HoSo56 & 5879 OD and Dual Pentode amp ideas

[tubenit]

Guys, I have not built either of these amps yet.  I am leaning towards the HoSo56 with 5879 OD.  I have built numerous HoSo56 amps with different power tubes including the 5881's  (6V6, El84, 6BM8,6AQ5). 

The HoSo56 is one of the most touch sensitive amps I've ever played. The tone changes significantly with your picking. Very sweet amp and I miss having a HoSo56.   And I have built an amp using a 5879 for the OD and it works great!  My son has it. Very nice sounding amp. So, this is a fusion of those two ideas. The HoSo56 is Geezer's innovation, BTW.

The Dual Pentode idea is sort of a conversion of my current D'Mars ODS amp simply changing the clean channel to a single 5879 with a CF to drive the tone stack.

The SCH schematic and corresponding layouts are here:
http://el34world.com/Forum/index.php?topic=20017.new#new

It's been awhile since I've posted a new idea, so I thought I'd share these.  I have yet to build a clone of a manufactured amp & have always preferred to try new ideas.

With respect, Tubenit

[kagliostro]

Ciao Tubenit

Your schematic show a CF after the 5879 but the triode count is odd, so, or you use a double triode + a single triode (6av6)

or, if you use double triodes,  you'll have an unused triode

Why don't use a Source Follower as in many of your amps ?

Franco

[tubenit]

The CF after the V1 5879 is V2a.   Look at the first gain stage in the OD.  It is V2b. 

You can look at the SCH layout in the SCH Library of schematics to see how this is wired up.

With respect, Tubenit

[kagliostro]

Ooppsss !



Franco

[Paul1453]

So your B+ is obviously below +450,
about what does it run?
Below +400 on the plates of the output tubes?

The reason I ask those silly questions.
I've been looking for a 6L6 amp to build.
Would this design be OK with the 6L6G or metal 6L6's?
I have the most of those tubes, but I do have a pair of 6L6GCs if required.

After hearing your description of this amp,
I think I might like to build this.   

[tubenit]

300-0-300 PT

With 5V4   300 X 1.2 = 360v  guesstimated
with GZ34  300 X 1.3 = 390
With solid state  300 X 1.4 = 420

I don't know anything bout metal 6L6's?   I think you could do this amp with even 6V6's with tube rectification.

Paul,  how about downloading the attached Tube Data Cheat Sheet, please?

With respect, Tubenit

[Paul1453]

Cool, so it is currently running around +390V B+.
That is a big plus for my parts inventory.

I had that sheet from you before, and it is a great resource.   

Is the expensive tube rectifier, which I don't have in stock, a vital component to the sound?

The metal 6L6 is the oldest 6L6 and the same as the 6L6G.
Basically, it cannot take the over 400 V B+ used by the GB's and GC's.
I think +390 is all that the metal 6L6 is rated for.
In a circuit designed for 6L6Gs, +390V B+, I could not hear any difference between the metal 6L6, G, GB, or GC.
I have the most metal 6L6s maybe 6 of them, 2 6l6Gs, and now 4 6L6GCs.
If this amp can use my old metal 6L6s, that is a plus for me.
The newer amps all seem to want to put +450V on the plate of the 6L6s.
So those designs rule out most of my 6L6 stock.   

I have my old Hammond H100 organ chassis I think would work with your circuit.
It had 3 amps on it originally.  2 PP EL84s and 1 PP 6L6.
It didn't have a PT on this chassis, too many other transformers already on it. 
But it does have lots of 9 pin sockets to use, and the OT and output tubes are mounted in the far right corner.
I've stripped most everything off it now.

I've made a simple Airline 6L6 amp on my breadboard with the big OT.
Sounds good to me but not quite good enough to build in that chassis.
The other EL84 OTs have been breadboarded for the Hoffman Stout.
I'm satisfied with that circuit, and looking to build 2 of those into chassis' I have on hand.
Your design, seems like it would be a good fit to my Hammond chassis.

It also seems to fit a niche market better.
It is not the same as any other big name amp you could buy off the shelf.
I would plan to use my old 6L6G black plate tubes in one I would try to sell.
Would I need to send you a royalty payment if I built and sold an amp of your design? 
I've got some old vintage tubes or parts I could ship you as a royalty kick back. 

