I know many here are sick of my 6G2 posts but here is what I did .

[catnine]

I had the typical 5E3 power section only changed it to adj/fixed bias. I had the same 5K dropper ot the creens and then later chaned the 22K second dropper to the preamp to a 33K to get the voltage close to what fender shows on their schems so instead of 315 VDC rail feeding the preamp stage it was now 292VDC .

So with that said the last few nights I moved the bias board to another spot since I had it mounted on the 5E3 eyelet board I used right where the cathode bias resister and cap were supposed to be and then added another filter cap in it's place. So before it was 30uf 5K dropper 16uf and 33K and 16uf . So now I have a 30uf reservoir cap same as before , changed the 5k 1st dropper to a 1K then a 16uf then 22K dropper then a 16uf and 10K dropper then a 16uf cap. So now I have a 2 volt higher plate at idle on the screens instead of a 25 VDC lower screen. I always had 470 ohm screen resisters. I have 297 VDC on the rail to the preamp instead of 292 VDC.

The entire amp changed. Now instead of this raspy breakup just above 4 1/2 on the volume , strat single coils all controls full up. Now the amp does not break up until 6 1/2 and in a smooth way. I did notice that it seemed I had to raise the vol on the amp up 1/2 notch. Before I had no real sound until 2 now it's there at 2 1/2 . Here is the odd part. The volume pot used to react a lot by just one number now the vol reacts in a useable way, it's gradual , the same with the amps tone pot before it was the same as the vol , one notch made a great change now it's gradual/more useable as I raise it to 10.

And to top it all off I never used the strats pots because they did a lot of change with little movement now I need to move the vol a lot more and get a gradual change and the same with the strats tone controls before one number down on either tone it was treb to a mutted dark sound now they act a bit more treb cut and the muted bass tone is not until they are on almost 1.

The amp also sounds tighter and more focused and more clean headroom . Before I did these changes I added a switch so I could have the NFB of 56K like the 6G2 and at the same time take the second gain stage 25uf bypass cap out of the circuit but now I don't even need the NFB at all for some odd reason the speaker does not need the NFB to tighten the sound up.

I was leary of these changes , I was just going by what the SF AA964 uses with the 4 filter caps and set my build up the same way but instead of the two 18K droppers for 36K total I used a 22K and 10K for 32K total.

I do wonder and do not know how droppers work with filter caps and if it's better to use two droppers of the same value between filter caps even if the voltage end result is the same on the preamp section . I suppose it may make a difference how the filtering is done since the voltage drop is equal between the two caps using the same values . I am just not sure and can't seem to find any info on this. The fact is I really could not tell anyone how the changes I did made such a change in this build. I read about plate and screen current and all sorts of other topics trying to learn something.

 
 
 


    

[tubeswell]

Fun isn't it?

[catnine]

Fun isn't it?

 yes it is , at the same time for me i was just shooting in  the dark because I don't know the math and just tried to come close only based on fender schematic voltages in the rail. What I have been trying to figure out is why fender used droppers that progressively rise in value from the first dropper to the last dropper all between the same value filter caps. I used a 22K and 10K to get my preamp rail voltage down to AA964 spec , the 10K is the last resister , should have used the 22K as the last in the RC filter chain ? I can't find out what the relation of droppers has based on the uf value of the filter caps or if it even matters. Something tells me there is a relationship there. What makes me think this is the AA964 used two 18K droppers between the last two caps before the preamp stage . I read somewhere that the 5K 1st dropper between the plate and screens can cause a sag so that's why I chose the 1K and have the 470 ohm screen grid resisters . I guess the screen sag was the main issue as to why my build produced that harsh OD sound when driven because that's gone now. Then there are amps like the deluxe reverb using a choke in place of the 1K and they don't drop voltage due to the low dc resistance so the plates may be lower than the screens or the same , I don't know what is best. The only way I can find out is to replace the 22K and 10K with two 18K or two 15K one will lower the preamp and the 15K will raise it a bit. The amps sounds great now so I hate to change anything unless one way is better than the other. 

