help debubbing valve junior rebuild

[steve]

Hello,

I finished a complete rebuild of a Valve Junior a while back and have been tearing my hair out trying to quiet it down.

Some details of the rebuild are here:

http://www.diycustomamps.com/valvejunior.htm#vjrebuild

The amp uses one of these drop in replacement eyelet boards:

http://www.turretboards.com/valve_junior_page.htm

I used this layout with some minor changes:

http://www.turretboards.com/valvejr_layout_stock_v2.pdf

I replaced the stock OT with a Heyboer SE OT that I got from Doberman amps. The OT is fairly close to the tubes.

I added a boost switch by lifting the ground from one of the voltage divider resistors.

The guy I'm rebuilding the amp for wanted carbon comp resistors.

I added a standby switch and a 5F2-A tweed Princeton tone control using stock component values.

The problem is that I'm getting some buzzing (not hum). The buzzing starts out low when the volume level is low and gets louder as the volume and tone controls are turned up.

I tried redoing the grounding scheme thinking that there might be a ground loop somewhere in the amp.

Any suggestions?

TIA,

steve

[steve]

Bump:

Hello,

I finished a complete rebuild of a Valve Junior a while back and have been tearing my hair out trying to quiet it down.

Some details of the rebuild are here:

http://www.diycustomamps.com/valvejunior.htm#vjrebuild

The amp uses one of these drop in replacement eyelet boards:

http://www.turretboards.com/valve_junior_page.htm

I used this layout with some minor changes:

http://www.turretboards.com/valvejr_layout_stock_v2.pdf

I replaced the stock OT with a Heyboer SE OT that I got from Doberman amps. The OT is fairly close to the tubes.

I added a boost switch by lifting the ground from one of the voltage divider resistors.

The guy I'm rebuilding the amp for wanted carbon comp resistors.

I added a standby switch and a 5F2-A tweed Princeton tone control using stock component values.

The problem is that I'm getting some buzzing (not hum). The buzzing starts out low when the volume level is low and gets louder as the volume and tone controls are turned up.

I tried redoing the grounding scheme thinking that there might be a ground loop somewhere in the amp.

Any suggestions?

TIA,

steve

[Bruce / Mission Amps]

If not a simple B+ filtering issue, it seems like when I get a buzz, it is almost always filament supply noise, like an improper ground with respect to the high impedance of a grid and the filament supply.
The filament buzz is a ratty and lower freq noise compared to B+ hum.
Any reason why you didn't wire the heaters like you did (do) in your other projects with both filament leads to the tube sockets and the 100ohm virtual center tap resistors grounded instead of the way this one is done?
Also... with all those twisted ground wires around the grid leads, I wonder if there could be an issue with the attempted shielding properties working with the shared audio ground and filament grounded wire.

[steve]

Bruce,

Thanks for your help.

I used the drop-in board from this vendor:

http://www.turretboards.com/

Here is the layout I used:

http://www.turretboards.com/valvejr_layout_stock_v2.pdf

Instead of referencing the two 100 ohm virtual CT resistors to ground, I connected them to the EL84 cathode.

I also ditched the grounding bolt near the pots and connected all grounds to the bolt near the IEC inlet.

Your description fits perfectly: low level nasty buzz. It sounds like a flourescent light interference, but I don't have flourescent lights in my shop.

I think I'll try reworking the filament supply next.

BTW, did you get my emails? I sent one of them yesterday and one last week.

Regards,

steve

If not a simple B+ filtering issue, it seems like when I get a buzz, it is almost always filament supply noise, like an improper ground with respect to the high impedance of a grid and the filament supply.
The filament buzz is a ratty and lower freq noise compared to B+ hum.
Any reason why you didn't wire the heaters like you did (do) in your other projects with both filament leads to the tube sockets and the 100ohm virtual center tap resistors grounded instead of the way this one is done?
Also... with all those twisted ground wires around the grid leads, I wonder if there could be an issue with the attempted shielding properties working with the shared audio ground and filament grounded wire.

[Bruce / Mission Amps]

No I must have missed the emails Steve.
I get around +120 to 150 emails a day of which 85% are total trash spam and I have set the filters set pretty tight over the last few weeks ....
so they might have been stripped.

[hasserl]

Try insulating the input jacks. I just assembled an amp using a Hoffman turret board that someone else had picked up in a horse trade and asked me to use in this build for them. I used Switchcraft jacks and they caused a pretty loud hum until I insulated them from the chassis and ran a ground wire from the jacks to the ground bus on the turret board.

[steve]

Try insulating the input jacks. I just assembled an amp using a Hoffman turret board that someone else had picked up in a horse trade and asked me to use in this build for them. I used Switchcraft jacks and they caused a pretty loud hum until I insulated them from the chassis and ran a ground wire from the jacks to the ground bus on the turret board.

Thanks for your reply.

All the jacks are insulated from the chassis. At first I had the speaker jacks grounded to the chassis, but I took out the star washers and insulated them with Keystone fiber washers. The input jack was always was insulated from the chassis with a ground wire running to the board.

No luck chasing down the buzz yet.

steve

[hasserl]

Is it 60 cycles? Got to be a ground issue.

[steve]

Is it 60 cycles? Got to be a ground issue.

I think I got the problem solved. On a hunch I wired up a DC heater supply using four 1n4007 diodes and a 10,000uF cap. Killed the buzz dead.

I think this might be a problem due to the close proximity of the tubes.

Version 1 of the VJ had this problem, and went away with the addition of DC filaments in version 2.

There is still some white noise in the amp but I believe this is due to thermal noise and the carbon comp resistors (which the owner wanted in the amp).

Thanks to all who replied.

steve