Low Harmonics on 6L6 Tubes...need help.

[twangmeisternyc]

It seemed like a good time to change out phase inverter and power tubes on my Custom Vibrolux Reverb. I thought I was noticing a bit more reverberance and shimmer, whatever the correct terminology, and I had a matched set of Winged C's in the drawer.

I had no real issues with the Sovtek 6L6WXT+ tubes, and they had seen daily use for about 2 years. I liked them, sounded nice.

Now...my problem.

I put these Winged C's in and I get this deep, obnoxious buzz when striking a Low E. I went through every mechanical possibility, checked speaker mounts, baffle mount, loose anything...

After all that, I put the Sovtek's back in...sounds great.

I think the Winged C's are putting out a low harmonic which is a frequency my Jensen P10R's cannot handle. I switched to my second 15" C15N enclosure. Not as noticeable... but still there.

Any body ever go through this? Comments?

[Mesotech]

When you change power tubes, it's standard practice to rebias the amp. This is most likely the issue you are experiencing.

Rebiasing isn't a difficult task, but if you do not have the experience or knowledge, then take it to a tech to have them do it. You could learn to do it yourself, but it would take some time to gain the skills involved, and cost some additional money in the proper tools.


Oh yeah, and it's very dangerous, so it's not something you would want to attempt on a whim.

[twangmeisternyc]

It is a fixed bias amp...with the power tubes selected for their draw. Mine is in the Fender "white" bias range.

I've got a note on to the outfit that sent the tubes...see what they suggest. I've ordered from them several times, always seemed like a good crew.

It just feels like I'm getting a great deal of energy at 41hz, or a half cycle, off the Low E string and the speakers cannot do it.

I'll give it another round a tube swapping today, changing to a different brand of phase inverter tube, but I think the bias is certainly a question. As is just a bad tube.

[Cygnus X1]

Meso is correct.
"Fixed Bias" does NOT mean "self biasing".

[twangmeisternyc]

I have always known about the mod to make adjustable bias...maybe this just gets me there. The mod is simple enough, I'll just need to buy more gadgets and possibly be happier...

[twangmeisternyc]

The other comment coming back around is that I might just be getting a mechanical vibration and that using a pair of tube dampers is the answer.

Can anybody qualify the benefit of tube dampers?

[twangmeisternyc]

Curious conclusion for now...loose caster?

I had recently moved my stack to another spot...maybe the floor isn't as even. When I went through everything again this morning I decided to take the casters off. No buzz with the Winged "C"'s.

Which means...they put out a lot more lower frequencies than the Sovtek 6L6WXT+.

[Mesotech]

Mechanical vibration could cause a lot of intermittent issues that are difficult to nail down.

You asked about tube dampers, and I've never heard any negative comments on them (except some studio musicians swear by taking the shield covers off of their preamp tubes when recording). Every amp I own has dampers or retainers of some sort.

As for the frequency response question of the different tubes, each tube manufacturer should have a chart available to show the freq response and other tube chacteristics, but you'll need to do a bit of math to determine precisely how the tube will operate in your specific amp.

[Offshore Angler]

Could be the filer caps too. They can cause weird sounds, although they usually manifest themselves on B or Bb.

[Cygnus X1]

Which brings up a really dumb question:

I never glue in my filter caps.
Will I end up paying (in a bad way) for it?

[yankeerob]

As for the frequency response question of the different tubes, each tube manufacturer should have a chart available to show the freq response and other tube chacteristics...

Except New Sensor - well OK they're the corporation that distributes more of the danged things than anyone else - but you won't get any specs outta them - they're obviously above assisting lowly mortals...

[yankeerob]

Which brings up a really dumb question:

I never glue in my filter caps.
Will I end up paying (in a bad way) for it?

Though it is generally good practice to ensure all components are as secure as poss - it's unlikely that not gluing 'em down will directly result in any major malfunctions - I usually think about gluing 'em down as I'm populating a board but don't in case I've got a dud - then once it's done and tested forget to do it

[twangmeisternyc]

Well, add another day's experience to all this...