[tubeswell]

The resistor/capacitor dropping in the power supply is just another form of resistor/capacitor filter. From Merlin's 2nd book (Ch4), "With increasing frequency the reactance of the capacitor falls, and so the attenuation of high frequencies is greater than for low frequencies; it is a low-pass or treble-cut filter."

In the old days of small (4-8uF) value e-caps, it used to be more of a concern that there was a balance between how big to make the resistor without avoiding serious voltage loss in the power rail, versus the limited capacitance available in those smaller value filter caps of yore. (a smaller resistance would've meant increasing the capacitance to keep the same filter roll-off point). But nowadays its not a problem with 22uF or 47uF etc filter caps being readily available, so modern design consideration with power supply is amore about dropping to the desired HT voltage with your choice of resistances (rather than worrying about the frequency roll-off of the RC filter).  Does that help explain it?

[catnine]

The resistor/capacitor dropping in the power supply is just another form of resistor/capacitor filter. From Merlin's 2nd book (Ch4), "With increasing frequency the reactance of the capacitor falls, and so the attenuation of high frequencies is greater than for low frequencies; it is a low-pass or treble-cut filter."

In the old days of small (4-8uF) value e-caps, it used to be more of a concern that there was a balance between how big to make the resistor without avoiding serious voltage loss in the power rail, versus the limited capacitance available in those smaller value filter caps of yore. (a smaller resistance would've meant increasing the capacitance to keep the same filter roll-off point). But nowadays its not a problem with 22uF or 47uF etc filter caps being readily available, so modern design consideration with power supply is amore about dropping to the desired HT voltage with your choice of resistances (rather than worrying about the frequency roll-off of the RC filter).  Does that help explain it?

 Yes it helps . I can't really say that my build is a modern design considering it's design was from 40 odd years ago yet my filter caps are  three 16uf 475 volt and the reservoir cap is 30uf 500 volt a far cry from 4 or 8uf . I guess the man point is filter caps are there to cancel out the AC ripple riding on the DC and of course a choke does a better job of this plus it allows better voltage regulation .

 Before I did anything I went through all sorts of reading and searching and then decided to just parallel one than two 5K droppers with the existing 5K to see what the screen would read and also to show me what the preamp would read . I just clipped them on with aligator clips . the preamp did not change and ending up with three 5K's in parallel I had 1.647K and the screen was close to 7 volts lower than the plates . I tried to calculate what 647 ohm would change if I went with the 1K dropper and it worked out to close to a 3 volt more drop but ended up being a 5 volt drop by doing so and adding the extra 16uf cap and to add the extra cap I needed to split the 33K I had feeding the preamp rail . All I had were the 22K and 10K 2 watters so I just used the 22K then the 16uf cap then the 10K and the last 16uf . ended up with a preamp rail of 299 volts instead of 293 volts. I even checked the OT primary resistance and had 133 ohms on one side and 120 ohms on the other with a totol of 252 ohm and then checked the voltage drop from the plates to the OT prim center tap (B+ against plate) = 2 volts at idle. Difficult task considering my line VAC jumps up and down so I had a DVOM on the line and one on the B+ trying to read when the line near it's top which is 120VAC then take the readings . Best guess was a 2 volt drop so I can't really say what the 1K dropper is actually dropping I just read a 2 volt lower screen than plate.

 I played the amp for at least 2 hours and nothing smoked or got hot the 6V6's didn't glow and the screens did not smoke the PT was just warm same as it always gets not even close to hot .

 One thing did stand out though . after a half hour or so I could hear this tiny bit of a rattle only past the 12th fret so if I hit a high e on the 12th fret there was a short and very slight sort of rattle sound but then after a while this went away. Could have been the new cap forming can't say. I thought it was something in the room but I could hear it best with my ear on the amp cab or bent over behind the amp forcing that high E and there it was a quick slight noise trailing the note but not when the string was plucked. 

