Here's What Happens When You Have Too Much Time On Your Hands

[dude]

My Hammond AO43 Plexi 6V6 Build, just too much time now that I'm old and retired, well semi-retired 

[mresistor]

That kinda looks like my Baldwin chassis, I had to get the grinder(s) out and rearrange things, then cut some stainless to make new panels, mount and then drill them.  It was boatloads of fun, but in the end the amp works great and that's the reward. Too much time is not a problem is it? Looks like your having fun.

[dude]

You know what, Yeah, I'm hav'n fun !


Now do I worry about tube shields on the two 12ax7's .... Not going to take those sockets out..


Need some vintage shields, ha

[sluckey]

I love blank chassis. 

[dude]

Cleaned the board, now the fun part...


Working on a head cab is like working upside down, everything"s reversed....

[RWood]

Lookin' good, Al!

On mine I mounted the board flat, on 1/2" standoffs. I used those two holes you see just to the east of your board. Worked very well although It was close above the power tube sockets. And your power tubes are set back, and octal, so it might not work on yours but worth a look-see.

DF

[dude]

If I wanted to try 6L6's (in this 6V6 plexi), would I used Doug's 50mA, 4 Henry choke or the one that came with the AO-43, I think it's 14 Henry and much bigger probably, 90 to 100 mA.  I only have those two on hand. Need to drill holes, does it make a difference how the choke is orientated to the OT or PT, it will be close.


Thanks, al

[dude]

Makes no difference?

[sluckey]

correct

[dude]

Dry fit, any mistakes.

[sluckey]

Starting to look like a guitar amp!

[dude]

Is it worth the extra effort to put in a PPIMV in this 6V6 plexi?  I read somewhere, maybe here that the PPIMV doesn't sound that good or work that well "in this particular amp" with the two volumes to blend. 


Or is all this just subjective BS...


I used a MV after the tone stack, before the PI in Sluckey's Deluxe Lite and it works very well in that amp. Was going to do this in this plexi but all the hear-say how great a PPIMV is....


Any opinions


al

[sluckey]

Is it worth the extra effort to put in a PPIMV in this 6V6 plexi?

I think so. Hoffman thinks so. I use the volume controls to blend the channels for the tone I want. Then I just use the master to set the overall loudness.

[dude]

Thanks Sluckey, I noticed the November Amp is very similar to this 6V6 plexi except EL84s. Came across a schematic you did in 2007, as I have another AO-43 chassis and maybe want to run the EL84s in this circuit. I have never played either of these amps but an 18 watt TMB (Trinity design, made cleaner) extensively and like it. What is the difference in tone between these two plexi type amps, November and 6V6 I'm doing? 


Also, using the AO-43 board, it's easier to filter the second 12Ax7 plate putting that ground to the main star ground with CT from PT, etc. Rather than like Huss does at the preamp side. Would this create a chance for noise?


Just found your 6V6 build from 2007 or so, halfway down the first picture with the AO-43 PT wires hooked up, I noticed what looks to be the RED PT wires tied to the 6V6 heaters...? Obliviously I have the wires on my AO43's PT marked wrong. I have the red as HV, White as 6.3vac, and yellow as 5vac...?     http://sluckeyamps.com/6v6plexi/6v6plexi.htm


Time to plug this PT in and check voltage: on Rectifier 5AR4, what voltage goes to 2 and 8 pins, and what goes to 4 and 6? I think I'm losing it, ha. Hook this wrong and bang.


al     

[sluckey]

My ears are not good enough to give you a "tone" comparison of EL84s v. 6V6s.

If you look at my Plexi6V6 or even Hoffman's Plexi6V6 you'll see that we both used cap cans and both of us grounded the cans near the PT. However, we also both connected the V2 board circuit components to ground at the input jacks.

[dude]

Sluckey, look at my last post, there's more. I guess your AO43 PT has the white as the 340vac and what looks to be red is brown to the 6.3v filaments.   


I just checked the voltage on the PT, has two reds, two yellows, two whites. Check with meter, both CTs on PT to blk lead, red to PT wiires


Both reds are 340vac, both whites are 3.6vac


But one yellow is 12.1vac the other 6.9vac.   (what's this?)


The reds go to rectifier tube 5AR4, pins 4 and 6 Correct?
The yellow go to rectifier tube pins 2 and 8   pin 8 is B+  but these two yellows are different voltage, one is 12.2vac the other 6.9vac ?
The two whites go to 12Ax7 heaters
Is this right, why are two yellow wires different voltages and do they go to the 5AR4 pins 2 and 8

Note:  Well, I have two of these AO43 PT's and both read basically the same.  I  assume with "no load" on these PT's is the reason for the 5V tap to read off, the other PT reads 13v and 7.1v, close but basically the same.
Just trying to find some info that will explain this to me.

