AO-44 fun

[SILVERGUN]

This is my first cheap old Hammond score so I figured I'd share.
I cobbled together sluckey's AO-44 and AO-39 conversions and edited his schematics to give a quick idea of what I'm thinking.I like the looks of it. I removed the NFB, added a bypass cap, axe'd the cut control, got rid of the 470K grid leak before the 2nd stage and I think I'm good. Please let me know if you see an opportunity to improve anything.
I had no idea these things were this small.
Should be fun.

[sluckey]

Looks like fun. A Voxy Pee Wee!   

Checked the price of 6GW8s yet?   

[SILVERGUN]

Looks like fun. A Voxy Pee Wee!   

Checked the price of 6GW8s yet?   

Awwww..now you tell me.
 
Luckily, the guy sent me 2 pairs. One has the Hammond markings and the other are a used pair of GE that look pretty nice.
He Priority mailed this from NJ on 12/19 and told me I should have it on 12/21. It made a brief trip to Jacksonville, FL and then fell off the radar with the USPS giving all sorts of bogus tracking updates. It just got here to PA, today 1/18. It went hundreds of miles to go about 30 miles from A to B. Luckily, the packaging was in tact and all the tubes, including the rectifier, where still vacuum sealed. I was picturing a box full of smashed glass.
I have one Winged C EF86 that I'll try in the front end. This will be my first venture into Voxyland. Although, with the change in PI I'm not sure I'm allowed to call it that. If the internet Vox police show up I'm screwed.

[sluckey]

Build it just like your schematic. You can always change it later if you think you rather have a LTP.

[thetragichero]

these are certainly an exercise in fitting a ton of stuff in a small package!

[glass54]

+1 thetragichero
Did I see a crack in the 1K Carbon Comp resistor (PS Node A to Node B).
Time for a Metal Oxide 
Kind regards
Mirek

[jojokeo]

Hey boys! Happy New Year! SG great minds think alike. I had an idea using 6AQ5s created for months and finally got to building after a previous AO39 build...this is kind of a 50's Vox meets Marsha(ll) from the Brady Bunch? Then got into Alice's kitchen to see what was on the snacks shelf? Before anyone knew it flour, sugar, and eggs were all over the place!    This is the original idea and version. The amp is still undergoing various ideas. I originally wanted to create a SAG control but after messing around with the plate then screen voltages it seemed to not quite do enough justice to warrant leaving these in. Then I started messing with the EF-86 screen compression and am getting closer. I've got that going pretty well where I'm satisfied and have a couple more ideas to try before calling things good. I love converting the old Hammonds...


Joe

[DummyLoad]

SG, those Hammond 6GW8 are quite likely Mullards, i have seen GE & RCA 6GW8 with made in markings of, Holland, Gt. Btn, & W. Germany.

the Hammonds sounded best to me, however, still too EL84-ish sounding, so I passed. i have some of that AO-44 iron that i still haven't a clue what to do with... perhaps another 6005/6AQ5 amp? 

SG, voxy cops are watching your vox violations and such shenanigans. you have 24hrs to change cathodyne PI to LT, or else! you have been warned! :p

HNY jojo!

---pete

[SILVERGUN]

Hey boys! Happy New Year! SG great minds think alike.

HNY, old timer! Yeah, we must be drinkin' the same KoolAid.
I was gonna turn this into a Mini Micro Major, but we all know Majors suck so I decided to go down this already mostly paved path.
I'm thinkin I'm gonna call this one The Drama Queen after one of our long lost friends who so tragically lost his way over the last few years with the emergence of modeling technology, the acquisition of cheap overseas guitars, and just flat out fake news. An alternative name for the amp would be The Melted Snowflake. I'm torn.

I usually spend wayyyy too much time trying to make everything look perfect so I can never take pictures and then not post anything anyway.
It will be a joy to throw a couple parts at this and see where it lands. In the process I'll try to snap some pics and maybe even play a couple riffs through it.
As long as nobody hurts my feelings I'll stick around. 

