Hammond AO-43 build

[NO_H2O]

The EL84's should have been a pair of EH's. So much for that. I got the Hammond 6BQ5's (I think they are Sylvia) out and plugged them in and remeasure V1, V4 and V5. Heater voltage remained the same.

V1 12AX7
Pin 1 142 vdc
Pin 2 0
Pin 3 1.3 vdc
Pin 6 143 vdc
Pin 7 0
Pin 8 1.3 vdc

V4 6BQ5
Pin 1 0
Pin 2 0
Pin 3 12.7 vdc
Pin 6 0
Pin 7 352 vdc
Pin 8 0
Pin 9 356 vdc

V5 6BQ5
Pin 1 0
Pin 2 0
Pin 3 12.7 vdc
Pin 6 0
Pin 7 351 vdc
Pin 8 0
Pin 9 357 vdc

And it is bit quieter.

[sluckey]

Those voltages look like they should make a joyful noise.

Take a look at this short thread about EL84/6BQ5...

    http://el34world.com/Forum/index.php?topic=18789.msg192602#msg192602

[NO_H2O]

So no "standard" for the EL84's. That is good info when selecting replacement tubes. I was thinking that 350 vdc was a bit high for plate voltage on a 6BQ5 and was thinking of building a bucking transformer and mounting it in the cabinet when I put it together. I can't wait to hear this thing, but I will have to wait a bit.
Thanks for your help. When I get this one done. I think I might take a stab at a Re-Vibe to go with it

[sluckey]

The safe way to treat an EL84/6BQ5 is to not use any of the "extra" pins for tie points. They may not really be free. If this were my amp I'd move that grid stopper resistor off pin 1.

[NO_H2O]

When you say remove the grid stop resisters from pin 1. I take that as just remove them all together. True?
Also. It looks like I will have to go back in it to increase the cathode resister a good bit to get the plate disapation down. I increased the resister value in the Hoffman AC30 layout from 50 ohm 10 watt to 120 ohm 10 watt because this amp is a 2 output tube 15 watt. I doubled the value and added 20 ohms for today's household voltage.
As I calculate it. With a plate voltage of 352 vdc, and measured cathode resistance of 119.3, and a voltage drop across that of 12.68 vdc. The plate disapation for each output tube is 18.7 watts. I don't think that will make the tubes very happy. I bought a few 10 watt resisters ranging from 100 to 150 ohms to dial it in and started with a middle of the range 120 ohm. I think it will take something more along the lines of 200 to find the happy spot.
Would you agree? Or am I an idiot? Or should I use a bucking transformer and knock everything down to 115 at the plug and start calculating again?

[sluckey]

We knew that AO-43 PT would be too hot. But you're on the right track to tame it a bit. I would use one of those 150Ω 10W resistors to knock the B+ down. Put it between the rectifier and the first filter cap. Then mess with the cathode resistor.

[NO_H2O]

I had the same thought just now as I have an unused pair of turrets at that end of the board. I will ad the 150 ohm 10 watt there. Run thru it and then to filter cap A and see what I get.

[jojokeo]

We knew that AO-43 PT would be too hot. But you're on the right track to tame it a bit. I would use one of those 150Ω 10W resistors to knock the B+ down. Put it between the rectifier and the first filter cap. Then mess with the cathode resistor.

Hmm, using a 5Y3 I get 322Vdc at the first node. Maybe no_water is using the 5U4 that comes with these?

[NO_H2O]

Nope. I used a 5Y3 in the hopes it would knock the voltage down enough.
So the 10 watt 150 ohm is now in line between the rectifier and the first filter cap using the prev empty turrets on the end of the board. I tried to be as neat as possible so it did not look like the after thought that it is.
I had to desolder some things to give myself some room to work, them solder them back in place.
I will now do the power up as if it were the first time again and post the results.

[NO_H2O]

Ok. It is happier, but I don't think it is in its happy place just yet. Heater values are unchanged.