I'm tired of making sh*t work but not knowing why.

 

[sluckey]

The yellow go to rectifier tube pins 2 and 8   pin 8 is B+  but these two yellows are different voltage, one is 12.2vac the other 6.9vac ?

Connect the yellow wires to pins 2 and 8.

There is only one proper way to measure the voltage on this winding... One meter lead connects to one yellow wire, the other meter lead connects to the other yellow wire. You will measure 5VAC ***BETWEEN*** the two yellow wires. If you deviate from this in any way you will be wrong.

Now for my PT... There ain't no white wires on my PT. What you think is white is really faded red. My 6.3 filament wires are brown, although they are faded also. My yellow wires are still identifiable as yellow wires.

Here's a big tip. Don't forget it... When using transformers that you robbed from another amp, take notes, pics, whatever you need to know for sure how you will be connecting those wires later. I like to twist all wires of a particular secondary winding together, tape them together, then label the tape. You absolutely cannot depend on the color of a wire to identify it. Wire colors fade, especially cloth covered wires. In 1955 it was common to use brown for 6.3v filaments. That later changed to green. Heck, it may even change again.

[dude]

Thanks

[dude]

Only have the board left, still drawing a layout to fit the original Hammond eyelet board that came with the AO43. Now I see where a program can come in handy, I have to do it the old way, ha. Best way to learn though.


Any mistakes...? My filament wiring isn't the greatest hope I don't have any major hum... And my soldering could be better...


 

[dude]

Since this amp has NF, would I want to run a ground over from the spk jack, under the bd. to a ground on the buss bar near the PI?  Though  I read something about this at Alkins site.

[sluckey]

Since this amp has NF, would I want to run a ground over from the spk jack, under the bd. to a ground on the buss bar near the PI?  Though  I read something about this at Alkins site.

The PI gets it's ground through the Presence pot. So, you could just run the speaker ground to the same point the Presence pot is grounded. Then all the interweb purists will be happy. Or....

In my Plexi6V6 I just rely on the speaker jack to chassis contact to provide the ground. So does Hoffman. This method has worked very well for Fender for hundreds of years.

[davidwpack]

Yeah, the pilgrims incorporated that design into their amps even centuries before that.

[dude]

Any problems seen with the power supply filtering?  Using the A043 bd, a little small, no room for dropping resistors on bd., put them on the filter caps and running wires, twisted, under board to feed the plates. Any problem running these wires under the board as seen in preliminary picture.


Took a while to arrange the schematic to the Hammond bd. but all looks good, not too sure about running HV under board but don't have many options, room is tight and bd is small.


al

[dude]

Finished Amp, 6V6 PLexi, haven't turned on yet as I  need to recheck everything and use a light bulb limiter.
Was thinking of getting a metal or nice plastic faceplates made for this conversion but would need to buy at least ten or more sets as one set would cost a ton. Just wondering if anyone would be interested in a set, of course they would have to use the Hammond A043 chassis. I could supply the paper template as you see for drilling.
Just wondering if there are others who might be interested...? . Otherwise I'll just have a set made at a print shop, heavy paper, from the PDF file  and cover it with thin plexiglass or the like. 


If anyone sees a mistake, please let me know. It's basically Mark Huss 6V6 schematic using the original Hammond AO43 iron and chassis. I used sluckeys and Hoffman's schematic too for some changes. I also made a few small changes so 6L6's can be used, also EL34's, if the PT can handle it, I think it can but no t100% sure, yet . Just a wider bias range and 750 ohm screen R's. To run 6L6's or EL34's replace the 5AR4 with a solid state plug-in, and adjust bias.


al 

[dude]

Additional pic's,


I see a mistake already, the bias is not grounded, pins 1 and 8 of power tubes are not connected to ground.

[dude]

Besides the bias miswire, everything looked good, past limiter test. Voltages checked out OK.


Amp plays and sounds decent. Tubes in (6V6) 5AR4, voltages:


A 412v
B 408v
C 281v
D 240v
E 224v


Look's ok


Amp sounds ok but turning up presence causes a slight squeal pass 7 on either vol 1 or presence pot. (both turned up causes the slight squeal more). All amp values are same the as Sluckeys and Hoffman's 6V6 plexi except I lowered the feedback R to 22K to get more feedback, maybe too much, should I go higher...? 


Also, used 820 ohm & 22uf on normal vol channel's cathode, figured the 220uf/330 would be too much bass for me, and the other side 2K1, .68uf. Didn't have a 2K7.
Would any of these changes cause the slight squeal or high pitched wine...?


