New Build Alive and happy

[Ed_Chambley]

Finally began a new build.  Thought I would post a little as I go as I promised a Ritchie (Jim) I would. Not very good at the photo posting. Amp will be a UL design and the cab is 3/4 inch pine with a ported front and open or closed back for each side.  Very versatile cab with the option of using it in stereo, half open, all open all closed. Ported closed or open.  Half and half and will be able to use 2 amps.  Covering is red marshall and salt and pepper grill.

Plan on using 2 KT120, a 12A_7 at the PI and EF86 in V1.  Lets see how it goes.

[Ed_Chambley]

Question 1 of many I will likely have.

Is it possible to reverse a UL OT and get a squeal?

More photos

[Ed_Chambley]

Couple of more.  Probably be the last for a few days.  Every time I begin a new build I get calls for repairs.  Anyway, it is basically a Dynaco.  When I figure out exactly what all my dropping resistors will need to be, I will post a corrected schematic if anyone is interested.

[TubeGeek]

Nice progress!  I have been meaning to use PEC's but haven't had a scratch build in a while, they can be a little large for existing amps or kits.

Very nice work on the cabinet

Keep us updated.

[TIMBO]

Look'n good 

[sluckey]

Is it possible to reverse a UL OT and get a squeal?

yes

[Ed_Chambley]

Is it possible to reverse a UL OT and get a squeal?

yes

Then I got lucky last time.  If it happens should you change both the plate and screen on both tubes?

[DummyLoad]

If it happens should you change both the plate and screen on both tubes?


absolutely.

--pete

btw, nice work & looks good. 

[terminalgs]

  Anyway, it is basically a Dynaco. 

Like an early Sunn?  I worked on a 1965 or so sunn with controls on the top of the amp.  It was a Dynaco Mk-3 chassis in a Sunn head, with a extra 12ax7 preamp folded steel chassis up top with the controls.

[Ed_Chambley]

  Anyway, it is basically a Dynaco. 

Like an early Sunn?  I worked on a 1965 or so sunn with controls on the top of the amp.  It was a Dynaco Mk-3 chassis in a Sunn head, with a extra 12ax7 preamp folded steel chassis up top with the controls.

Very much like a Sunn.  I have built a similar amp using a 12AX7 in v1 and a James tone stack.  Very clean and powerful, but it was for a friend.  He is loving it.  I liked some things about it.  I am curious what the EF86 and the LARMAR PPMIV is going to do to the tone.  So pretty much a Dynaco with an EF86.  Fairly simple build in reality.  The voltages have a long way to drop to get the EF86 happy.  Since I am not sure what the SS rectified PT is going to give me on the plates of the power tubes I am not sure of the size of the needed dropping resistor between the 2nd and 3rd node.  Probably be the same as the Sunn I just repaired or close.  The plates measured 563v.

I have tried the KT 120 in both the Sunn amp I just repaired and the Dynaco I have and they sound really nice with an insane amount of headroom.  Problem is I am not sure how where bias the KT 120 yet.  Most things I have read on the audiophile forums, they are simply replacing KT88 with them and bias the same.  I usually just bias for sound/tone and make sure I am not redplating since it seems like every new production tube varies quite a bit.

[eleventeen]

Did you buy new trannies or did you salvage them from a MkIII?

[Ed_Chambley]

Did you buy new trannies or did you salvage them from a MkIII?

Bought them.  I have never been able to scrap a Dynaco.

[Ed_Chambley]

Nice progress!  I have been meaning to use PEC's but haven't had a scratch build in a while, they can be a little large for existing amps or kits.

Very nice work on the cabinet

Keep us updated.

Thanks TG.  I have had that idea for a cabinet ever since I got the 62 bassman.  I kept saying what if until I what iffed it to death.  I am waiting for the amp to decide on speakers.

[Ed_Chambley]

Fired up the amp this morning using an inductor instead to series caps since I fried one set of caps.  The PT is rated at 780v at 300ma.  B+ unloaded is 563vDc.  Loaded with 6550 (did not want to start with the KT-120).  Loaded down the voltage on the plates is 430 with 6550 and 398 with KT-120.  The KT-120 have a tone similar to KT-66 with that nice round sounding lower mid.

I did not expect this much voltage drop, but I have never tried the inductor to cap.  I understand this can lead to lower voltages.  I will find out when the new caps arrive.  Until then, can someone who has experience with inductor give me a guess at the voltage loss.  I read that it happens.  Is it simply because the drain on the cap and when you have Pi Filter input there is simply more reserve so the PT doesn't sag as much?

The Sunn amp I restored seemed very similar in design, except for the PI tube, but the loaded voltage drop was from 560 unloaded and to 520 loaded with Tung-sol NOS 6550.