V1 12Ax7
Pin 1  130.5 vdc
Pin 2  0
Pin 3  1.24 vdc
Pin 6  131.5 vdc
Pin 7  0
Pin 8  1.25 vdc

V2 12AX7
Pin 1  177.5 vdc
Pin 2  0
Pin 3  1.24 vdc
Pin 6  286.2 vdc
Pin 7  177.1 vdc
Pin 8  176.9 vdc

V3 PI 12AX7
Pin 1  225.7 vdc
Pin 2  43.8 vdc
Pin 3  65.4 vdc
Pin 6  227.5 vdc
Pin 7  44.1 vdc
Pin 8  65.4 vdc

V4 6BQ5
Pin 1  0
Pin 2  0
Pin 3  11.4 vdc
Pin 6  0
Pin 7  322 vdc
Pin 8  0
Pin 9  325.7 vdc

V5 6BQ5
Pin 1  0
Pin 2  0
Pin 3  11.4 vdc
Pin 6  0
Pin 7  320 vdc
Pin 8  0
Pin 9  325.7

Cathode resister 119.3 ohms
Voltage drop across it. 11.20
Plate voltage 322 vdc
Plate current 46.9 mA
Plate disapation 15.1 watts.

[NO_H2O]

I got my son to move the behemoth variable power supply down to the work area. I plugged the amp into it and dialed up the wall voltage of yesteryear, 110 and ran the numbers again. I won't post them all but here are the results. The heaters are now 6.25 vac. Plate voltage is 294 vdc. Plate current is 42.3 mA. Voltage drop across the 119.3 ohm cathode resister is 10.1 vdc. And plate disapation is 12.4 watts. That is damn near happyville USA. And the amp is dead quiet until I put a 500Hz tone thru it.

[sluckey]

I think you are about there. 150Ω cathode resistor may just do it for you. Oh, if you build a bucking transformer for this amp, consider building it in a small box that can be used with any of your amps.

[NO_H2O]

I see you used a transformer from Radio Shack. Be that we have no more RS stores does Doug sell one for use as a bucking transformer? I think I would build one and mount it in the amps cabinet permanently as it will always need one.
Would a Hammond 186D12 be what I need?

[sluckey]

That will work. I'd rather have this one...

     https://www.tubesandmore.com/products/transformer-hammond-filament-126-vct-4

[NO_H2O]

What if I up the B+ resister to 300 or so 10 watt and move the 150 to the cathode resister spot? It would make for a cleaner combo build. I think a 10 watt would have the duty life. What say you?

[sluckey]

Sure. Just play around with it. Just do some math to make sure you don't exceed the power rating of the B+ dropping resistor. Measure the voltage dropped across the resistor. Square the voltage and divide by the resistance (P = V²/R). Then double that actual power for a safety margin and get the next available wattage resistor. For example, say you measure 40v across a 250Ω resistor. Then, P = 40²/250 = 1600/250 = 6.4 watts. Double that to 12.8W and use the next larger available power rating, probably 20 watts.

[jojokeo]

sluckey you answered as I was figuring things out but ball parked it about the same:

But if you want to test things out then think about to get the same power out when dropping more voltage then it requires more current to operate. The Hammond PT has plenty of reserve capacity. Next going by your unloaded voltage of appx 360 and with your increase in voltage drop guessing a round number to be 300v = 60v dropped across the 300r/10w resistor? And since it will be running a higher current - going by the data sheet info @ max signal current at 300V = 46mA (x2) + screens 11mA (x2) + 12ax7's 3mA (x3) = 123mA total (potentially). 60v * .123A = 7.38w x2 for safety = 14.76w 300r resistor wanted.

[NO_H2O]

True. I will hit the calculator.

[NO_H2O]

I ordered the bucking transformer Sluckey recommended along with a box and strain reliefs to mount everything in. I will mount it inside the combo cabinet.

[NO_H2O]

I found a 300 and a 350 ohm 20 watt resister a mouser. Swapped the 150 ohm 10 watt B+ resister to a 300 ohm 20 watt. Moved the 150 ohm 10 watt to the cathode bias spot in place of the 120. Parts for the bucking transformer came today's as well but I have not started that yet.
Plate voltage is now 309. Plate current is now 38 ish Ma. And plate disapation is 11.8 watts. And no bucking transformer yet.
What say you guys?