 I try and read all of this techical stuff and understand it but after a while it just blurs me and I can't get it to sink in. The math and all the symbles representing what each part of the math they represent just slams me. When I heard that slight noise my first thought was OH MAN WHAT did I do Now . Yet it sounded so much better I just kept playing it louder and louder then heard the new sound of the smooth breakup . I can't say if that noise is gone for good until monday when I get the play it again . In a gig I would have never heard it. It may have been anything in the amp vibrating a bit.

[HotBluePlates]

HBP has left the building.

[Ed_Chambley]

So you are getting breakup at just past 1/2 turn on volume.  Does your volume have a large noticeable increase from to 12?  I am assuming since it was a 5E3 that the controls are numbered 1-12.  The reason I am asking is I am wondering if your breakup is coming from preamp or power tubes?

The 6G2 circuit is not favored by lots of players I know, but it seems like you may have a variation that is a little different.  After your last post I took my 6G2, a head version, large chassis with the tubes up and added 2 additional tubes.  Mine is clean until you pass 3/4 on the volume pot.  One is footswitchable and adds and additional gain stage from a 5751 tube and the other drives a reverb.  This was my first use of a relay.  Cool to have a little reverb.  With the added tube it took me a while to find the correct load as I was getting blocking distortion.  Once I did I started getting a Marshellesque preamp distortion tone.  Mind you, I do have the PI modded with the Paul C.

Also, I did make the fixed bias switchable to cathode as well.  I did not notice much difference at lower volume, but when you crank her up wide open she sings.  She cleans up nicely with a light touch or a small volume roll back on the guitar.

You never know what posting your work will inspire others to do.  After your last post I began looking at ways to increase versatility in this amp.

[catnine]

 Ed: My build has been a PITA from the beginning .  But this build I have now was never right . See since the only chassis I had was from a fried 77 fender MM bass amp same size as a SF champ . Not knowing much at all I looked through fender schems and thought well the 5E3 weber eyelet board will fit but tight not knowing at the time I could have built my own eyelet board which in later builds I did. What I never considered was how the 5E3 would sound like and I hated it, it just looked like a simple P-P build with a rect tube . I searched for better iron and then saw Allen Amps site and though well if I buy the TP25 and then the TO25 I have the choice of 6v6's or 6L6's .  So I though I can build a high powered 5E3 and with the 6L6's and 2 100 watt eminence twleves it was much better than 6V6's , cleaner and louder yet it still over reacted and acted like a 5E3 ( low clean till 3 and then high OD past that). I did get the Allen amps trannies when I first did this build.

 So to answer you . All I can say is looking at later fender schems it struck me the difference in the 5E3 seemed to be the dropping resisters . I then read about screen voltage and plate voltage and then looked back at the 6G2 and also the AA964 . I still had the harsh OD sound and not much else changed. So I took a risk and paralleld two 5K resisters with the one 5K just to get an idea what the actual plate to screen would be then figured I would go for the 1K dropper then add another filter cap and dropper to the preamp stage like the AA964 has. So now I guess my OD is more from the preamp section since now the screens are not sagging . Yes I have the fender style knobs like used on all BF and SF amps 1-10 . There is one more thing that changed . Before the amp would breakup near 4 no matter how light my pick attack was, worse on chords but even on single notes . Now it just begins to breakup at 6 1/2 on chords heavy pick attack but if I back off on the attack the breakup stops and on single notes or double stops and bends the breakup is slight until I crank it up to 8 then if I dig in it breaks up but in a smooth way and if I back off the attack it's clean again so the entire amp has changed . It never reacted to pick attack much at all before. To compare before to now ,it's was like using a full blown distortion pedal cranked as it acted before to a dailed back OD pedal now when it breaksup. I will point out I still use a 12AY7 for the preamp tube , a 12AX7 would probably only make the breakup come in only at a lower number but would be just as loud at a lower number so no point in doing that.  The best part since I play blues is I can dial in the vol I want and clean it up or break it up just by pick attack alone . It is not really a bedroom amp because I would need an OD at low levels . At 4 it is pretty LOUD now yet since the vol doesn't over react as it did before if I do bump it to 5 it's just a bit louder at each number so I can get enough breakup to get clean tone and dig in and have enough breakup to dig the blues. Where this build really shines is at 8 , it just sings and even at 10 it still sings. AS a bonus I can used the strats vol and tone since they now have a wide sweep so I can turn the amp to 8 and back off on the guitar vol and get the same breakup at a lower level same with the tone controls on the strat. The strat now on 5 the tone does not change where before I would just drop the vol to 9 and the tone changed to dull and forget the tone pots on the strat they were treb or muffled by one number now it's gradual and useable . My champ build worked well with the strats but not this build it sucked so I left the strats full up .