On the happy side.  This amp is really touch sensitive.  Has a tremendous amount if gain and the Larmar Master works quite well.  The gain is achieved in multiple ways.  The tone knobs and the master.  No problem with the EF86 and micro-phonics, but I do intend on trying a different toob in v1.  And if you want, it will play clean too.  It will do the old Vox tone if you bring up the treble.  Makes a chimey gainey tone reminding me of a 60's AC-15 I stupidly sold in 78.

Not ready to button it up, but getting close.  Still I am not sure of the dropping resistor needed between the Power Section to the Phase Inverter since loaded all it took was 33k.  Anyway the DR Z preamp used in the Route 66 and the 45 is very nice, simple and versatile and very quiet.  As it is, you low watt high gain fellers would love the choke input supply.

[sluckey]

read this...

http://www.aikenamps.com/Chokes.html

[Willabe]

and will be much more highly regulated than the capactor input filter (less variations in supply voltage with variations in load current).

This part, from Aiken, seems to go along with comments I've read where guys said the 2 different PSU made a large difference in the way the amp sounded and responded.

It would seem that a choke loaded PSU would have less sag available compared to a cap loaded PSU.


               Brad        

[Ed_Chambley]

I already read the link Steve, thanks.  The difference in voltage is quite surprising to me.  I did however learn a great deal from not having the proper caps on-hand.  I see where over 400 volts in Aiken becomes under 300 with inductor-cap input.  His example is 300v CT PT.

Brad,
The highly regulated input seems to very harmonically rich.  I do like it.  I have a few parts just itching to be used.  Don't really know why, but I will be looking into it more.

The UL transformer with no NFB is very nice, but I am going to have to add a switchable NFB.  It seems the NFB is tied to one of the screens on the Dynaco, but I would think there is another way.  I will wait and see what the additional voltage does first. Probably won't need it.

Next my least favorite thing.  Tolex a cab.

[sluckey]

It seems the NFB is tied to one of the screens on the Dynaco, but I would think there is another way.

That's just a tiny bit of the NFB. Most of the NFB is fed to the cathode of the pentode half of the 6AN8.

[Ed_Chambley]

I saw that the 6AN8 handles most of the NFB.  The PI in this design is a little different.  I have not decided exactly what tube I am going to use, but the 12AX7 is nice.  I will probably replace it with a 12AU7.  I have hand drawn my changes, but the attached schematic is close.  The Bias network resistors have been changed to be able to swing from -29 to -74.  The KT120's came from Tube Depot and are going to be returned.  Their 'matched' set is 25ma apart.  New tubes suck.  I put in some old Tungsol 6550's, used.  Pulls from a Leslie repair and they were exactly matched.  They sound a little dull compared to KT88, but I will not know anything for sure until I get the voltage correct. 

I am going to make myself draw it using PC Express since most of the folks here use it.  I cannot seem to find a .SCH file with a UL OT is I will have to draw one.  Maybe Jeff knows of one.  Hint Hint.  Weird thing about drawing schematics, once you learn to draw them and see the what each component does you don't really need it for designing.  It is a great communication tool tho.

The reason is that I want to get an editable format for others to be able to add ideas.  I plan to install a balanced line out using a Jensen Transformer.  The Hammond 109T does not have a Hz range I want.  The Jensen Transformers are expensive, but Whirlwind uses the in a direct box and I got one off Ebay.  It has all the parts I need and used it was 1/5th the price of the transformer by itself.

It will also need an effects loop as I don't think anything but maybe a compressor and overdrive would be suitable in front.  I have not tried any pedals, but this is my thinking.  This may come as a shock, but I have tried many tube loops and I prefer the board that Metro has.  The one from Mojo is fine, but you have to diddle with it.

I do not have a layout as I did not need one.  I scribed a layout on the chassis metal before punching, folding and welding.  I used a board, but i hindsight it would have been easier to use tagstrips.  Grounding is a simple copper 12ga starting at the EF86 all the way to a transformer bolt.  Everything is grounded here.

Looking at PI you will notice the Plate Resistors form a divider making a LT pair.  There is no snubber cap.  Plenty of things to try, but mostly I want to be able to send the preamp to other Power Sections and to a console..  The amp is crazy simple in its basic form.  The layout is so easy when using UT OT.  I used a Marshall type of layout, but I did make the switched go up for on.  Never really like the down on.

2 times lucky with the OT connections.  No squeal.

What is the actual cause of an OT squeal, as I have never known?  Out of phase?

This is one heavy chassis and I have concerns mounting it into a head box.  Normally I would just thread the chassis and bolt it in, but I don't think the aluminum threads will hold.  Probably just go through the chassis like fender unless someone knows a better way.

[Willabe]

What is the actual cause of an OT squeal, as I have never known?  Out of phase?

Negative FB will now be positive FB.


               Brad     

[sluckey]

The UL transformer with no NFB is very nice, but I am going to have to add a switchable NFB.

Since you have a LTP PI you may want to just copy the Fender AB763 NFB.

2 times lucky with the OT connections.  No squeal.

Well, when you don't have a NFB loop from the OT secondary, you have a 100% chance of getting the OT phase correct.

