I built the Bluezmeister Sort of..

[JustMike]

The clean section sounds great but the drive side sounds "ratty". The "Sort of" part of the title refers to mine being fixed bias rather than Cathode biased. I used the V4.1 schematic dated 01-04-2011. My voltages are Node A-407, B-405, C-377, D-337, E-335. I'm running JJ 6V6's.
 I know there have been some revisions since the V4.1 schematic, but it was suggested that one should start there and then tweak to taste. Also, I have Tubenit's tube fx loop installed, but not hooked up yet. I want to get the base sound right first.

[tubenit]

What type of resistors and capacitors are you using in the amp?   Any changes to the schematic beyond installing an active FX loop?  What speaker are you using?


IF you provided your exact schematic for us, it would be a significant help in helping you?   Are you using smoothing caps?  What values?   Do you have an "enhance cap" on the plate resistor of the LTPI?


Is this the schematic you've referred to?  Please indicate any and all changes you may have made.   


With respect, Tubenit

[JustMike]

What type of resistors and capacitors are you using in the amp?   Mostly 1/2w MF. Sozo & Orange drop caps
Any changes to the schematic beyond installing an active FX loop?  Fixed Bias, minor R values as noted on my attached dwg.
What speaker are you using? 16Ω Celestion out of an old Valvestate. I'm running JJ 6V6's and the OT only has an 8Ω sec. It came from an Ampeg Reverbrocket reissue that showed it as an 8Ω with 6L6's. So as I understand it 6V6's should match better to a 16Ω load thru this xfmr.


IF you provided your exact schematic for us, it would be a significant help in helping you?   Dunno, but here it is.
Are you using smoothing caps?  Not yet.
What values?   Do you have an "enhance cap" on the plate resistor of the LTPI? Not yet.


Is this the schematic you've referred to?  Please indicate any and all changes you may have made.   


With respect, Tubenit

[Latole]

Did you forget to show your fixed bias circuit ?

Negative bias power supply and 6L6's grid resistors are missing on schematic

[JustMike]

Yes, I omitted it because it works!

[Latole]

You do a good job,

Schematic as built is very useful to help you.

[JustMike]

 I've been focusing on the V2 section because the clean side works fine. Everything looks OK. But once again I assumed the PA to be OK. Upon closer inspection I saw that I had neglected to connect the NFB ckt to the OT  . Preliminary testing indicates that the drive side now sounds better.


BUT-the schematic shows the 47Ω +10kΩ NFB circuit hooked to the 16Ω secondary. I only have an 8Ω secondary. How does this affect the NFB R values?



 Obviously, I'm building this in pursuit of the legendary or mythical Dumble sound just to give a frame of reference when it comes to tweaking, but before I move on to that, I'd like some thoughts on speakers. I have at my disposal an EVM12L. I know some of the Dumble guys like these as well as the Celestion G12-65's or Creambacks. What's the consensus here?



 Also, am I missing out on anything soundwise by running fixed bias?

[Keppy]

I have at my disposal an EVM12L. I know some of the Dumble guys like these as well as the Celestion G12-65's or Creambacks. What's the consensus here?

I recently built a Ceriatone Dumble clone. I used a WGS ET-65 on the advice of Nik at Ceriatone, and I love the sound (even before it's broken in). That speaker is supposed to be the WGS version of the G12-65.


I also saw a youtube video with a real Dumble ODS that had the EV speaker original to the amp, so it seems like you oughta at least TRY that one if you have it available.

[SILVERGUN]

My experience has been that the EV is just too revealing for my playing. I am a loud, sloppy, edge of feedback type guy and it's just too transparent. It's a very sensitive speaker and there is nowhere to hide.
The G12-65 on the other hand is less efficient and I enjoy that it takes off the edge.

Watch how you setup the drive, ratio and trim controls. Drive and trim can be set very low because there is plenty of overdrive on tap.
Higher settings in these 3 controls can lead to an overly squashed OD tone.

Most of the guys that could afford these amps were great players who didn't need to hide behind speakers or excessive OD.
Search online for some of the settings of your favorite players.

-the schematic shows the 47Ω +10kΩ NFB circuit hooked to the 16Ω secondary. I only have an 8Ω secondary. How does this affect the NFB R values?

You would want to reduce the value of the 10K series resistor to keep the same NFB voltage. 6.8K is close enough for rock and roll.
I doubt you'll notice a difference.

[tubenit]

I have an ET-65 and also think it would be "better" sounding for the OD tone.   


I would highly recommend the "enhance cap" across the LTPI entrance plate resistor.  I like 220p there and feel like it removes the high end harshness and smooths it out.  You can do a search on the "enhance cap" for more information.




Smoothing caps on the OD triodes plate to cathode help alot with smoothing the tone.   


Orange Drop PS caps in the OD section and post LTPI may help also IF you are not already using them?


with respect, Tubenit

[JustMike]

baby steps...I tried it with 6L6's and the EV. It sounds pretty good but not very loud. With 400 plate volts and 6L6's I think this would blow me out of the room with the volume at 3-4. To me, it sounds like a 10-15w amp. This amp should put out around 40w, right? So I changed out the speaker to an Eminence CV-65 which is a fav of mine and a Celestion G1265 inspired design they made for Robben that he didn't like. The speaker was not causing the volume issue. So I checked voltages. Some of these seem odd to me.


V1 pin 1-250
V1 pin 6-233
V2 pin 1-150(?)
V2 pin 6-156(?)


By the way, this is the quietest amp I've ever built. I put it on the bench to read the voltages and when I took it out of standby I panicked for a sec because I thought I forgot to hook up the speaker. But maybe that's because of the lower plate voltages (and so is the lower volume)?

[tubenit]

I typically look to try and have 160 - 200v on 12AX7 plates.  Sometimes 140 on some specific amps.  The other types of 12A_7's will show lower voltage than the 12Ax7.


My cathode biased 6L6 amps are around 23 watts.  My cathode biased 6V6 amps are around 12-14 watts.   Someone can correct me, but I think it takes almost twice the wattage to increase the volume by around 3-6db??


Fixed biased amp like yours with 6L6's, I would think you'd have 30-40w at least?


With respect, Tubenit

[JustMike]

I've been playing with it and I'm getting some really nice sounds out of the drive "channel". But with it's just not very loud which in itself isn't necessarily a bad thing. This morning I took it down to the lab (my garage) and hooked up the tube fx loop. Lugged it back upstairs to my music loft and now it's LOUD, like I would expect. AND I noticed when I play, the speaker is really bouncing even after I stop playing. Some type of oscillation that I can't hear? Any ideas?