[shooter]

I'm torn.

Creed?? 

[SILVERGUN]

SG, those Hammond 6GW8 are quite likely Mullards, i have seen GE & RCA 6GW8 with made in markings of, Holland, Gt. Btn, & W. Germany.

Cool, I'll snap a couple pics you can tell me if I've got the good stuff. I've never spent much time thinking about old type brands. I was a late bloomer with little money....not a good combo.

the Hammonds sounded best to me, however, still too EL84-ish sounding, so I passed. i have some of that AO-44 iron that i still haven't a clue what to do with... perhaps another 6005/6AQ5 amp? 

So maybe this is the destiny of the 6GW8? A poor mans single channel AC?
If someone just handed me this iron without the cool old caps in this adorable little chassis it would probably just go into a drawer with my parametric EQ pedal project.
I have not spent anytime with the EL84, but Vox'ites everywhere swear by it so we'll just see.

SG, voxy cops are watching your vox violations and such shenanigans. you have 24hrs to change cathodyne PI to LT, or else! you have been warned! :p

I ain't scared. I'm all stocked up on ammo, whiskey, anti-inflammatories, capacitors, and bulk bridge rectifiers. They can't hurt me.

[SILVERGUN]

Did I see a crack in the 1K Carbon Comp resistor (PS Node A to Node B).

Nice catch, I'll keep an eye on that.

[sluckey]

If that resistor is cracked, check for shorts on the cap can too.

And before you start ripping things out, connect a power cord and check for proper AC voltages on the rectifier socket. If good, plug in ***ONLY*** the recto tube and check for proper B+ voltages. Even better, if you have a variac, use it to slowly bring up the primary voltage to 120 over a few hours. You may get lucky and be able to use the original cap can. I was lucky. In fact, I havent found a single can to be defective in the few Hammonds I've played with.

[SILVERGUN]

If that resistor is cracked, check for shorts on the cap can too.

And before you start ripping things out, connect a power cord and check for proper AC voltages on the rectifier socket. If good, plug in ***ONLY*** the recto tube and check for proper B+ voltages. Even better, if you have a variac, use it to slowly bring up the primary voltage to 120 over a few hours. You may get lucky and be able to use the original cap can. I was lucky. In fact, I havent found a single can to be defective in the few Hammonds I've played with.

I was gonna ask you about that cap. I've never messed with re-using old parts.
Thanks for the tips. Will do. I'm always looking for a reason to break out the Variac.

[SILVERGUN]

Did I see a crack in the 1K Carbon Comp resistor (PS Node A to Node B).

Nice catch, I'll keep an eye on that.

Yup, it's cracked and only reads 274 ohms. The other 2 are good @ 5.7k and 9.8k.
I'll replace it before I proceed and check the xfmr secondaries with it out of circuit before I apply V to the cap.
No shorts on the cap.

[DummyLoad]

if you are open to suggestions... easy enough to add & remove if you don't like. helps immensely with cathodyne doubling distortion.

--pete

[SILVERGUN]

if you are open to suggestions... easy enough to add & remove if you don't like. helps immensely with cathodyne doubling distortion.

--pete

That looks good. Should I consider bypassing it with a cap to retain highs?

I want it to sound exactly like a cranked Major through a full stack, so whatever I have to do to get there.
I trust you.

[MWaldorf]

I built one of Sluckey's Voxy Pee Wees over the summer, great amp.  I added switchable morph controls on the EF86 and bypass cap on V1a.  I had no problems with the original cap can either.  My variant schematic attached.

[SILVERGUN]

I pulled that resistor out and it broke in half while I was desoldering it.
Again, good catch glass54. You saved me some bench time.

[sluckey]

I built one of Sluckey's Voxy Pee Wees over the summer, great amp.

