ampgeek wrote:LOL! Clue!! I took a couple of days off from the frustration and perused the whole thread to better understand the sequence of events and couldn't agree with you more.
And....came back with "Professor Dumbell in the bias circuit with(out) a soldering iron"!! Morcoloco gets the detective award on that one.
Soldered up the bias pot (had previously used push sockets), biased it up (required a MAJOR adjustment of the bias pot which was a clue that something had changed!), plugged it into a 1X12" loaded with a G1265 and let it rip with the VVR dimed and everything else at high noon and... !!!! It sounds REAL close to Strato17's "Shaky Ground" clip which was my motivation to give this a go in the first place.
I wouldn't say it is perfect yet and there is lots of knob tweaking and much housekeeping to be done as identified in all of the gracious posts...but...it is the good kind of tweaking left to be done (I think!).
I still have a factor of 2X power tube current draw mismatch over all volume settings when playing (perfect match at idle). I would like to sort that one out first.
Has anyone ever done similar measurements on their builds? Could that be a normal condition?
I have a shielded V2 grid line and a whopping ~22K grid stopper currently and the amp is way stable. Lying on it's back with no cover plate and nothing plugged into the input jack, I can dime everysetting and get no feedback. A bit of hiss is present but that seems normal.
I also appear to be experiencing excessive voltage drop across the diode string. I have 601 VAC going in and ~389 VDC coming out. That appears to be way off from expected. I will change those out and report back.
I will mention that I have the power tube plate to ground diode bridge disconnected as Richie suggests so that doesn't appear to be playing a role in the low B+ observation.
Regardless...I am a happy camper! I am resisting plugging in the NOS Siemens until the mismatch power draw observation gets resolved. But can't wait to give them a whirl!
TIA,
Dave O.
I checked mine the other day and did notice that when playing one tube goes higher than the other, a lot. I have one that gets into the hundreds and one that doesn't. I didn't have a problem with v2 grid wire and used a plain wire with no grid resistor. I did use padded foam with it taped under the turret board and get no microphonics at all. I too removed the diode string as well thinking they were causing something and never put them back. I am running winged C EL34's right now at 400 volts on the plate and 55ma of bias. I am thinking of trying them a bit colder as they seem to be cleaning up for some reason at this high a bias. They lost their mist is the only way I can explain it. I swap EL34's and 6L6GC's and the 34's are starting to sound like the 6L6's. Glad you found it. Play the crap ouyt of it now Dave.
Thanks passfan!
You betcha I am going to play the crap out of it! Like I said, still lots of "get aquainted" time required to find the sweet spots and more questions I am sure. But...I can just tell it's going to be a great "little" amp. Now I really know what "JCM-800 on steriods" means!
Thanks for taking those measurements. Really helpful. With the VVR dimed and everything else at high noon, I see ~60-65 ma at V4 cathode and ~120 to 130 ma at V5 cathode depending on how hard I stroke the an A power chord.
ampgeek wrote:Thanks passfan!
You betcha I am going to play the crap out of it! Like I said, still lots of "get aquainted" time required to find the sweet spots and more questions I am sure. But...I can just tell it's going to be a great "little" amp. Now I really know what "JCM-800 on steriods" means!
Thanks for taking those measurements. Really helpful. With the VVR dimed and everything else at high noon, I see ~60-65 ma at V4 cathode and ~120 to 130 ma at V5 cathode depending on how hard I stroke the an A power chord.
Thanks again,
Dave O.
I know both of my builds can reach a several hundred mA spike when hitting a power chord. If I remember right, I hit the max. hold button a couple of times and got a reading in the hundreds. To be honest, I really didn't compare one tube to the other. If it sounds good and is not malfunctioning, play that baby. One thing I noticed right off the bat, is the longer you play, the sweeter the tone gets. I think tubes and caps need to be put through the paces before it all smoothes out. It seems each time I play one of mine, it sounds a little better than the time before.
ampgeek wrote:Thanks passfan!
You betcha I am going to play the crap out of it! Like I said, still lots of "get aquainted" time required to find the sweet spots and more questions I am sure. But...I can just tell it's going to be a great "little" amp. Now I really know what "JCM-800 on steriods" means!