A sophisticated player might appreciate that slight difference in sound from all the other amps he has played.
For a hack player like me, it might not be noticeable. 

If I really like the sound of this amp, and with your endorsement I fully expect to.
I would seek to build a 2nd one with metal 6L6s for me to keep.
I'd only need another OT, as I think I have most of the other parts already in stock.
The tube rectifier is the big question for me.  I've got 2 PT's I think that would work with that.
I've got 4 or more PTs that would work with a SS recticifer.
This design also doesn't use the negative grid bias, from what I see.   
That is another plus for my PTs and novice builder status.   

[tubenit]

Paul,

Anything I share on this forum is totally free to others and I don't even care if I am "credited" with some idea. 

And in reality, pretty much everytime I think I've come up with some innovative idea ............ I discovered someone else had already thought of it and I didn't know about it.  At the most, I simply discover I've repackaged someone else's ingenuity.

I have had so many wonderful people here help me out including HotBluePlates, Sluckey and many many others that anything I contribute still falls short of what I have received.

With respect, Tubenit

[2deaf]

And in reality, pretty much everytime I think I've come up with some innovative idea ............ I discovered someone else had already thought of it and I didn't know about it.

I call this my Thousand Person Rule that goes something like "No matter what I come up with, a minimum of one thousand people have already done it."  There could be millions that have also formulated this rule.

Your original ideas really are your ideas that you designed all by yourself with no outside influence.  It's just that you aren't the only one.

I recently saw the first two stages of an amp that were so similar to what I thought was a unique design that I was considering the possibility that there had been a break-in at my house.

[Paul1453]

Gathering up the parts.

I only have 1 12AY7 and 0 5751s 

I  do have 3 of the 5879s in stock.

12AX7s are no problem, and a few different flavors of 6L6s to try out.

I put the tubes in as I think will work, I could shift them down more away from the output tubes.

What do you think of this Hammond chassis for this amp?

Is there another tube I can sub for the missing 5751? 
12AT7 or 12AU7 or 12AZ7   
I do have some of those.

I need to learn all the little details of this circuit before I try any E130L tubes with it.   

[tubenit]

Paul,

This will be a reasonably high gain amp which means it is critical that one has a well thought out (and perhaps proven) layout in order to avoid oscillation problems.  I do not know if your chassis will work or not?

I drew up a HoSo56 for you on the other thread without the switchable gain stage.  I think that might work in this chassis?

12AX7= 100
5751 = 70
12AT7 = 60
12AY7 = 47
12AU7 = 20

I switch preamp tubes somewhat frequently in my amps depending on what type of music I am playing. I simply will put a tube in with a higher gain or lower gain factor depending what I am after.   

Try different 12A_7 tubes and see what you like.

With respect, Tubenit

[tubenit]

OK,  I built the HoSo56 & 5879 OD amp.  I will refer to it as the HoSo56-OD from here out.

Essentially, what I did was convert my D'Mars ODS amp to this.  There was nothing wrong with the D'Mars. In fact, it has been my favorite amp that I've built.  Having said that,  I was very very curious what this HoSo56 & 5897 OD would sound like?  And my curiousity won out.  I've tried to limit myself to 2 amps and 4 guitars.  So that is why I did not make another amp and converted the D'Mars instead.

They are different, I can not say one is "better" then the other one.  Here are my observations after playing this HoSo56-OD for a while. IF my impressions change over time, I will update the review.

The D'Mars has a wider range of clean to OD.  The clean on the D'Mars would make a great sounding jazz amp, IMO. Very full clean tone using a 12AY7 in V1.   The OD on the D'Mars has more sustain, but can get a little distorted if really cranked way up. You can get great sustain on the D'Mars OD without it being cranked up. In fact, you can actually get quite a sustain with a reasonably clean sounding overdrive with the D'Mars.

The HoSo56-OD is waaayyy more touch sensitive. Play light it's a clean tone.  Play moderate it's on the edge of breaking up.  Play aggressively and you've got some break up & OD going on with just the clean channel alone .......... all at the same volume pot settings.  Very nice harmonics.  It does have a dash of chime in the tone.  Very FAT tone.  Ironically, I have that of the D'Mars clean being a very full tone but the HoSo56-OD is just a super lush FAT tone.