Haha. I had already forgotten about that! Sho nuff. I have the Visio file in my Pee Wee folder. SG should save your modified schematic. Could be something there that he needs/wants.

[SILVERGUN]

I built one of Sluckey's Voxy Pee Wees over the summer, great amp.

Haha. I had already forgotten about that! Sho nuff. I have the Visio file in my Pee Wee folder. SG should save your modified schematic. Could be something there that he needs/wants.

Done deal. I'm a schematic hoarder. I'm gonna start out super simple and then see if it needs anything. I've learned that less options is better options for me.


Unloaded secondary testing is done and all good. 278-0-278 and 7VAC
I'll replace that resistor, punch some holes and do the Variac burn in tonight. Just typing that reminded me to take my punch home, so that's a win right there.

[DummyLoad]

if you are open to suggestions... easy enough to add & remove if you don't like. helps immensely with cathodyne doubling distortion.

--pete

That looks good. Should I consider bypassing it with a cap to retain highs?

I want it to sound exactly like a cranked Major through a full stack, so whatever I have to do to get there.
I trust you.

yes, switchable would be cool to have clean-ish option as well.

jim bob is gonna hunt you down for even comparing to a Major.   

[SILVERGUN]

jim bob is gonna ...

still. not. scared.

But I've got a couple questions:
1) I don't see a center tap for the filament winding in my amp or the pics of sluckey's. Where is it?
2) Whats the best way to run the cap(s) at low voltage since I need to feed the rectifier filaments for it to light up?..I'm guessing I should just jump a couple diodes over for now?Did just that but now I cant get the damn line out of my typing. The button wont come unpushed. How long could this go on?Could it be that everything I type from now on will have a line through it?

[thetragichero]

to answer #1, the center tap is where two 100 ohm resistors meet, one from each filament ta}

[sluckey]

But I've got a couple questions:
1) I don't see a center tap for the filament winding in my amp or the pics of sluckey's. Where is it?

2) Whats the best way to run the cap(s) at low voltage since I need to feed the rectifier filaments for it to light up?..I'm guessing I should just jump a couple diodes over for now?

1. Look closely at the AO-44 schematic. What do you see?    http://sluckeyamps.com/PeeWee/PeeWee.pdf

2. Just plug the recto tube in.

[SILVERGUN]

Ahhhhh...I see it now. Internally connected to the other CT. I had never seen that before.

I tacked some diodes on to trickle the cap(s). So far I'm up to 68VDC and I'm seeing .2V drop across the 1K, 1.2V across the 5.7K and 2V across the 9.8K.
How often would you bump up the voltage before getting all the way to 300VDC?...I do realize that I could get to 380V with the diodes in there so I'll limit it to 300ish to not push it.

[thetragichero]

oh dang i never noticed that. guess i should've looked closer at the original schematic

[jojokeo]

Hey boys! Happy New Year! SG great minds think alike.

HNY, old timer! Yeah, we must be drinkin' the same KoolAid.
I was gonna turn this into a Mini Micro Major, but we all know Majors suck so I decided to go down this already mostly paved path.
I'm thinkin I'm gonna call this one The Drama Queen after one of our long lost friends who so tragically lost his way over the last few years with the emergence of modeling technology, the acquisition of cheap overseas guitars, and just flat out fake news. An alternative name for the amp would be The Melted Snowflake. I'm torn.

I usually spend wayyyy too much time trying to make everything look perfect so I can never take pictures and then not post anything anyway.
It will be a joy to throw a couple parts at this and see where it lands. In the process I'll try to snap some pics and maybe even play a couple riffs through it.
As long as nobody hurts my feelings I'll stick around. 

That is awesome SG, your smack attack is so majorly good especially when targeting our favorite principled boy karen. Solder on my friend...

[jojokeo]

if you are open to suggestions... easy enough to add & remove if you don't like. helps immensely with cathodyne doubling distortion.

--pete

That looks good. Should I consider bypassing it with a cap to retain highs?

