Bottlehead Forum

Bottlehead Kits => Legacy Kit Products => Topic started by: Paul Folbrecht on February 24, 2014, 01:37:52 PM

Title: Mesh = hum
Post by: Paul Folbrecht on February 24, 2014, 01:37:52 PM

Could somebody tell me why the AC filament hum of my Parabees is quite substantially louder with mesh (well, perforated TJ/Psvane "mesh") tubes? 

This holds across multiple pairs of tubes.

Thank you.

Title: Re: Mesh = hum
Post by: johnsonad on February 24, 2014, 02:22:12 PM

I had the same experience with TJ's (300B).  I'm running EML mesh now and have higher white noise but don't have another pair of tubes not being used to see if it's the mesh tubes contributing to that noise or something else.

Btw, what speakers are you currently using Paul?

Title: Re: Mesh = hum
Post by: Doc B. on February 24, 2014, 02:59:14 PM

Quote from: Paul Folbrecht on February 24, 2014, 01:37:52 PM

Could somebody tell me why the AC filament hum of my Parabees is quite substantially louder with mesh (well, perforated TJ/Psvane "mesh") tubes? 

This holds across multiple pairs of tubes.

Thank you.

Presumably you are adjusting the hum balance for minimum hum each time you change tubes. The Parabee is a tight layout and it may be that the Psvane is more sensitive to fields radiated from the other components. Or maybe they just hum more than other 300Bs due to their filament configuration.

Title: Re: Mesh = hum
Post by: Paul Folbrecht on February 24, 2014, 03:03:16 PM

Quote from: Doc B. on February 24, 2014, 02:59:14 PM

Quote from: Paul Folbrecht on February 24, 2014, 01:37:52 PM

Could somebody tell me why the AC filament hum of my Parabees is quite substantially louder with mesh (well, perforated TJ/Psvane "mesh") tubes? 

This holds across multiple pairs of tubes.

Thank you.

Presumably you are adjusting the hum balance for minimum hum each time you change tubes. The Parabee is a tight layout and it may be that the Psvane is more sensitive to fields radiated from the other components. Or maybe they just hum more than other 300Bs due to their filament configuration.

Curious thing is I've never located any hum pots.  Do I need to turn them over?  That'll be awkward!  Anyway, thanks.

Title: Re: Mesh = hum
Post by: Doc B. on February 24, 2014, 03:10:45 PM

Yes, they are underneath. They must be adjusted whenever you change 300Bs.

Title: Re: Mesh = hum
Post by: Grainger49 on February 25, 2014, 06:18:03 AM

The Paramour II was the first Bottlehead product with top plate hum pots.  Mine are just Paramours.  I drilled a hole and rearranged the wires so I could do it from above.

You are right, it is awkward.

Title: Re: Mesh = hum
Post by: Paul Folbrecht on February 25, 2014, 01:57:14 PM

I searched the underside of one of my amps for five minutes and could not locate a hum pot. 

I will need to write the builder.

Title: Re: Mesh = hum
Post by: Doc B. on February 25, 2014, 02:43:51 PM

The pots should be right by the 4 pin sockets. They would be very easy to spot as they are nearly as large in diameter as the sockets and have a 1/4" shaft. If they are not there you need to talk to the builder and find out how they intended to do hum balance after changing tubes.

Title: Re: Mesh = hum
Post by: Paul Folbrecht on February 26, 2014, 11:26:48 AM

I didn't find the pots because 1) they are not in the standard location 2) I was looking for a little setscrew.  The buy who built the amps, being the master builder he is, made them giant knobs you can turn by hand!  Awesome!