The HoSo56-OD is the most creamy smooth touch sensitive OD I've gotten out of any amp. This was very much a surprise to me!  I thought it would have less smoothness then the D'Mars but I was wrong. It is significantly smoother.  I was expecting the possibility of too much chime in the OD channel, but it's really a smooth tone.

However the HoSo56-OD overdrive does NOT have as much sustain as the D'Mars.  Maybe 75-80% as much sustain.  So it is a trade off. It was possible to get the D'Mars to sustain into feedback.  This amp will not do that. 

The thing I noticed about this HoSo56-OD is that even when I crank it up on clean and/or OD,  .............. it continues to have remarkable note definition whether chording or solo-ing.  IF I put the volume knob on the D'Mars at 7-8,  the tone got somewhat gritty and had some mud in it. Not so with the HoSo56-OD.  It just gives a more aggressive articulate touch sensitive tone that still has good note definition.

There is not as much of a spread or contrast between clean to OD on this amp compared to the D'Mars that had a very diverse range from clean to OD.

The HoSo56-OD sort of hangs on that edge of breaking up even on clean with moderate playing.  The OD kicked in is more like a boost that adds a big dose of creamy overdrive.  Still very touch sensitive and still has good note definition. 

On clean, you notice a dash of chime in the tone.  On OD, you notice the creamy smooth boost tone.  Very nice contrast but at the core, you can tell it's still the same amp just boosted and creamier.  There is more sustain on the OD channel, but honestly ....... the clean channel of the HoSo56-OD has quite a bit of sustain to it also.  The OD channel is creamier, smoother and maybe more compressed/boosted. 

This is a very unique amp with a beautiful tone, IMO.  I think for anyone who enjoys the little nuances of playing light to aggressive and enjoys playing some riffs inside chording etc.........  this could possibly be an ideal amp for that.  I think for super sustain, one would need a fuzz or boost or overdrive pedal added.

I updated the schematic and layout in the SCH file.

with respect, Tubenit

[Paul1453]

For me on this 1st build of the HoSo, I'd like to do better than my normal standard of:

1.  Does it work?
2.  Does it sound good?

To add #3

3.  Does it look like a high quality amp in it's completed state?

Inspired by MScaggs continued posting of top quality constructions.   
I'm seeking to much better than my original standard on this one.
To make something that could possibly sell for a significant profit.
If I ever stumble across the right buyer.   

On a second build of this for me keep, I might revert back to my old standard.   

So, I stripped the H100 chassis and am replacing all the sockets.
I'm trying to make a good plan for the layout with what I have.
I laid out most of the required components and took a top down shot for further planning.
I  also show what I propose to use for PT and choke.

On the layout overview nothing is really set in stone.
I'd like a little feedback on how I can configure what I have,
or what I need to change, into something that has good chances
of being a no problems found design.

[Paul1453]

Overhead view proposal # 1.

The PT in the left corner.
next the tube rectifier, SS rectifier, or some combination of both?
moving right to the choke, OT, and Output tubes in the right corner.
Output Jack somewhere between the 2 shown on the back.

Front lineup has a cap can in the left corner.
Power switch?
Then there are parts laid across for what holes are already there.
The 9 pin sockets could move left 1 spot and leave a hole somewhere else,if that helped the pre-amp tubes.
5 holes potential for input and send and return jacks.
I'm currently considering the 3rd hole for the input jack for a short shielded run to 1 of the 2 far left sockets.   

Comments, suggestions, criticisms??

[tubenit]

My comment and suggestion.  Paul,  I don't think anyone can predict if your approach will work or not?  You'll just have to use common sense as best you can and give it a try.

I also would say to look at chassis layouts of high gain amps and draw ideas from them.  Google photos of Dumble amps, Soldano, Mesa Boogie, Cornford, some of the Bad Cat amps and others. 


IF it is not laid out well, you may have oscillation problems and/or a noisey amp.