I want it to sound exactly like a cranked Major through a full stack, so whatever I have to do to get there.
I trust you.

yes, switchable would be cool to have clean-ish option as well.

jim bob is gonna hunt you down for even comparing to a Major. 

Thanks Pete, I have to remember that grid stopper trick. I think Merlin describes that a high value doesn't mess with the high end correct? It's very late for me and I have no time to look up the exact reason why?
SG - I've build the CAT pi w/ ECL86s and I had to lower the load resistors down to 56k to lessen the output. BUT, if I'd added that grid stopper maybe I could've left them at 100k like your schematic? Pete please confirm if possible? Thanks brother

[DummyLoad]

if you are open to suggestions... easy enough to add & remove if you don't like. helps immensely with cathodyne doubling distortion.

--pete

That looks good. Should I consider bypassing it with a cap to retain highs?

I want it to sound exactly like a cranked Major through a full stack, so whatever I have to do to get there.
I trust you.

yes, switchable would be cool to have clean-ish option as well.

jim bob is gonna hunt you down for even comparing to a Major. 

Thanks Pete, I have to remember that grid stopper trick. I think Merlin describes that a high value doesn't mess with the high end correct? It's very late for me and I have no time to look up the exact reason why?
SG - I've build the CAT pi w/ ECL86s and I had to lower the load resistors down to 56k to lessen the output. BUT, if I'd added that grid stopper maybe I could've left them at 100k like your schematic? Pete please confirm if possible? Thanks brother

6GW8 are easy drive -10Vrms to clip. the cathodyne grid stopper helps reduce the freq. doubling effect when pushing the cathodyne out of bias balance and minimizes the g1 current flow during that excursion. 470K and > for the cathodyne grid stopper will start to shave off HF noticeably. knee is 100KHz with 470K with 1M halves the HF rolloff knee to about 50KHZ.

fender 112K cathodyne load line would swing less, 94K even less. shoot for about 1.2mA Ib at 270V B+ with either. however, with the fender or hammond plan, the output swing will still be pushed though a stage with a gain of 1 - limiting the drive swing from the preceding stage would make more sense. one way would be to split the anode R of the cathodyne driver and requires just 1 part.

sandwich TS inside of the NFB loop for that major major tone. oh wait, this is a ¿¿vox?? now i'm confused. oh hell, just insert TS in front of cathodyne & ditch NFB and viola! Major Vox? meh! peace out!

--pete 

[SILVERGUN]

SG, those Hammond 6GW8 are quite likely Mullards, i have seen GE & RCA 6GW8 with made in markings of, Holland, Gt. Btn, & W. Germany.

Here's some pics

[shooter]

so how many of those cute tubes fit inside a KT88 

[SILVERGUN]

so how many of those cute tubes fit inside a KT88 

17?

[SILVERGUN]

I got the cap up close to working V, took out the diodes and with just the 6CA4 in I'm at 330VDC with 103VAC input. I'll leave it there for a while and be ready to start stripping. The lowest V rating on the cap is 350V.

[jojokeo]

so how many of those cute tubes fit inside a KT88 

17?

17? As in the letter Q??? 


Ahem, from Boy-Drama - Major rules, SG drools. Don't shoot the messenger... I had a good laugh at his expense and it feels GOOD! 

[jojokeo]

...sandwich TS inside of the NFB loop for that major major tone. oh wait, this is a ¿¿vox?? now i'm confused. oh hell, just insert TS in front of cathodyne & ditch NFB and viola! Major Vox? meh! peace out!

--pete

Blasphemy! Boy-Drama says...there's nothing that can replace or sound as good as KT88s, NOTHING! I say, "what did you say?" Who can hear anything after actually playing KT88s???

[HotBluePlates]

SG, those Hammond 6GW8 are quite likely Mullards, i have seen GE & RCA 6GW8 with made in markings of, Holland, Gt. Btn, & W. Germany.