The Winged "C"'s are a lot different that the Sovtek's I used for the last two years in this set-up. Much more content, more overtones and undertones...thick, and easily set free.

I thought the Sovtek 6L6WXT+ were just fine...very nice, clear, unimposing tone.

Been through most of the guitars seeking "new" dial-in settings...both on the amp and the guitars. So much more chiming and ringing.

The 400 and Byrdland are doing quite well, the Gretsch just found its sweet spot, and the Strat is still a "seeker".

I think having had the tubes on for the last couple days has allowed them to settle in, too. Maybe a bit less bassy than Saturday afternoon's apartment building shakedown event.

Also, the degree to which they were displaying "microphonics" is a lot less. I had checked the pair when I received a couple years ago, just chose to use the Sovtek's first. On Saturday, I could tap the faceplate and get ringing...

Solid-State is so easy! ;-)

[yankeerob]

The Winged "C"'s are a lot different that the Sovtek's I used for the last two years in this set-up. Much more content, more overtones and undertones...thick, and easily set free.

I thought the Sovtek 6L6WXT+ were just fine...very nice, clear, unimposing tone... Solid-State is so easy! ;-)

Truth of the matter is that =C='s do have a more natural sounding easy breezy harmonic content than Sovvies - my gripe is they cost a lot more and don't last as long (I've done the exercise - twice) - most working musicians'd trade a little bit o' snake oil for the next best remedy if it delivers consistently... as far as we're concerned Reflektor mftr'ed 6n3c's and 6n3c-E's from the 80's (and they appear to be as good as those we've got that date back to the 50's and 60's) deliver the goods as reliably or better than =C='s for less than a third of the price... they just don't sound as good straight outta the box - they take a little patience... but once they break in they're sweet little bottles....

Sovvie 5881WXT's or WGC's could never be described as as harmonically rich as =C='s - they do however - tolerate the higher than 450V plate voltages that many modern amps produce for a lot longer and aren't all that bad after 20-30 or so hrs of service - and for the money - even though you'll have to buy enough to match up you own prs/quads/etc if yer that anal about it - the best buy are still those 6n3c's

[twangmeisternyc]

A final set of notes...

Only easy problems have a single source. This whole event multi-tasked.

The first issue was a microphonic tube...that has since found its way.

The second issue was a Super 400 with P-94's that could generate deep harmonics...

And the third issue was Beam Blockers that just couldn't handle the first two issues.

I'll need to find a new mounting scheme for the Beam Blockers if I choose to use them on the Jensen P10R's. Now, having tried with and without...not sure of the benefit...need to play through more time and all instruments.

I know I like the Beam Blocker on the C15N, it has a bigger cone.

The Winged C's are different, but now the differences/benefits compared to the Sovtek 6L6WXT+ is more idealic. I did reorder the Sovtek's.

And finally, finding the tube line-up you like down the chain is probably the most important. People either hate or love a Fender CVR...but, it's my project. I would say today, I found all the settings for all the electric guitars I have.

The Super 400 sounds like I am hearing a CD playing in the background...I just happen to be in perfect synchonicity. I cannot tell any added hiss or noise from the single coil P-94's.

The Gretsch 6120 puts out tones I hear on dozens of records I've loved over the years.

The Strat Plus found its tone. It can sustain until next week if I choose to leave my finger there...I think it made "a minute" with a little vibrato.

The ByrdLand is like the Super but set-up to BeBop and Hippity-Hop.

I'll get on the Acoustic-Electrics next...

I do need to decide about adding the Bias Pot and getting myself set-up to make the tests and readings. I bought everything...need to pull the chassis out and find a good mounting spot.

[marks sonics]

hi guys i have a blues deville reissue with stock 5881in it.just orderd a set of sed 6l6gc. is the reissue a fixed bias or adjustable. what needs to be done to fit the sed 6l6gc to my blues deville reissue.thanks