[hebrer]

I was hoping someone technically more competent than myself would be able to bring some light on the effect different switching power supplies have on tube functioning.

Specifically, I have been using a SET headamp (http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=260503007690#ht_5197wt_1162) with 6N11 tube and power supply 24V 1A.

I tried to replace 6N11 with Sylvania 6922 but one channel always stopped working after a few seconds. When I used Phillips 6922 (http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=400076713824#ht_2279wt_936), the sound deteriorated after a some longer time (few minutes).

Could this be a question of the tube heater or how much current the tube draws? Does the power supply play any role in this? I tried to use a laptop power supply 24V 3.5A, but it did not help.

I heard Sylvania 6922 or other 5922/6DJ8 equivalents sound better than 6N11 but there seems to a problem with simply replacing 6N11 in my headamp.

Thanks for any ideas/links to explanations on what you think is going on...

Peter

[FullRangeMan]

This is a guitar or e-bass head amp??  I do not know much about it, but the experts will need to know the brand/model and other details.

[hebrer]

Hi, it is an inexpensive amplifier Bravo Audio (I included a link above). Not a guitar amp. I sometimes use it as headphone amp and other times as a simple preamp for active speakers in my computer setup.

I believe the schematics is similar to another product Indeed headphone amp (schematics at http://cgi.ebay.co.uk/Valve-Class-A-Hybrid-Tube-Headphone-Amplifier-Indeed_W0QQitemZ250560377251QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item3a568ff1a3#ht_7032wt_1162).

Peter

[jules]

Not good! Are these tubes going to an early grave or is the failure temporary?

but one channel always stopped working after a few seconds.

Is the failure only happening on one side? If so, it looks like a component, wiring or pcb fault.

Could this be a question of the tube heater or how much current the tube draws?

Do you have reason to think the heater filament has died? Have the "lights gone out"? The 6dj8 uses 9V for the heater element. AC is apparently best and a good high speed switching ps shouldn't cause a prob. [I've used one for years].

Beyond that, I leave it to the experts.

jules

[Ericus Rex]

Hmm.  I thought the "6" in 6DJ8 meant '6-volt filament'.   

The 6dj8 uses 9V for the heater element.

[FullRangeMan]

Hi, it is an inexpensive amplifier Bravo Audio (I included a link above). Not a guitar amp. I sometimes use it as headphone amp and other times as a simple preamp for active speakers in my computer setup.

I believe the schematics is similar to another product Indeed headphone amp (schematics at http://cgi.ebay.co.uk/Valve-Class-A-Hybrid-Tube-Headphone-Amplifier-Indeed_W0QQitemZ250560377251QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item3a568ff1a3#ht_7032wt_1162).

Peter

Nice headphone preamp for 57 dollars!!    How about the sound quality as a preamp for a poweramp??

[Wayne1]

From what little I know, the 6922 series will draw 0.365 amp of filament current. I do not see what the filament draw is for the 6N11 tube.

If possible, try to measure the filament voltage with both the 6N11 and a 6922 in place to see if there is any difference.

The schematic does show a potentiometer to adjust bias. You might want to carefully try adjusting them.

A 1 amp switching supply may be a bit low in current. Personally I prefer linear supplies, but they can get expensive. Make sure the connector on you larger supply is wired correctly.

[jules]

Hmm.  I thought the "6" in 6DJ8 meant '6-volt filament'.   

Sorry, absolutely correct, my mind was elsewhere. I've used 7V, 7DJ8 heater filament tubes in the place of 6V tubes and the light output is significantly lower so I'd expect that if you had a high voltage problem, particularly one that burned out a filament in a matter of minutes, you'd also notice that the offending tube would be much brighter than normal.

jules 

[hebrer]

Thanks guys for your replies.

It turns out there is a quality issue with my amp - the tube socket does not hold the pins of the tube firmly enough to ensure contact when the amp is moved.

Thanks Wayne for pointing out the bias adjustment option on the pot. I used it with good results. Now I am using Phillips 6922 instead of supplied 6N11 (Sylvania 6922 does not work - at least with this particular amp).

Using the higher current power supply causes hiss in the sound and I guess using the original power supply is fine.

FYI, when set up as a pre-amp with my Yamaha active speakers, this headamp makes noticeable improvement in the sound. The sound is fuller and more "live". Still, in terms of build quality, I would not recommend it for frequent changes of tubes or cables.