With respect, Tubenit

[Paul1453]

My proposed PT will only do around +300 to +325 B+ tube rectified or +375 SS.
I think that may be OK since I'd like to use my older 6L6 output tubes.
Do you think that will work, or should I try again on PT choice?
I have 2 other (old and not quite as pretty) higher voltage PTs,
but would like to use them on other higher voltage required circuits.

If this PT is OK, I still have to cut up the chassis to make it fit.
I'm thinking that whatever PT I choose, there will be metal cutting required.
It looks like the choke just needs a hole or 2 drilled for mounting in its current position.
The rectifier hole would need to be made, but with this PT it would seem to waste the 5VAC.
If I didn't include a tube rectifier.
No more metal work required for the SS rectifier.

I'm still thinking about what would be required to have a switchable tube/SS PS.
There seems to be room to include both, but I don't have a clear idea how I could do that yet.   

One other quick question.
The cap can I have proposed is 50/50 uF 450V.  It is what I have.
This is different from your PS with 40/40 uF 450V design for the 1st 2 caps.
Is 50uF too much for a tube rectifier, or will the 50/50 cap be OK?

[DummyLoad]

580VCT 300mA PT will work fine with 6L6,5881,EL34,6V6,7591, etc..


--pete

[Paul1453]

Thanks Pete.

I miscalculated, I used 270VAC.   

290VAC gives me almost 50 more volts either way.

I think I will try to figure out how to best mount this one then.   

Power switch in the front left corner OK, or maybe better on the back?

More convenient on the front.   

[tubenit]

Paul,

Mediocre neatness, but the HoSo56-OD is very quiet at idle.

with respect, Tubenit

[Paul1453]

Paul,

This will be a reasonably high gain amp which means it is critical that one has a well thought out (and perhaps proven) layout in order to avoid oscillation problems.  I do not know if your chassis will work or not?

I drew up a HoSo56 for you on the other thread without the switchable gain stage.  I think that might work in this chassis?

12AX7= 100
5751 = 70
12AT7 = 60
12AY7 = 47
12AU7 = 20

I switch preamp tubes somewhat frequently in my amps depending on what type of music I am playing. I simply will put a tube in with a higher gain or lower gain factor depending what I am after.   

Try different 12A_7 tubes and see what you like.

With respect, Tubenit

Thanks,
I thought you might use multiple flavors of 12A_7 in those spots.

There is another twin triode, of which I have a number of premium tubes, that only seems to be used in Hi-Fi amps.
The 6DJ8/ECC88/6922 has an amplification factor of 33, just in the middle of the AU and AY.
Have you used this twin triode in a guitar amp before?

Once I learn the details of this design, I'd like to see if I can't breadboard this circuit with 6DJ8s.
I have about a dozen of these, and would like to have an amp to test the sound of these.
Even if I just continue to sell them off on Ebay.
Besides knowing my testers results, I'd also know if tested tubes sound good or not.   

[Paul1453]

Your picture gives me some more clues about your layout.

Only jack on the front is the input.
Power switch is on the back.

Other switches seem to have some chips wired to them?
Looks like those are footswitch controls?
Have you dropped those chips now?

No cap can, so is my 50/50 useable as a replacement for your 40/40s?

A couple of E-caps tied to the power LED, maybe I missed that on the schematic?

NFB pot and effects pots and jacks on the back.

The double pots connected to the output tubes located on the front.

Your proven layout gives me some standards to try to copy.   

Thanks! and I'll be pretty happy if I can meet your mediocre neatness standard.   

Wow, 11 pots, 3 switches, the input  jack and a power indicator all on the front panel.
That will take some serious consideration on how to make that work on my chassis.
My chassis measures approximately 17" L x 7" W x 2" H.

[Paul1453]

I'm trying to do the PSU simulation with my PT/parts specs.

I can't seem to put in the 220K bleeder resistor.
No worries, or will that lower my B-E voltages?

Simulated voltages:

A=+385
B=+380
So far so good.
C=+295
D=+162
E=+125

What voltages should I aim at for C-E?
C seems a little high to me.
D&E seem a little low.

I can configure this for the voltages you specify.   

[DummyLoad]

try this way...


--pete

[Paul1453]

Thanks Pete,

Added the current taps as you showed.
I didn't change any other values.
My voltages changed drastically.