[jojokeo]

I found a 300 and a 350 ohm 20 watt resister a mouser. Swapped the 150 ohm 10 watt B+ resister to a 300 ohm 20 watt. Moved the 150 ohm 10 watt to the cathode bias spot in place of the 120. Parts for the bucking transformer came today's as well but I have not started that yet.
Plate voltage is now 309. Plate current is now 38 ish Ma. And plate disapation is 11.8 watts. And no bucking transformer yet.
What say you guys?

Those are all good numbers - right there. You don't need no stinking bucking transformer now 
How warm does the 20watter get? Just slightly?

[NO_H2O]

It stays cool at idle. I will have to give it a workout to know for sure.
I am still going to build the bucking transformer as a stand alone tool. Just so I have one.

[NO_H2O]

I took the amp down to my buddy's place for a tone test today. Put it thru an 8 ohm 4x12 cabinet full of greenbacks. Ran a Tele-Sonic, Sheraton and standard Telecaster thru it. Had to sort out one preamp tube that was not up to the task and sadly had to put a Russian 12AX7 in its place. But the result was fantastic. The normal channel was very Vox like and the top boost channel no dought a top boost Vox tone. Even with greenbacks it had all the chime you could ever want. I could drive the top end past the sweet chime spot if I wanted to and dial it right back. Lows and mids were right there. Great response and definition. My hat is off to Hoffman Amps and anyone that had a hand in the design. And thanks to Sluckey and all the fine folks on this forum for your help.
Now I have to hit the wood shop and build a cabinet. Then pick out tolex and grill cloth, or do a wood finish. Even more tasking, select a 12 inch speaker to pair up with it. I was leaning toward the Weber Blue Dog Alnico. But I don't think this amp will have any shortage of chime after hearing it with greenbacks.
Once I have it put together I will have to record a few tracks and link them here.

[NO_H2O]

Also. The 300 ohm 20 watt did not heat up too bad. The amp was driven fairly hard for an hour solid.
So my short list for sealers is the Weber Blue Dog, Weber Silver Bell, Weber Grey Wolf, Scumback Scumnico. I have the Blue Pup in a Champ and like it. I have built a single 12 with a smooth cone WGS and a 4x12 with Eminance (can't remember the model). I have never owned a Scumback.
Anyone have recommendations?

[sluckey]

I really like the Celestion blue with a Vox AC-15. The Celestion gold is supposed to sound similar but at a higher power rating. Ed Chambley knows this stuff pretty well. I trust his ears.

[jojokeo]

I really like the Celestion blue with a Vox AC-15. The Celestion gold is supposed to sound similar but at a higher power rating. Ed Chambley knows this stuff pretty well. I trust his ears.

The Gold needs to be pushed, use the Blue if considering this speaker? I love Scumbacks and have the Scumnico & PVC alnico & ceramic both (& others too). For Webers, the blue dog in a low watt 15w or no more than 30w as they get darker with higher wattage and the 12A125A & 12A150A are maybe better? The Silver alnico is dark, not chimey. WGS also is good & a great bargain. Check out the "speakers section" for further info & feedback.

[NO_H2O]

15 watt 8 ohm Celestion Blue (made in UK) on the way. Now to clean out my wood shop and start on a cabinet.

[EKDENTON]

When you say remove the grid stop resisters from pin 1. I take that as just remove them all together. True?

I think Sluckey meant that if you use a different type tube someday in the future that has an internal connection at pin 1, the tube may become very angry with you (or the reisistor on pin 1 LOL). If you dissconnect that side of the resistor and attach it to an insulated lug on the chassis or somwhere besides pin one and leave the other side of the resistor where it is

[jojokeo]

All grid resistors function best when attached directly to the tube socket. In lieu of another point available for that free floating other end you can solder a wire directly to it, and helps to make a mechanical connection by crimping or twisting the two together before soldering. Then protect if possible with a little heat shrink tubing and you're set.

[NO_H2O]

My Celestion Blue made it here. It is made in the UK and date coded Aprill 30 1991. I mounted it in a 1x12 open back cab and had my son give the combo a test drive. It is the perfect speaker for this amp. It still needs some brake in. I don't think the prev. owner gave it much playing time at all.
I got started on the cabinet and got the 4 sides glued up.