Last, I did not use shielded wire on the 470K's to volume pots, from V2, pin 2. I put the 470K's on the board but the wires are "very short". I'm thinking I should put the 470k's right on the volume pots and use shielded wire...? This is my first guess that's causing the squeal...? Didn't get any noticeable squeal chop sticking around these wires but a lot of signal was there.


Or raise the feedback to 47K.


Which changes would be most likely be causing the squeal?


I appreciate all the info you all posted, without it I wouldn't have this amp, thank you


al 

[sluckey]

Swap the blue and brown OT plate wires. Better or worse?

[dude]

Well, that's not it. Turned on, loudest noise I ever heard, off in one second.


But I did find the problem, deviating from your layout even with very short wires to vol pot's voltage dividers (470 k's) was the problem. Put the R's on the pots with bright cap (lowered it to 400p, those mica 500's are really, like 525p, very bright) used shielded wire to grid of V2,pin2 and the amp has no squeal anywhere, the feedback with a 22k on the 8 ohm tap works great anywhere on dial, no static when turning it, too. I learned something, all my presence pots had that scratchiness when turning the knob, I bet shielded wire in the right place would cure this.


I'm stoked, this amp is fantastic, blending the two vol's is amazing, the tone stack isn't as good as my Allen Old Flame (super Reverb copy) but not bad. I put in a pair of Old Stock Fat Bottle 6L6's GE's that are almost new. Wow, with both volumes to blend out the any mud, this amp is one of my best, maybe the best, loud too.


I have one question and I hope you can help me.


The OT I used was for an 18 watt but it's pretty big, probably at least 20 watts, maybe a little more. I lost the spec sheet and it's an older one, looks like a Mojo but it's not on their site. I think I might have the 8 and 4 ohm taps mixed?


I'm almost positive it's 8K for an 18 watt with four secondaries, orange, green, yellow and black, all in that order coming out of the bottom of the OT.  No marking on the paper wrapped OT but in that order I figured, 16, 8, 4 and the ground. But when playing with 6L6's, I put the selector on 4 ohms (8 ohms spk in cap) figuring the 6L6s would see 4K load. But the amp's volume lowered, not raised, went back and forth with the selector, definitely on the 4 ohm sec the amp is not as loud, with 6L6s.


Even though the order and color out of the OT would seem to be 16, 8, 4... could it be off? Shouldn't this amp with an 8 ohm speaker, 6L6's be on the 4 ohm tap (if it's an 8K OT) get louder with the 4 ohm tap, seeing 4K?


How can I tell, which is for sure the 8 and 4 ohms taps.  The OT says:


7000118
HT-6135
9961518


al

[sluckey]

I learned something, all my presence pots had that scratchiness when turning the knob, I bet shielded wire in the right place would cure this.

No fix for that. The presence pot will always be scratchy in that circuit because of the dc voltage on the pot. You can easily modify the presence circuit to look like the later Marshall amps to eliminate the scratchy pot. See this schematic...

     http://el34world.com/charts/Schematics/files/marshall/Marshall_jcm800_lead_50w_1987.pdf

Here's your OT...

     http://el34world.com/Transformers/files/BRITISH-18W-OT.pdf

[dude]

Thanks Sluckey


This amp presence doesn't act like it has dc, but I didn't check.
So.., I wired this OT"s taps correct and it's for an 18 watt, 8K. 
With 8 ohm spk use:
6V6 - 8 ohm tap,
6L6 - 4 ohm tap
I'm not positive, so i ask?


My review:
I tried EL34's, 6L6's and 6V6's. I didn't like the EL34's (nice pair of old new Svetlana gold), even with SS plug'n. I got 405v to the plates, maybe be too low? The 6L6 big fat GE's sounded great, loud, but the bottom line 6V6's shine in this amp.  I have a pair of different NOS 6V6s, both draws the same current and strong. Three NOS 12ax7s. I have to say this amp has magic, makes me play better and is in the top pick of "any amp" I played.
 
Thanks, al


I have one more AO-43 chassis and want to make a combo, maybe Marshall style drilling out the side for the tubes     

[sluckey]

You have an 8K primary that you want to call 4K for the 6L6. You half the impedance value on the primary so you must half the impedance value on the secondary. This means the 16Ω tap will look like an 8Ω tap. Connect the 8Ω speaker to the orange wire.

[dude]

Totally opposite of what I thought, go to 16 instead of 4.


Anyway, I'm out with EL34s and I'd use 6L6's if I played out anymore, so 6V6 do sound the best to my ears. Maybe I'll try those EL34s switched to 16 ohms. I had them on 4, probably not audible difference..?


So, thanks for getting to me.


al