Ceriatone Forum

All, I just got a new gold pin JJ "balanced" tube for the PI slot in my BM50.  I coudn't set the PI trim any closer than +15V even moving the dial all the way left so I reverted back to the prior tube which was easy to get back to the recommended +6V.  In fact, moving the dial either way had little effect on the voltages with this particular tube.  Is this something that happens with some tubes?  I don't have any good test tools other than my meter but is it possible that my new tube is way off or something?

Ah, the dreaded phase inverter adjustment. The problem with this whole issue is that what really needs to be measured here is AC voltage and not DC. But without a scope it's rather difficult to get good AC measurements. Wiith my balanced tube, getting a DC voltage swing like the manual states and like you're seeing was impossible. Atleast with the size trimmer on the amp. But it's quite visually and measurably noticable observing the AC shift with a scope.

What I did and my only advice would be to put back in the balanced tube and set the trimmer at halfway, then move it CW when facing the trimmer from the PI tube in small increments while strumming a chord with some nice harmonic content going and see if there's a position that makes the chord and then notes ring longer/better. IMHO, it's all very subjective, and if you think the old tube sounds "better" (and where you had it set) then that's what is best.

I have mine set about 1:00 facing the trimmer or 11:00 looking at the trimmer from the front of the amp.

You can adjust the PI trimmer without a scope.

Inject a sine wave signal ~ 400Hz -1000Hz at the amp input (or at power amp input, labeled 'return') and measure the AC voltage at the power tube grids. I set it about 20-30 v AC -between the grids - and use the trim to set each grid the same -measured from grid to ground. Don't forget the dummy load on the speaker out. I use a 10 watt 8 ohm resistor. It gets a little hot, but thats not an issue since the whole procedure takes about 2-5minutes.

This gives you the correct balance, with max signal possible out off the PI. And it'll look great on the scope.

Mark the trimmer position with a pen.

Remove the dummy load and connect your guitar. Turn up the amp volume and presence pot, carefully rub the strings with your palm and slowly try adjusting the trim around the point you marked, listening for max amount of harmonics.

Hey blues, do you use the clean channel or OD channel when rubbing the strings? I guess my question is...overall is there settings aside from presence (ie: gain levels, rock/jazz switch, etc.) that makes it easier to hear the "sweet spot"? I used the OD channel when adjusting, but didn't know for sure what was best.

Thanks for the tips!  I didn't think to use my ears for this, but I will for sure be giving that a try.  Now to take it back out of the head cab for about the 5th time this week.....

I'm not an expert on the subject, but I guess you can use both. I you use the clean channel, listen for sparkle in open G chord. If you use the OD listen for the OD overtones or even feedback.....the point where you can feedback easily is THE point.

Many people try to turn this subject into a Dumble voodoo for the selected few. IMO it's not that hard to adjust. It takes max 5 min. after the get the chassis out of the head cab.

Yeah, I don't think it's voodoo. It does take a certain tool & skill set to do it. But after that it's nothing.

I'm pretty sure I have it set where it's best. The only thing is, I hear some clips where the amp is about to feedback or "bloom" at will and what appears to be at lower volume (or gain level). I can't get that happening (atleast not yet) with my amp.

I think I read that the HRM circuit isn't as quick to do this. Is this correct?

I can say I've noticed the more I play it the more it seems to be relaxing and getting closer to the tone of some of the killer clips I hear.

Thats right, at least thats my experience. Think it's due to the fact that the HRM and BM has a little less midrange than the Standard (RF) amp.

However, the HRM's (Bluesmaster and HRM) seem to blend in more easily. I usually bring my Bluesmaster to rehersals or gigs, but love to play the standard amps at home with feedback and all. Te Standard amps are more of a soloist amp - think RF or Santana.

Using a Dumbleator relly helps the amps to breath and feedback at low volumes, because you run the master(s) around noon and adjust master level on the Dumbleator.


Yep, this is a fact. A new amp sounds harsh, but after a couple of months of exercise, it mellows and opens up nicely.

Yep, the D-lator is next on my list!! I'm either buiding from scratch or getting the C-lator kit.

Hey I played with my PI yesterday, I also adjusted the phase inverter. :D
I decided to just play with it until it sounded good to me. I ended up at about 1:00 exactly just like Soundperf, or 11:00 from the front. I used only the clean channel and rubbed palm on strings as suggested to listen for harmonics and around the 1:00 mark is where I heard the most. Very subtle change though. I am surprised I ended in the same spot as Soundperf though because the setting should depend on the tube in V3.
Anyways guys thank you for taking most of the guess work out of this for me.

Todd

 I also ended up in the same spot, more or less, at around +8DC at V3A.  For whatever reason I get a lot more of the "bloom" on higher "A" notes (especially 10th fret, B string) and that's what I used to gauge it.  Go figure.  We'll see if other notes come out as my amp burns in, but I've vowed to stop tweaking for a while and actually play again!