 I wish I could say what mathmatically changed all I can offer is it had to be the 6V6's that were producing the OD in a bad way. There is a direct relationship between the plate and screen I read this on Aiken in the bias section. I guess I prefer preamp breakup to output if what I have is true.
 I tried everything I could think of at the time and even tried a BF tone stack with VOL, TREB and BASS and all that did was kill the tone to bland. So from that frame of thought sort of proves the OD I had was  in the output section because even with that stack it still had the harsh OD all it did was allow me to turn the vol up more to get there. I would say now my build is a loud version of a AA964 closer to a BF deluxe . Another odd part is the speaker in this build is a weber sig 12S alnico 25 watt and it holds up well solid bottom not flabbing out and I still have the NFB switch and don't need it now , maybe if I used the 12AX7 it might work ok or if I change the NFB to what the AA964 has yet that seems to be more NFB and perhaps works better with the BF tone stack .

  So there it is , a VERY long answer to a short question as usual for me. sorry .

[catnine]

... What I have been trying to figure out is why fender used droppers that progressively rise in value from the first dropper to the last dropper ...

Along with determining the effectiveness of the filter formed by the R and the filter cap, the dropper resistors do exactly that: drop the voltage between filter nodes.

So every amp maker sizes the resistor to tune what voltage is present at the following filter cap node, for use by the stages attached to that node.

As you work through the power supply from the main filter cap back to the node feeding the input stage, the current drawn through each resistor decreases. Also, the amount of voltage drop desired increases. Both these factors lead to the series dropping resistors feeding the first preamp stages will be the largest values.

 Yes , but what I was curious about is would it matter much if I placed the 10K dropper before the 22K dropper or used two or the same value droppers between the two 16UF filter caps due to the time constant or discharge rate of the caps ? right now the 30UF is the reservoir and the screen runs off a 16uf with a 1K dropper . I think about it and can't imagine the three triodes draw enough current to  drain the two 16uf caps to make a difference. I was just going by the schems fender has and not the actual math. Perhaps you already answered my question and I can't grasp it. I get what you are saying I just question myself .

[catnine]

Ed:

 I ran out of the allowed 5000 charactors . I wish I had a larger chassis . I used a 77 fender music mastar bass amp chassis that same size as a SF Champ. JUst to add one more filter cap I had to move the bias board I made which I had mounted where the cathode bias resister and bypass cap normally would be on a 5E3 eyelet board and mount it between the PT and eyelet board then use the two eyelets to move the 30uf cap over and had just enough room for the 1K 3 watt dropper then I had just enough room to fit in another 16uf sprague cap . There is not even enough room between the front of the chassis to un-solder the ground end of the caps to get a solder sucker in there but since the 30 uf was moved and I had not yet installed the extra 16uf I had room but now with everything all in place I can't get in there. I just used what I had to work with .

 Perhaps one day I will make my own eyelet board like I used to do and use F&T caps and have more room to work . As long as this works I'll let it be.

 Also in my earlier posts I showed photo's of this build . I had a BF faceplate that was one when fender went back to the BF in 1980 so I dug out the old 77 music master bass amp SF faceplate and put that back on and finally put the fender logo with the tail  on the new grill cloth since long ago I removed the partical board baffle and made a new ply baffle since with the Large Allen Amps OT hit the old baffle in the 71 pine MM bass amp cab the 77 chassis sets in, just so it looks like it did when I got it even though it's not a MM bass amp anymore . I liked the 71 cab better since it is pine and has the metal corners and glides , can't say why fender put a glued in partical board baffle in a pine cab but they did. So it's a bit of the old and newer.