No current tap on Node A.
Do I calculate max current loads on each node and use those values as current taps?

I was thinking I should be aiming for C-E voltages more like these:
C = 275
D = 225
E = 200
Is that wrong?  What should they be?
I'll reconfigure to hit those numbers.

I appreciate the help guys!
Once I get a better grasp on these things,
I'll stop asking you guys so many stupid questions.   

[DummyLoad]

Thanks Pete,

Added the current taps as you showed.
I didn't change any other values.
My voltages changed drastically.

No current tap on Node A.
Do I calculate max current loads on each node and use those values as current taps?

I was thinking I should be aiming for C-E voltages more like these:
C = 275
D = 225
E = 200
Is that wrong?  What should they be?
I'll reconfigure to hit those numbers.

I appreciate the help guys!
Once I get a better grasp on these things,
I'll stop asking you guys so many stupid questions.   

simulate at idle and use a stepped load for plate and g2. the rest of the preamp tubes don't vary significantly. for now, use the spec sheets for current draw at full power output for approximations. step current loads after 5 seconds.


--pete

[tubenit]

Node A= 365    Node B = 364  Node C = 330   Node D = 277  Node E = 271

I think this is using a GZ34 with 300-0-300 PT.  If not, I was using a 5V4?

[Paul1453]

Changes made, incorporating DL's stepped current requirements.

I get an error, attached below, shortly after current steps up.

I'm not sure as to which voltage #s provided by the program I should use.

The Mean Voltage Numbers are very close to the specs you gave me.   

[Paul1453]

I don't have 1 of those GZ34s, so I tried 2 others from the rectifier cheat sheet,
That I do have, the 5V4 and the 5U4G.

The 5V4 gives an error message even sooner than the GZ34.

The 5U4G makes it through without any error message.
The problem is I also lose 30V on each of my voltages.

Experimenting and learning, as quickly and best as I can.   

[DummyLoad]

ignore the error. nothing is catastrophically wrong.


increase the sim time to 8000ms and step current source loads at 5sec. that way you see the idle and full load graphs.


with SSR you'll be happier with the results. filter the whole amp with the choke or use a smaller one. using a 250mA choke for just screens and preamp is such a waste.



--pete

[Paul1453]

Moved choke upstream, made other changes as required.

Using the MEAN voltage column for results.
Comes pretty close.

Did the SSR too.
Now A + B are higher, not more than my 6L6Gs can take, though.
C - E's mean voltages are in line with the specs given.

[Paul1453]

I got some Sovtek 5881s today.

Both tested good.  Any opinions on Sovtek 5881s?

These are the first 5881 tubes I've had.
I think I got a good deal on these.   

Data sheet indicates 5881s are an improvement on the 6L6GC design.
Any noticeable sonic improvements over the 6L6GC?

Got a cheap Chinese 12AX7 thrown in the deal.
It tested good, not extremely high, and has much different guts than my other 12AX7s.
It will give me an idea how much better my old Mullard/Amperex 12AX7s are in comparison.   

[Paul1453]

Back to PS design.   

Do you think it might be possible for me to implement something like this in the HoSo58 PS?

Mesa Boogie's switchable Dual Rectifier/SS PS.
Not exactly this, but something like it with a single rectifier tube or SS rectifier selector switch.
I think that would be a nice added feature for this amp.
If your tube rectifier craps out during a gig, you just flip the switch because the show must go on.

[Paul1453]

I re-use my salvaged quality parts whenever I can.

I was trying to select the best caps to use on this.

My layout board is a couple of turrets short, 25 not 28, so  probably need to have another small board.
I'm wondering the best point to make that split, and which signal caps I should use?
I'm currently thinking of splitting off 26-28 with the higher C voltage supply.
I've selected 400V caps, saving the 600V for higher voltage amps.
Those little tootsie roll brown ones are 10%, along with the Astron caps.
I'm trying to use those type as much as possible, avoiding the ceramic disk type if I can.
I've also got those old domino type, but I'm unsure about them.
Don't know exactly how to read their value, and don't have a cap meter yet, but plan on getting one soon.

Any feedback on these caps and my split layout plan?