Wilcox and Mojo,

Great you found the sweet spot on your PI's - now lets play!!

Cool guys, glad you got it.  It is a subtle thing for sure, but it is noticable.

sonicmojo, the 10th fret B string does seem to be a good spot to get loads of bloom. I don't know if it's the frequency or a very resonant part of most necks.

Todd, very likely our tubes are balance closely and of the same gain. Just guess'n....

I finally got some interest in another amp I'm selling so I can get some speakers to fill my Avatar open back cab. Supposedly this guy will have the money tomorrow. I will have to go a few days without playing the OTS because the speaker I'm using now is in the amp being sold.

I'm gonna be jones'n for a bit. Hopfully WGS speakers have fast shipping. ;D

As I'll swap the power tubes in my amp I guess I have to check both bias and trim the PI, correct?
 
I don't have the equipment (scope and all) but I'll try to do it by ear.
Hopefully I'll find the G-spot ;D ;D :chairdance:
(8th fret of B-string)

I just ordered a vet 30 from WGS on 4-6-11 and ups shows it arriving on the 13th so its about a week.
Got an acoustic?

What's the Vet 30 for?

Yeah, I decided to put some of my equipment in the sig lastnight. I just put up the other acoustic I have. It was late and I couldn't remember the exact model number.

But yeah, the Tacoma is a very nice guitar. Solid Sitka top & nicely figured Koa sides & back. The other is a 12 string Seagull. A less expensive guitar, but still a nice guitar.

The veteran 30 is going in the 2x12 from tenguitars with an ET-65.
I know its not completely recommended, we'll see.
I find the ET-65 to be really good by itself, a little dark though.
Those acoustics should keep your fingers movin while your waiting for speakers
Todd

The reason I asked is I was considering this same thing. As you know I've been playing through a Vintage 30 and even though it doesn't get much praise here, I can get it to sound decent. Plus supposedly the Vet 30 is voiced a bit differently to smooth out the mid spike.

Something tells me the ET65 & Vet 30 would be a killer combination.

I will let you know in about a week hopefully.
I remember when I first fired up the ET-65 it was pretty harsh sounding.
I read reviews where people put speakers in play for a little while then judge the tone.
When I got the speaker I played a rhytm loop on my GT-10, set the volume very high ( I live on a few acres so can get as loud as my ears can handle ), then went out for the day with my wife.
Came home a few hours later and could already hear much smoother tone coming from speaker.
This helped break in the tubes, amp and speakers and I didnt even have to be there.

I will give an assessment once the V30 has a few hours play time on it.

Todd

I finally got around to adjusting mine the other day. mine took a little more twiddling to get the balance where i wanted it due to the fact that my PI tube is one of the Mullard CV4024's with "balanced" triodes, and brother they mean balnced!! I had to set the trimmer to 3'o clock (looking from the rear of chassis to the front) to get the voltage difference of about 6 volts, and then about 4'o clock to get it where it wanted it. It does take a little more of inbalance on the HRM BM (at least on mine) to get that bloom, but when it gets there it is tonal nirvana, and when i engage the Mega PAB holy crap!!!

I was about to sell my Strat because it sounded like crap through the BM (awesome amps can show either how good or bad your guitar is), but after tweaking the PI trimer, i have fallen in love with my strat again, and all my other axes sound even better now.

That being said, i don't think it's voodoo either, but i encourage everyone to give it a try, especially if you are using non stock PI tubes...

Hope this helps!

Gregg

I use a LPS sovtek PI and finding the sweet spot on the PI trimmer - never changed my amp to the degree you describe, up to the point where your guitar sounds bad.  ??? ???

IMO You must have had a bad tube in there in the first place.

IME The PI trim has an important but minor impact on the tone.

i should probably restate what i said :)

i think it's more in my head than anything ;) not so much that it sounded bad, just wasn't getting quite what i wanted out of it. sounded good, but not great, and indeed when i put the meter on the pi trimmer circuit it was perfectly balanced, ie no voltage difference V3a and V3b at all, so the "balanced" triodes were doing what they were designed to do, and the amp sounded great and, well, balanced, for lack of a better term, but didn't quite get the bloom as i was after. after i made the adjustment though, i got that elusive bloom and all is well.
i think it had more to do with the tube that anything, not that it was bad, just that it is a lower gain tube and set up to be balanced and needed a little help getting that voltage swing. Long story short, making that adjustment made a great amp sound even greater :)

Plastic, are you measuring DC or AC on the PI tube .

You should adjust the trimmer with a tonegenerator connected, measuring AC and trimming until you get an equal amount of AC on each side with reference to ground. Forget the DC difference between the two halves, it will be different from tube to tube. A balanced tube will put close to equal amount of AC from each triode.

i'm doin the dc voltage difference that nik has in the manual. you are correct of, course i should be doing measurent in AC with a tone generator, just haven't gotten around to it yet. Although, if i have it set to where it sounds good now, is it worth doing it via the tone generator method, or should i just leave it alone for now and let it ride?