6V6 plexi

[EKDENTON]

Has anyone done the 6V6 plexi build with the master volume like the Hoffman schematics show? Iv'e done Three now without the master volume.
 



I was thinking of building another one and trying the MV.


(typing what i am thinking) ........ and adding a bypass switch for the MV.




Has anyone tried this before?

[sluckey]

Welcome back stranger! I have a plexi 6v6 with MV. It's a more traditional Marshall layout. The MV works fine and I use it to control overall volume after setting the other Volume pots to blend between dark and bright channels. You can see it on my website.

[EKDENTON]

Hi Sluckey!  What's your web address? I will take a look see.

[jjasilli]

+1: welcome back stranger

[sluckey]

Just click the world icon under my name. My warbler and revibe projects are built in those chassis you sent me.

[EKDENTON]

Very nice build on the 6V6 Steve, that is about the most organized wiring layout I have seen.


Did you polish the aluminum boxes I sent you? They look nice also.


What program is that your using to do the amp layouts on your website?

[EKDENTON]

Hi jjasilli!

[sluckey]

I did polish those chassis. I'm using Visio for all my schematics and layouts.

[Fresh_Start]

SLuckey - that Plexi 6V6 build is beautiful in every way.  The layout is extremely efficient in use of space.  There's a lot to learn from your lead dress, etc.

Thanks for sharing those photos.

Chip

P.S.  Welcome back Mr. Denton!

[EKDENTON]

Just the transformers, and choke are almost 230.00 at antique electronics
hammond
pt272fx
pt1650g
pt159q
 
Used to be 140.55

Is there a place to get these at a better price?

[sluckey]

I didn't use expensive 'store bought' iron on my amp. My PT, OT, and choke came from a Hammond AO-43 organ amp that I bought on eBay for $40. If this idea appeals to you and you are patient, you can still find AO-43s on eBay for $50 to $60. If you are eager, expect to pay $80-$100.

You may want to check Hoffman's prices too.

[EKDENTON]

Good idea, I didn't even think to check on ebay.

[Paul1453]

A few from my Ebay watch list to get you started:

http://www.ebay.com/itm/VINTAGE-HAMMOND-H-AO-44-1-REVERB-TUBE-AMP-GUITAR-PROJECT-CLEAN-HIFI/172123003290

http://www.ebay.com/itm/151999151365

http://www.ebay.com/itm/222045529070

http://www.ebay.com/itm/222024514976

http://www.ebay.com/itm/311527775958

 

[DummyLoad]

all from doug.

Mojo768sp 56.00

PT for 18W stout  70.00

use large fender choke 21.00

147.65 plus freight.

PT, OT & choke all fit the stout chassis..

the PT specified puts B+ up in the 400V range with SS rectifiers.

--pete

[EKDENTON]

I Finally have my turret board populated. Waiting for aluminum to make the chassis.

[turtle441]

Since the topic came up, can you educate me a bit on transformer/choke choice?  I note that on Hoffman's parts list for the 6V6 Plexi, he lists an 18W PT and OT and the smaller  choke.  I notice you priced out the Mojotone Deluxe OT (which makes more sense to me, given that we're running 6V6's, I'm assuming gives a better impedance match), and the Large choke.  Any reasoning for that vs the ones on the parts list?

[mresistor]

That looks very nice.  Where did you get a Garolite board with all the component places etched into it?  That's pretty nice.  :-)   

[kagliostro]

WOW EKDENTON


which a fantastic idea !!!

the components/layout engraved on the board looks Really Cool

Doug, give a look at it and think about an improvement on your boards, don't you think it is charming ?

Franco

[Paul1453]

WOW EKDENTON


which a fantastic idea !!!

the components/layout engraved on the board looks Really Cool

Franco

I thought so too.  So I copied the pictures you posted.   

I have a few questions if you don't mind.

I noticed you upped the filtering on the bias circuit.
Was that just because you had those caps in stock, or have you noticed better performance with more filtering?
I thought it would be nice to mount the bias pot adjustment and test points on the top side.
I figured it would make swapping and balancing 6V6 tubes easier.
What do you think of that idea?

