A different voltage problem

[canadianwheelman]

So I have completed my Eros, and have a bit of a problem with the voltages - the Kreg is reading at .5V on one output board and 1.5V on other, the manual says I should get 1V on both.  This is a pretty big percent error, and I am also concerned that they aren't reading the same.

Any ideas?

[Paul Joppa]

Swap the EF86s and see if the voltage follows the tube. I'll bet it does, and that just shows how different the "same" tube can be. If that's the case, let it run - it should be working if all the other voltages are reasonable - and there's a good chance that 0.5v will pull up as the tube "forms" its cathode. If it stays at 0.5v for 100 hours or more of running then I'd say it's an underachiever - ping Eileen and get a replacement.

[canadianwheelman]

Thanks!!!  That's exactly what it is - and also explains some of the white noise coming out of that channel as well.   I have about 40 hours on the Eros now, so will continue to enjoy, and see if things settle down in time.

Last question, and it's a good newbie one - If my amp (generic Denon home theater model) is already on and listening to another source and I turn on the Eros, my Denon immediately powers down like it has gone into a protection mode.  I'm new to tube audio, is there some sort of power spike through the outputs on power up?

[grufti]

There are at least two possible reasons why the Denon might shut down. The Eros might pull your line voltage so low on turn on that the Denon turns off ... not very likely. Two, your Eros might produce some weird signal on its outputs when it turns on and your Denon might have some strange protection circuit that tells it to shut down.

Scenario two is even more unlikely than scenario one. I know my Eros doesn't produce signal spikes on the output when I turn it on ... and your Denon should also be pretty much immune to anything that shows up on one of its inputs. Scenario one is easy to test: run a long extension cord from somewhere in your house that isn't on the same circuit breaker/fuse as your Denon and connect your Eros to that extension cord [or vice versa]. That should eliminate most if not all turn on related line voltage sag.

Weird!

[Doc B.]

Do you hear a pop thru the speakers when you turn the Eros on?

[canadianwheelman]

There are two soft pop's when I turn the Eros on - not loud enough that I am worried about blowing speakers, but definitely there.  The first pop is when I turn it on, the second happens a couple seconds later.  Strangely this happens even when I am listening to another source (my cable box) as well...   I did this test today when the Eros was already warmed up, and it didn't shutdown the Denon this time - in the past, the pop was LOUD!!!  I always power up the Eros before my amp when listening to music, and only found out about this glitch when I was watching TV, and thought about putting on some vinyl.

In addition, I just ran an extension cord to another room and another known breaker with the same results.

[Paul Birkeland]

Do both channels pop?

[canadianwheelman]

Both channels have the initial power-up pop.  Only the right channel (I'll call this the good EF86 tube) has the secondary pop after a couple seconds.  I think that no second pop on the left channel can be attributed to the EF86 tube on that channel (when I measure the KReg voltage, on power up, it starts at .25V and rises to .5V after 20 seconds).  When listening, that channel is much quieter, has a poor noise floor of white noise, and some pops.  I will wait and see if this clears up after more hours of burn in.

I can reconfirm that the level of the power on pops is heat related - if I let the Eros cool down for an hour, I get a single LOUD pop, and my Denon shuts down - there is no secondary pop, as the amp is already off.  If I only wait 30 seconds after turning off the Eros before powering it back on, I get a much quieter pop, and everything stays on.

Thanks for all the help guys!

[Doc B.]

Try swapping the ef86s and see if the secondary pop follows the tube.

[canadianwheelman]

I'm going off memory here, but I do think the secondary pop happened on both channels when using the good tube.  I am now on the road for a few days, so won't be able to confirm this until early next week.

[canadianwheelman]

I can confirm the 2nd pop follows the good tube - this one constantly measures 1.5V on the Kreg.

The other (possibly bad) EF86 is much quieter, has a significant noise floor, and some pops.  The Kreg on this one starts at .2V and over 20~30 seconds climbs to .5V.

[Doc B.]

If the tubes haven't settled in by 100 hours or so contact Eileen at [email protected] and she can send you another pair of EF86s.

[canadianwheelman]

Thanks Doc!!!  I'll keep an eye on things and touch base with Eileen if I still have problems after some burn-in time.