Here's some pics

Those "G.E." tubes have Mullard-style print at the top.  Look closely at the glass sides near the base for codes.

In your 1st "Hammond" photo, the left tube appears to show some of those codes near the base.  1st character of the bottom line will indicate the factory.

In your 2nd "Hammond" photo, the right tube shows some of the code near the base.  It's not clear enough to make out, but if the first letter shown is "B" that's Mullard's Blackburn factory.  Below is an example of a G.E.-branded Mullard ECL86, with a clear "B" in the first position of the 2nd line of code.

[SILVERGUN]

Here's a better shot of the printing on the Hammond labeled pair. The first mark appears to be some sort of triangle(?) followed by 613.

I left the GEs at home but they clearly have "Gt. Brittain" printed on the top line. 

[SILVERGUN]

Here's some progress pics. if you look closely you'll notice that the bypass cap I added to the second stage is snipped out and the bypass cap on the output tubes is snipped out.
So there was sound. I have a nice sweet chime up til about 3 on the volume and then it starts getting unruly. I don't think I ever got it up to 10 because it was just a screeching little bees nest of distortion and oscillation, before I could even get my guitar volume up.
So I started by snipping out the 2nd stage cap and that was better.
Then I snipped out the power stage bypass cap and that sounded better to me also. Less overall noise.
It was too late to continue sound testing in the basement but I could tell it's gonna take some taming.
Also found time to cut some plywood and put her on some temporary crutches. I'll keep them there until she's well.

When it sounds good it sounds great.

[SILVERGUN]

Pete, I tried it first without your grid stopper and then when it started hemin and hawin I shut it down and put it in there. I didn't have the scope on it but it did seem to help. There was just so much else going on that I don't have any scientific data. If you look close you can see how I just tacked it in to try. It will stay and I'll clean it up once we get the rest squared away. It did not effect highs to any noticeable degree. There are PLENTY of highs here
Here's a quick markup of a couple ideas to start to tame it.
The 470Ks before the power tube grid leaks would form a fixed PPIMV.
Then I figured it would benefit from some grid stoppers.
At that point I would determine whether the power tube bypass cap would stay or go.

And I'm considering putting the NFB right back where sluckey had it. (not pictured)

Any other thoughts are greatly appreciated.

[DummyLoad]

So there was sound. I have a nice sweet chime up til about 3 on the volume and then it starts getting unruly. I don't think I ever got it up to 10 because it was just a screeching little bees nest of distortion and oscillation, before I could even get my guitar volume up.

oh, so what you're really saying is that it sounds just like a major? 

--pete

[SILVERGUN]

So there was sound. I have a nice sweet chime up til about 3 on the volume and then it starts getting unruly. I don't think I ever got it up to 10 because it was just a screeching little bees nest of distortion and oscillation, before I could even get my guitar volume up.

oh, so what you're really saying is that it sounds just like a major? 

--pete

  The only thing missing was the FIRE

[jojokeo]

You shouldn't need the voltage dividers in there after the pi coupling caps if you lowered the 100ks to 56ks... Just saying. And no power tube cathode bypass cap?! Sacrilege... If it were me I'd throw in a simple crossline MV... but I always mod the pot filing away the uppermost trace. When full up it's out of circuit without a switch. A nice little feature having it your way just like Burger queen.


FIRE isn't what it used to be... you can find it being applied to old glory nightly in about any major US city near you... 

[SILVERGUN]

You shouldn't need the voltage dividers in there after the pi coupling caps if you lowered the 100ks to 56ks... Just saying. And no power tube cathode bypass cap?! Sacrilege... If it were me I'd throw in a simple crossline MV... but I always mod the pot filing away the uppermost trace. When full up it's out of circuit without a switch. A nice little feature having it your way just like Burger queen.


FIRE isn't what it used to be... you can find it being applied to old glory nightly in about any major US city near you... 