Thanks for taking those measurements. Really helpful. With the VVR dimed and everything else at high noon, I see ~60-65 ma at V4 cathode and ~120 to 130 ma at V5 cathode depending on how hard I stroke the an A power chord.
Thanks again,
Dave O.
That right there is the real test of an amp ain't it ? It's an unwritten, worldwide test of an amps mettle. From that one stroke all is known.
Finally got around to packaging this up. Had a couple builds for others in the qeue that caught up with me.
Chose the Duratex route because each new ding in my current hardwood combo is like another nail in my heart and I REALLY suck at fabrics!! My own art faceplates done at BNP Laser (Jeanne is simply the bomb!) and aluminum knobs from AES (via robbery from my D'Light build).
Current tube line up is Tungsram, NOS Mullard, Tungsram and NOS Siemens in the PA. Many more combinations to try but want to get the speakers nailed down before spending any more time on tube swapping.
I have logged about 50 hrs with a dozen or more different speaker/cab combinations and the one "constant" is that the older more broken in speakers almost always sounded the best. One exception being my early 70's Ampeg V-4 cab with it's original (but in great shape) speakers. Sounds great with other builds but not as good as many others with this amp.
Truth be told, one of the very best was a Line 6 cab with ?? speakers at our rehearsal studio. Having been beat on endlessly by the clientel for ~18 hrs/day for more than 3 years must have done something right to it!
Just slipped in a polystyrene treble cap and could tell instantly that it needs to be excercised a bit to get right.
Dinked around almost endlessly in the PI and reached a point where the V4 and V5 current draws were w/in ~10% but didn't like that much at all. So...right back to stock and I like it alot. I have to assume that a significant imbalance is normal. Still hoping for others to weigh in on that though.
So...scheming on a pair of Scumback M75s broken in with the ole variac in my work lab (no police to bother me there!). One each in an Avatar partially closed back and a Crystal Cabs closed back. I like the idea of being able to stack everything up and splay the cubes in different directions.
Any thoughts/advice on that scheme?
Many thanks again to everyone who stuck with me on this project!
Sincerely,
Dave O.
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Yep..that stuff is tougher than nails. Just what I wanted for a road-ready unit.
I ended up using the Duratex recommended textured foam roller after all was said and done. Tried to get the leather look by scrunching up different types of plastic and pressing it onto sample swatches of board with the coating at varying levels of dryness. REALLY hard to get a consistent look as it sets up so quickly.
Even the textured roller gives varying levels of "knapp" depending on how hard you press down, how dry the coating is and how much material you have on the roller.
Outdoor July 4th gig/jam with a 1X12 partially closed back Avatar cab w/G1265H, 72 Les Paul Deluxe with Seymour Duncans (a little hotter than stock) and...no pedals! Loved it! I wasn't quite as smooth on the rolling of the volume knob and slapping back and forth between the pickups as I would have liked...but...that will come with little time.
Can't wait to get better matched speakers. Snatched one of the $99 Lopo Line closed backs and am about to pull the trigger on a pair of Scumbacks. Although....the not yet broken in G1265 was a lot better than what I expected.
Thanks again to everyone who helped out along the way. This is a great "little" circuit and anyone sitting on the fence about building one ought to jump right in without hesitation. I had built a dozen or so kit and scratch amps before this one but even a festidious beginner who is good with his/her hands could tackle it due to the guidance so freely given here.
KF sure had a wonderful vision in his head and the magic in his hands to bring it to fruition. I can only hope that he can see the joy that he has brought to this two-bit guitarist!!
I really appreciated your sage advice along the way RJ! I definitely have a keeper with this one.
A couple of guitar playing folks at the holiday jam had great interest in it. They were impressed with the musicality of the tone and observed the clean-to-mean character sans pedals.
I made sure that they knew that I already had an extra head cab, OT and most of the parts to build another one.
LOL!! "Clean" bench only because I had to clear away a spot to set the head down to take a picture!!
!!!! It sounds REAL close to Strato17's "Shaky Ground" clip which was my motivation to give this a go in the first place.
