and Phonograph cutter schematic
 

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.