[NO_H2O]

Made some more sawdust and some forward progress. 2 more back panels and cleats left to fit and it will be time to dress it in tolex and grill cloth.

[NO_H2O]

One more for today.

[NO_H2O]

Back panels fitted. Tolex and grill cloth will have to wait a week or so.

[NO_H2O]

I got the baffle and panels covered today. Main cabinet left for another day. The damn piping is very stiff. It will be super tight going together. Might have to lube it up and drive it together. Or ditch the piping.

[pompeiisneaks]

I really like the Celestion blue with a Vox AC-15. The Celestion gold is supposed to sound similar but at a higher power rating. Ed Chambley knows this stuff pretty well. I trust his ears.

I've got the gold on my current AC30, and it sounds incredible.  Love it.  I can't wait to hear it on my AC30/4 I'm starting now.

~Phil

[NO_H2O]

I got busy in the shop today and started wrapping the cabinet. I did get the baffle and front upper panel in with the piping on. Had to use a bit of dish soap to help it slide in place. It was a tight fit. It did take some tension out of my grill cloth but I am not going to pull it back apart. Still have to modify a couple corners for the upper back corners.

[Willabe]

Looks great!!! 

Where did you get the tolex?
 

[NO_H2O]

Found it at Mojotone. They had some at my local fibric store but they were sold out and would not get more until October.

[NO_H2O]

Has anyone used a hair dryer or heat gum to snug up grill cloth?

[Willabe]

Found it at Mojotone. They had some at my local fabric store but they were sold out and would not get more until October.

I thought it looked like Mojo stuff. 

The stuff at your local fabric store is it the same or a little different? Gator is my favorite but I like the kind with what they call the 'medallion' included in the skin pattern. The 'medallion' is a roundish plate on the back of the neck just behind the head that has like 4 to 7(?) raised bumps.

Faux gator/crock patterns are different, some are copies of the belly skin, some are the back and sides and some are the back and sides with the 'medallion'. I like those the best as they have more variation of pattern texture and shape.

Mesa has some amps with the 'medallion' gator skin that look great to me from pics on line but you have to see them in person to be sure.

I have at least 50 different samples that I requested from different fabric store and tolex dealers and they all are terrible looking and/or to soft to use on an amp.            (I have well over 300(?) possible samples for amp coverings and over 100 grill cloth samples.) 

I can't find the good stuff anywhere.

Has anyone used a hair dryer or heat gum to snug up grill cloth?

 

Yes. I used 1 on my old BF SR and it worked great, also used it on a few new builds.

Others here have also used a heat gun to tighten up grill cloth. 

[Willabe]

This is the pattern I like best. 

So as not to hijack this thread, I started a thread here;

http://el34world.com/Forum/index.php?topic=20822.msg220137#msg220137
 
The medallion is under the left side of the handle, by the right chassis strap and on the top of the left side center in the 2nd/bottom pic.   
 

[NO_H2O]

The gator on that Mesa looks nice. The ostrich in my local fibric store was very close to the mojo stuff. They had black and brown. They also had a lighter lizard that I almost went with. But the backing had too much contrast and I did not want to risk it.
I am going to pull the speaker back out and try the hair dryer trick to snug the grill cloth back up.

[Willabe]

I like the look of faux ostrich very much. Mesa has a very nice tan faux ostrich. I have been able to find several good looking and tough faux ostrich patterns. They do cost more then the common tolex colors/patterns like from Mojo, but tweed costs more then tolex too. And you have to add a little more to have it lacquered. So.......   

[NO_H2O]

I like that ostrich a lot too.
I used my daughters hair dryer and fanned my grill cloth with the speaker out for quite sometime with little results. So I pulled up the big boy pants and got out my variable Millwaukee heat gun and dialed it down. I was very carefull and found the sweet spot. The grill cloth is nice and tight now.i got all the corners installed. I had to modify to upper back corners due to the way I did the cutout for the controls.
Guess I will color this one done. I have really enjoyed this project. Thanks to everyone for all your help.
Now the question is. What will I pick up for my next up cycle amp build. Hummmm I wonder.