Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on July 15, 2014, 02:53:03 pm

Title: Shielding a cap
Post by: kagliostro on July 15, 2014, 02:53:03 pm

Old remedy to noise capture  :grin:

Look to the wrapped capacitor

(https://dl.dropboxusercontent.com/u/15423022/2014-07-14%2007.49.48%201.jpg)


K

Title: Re: Shielding a cap
Post by: HotBluePlates on July 15, 2014, 03:20:39 pm

Usually not needed, especially if you orient the outside foil towards the lowest impedance to ground (because then it acts as its own shield).

The rules sometimes change with radio, so if this is a radio chassis, all bets are off.

Title: Re: Shielding a cap
Post by: kagliostro on July 15, 2014, 04:01:21 pm

Ciao HotBluePlates

No, no radio, old unknown guitar amp

(https://dl.dropboxusercontent.com/u/15423022/2014-07-14%2007.44.47%201.jpg)

(https://dl.dropboxusercontent.com/u/15423022/2014-07-14%2007.49.17%201.jpg)

Quote

Usually not needed, especially if you orient the outside foil towards the lowest impedance to ground

yes, I agree, but want to put in comparison with such a note of folklore  :icon_biggrin:


Franco

Title: Re: Shielding a cap
Post by: shooter on July 15, 2014, 05:41:21 pm

I found the same setup but on a resistor, but it was from a radio chassis, I figured it was either noise or a hand-wound choke in parallel with the resistor.  I like looking back in time, so much more artisan than a sterile pcb
 

Title: Re: Shielding a cap
Post by: kagliostro on July 16, 2014, 01:12:48 am

That was an inductor for sure

I've seen such a thing also in audio amp

as you say, in RF, it was common to wrap a small number of turn of wire around a non inductive resistor to obtain an inductor

(http://www.amplifiers-with-valves.nl/images/big/image017.jpg)

(http://www.amplifiers-with-valves.nl/images/big/image020.png)

K

Title: Re: Shielding a cap
Post by: jazbo8 on July 16, 2014, 01:32:53 am

Quote from: kagliostro on July 15, 2014, 04:01:21 pm

Ciao HotBluePlates

No, no radio, old unknown guitar amp
Franco

Yup, the origin of this amp (posted over at TAG) is driving me crazy  :help: , who made it? The tubes selection is a bit odd as well - 2 EF86s in the preamp (probably one per channel)?! But it's definitely not a "Tweed"...

Title: Re: Shielding a cap
Post by: kagliostro on July 16, 2014, 06:14:32 am

Quote

Yup, the origin of this amp (posted over at TAG) is driving me crazy   , who made it?

for that reason I like very much TIMBO's idea


http://el34world.com/Forum/index.php?topic=16986.msg169082#msg169082 (http://el34world.com/Forum/index.php?topic=16986.msg169082#msg169082)


K

Title: Re: Shielding a cap
Post by: Ed_Chambley on July 16, 2014, 08:54:36 am

Been looking all over for it as well.  I have encyclopedias of amp books and origins.  I have no idea as I have found nothing.  I am beginning to wonder if it was a build of some kind.  I noticed the speakers are very low in the cabinet, not really like a production amp would be IMO.


And yes, shielding can be done in this way.  I restored an old Flot-a-Tone amp with a crazy tremolo.  Sounded awful, but it had a .0022 cap wrapped.  Why, I do not know.  I replaced it and wrapped the new one.  Probably did not need it, but I am used to it.  I love my old radios and it is a great way to get noise down.

Title: Re: Shielding a cap
Post by: terminalgs on July 16, 2014, 11:22:25 am

Quote from: jazbo8 on July 16, 2014, 01:32:53 am

Quote from: kagliostro on July 15, 2014, 04:01:21 pm

Ciao HotBluePlates

No, no radio, old unknown guitar amp
Franco

Yup, the origin of this amp (posted over at TAG) is driving me crazy  :help: , who made it?

I see a pinex cap.  That's euro (West Germany?)... Rules out North America and Asia?

Title: Re: Shielding a cap
Post by: tubenit on July 16, 2014, 11:44:21 am

Thanks for sharing that!  I think that is an interesting idea and perhaps could be useful in some situations where orienting a cap or location of a cap is a challenge?

With respect, Tubenit