[tubenit]

Paul,

I built a D'Mars where I was short on the turret board and put turrets 26, 27, 28 on a separate board as you are suggesting.  Worked fine with no issues at all.

I don't know about the caps you're using. Not familiar with them.  I used mostly Orange Drop PS series with some Musicaps in certain places and did the cap orientation thing for a quiet amp.  The amp is amazingly quiet at idle even when the volume knobs are dialed up.

with respect, Tubenit

[tubenit]

An update on this amp. I've gotten a considerable amount of playing on this amp and it's definitely a sweet amp, IMO.  I've discovered the "shape" control going into the 5879 channel is quite useful.  Sort of hard to describe what it does, but it's kind of dials between a more subtle OD tone to a more in your face tone edge.  Very useful feature.

I've learned the amp has more sustain with the 5879 OD channel then I previously thought. 

While I love the D'Mars ODs,  it was possible to set the pots in ways where the amp didn't sound that great & it took some experimenting to find the sweet spots on the amp which I think are truly great sounding.   In contrast,  I am having a difficult time finding any settings on this amp that don't sound superb to my ears.  MUCH easier to dial in a good tone compared to the D'Mars.  Not saying it has a better tone, just easier to find on the dials. 

I will say this may be the most touch sensitive amp I've played & perhaps the first one where I liked the clean and the OD channel equally well. Previously, I tended to favor one channel somewhat more then another on my clean/OD amps.  The amp really is remarkable in it's ability to change the expression of the tone by the pick attack.  Very cool feature. 

I will continue to describe the OD as about 70% boost of the same clean tone with maybe 30% OD flavoring added in.  Not much distortion in the OD and note separation remains good even when chording.  I have found my Dano "fish & chips EQ" sounds great with this amp in the active FX loop prior to the delay.

I can recommend this build for someone who is looking for something a little different.  It is amazingly quiet at idle when the pot settings are cranked to a pretty loud volume.

My all time favorite builds:       D'Mars and HoSo56-OD,  Tweed BluezMeister,  Tweed Overdrive Special,  HoSo56 6BM8's (or 6V6's),  and then the Carolina Blues Special.   After that it would probably be the Dano Centurian Model 275 with the one tube reverb added.

Just an FYI and update.   I hope some of you will consider building this amp!  It is ALOT of fun to play and very expressive.

With respect, Tubenit

[Paul1453]

I too hope some others will join in and attempt this build.

I am going very slowly, and wanting to get this right the first time.

Your picture of your completed amp's guts and layout is helpful.
Do you have the dimensions of the chassis and maybe a visio or other file showing the placement of all the holes required?
I'm concerned about me trying to make this fit in my Hammond chassis.

After talking with Uki about his home-made chassis,
I think it might be better for me to get a sheet of aluminum and try to bend my own chassis to your proven layout design.
My PT an OT are not the exact same as you specified, but they are what I have and would like to use if possible.
That would require me to slightly modify any chassis designs you have, but would give me proper placements for everything else.
I'd hope to avoid problems in the completed amp by more closely following your layout.
Trying to make it fit in the Hammond chassis, might leave me with an amp that has issues that are difficult or unable to be corrected. 
I don't want that to happen.

Learning how to cut and hammer a sheet of aluminum into a proper chassis layout,
seems like it would be a valuable experience for me to add to my limited amp building skill set.   
Or maybe it will convince me to just pay the $75-$100 including shipping for a ready to go chassis from now on.   

[tubenit]

20 X 8 X 2.5 chassis.  No visio layout available.  You can figure out quite a bit from the photo though.

If you are wanting to eliminate a few things in the design ......................

I think you can eliminate the presence pot (which I have on the back),  FX send pot,  PPIMV and the shaping pot if you want.  All those pots are useful to me, but IF someone wanted to do the amp into a 18.5 X 8 X 2.5 chassis .......... you could consider eliminating those.

With respect, Tubenit

[Paul1453]

Thank you very much for those suggested deletions, Tubenit! 

The number of pots and their extra wiring was the cause of my doubting the Hammond chassis.
You also have a footswitch jack and associated components that I wonder if I can remove?
They don't seem to be on the schematic.

