50 Ohm 5w 10 turn wirewound resistors at a great price

[johnsonad]

Just passing this sale along. Jameco has 50 Ohm 5w 10 turn wirewound resistors on sale for $29 each. This is a great price if you want a 10 turn hum pot. No affiliation of course, just passing on the sale. The part number is 2200188

[wylymon]

I wonder if these hum pots would be a drop in replacement for the Paramounts?

[johnsonad]

Not sure.  PJ worked out the current configuration because 10 Ohm pots were available and cheap.  I picked up three pair of them, enough for a few future projects. Of note, these are 1960's vintage parts and very well constructed.  Also, the price dropped by 25% since I posted this.....

[wylymon]

Aaron....Thanks for the response. If my memory is correct I believe the pots in the Paramount are 10 ohm and 10 watt. Not sure this would would work in the Paramount......Perhaps someone from Bottlehead could respond

[fullheadofnothing]

The stock pot has a body diameter of approximately 24mm. The pot mentioned in this thread has a body diameter of just over 46mm. If you mount it in the existing hole, it will hit the terminal strip and the plate choke (and you'll need a new indexing pin hole, as this one is further from the shaft). If you make new holes to avoid those obstacles, you'll hit the power switch.

Also, FWIW, the stock pot is 10Ω 5W, not 10Ω 10W as stated earlier in the thread.

[Grainger49]

The pot is flanked by 22 Ohm 5W resistors.  The complete circuit is 54 Ohms.  So if you replace the pot and both resistors with a 50 Ohm 5W 10 turn pot you still have much higher resolution adjusting the hum circuit.

[wylymon]

Grainger .....how did you you get your pots into the Paramount...Thankyou.

[Grainger49]

I used a smaller pot than the one pictured for that item number.  I have a pot that size but it wouldn't fit in the Paramour. 

This is the size I used, but not this value:

http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2111880_-1

[Doc B.]

2x22 ohm resistors +1x10 ohm adjustable linear means that there is an adjustment ratio of one 270 degree turn for 10 ohms of adjustment. 1 50 ohm ten turn linear pot works out to 5 ohms per 360 degree turn, or 3.75 ohms per 270 degrees of adjustment. So it's roughly three times the resolution.

[wylymon]

Grainger,

Spent some time last night looking for 5 watt, 10 ohm linear 10 turn pots that would fit into the Paramount. Seems all I could find were the big ones which don't fit the plate. Any suggestions for a source of smaller pots that fit?
Best Regards, James

[Paul Joppa]

You do not need 5 watt dissipation - I chose the pot because it was wirewound, and hence likely to not make noise with current running through it. Five volts across 50 ohms is 0.5 watts; if you use 10 ohms with two series 22 ohm resistors (as in the stock Paramount) the pot dissipates 0.1 watt. I would want a pot rated for 5 times the actual dissipation for reliability reasons, but half watt pots should be easier to find ...

[Grainger49]

The 1/2W pots I found online at Mouser and Digi-Key were all PCB mount and tiny.  If you intend to put the shaft through the top plate like I did with my Paramours you will need to look at larger power ratings.  I have a hand full of 10 turn Bourns and Clarostat (sp?) but all in the 5k-20k range.  They do not have a power rating printed on them. 

I see some online that are 2W rated but they do no go as low as 10 Ohms according to the data sheets.  Those were all under $20 each.

I turned over my Paramours and couldn't see the printing to give you a part number.  I'll bring them downstairs and get them under the light/magnifying glass later.

[2wo]

I have never had a problem dialing in a 3/4 turn hum pot...John 

[wylymon]

Hiss or noise can drive you insane with Highly efficient 105 dB 1W / 1M speakers. A 270 degree pot makes it very difficult to get the noise to a minimum.
Best Regards, James

[Grainger49]

John,

I was able to tweak my hum balance pots down to 1mV and 1.8mV when I put in the 10 turn pots.  I hadn't been able to get them that low before.  You get to a "one knuckle" resolution on the old 3/4 turn pot. 

But it wasn't a noise problem for me, I just wanted the hum numbers down.