[Ed_Chambley]

OT secondary, you have a 100% chance of getting the OT phase correct.
[/quote]
I remember how it works now.  You explained this to me before.  I guess we will find out when I do install a NFB.

[Ed_Chambley]

Finally, the amp is stable and running.  We will see how it goes.  Sounds really nice.  Keeping my fingers crossed I have no more trouble.  Back to tolex and making a head cabinet.

[zendragon63]

Nice work Ed. Apparently you are using a different schemo than the posted Route 66. I haven't had much luck with new production power tubes either. Enjoy. Regards

dennis

[DummyLoad]

chassis like fender unless someone knows a better way

you could use cage nuts. downside is you need to cut/punch square holes for them. through chassis may be easiest and just as durable, maybe more so.

http://www.stayonline.com/snap-in-cage-nuts.aspx 

use 12-24 or M6

--pete

[Ed_Chambley]

Nice work Ed. Apparently you are using a different schemo than the posted Route 66. I haven't had much luck with new production power tubes either. Enjoy. Regards

dennis

Yes, It is somewhat different.  I have completed the revised schematic with voltages.  I will post later.  Running KT88's.  Similar in tone to a point.  Breaks up easily if you want or not if you don't.  Of course, there is nothing flabby or harsh and it will peel the paint if you desire, but not necessary for a good tone.

[Ed_Chambley]

chassis like fender unless someone knows a better way

you could use cage nuts. downside is you need to cut/punch square holes for them. through chassis may be easiest and just as durable, maybe more so.

http://www.stayonline.com/snap-in-cage-nuts.aspx 

use 12-24 or M6

--pete

Thought of these, but I do not have a square punch.  I guess it would be easy enough to drill it and file it more square.  If the chassis was not as thick I could use SK rack nuts, but they spring open if pulled that much.  It probably would look nice to use these.

[Willabe]

Finally, the amp is stable and running.  We will see how it goes.  Sounds really nice. 

Alright!     



              Brad     

[Ed_Chambley]

Here is the revised schematic with correct voltages using KT88.  Valve Art tubes, just another name for a chinese tube.  I could not get a pair of KT120's matched close enough.  While they do have a tad more bottom, you cannot notice with guitar.  The Valve Art tubes are within 1 ma and this amp really prefers match.  It is quiet, very quiet.

I put in a fender style NFB and it killed the character and greatly reduced harmonics and some touch sensitivity.  I left it in and put it on a switch.  Also, in v1 a EF86 makes a huge difference.  I have a mullard in and it is very smooth, but a Tesla is raw sounding.

I do not understand, but all the overdrive/distortion is in the tone stack.

[Ritchie200]

That means you just have not turned it up high enough!!!

Cant wait to hear some clips!

Jim

[Ed_Chambley]

That means you just have not turned it up high enough!!!

Cant wait to hear some clips!

Jim

Jim, buddy, I have you in mind.  I promise I have had it turned up enough.  I do not own a single cab capable of reproducing everything the amp has to offer.  The damn thing made my 2, 12 100watt cab move on the floor and I am getting ready to go to Lowes to get some paint for my studio walls.

I finished the head box last night and the glue is dry.  I am going to complete the head and test some different full range speakers with it.  I tested it with some bass speakers and it will produce lower harmonics which cannot be heard with guitar speakers.  That is why the cab is ported.  Like I mentioned, I still have a ways to go with tolex and grille.  I did drill the faceplate with the chassis.

The coolest thing about the amp is it does not have to be cranked to sound good.  The first clip will be Amos Moses played on a Telecaster, just for you because I know you love the twang of an old tele. Really, I have never grown to like a Strat, but I do have a Telecaster with a 5 position switch and setup with Lace Sensors and they are a strat setup.  A James Burton model and the neck tone is very strat like.  I prefer the modern neck of the telecaster and I have never found the strat, at the price, that I want.  I do not like the feel of the new ones.  I have played a 60's white large headstock that I really like and am currently looking for one or a custom job made to this spec.   Nash in particular, but I do not like road worn guitars.  I guess I am too old to be that cool.  Why anyone would want a beat up new guitar is beyond me.

I got a Les Paul and a 335 as well.  Probably make a clip using all of them so you can hear how what the amp has to say to the 335.

[smackoj]

EC; that is so impressive. I see the hints of vintage and the power of modern in this amp. congrats on a very nice expression of your ability and skill.

Could you post a Bill of Materials for newbies?

regards, smacko jack   

[Ed_Chambley]

EC; that is so impressive. I see the hints of vintage and the power of modern in this amp. congrats on a very nice expression of your ability and skill.

Could you post a Bill of Materials for newbies?

regards, smacko jack   

I did not make a Materials list or a layout.  I did include on the schematic the transformers.  Pots are 4 x PEC and caps are 715 Sprague Orange Drops.  Resistors are all 1 watt Dale 1% except the dropping resistors which are 3 watt, wirewound ohmite.