Let's see if I identified the right components.  What are the caps with the ? on them?

I'm working on seeing if I can make the proper edits to the schematic.

I'll post that when I think I got it right.

Maybe, if I'm lucky, with the reduced component count it might fit in the Hammond chassis yet.
It would save a big delay in me trying to build my own chassis.
For a simple guy like me, the less knobs and switches to mess with, the better.   

[Paul1453]

If you are wanting to eliminate a few things in the design ......................

I think you can eliminate the presence pot (which I have on the back),  FX send pot,  PPIMV and the shaping pot if you want.  All those pots are useful to me, but IF someone wanted to do the amp into a 18.5 X 8 X 2.5 chassis .......... you could consider eliminating those.

With respect, Tubenit

I tried to remove those items, but probably got it wrong.

The only one I think I did right was the PPIMV pot.
Now I don't even think I got this one right.     Grid Leak resistors maybe?
I'm really tired.  You have a good night.
And thanks for all your help!   

Any other simplifications that could be made without drastically changing the tone of the amp? 

[tubenit]

Paul,

There are significant errors in your drawing.  The amp will not work as you have redrawn it.

Here are examples of how to eliminate those pots.

Tubenit

*** See attached

[tubenit]

Paul,

I was concerned you would have trouble figuring out the layout for the Minimalist Max HoSo56-OD so I have drawn it up for you.

Compare schematic with layout, if there is a discrepancy ......... go with schematic. 

I eliminated as much in switching and pots as I could and still keep the essence of the tone of the amp, IMO.

with respect, Tubenit

[Paul1453]

That was extremely generous of you!   

I certainly hope there are some lurkers who can also make use of this.

This design has been reduced to such an extent,
that I believe it now has a reasonably high chance of working in my Hammond chassis.

I'm going to try to keep it simple, and get a GZ34 as cheaply as possible.
Just having a tube rectifier, as you have designed, for now.

I will definitely keep you posted of my slow progress.

[kagliostro]

Just an idea

Where you can't fit a potentiometer you can use an internal trimmer (set and forget)

this way you will be facilitated in the settings to you more congenial

I repeat it is just an idea

Franco

[Paul1453]

That is a good idea, K.

One I had not considered before.

Something to think about, for sure.

[tubenit]

Very good idea !  If I were to add 2 trimmers, the most useful would be a 100k trimmer instead of 56k mid resistor & 100k instead of 82k FX return resistor.


With respect, Tubenit

[Paul1453]

Got a new JJ GZ34 on the way.

These are not cheap rectifiers, but I think I got a pretty good deal.

Too bad I didn't have an old Mullard or Amperex GZ34 in my tube inventory.
Those appear to go for more than $100 on Ebay. 
I really don't understand why a rectifier tube would cost sooooo much.
It's easy to see why SS rectifiers would be used by cost-conscious manufacturers/builders.

[kagliostro]

I think you will be happy with the tube you have find


Franco

[Paul1453]

Project on Hold until I get proper chassis fabricating tools.

I appreciate your efforts in making the Minimalist Max modifications!
I learned some important things from that.

I think that when I get my tools, I will try to adhere to your original design.
Only making slight layout adjustments to accommodate my different PT and OT.
I hope to produce a high quality build of your design, that even you can be proud of.
Thanks for all your help, and I'm staying on the lookout for more 5879 tube deals .   

Best regards,
Paul

[Paul1453]

Tubenit, could you please post a few more pictures?

A top view, and front and back view would be great.   

I'm trying to make a chassis layout diagram.

I plan on making a chassis with the same dimensions as yours.
And to have everything spaced like you do,
or as close as I can be to it, with my transformers.

I understand this is an advanced build and I want to make sure I do things right.
By following your example as closely as possible, I think I have a reasonably good chance at a successful outcome.
I'm going to need to order some parts from Doug for this, for sure.   

Thank you very much!
Best regards,
Paul

[tubenit]

20" x 8" x 2.5"

Only thing I would do differently, is have the rectifier tube more in line with the power tubes.

I used a standup PT and a standup OT.  They are next to each other with the choke on the other side of the OT more towards middle of chassis like on Marshall amps.

With respect, Tubenit