Where do you get your aluminum sheets?
What thickness do you use, and how much do you pay for a sheet?
I got a quote for a 4'x10' 20 gauge aluminum sheet.
After tax it will cost me almost $160.
That could make quite a few chassis', but others have told me 20 gauge is too thin.
A 16 gauge sheet will likely cost significantly more.
There is a scrap metal place near my house that I haven't checked out yet.
I doubted they would have the nice sheets of aluminum that I am looking for.

[EKDENTON]

Turtle441I have tried several size chokes and they all seem to work fine. The one i just got from Doug is the large fender choke 3 henry.


If you have not ordered the PT yet you might want to consider one with a little higher voltage than the 18 watt. I'm sure it would work with that PT but it may not sound like the 6v6 plexi was intended to sound with higher plate voltages. Check out the maximum voltages on the 6v6tube from two different manufacturers:


https://www.tubesandmore.com/sites/default/files/associated_files/t-6v6-s-jj_specificationsheet.pdf
http://www.r-type.org/pdfs/6v6g.pdf


There was a lot of folks making this amp over at 18watt.com a few years back. Check there for more info on this amp and also do a search for Mark Huss. He also has a lot of info on this peticular build. Slucky did a beautiful build with a new layout here using parts from an old Hammond. I think he said his B+ is around 400v.

[EKDENTON]

Hey Paul,


No on the caps, I put the smallest that i could find without going undersize that i could find online. I searched for the ones on the schematic and gave up.  The board is what Doug sells and its not etched its engraved with my cnc router table. It's kinda pointless to engrave it, but I like to spend the extra time to do it. The first one takes time to set up but once you have it done then you have all the spec parts on the board. No don't waste money on the 20ga aluminum that is way too light. I just tried to make one from 16ga or .060 aluminum and it was also to light . The transformers are so heavy if you even drop the amp a few inches the impact and weight of the tranformers could wreck the chassis and break your turret board. Better to go with .080 but make sure it is not tempered. Dont get T6 grade you wont bend that. Try to get 5052 or 3003 either of these are bendable

[Shack]

Man Sluckey.....that is an awesome build, very inspiring

[EKDENTON]

Hey Paul, I get the aluminum at Aarmor metals, in El Paso TX.


 20 gauge(.035) will be too light to support much even after all the bending. If you ever drop the amp even a few inches the impact from the weight of the heavy tranformers will deform the chassis and could break the turret board even using the 16ga. I would suggest using .080 in grade 5052 for the chassis. It is good and sturdy yet soft enough to be bendable. You would probably need someone with a box pan brake to bend it for you. I just ordered a 48" x 80" pc. of the .080 and it was $75. thats enough for about 12 chassis.


On the bias pot yes, that is a good idea. I put one on the board because I did that in the past but for this one i ordered a regular fender bias pot that takes a screwdriver to adjust and it mounts through the chassis in the back. I will take the little blue bias pot off before i finish and use the the new one.

[EKDENTON]

close to finishing this one and i am having a problem. When i turn it on without the guitar cord plugged in it's quiet but with the cord plugged in makes a pretty awful buzzing that gets  louder or quieter by turning the volumes up or down. when i plug in the guitar there is no sound from the guitar coming through. When i unplug the guitar from the cord and touch my finger on the cord tip I can hear a slight change in the buzzing sound.  I keep checking the guitar jack for a mistake on wiring but I do not see anything wrong. Iv'e double checked and my grounds are all connected. I switched the OT leads and that is not it. It does not sound like a hum really but a little like buzzing. I did add the artificial center tap on the heater windings since the secondary only had the center tap on the High Voltage winding. Was that correct to add the artificial center tap?


Aww shoot, the fuse blew while taking voltages. 

[sluckey]

Let's see some close up pics of the input jacks.

Artificial center tap on heaters is a good thing to help reduce 60Hz hum.

