Quickie mods

[charger]

sometime the Q pick up some noise such for example mobile interference , is there a way to stop it ?

[corndog71]

sometime the Q pick up some noise such for example mobile interference , is there a way to stop it ?

Keep your phone away from it.

[charger]

it pick up even in long distance

[4krow]

 It might need to be shielded. Guys, what do you think of this? Maybe a part is acting as an antennae.

[earwaxxer]

The Q is SUPER micro-phonic. Thats her nature. You have to try different thinks, shielding, damping of the chassis, position away from sources, etc. That goes with tubes. Plug and play is what we get this transistors. We use tubes for other reasons.

[Paul Joppa]

We have not experimented with extreme measures to kill unwanted RF interference, but here is an approach that might be effective:

1) put a small NPO ceramic cap, 27pF to 100pF, from tube grid (pin 3) to cathode (pin5). This shorts the RF energy so that it cannot appear between grid and cathode.

2) (optional) another small cap, around twice as large (56 to 220pF?) from pin5 to ground - this bypasses the cathode bypass cap to take that energy to ground.

Ceramic capacitors perform well at very high radio frequencies; and alternative is silver-mica caps. You want a physically small cap as well, so that it does not act as much of an antenna by itself.

Of course, replacing the chassis plate with a metal one, and fitting it into a metal box in place of the wood frame, and installing a tube shield, will shield all the circuitry, which may also help.

[4krow]

 Thanks Paul, now don't get me thinkin' too much. RF is all around us, NOW more than ever! No surprise that it can haunt our systems and brains. Might be time to sell those tin foil hats that I stored in the garage in case of alien attack.

[charger]

I will try Paul advice on putting ceramic caps, but will this affect the sound ?

[4krow]

 I doubt it, since the cap is of a value that is not in the range of hearing. and if I got it right, it goes to ground.

[charger]

why this was not included in the original stock project?

[4krow]

 Maybe you can only give so much for the money. I do upgrades on some Carver circuits, and while I could do more for a given circuit, I simply would have to charge more. Now, having said that, I do see your point. RFI is eveeeryahere!. When I used to work in central offices for the phone comp[nay, you could feeel the singing of the equipment . I was not totally comfortable in microwave sites.  But as bad as it is, some parts of the country are definately worse than others, just like dirty power.

[adamct]

why this was not included in the original stock project?

Presumably because lots of people don't need it, and it wouldn't make sense to add a part and increase the cost of the kit for everyone, to address a problem only experienced by a few.

[Wanderer]

Presumably because lots of people don't need it, and it wouldn't make sense to add a part and increase the cost of the kit for everyone, to address a problem only experienced by a few.

+1 on that thought.

One of the things you win building kits in general and Bottlehead in particular is the abilty to do simple mods to make a unit fit your particular needs.  I have never had an rf issue with my Quickie. I have modded mine to a headphone amp, tried the plate chokes, tried the PJCCS and prefer it to chokes. None of this fussing about would be so painless with an off-the-shelf unit.       

[Paul Joppa]

I will try Paul advice on putting ceramic caps, but will this affect the sound ?

I have chosen values that will not affect audio frequencies. Worst case is a corner at 64kHz.

[Paul Joppa]

why this was not included in the original stock project?

Normally this is not a problem. In classic circuits, such an RFI control cap is only occasionally used (Marantz for instance) and even then, only for very high-gain phono preamp circuits, not for preamps and amps. I think this is the first time I've posted this idea, possibly the second time, in 15+ years of active posting.