I did put the voltage divider after the PI and it worked like I wanted. I put some bypass caps across the series resistors and it made a noticeable improvement.
I am still getting too much distortion but I haven't had enough time to put the scope on it. I'm considering a V divider before the PI but before I do that I'll try tacking 100Ks across the existing 100Ks, like you suggested.
When I keep it dialed down it really does sound good and I see what Ed was talking about with the EF86 front end.I also see that the bypass cap on the output tubes does sound better now that I have less overall noise.I need more hours in a day or just a good old fashioned snow day.

Once I get the scope on it I should be able to tell where it's going wrong. I'm looking forward to getting back to it.

[SILVERGUN]

fender 112K cathodyne load line would swing less, 94K even less. shoot for about 1.2mA Ib at 270V B+ with either. however, with the fender or hammond plan, the output swing will still be pushed though a stage with a gain of 1 - limiting the drive swing from the preceding stage would make more sense. one way would be to split the anode R of the cathodyne driver and requires just 1 part.

I read right through this initially.
"limiting the drive swing from the preceding stage" is sounding about right to me.
Jojo always liked a split load so I don't know why he let me get away....maybe it's cause we already have one load who split?   

[jojokeo]

Too much distortion? Install a pent/triode switch. Remove or make adjustable bypass cap on Rk, increase load resistor & decrease screen resistor, put a voltage divider before pi (see my schemo on your cue stick named amp  )  if you want a bit of compression and bloom ground the screen bypass at cathode, if looking for more clean-ish hi-fi ground it to ground... The '86 has a LOT of things you can tweak to control the blow torch with... That's what makes them so much fun. I've got another where I paralleled an ax7 into the ef86 and it's also very nice to try (next project?) Then one where there's an '86 into another '86... this is plain evil... >:) Think of drag racing with two blowers or 4 kits of nitrous? It's more than needed but sure fun to play around with.

[shooter]

I read right through this initially.

An '84 is the snowflake of tubes, just whispering sends it into complete melt-down
sedate, scope, operate, and above all else make a fuzzy head shell for it to hide when the bars are real scary   

[SILVERGUN]

I've spent some time trying different tweaks to try to get this closer to under control.It sounds much better now but I haven't had much of a chance to play test it at full volume.The low volume chime is gorgeous and it has a tendency to fill out the notes with nice harmonic content.
It sustains beautifully and has a nice bloom as a driven clean tone.One of the moves I made was to just bypass the entire 2nd stage to confirm that my first stage sounded good alone. There wasn't enough signal to drive the amp but it confirmed that we were right and the problem was the 2nd stage. I used a 100K pot and dialed in a 68K/27K voltage divider that sounds right to me.I also tried to re-insert the global NFB and just felt like it took away from the chimeyness.I won't know where it stands until I can run it full out and see how it holds together.So far, I'm glad I tried it because I didn't really understand what all the hype was about.

[trobbins]

You may want to add 1N4007 diode protection in for each 6CA4 anode, just in case the 6CA4 is getting old.

Have the EF86 and the triode anode voltages all idle biased up ok?  One pain with the 6GW8 (and any triode pentode) in a PP arrangement is that not only do the two output stage pentodes need to have reasonable idle current balance, but the two triodes need to sit their anodes at reasonable idle levels, otherwise the signal can start to get wacky too early.

[DummyLoad]

Then one where there's an '86 into another '86... this is plain evil... >:)

richard kuehnel thought so too... there was a preamp that kuehnel built that was posted on the Pentode Press URL & taken down some time ago. that was my inspiration a few years back to build a dual SE with a pair EL34 driven by a pair of cascaded 5879.

during the year of COVID19, a co-conspirator and i built a distortion pedal on abreadboard with a pair of cascaded pentodes. i ditched the conventional PS arrangement and used a 200V DC/DC converter so that it can be powered by a wall wart. still fiddling with it, but it's been put aside for now - too much work getting in the way of the hobbies.

--pete