[EKDENTON]

Okay. here is the input jack photo. I took it out this morning in the light where i can actually see better. When I switched the OT leads one wasn't soldered. Let me fix that, check it and if it is still having a problem i will post some other photos. Can you check the jack wiring just in case but I don't see what could be wrong. the resistor is the 1M. The tip (input) is going to the two 68K resistors mounted on pin 2 and 7 of V1.

[sluckey]

Your input jack is wired wrong and has no ground connection. Wire it like this...

[EKDENTON]

Awesome, Thanks Steve. I will change it.

[sluckey]

If you want to do this the absolute easiest way just add one jumper...

[EKDENTON]

Okay I fixed the OT wire and rewired the jack. It's working now. Nice and quiet. It's gonna need some tweaking. Volume one and two sound simmilar both have tons of bass and not much treble. With the MV all the way up the preamp is distorting with either volume barely on. There is no clean like it is now. Once I get time I will check all the voltages and the bias settings tonight when i get off work.

[EKDENTON]

The only thing i have done on this one that is different from the last build is i changed the Mids pot to a 10k to try and get a more "scooped mids" sound, and also i used the GZ34 rectifier.  I'w wondering if the lower voltages from the tube rectifier is causing it to break up way too early.


However i am puzzled why volume two sounds like pure bass also.

[sluckey]

Be sure you used the correct cap values on the cathodes and plates of V1. None of those four caps are the same value.

Post some tube voltages.

[Paul1453]

If you could post the voltage readings on yours where ever there are readings on the schematic.

I had an issue with a leaky cap in my PI circuit when I first powered mine up.
It was quite obvious from the voltage readings I had an issue there.
If all the voltage readings match up, it eliminates a lot of things that could be causing your sound problems.

[EKDENTON]

Okay I will check caps, test voltages and post tonight.

[Paul1453]

Looking at the tone stack configuration has given me an idea about why you have too much bass now.

That 25K Mid pot is the Gnd connection for the whole tone stack.

I'm not sure how all those band pass filters work exactly,
but I think you may have thrown them all out of whack.

Adding a 15K resistor between your 10K Mid pot and Gnd might return those filters to their original values.   

I don't have any more 25K pots for my Quad 6V6 Plexi.
Closest I have measures 17.7K so I was thinking about what might happen if I just used that instead.
I concluded it might be OK to use that pot if I put an 8K resistor between it and Gnd.
I'm hoping one of the very knowledgeable moderators gives us the low down on the ramifications of changing the value of that pot. 

[EKDENTON]

It has all the correct caps and resistors on the plates at V1. I must have been looking at the wrong layout when wiring my volumes and I had the bright and normal wires switched. So I fixed that and it corrected the tone. I can't get any voltage tests yet because I went with the GZ34 rectifier and I didn't account for the extra filament draw and the 2 amp fuses are not happy with me. 


Is this the correct current draw for these tubes? I see differing data depending on what website you go to.


1@JJ brand GZ34 350mA
2@JJ brand 6V6S 450mA
3@JJ brand 12AX7S 300mA


2.15 amps total?

[sluckey]

GZ34 will draw 1.9 AMPS current from a 5 volt winding.

[EKDENTON]

Okay thanks. I have fuses ordered.

[EKDENTON]

All done. This one i followed the Mark Huss layout, with the exception of using the GZ34 rectifier tube, adding a MV, and a switch on the back to dissconnect the NFB. This one sounds pretty awesome. Very quiet amp. Photos are various stages in the build. I only had two small issues. I had the input jack wires on the opposite pins, and I forgot to adjust my fuse size for the added current current draw on the GZ34. All good now though.

[sluckey]

Well done. Looks very clean. Layout is very logical.

[EKDENTON]

Thanks, I had one other issue when working on my bias current setting. I forgot to hook the end of the bias supply wire that runs under the board so that when the solder melts the wire hangs on the turret and doesn't drop off the turret. So I wound up with no bias -voltage at all after i changed a resistor, and the tubes got pretty hot for a bit. I wound up just running a wire on top of the board so that I can see that it is there.


Link to voltages

[Ed_Chambley]

Love it!  Very nice build and I am a blond telex freak anyway.  Never seen the salt and pepper grill cloth with it but that looks great too.