Hoffman chassis 6V6 project

[MFowler]

A while back I bought this Hoffman chassis from Doug when they first were introduced.
 
 Decided I wanted to run 6V6 so ordered from Triodestore the 041318-48UL paper bobbin OT which was sitting on my shelf for just such a project. Primary is 6K6 and secondary 4/8/16 R for such projects as Fender Deluxe, Ampegs, and Silvertone amps.
 
 The PT is the PT290-50 HT-6179-50 from Hoffman which is an 18w 290-0-290.
   
 Looking for this to be a clean pedal platform small head amp.  Gain, treble, middle, bass, and master volume.

Using 2 preamp tubes into pair of 6V6's JJ's, solid state rectifier (removed the last octal tube socket) and installed JJ 40/20/20/20 can cap.

 
Plates: 358vdc   Screens: 367vdc bias -26vdc
 
 B+
 1. 370vdc
 2. 366vdc
 3.322vdc
 4.322vdc
 
 V1
PIN#
 1. 97vdc
 3. 3.4vdc
 6. 98vdc
 
 V2
 1. 244vdc
 6. 215vdc
 2. 41.54vdc
 7. 39.73vdc
 3-8. 67.2vdc

[TIMBO]

Hey mate, you might need to post a schematic if you can, those voltages don't look right.

[Blind Lemon]

Yep, B+ voltages look ok but voltages on V1/2 are not right for 12A#7 typically tubes.


BL

[sluckey]

V2 voltages look OK for a LTP PI. V1 does look odd. Schematic would help.

[Blind Lemon]

My bad on V2, should have read 2 pre tubes.


BL

[PRR]

V2 pins 2 and 7 read low due to meter loading.

I would expect V2 pins 1 and 6 to be more equal.

[MFowler]

I'm going to reduce my dropping string resistor to increase voltages to V1 and V2.


Might have to balance the PI


But this is with bench testing tubes straight out of my large tuna can.

[purpletele]

Mark,

That is some clever work in the chassis!

Are you using a grey shielding tube for your control wires?  Or is that just shrink tubing?

[pullshocks]

I have to agree with Purple Tele.  Some cool wiring.  What catches my eye is how the e-cap is mounted to the side wall of the chassis.  Where do you get those single turrets that attach right to the chassis?

[MFowler]

I have to agree with Purple Tele.  Some cool wiring.  What catches my eye is how the e-cap is mounted to the side wall of the chassis.  Where do you get those single turrets that attach right to the chassis?

Thanks http://www.surplussales.com/Hardware/Standoffs/dap.html

[MFowler]

Mark,

That is some clever work in the chassis!

Are you using a grey shielding tube for your control wires?  Or is that just shrink tubing?

Thanks yes, it's a 2 conductor shielded cable to connect the input from V1 and output to PI to the MV pot one end of shield grounds to MV pot.

[bnwitt]

Mark,
What gauge wire are you using for the potentiometer grounding bus?

[purpletele]

Mark,

Where to you get the 2 conductor cable?  That looks useful.

[MFowler]

Mark,
What gauge wire are you using for the potentiometer grounding bus?

Barry that wire is like around 12awg sold in rolls in many box stores, doesn't have coating so it solders very well.  To straighten the wire I chuck it up in a drill and hold the other end with pliers spin it and it straightens right out.


Romex in 14 or 12awg works well too.

[MFowler]

Mark,

Where to you get the 2 conductor cable?  That looks useful.

That dual lead one braided ground was given to me but I see it all the time.

[purpletele]

Mark,

Thanks Mark,  I have been using Mogami wire lately and that is easy to work with, and I have been successful.  I haven't found anything on Apex yet.

Looks like Apex has a lot of cool stuff!  I don't think I could work in that warehouse without straightening things up and organizing.  Then I would encourage a New Home Page Photo of a nice clean organized WH.

It has always seemed like a real weak but important connection, that is, the light gauge stranded wires.  Seems like there should be a better wire product, so I am always keen on things that others have already solved.

[MFowler]

I would get this two conductor shielded cable







EL34 edit:
Please don't link to other web stores when I have items in my stock that can do that
Two conductor cable with shield is here

http://hoffmanamps.com/MyStore/catalog/WireCableMobile.htm

[sluckey]

EL34 edit:
Please don't link to other web stores when I have items in my stock that can do that
Two conductor cable with shield is here

Talking about your footswitch cable with only one conductor shielded? The stuff MFowler used has both conductors shielded. I don't see any of that stuff in your store?

[Ed_Chambley]

I would get this two conductor shielded cable







EL34 edit:
Please don't link to other web stores when I have items in my stock that can do that
Two conductor cable with shield is here

http://hoffmanamps.com/MyStore/catalog/WireCableMobile.htm

EL34, are you referring to your foot switch 2 conductor cable?  I do not see any shielded 2 conductor wire.  I have some of your foot switch wire and only one of the conductors is shielded.


My apology if I have overlooked shielded 2 conductor wiring.

[Ed_Chambley]

Sorry Sluckey, you beat me to it.  I used some of the foot switch wire for a LARMAR MV as I thought the flat would be nice.  Was not as quite, so I replaced it with some Canare L-2T2S and the noise was gone.

[purpletele]

I would get this two conductor shielded cable


Doug,

My apologies, that was not intended to be uncouth.  I should have asked privately for outside info.

I'm always looking for tips and secrets from the vets. 









EL34 edit:
Please don't link to other web stores when I have items in my stock that can do that
Two conductor cable with shield is here

http://hoffmanamps.com/MyStore/catalog/WireCableMobile.htm

[pompeiisneaks]

Mark,

very cool looking build!  I do want to get me some of those single stand turrets, I think sluckey has some too and once linked to something similar. 

~Phil

[MFowler]

I apologize for my link, not the same kind of wire I use but still I respect Doug's note.


I will refrain from random postings, I'am not used to owner forums.


Mark

[EL34]

Sorry guys, I forgot that only one of the conductors is inside the shield

[bnwitt]

Barry that wire is like around 12awg sold in rolls in many box stores, doesn't have coating so it solders very well.  To straighten the wire I chuck it up in a drill and hold the other end with pliers spin it and it straightens right out.
Romex in 14 or 12awg works well too.

So what you are using is bare copper ground wire?

[Ed_Chambley]

Mr MFowler, would you mind saying what type of master volume you have used.  Is this basically like a fender deluxe?


Nice and clean.  You do very nice work.

[MFowler]

Barry that wire is like around 12awg sold in rolls in many box stores, doesn't have coating so it solders very well.  To straighten the wire I chuck it up in a drill and hold the other end with pliers spin it and it straightens right out.
Romex in 14 or 12awg works well too.

So what you are using is bare copper ground wire?

Yes that is exactly correct salvage from left over electrical job or they sell in box stores.
Hobby stores sell copper or brass in packaged rolls.  If hobby store just make sure it is uncoated, those hobby people like their wire coated.


Mark

[MFowler]

Mr MFowler, would you mind saying what type of master volume you have used.  Is this basically like a fender deluxe?


Nice and clean.  You do very nice work.

Thank you.


The MV is a V1B -022uf cap to 1MA right before the PI.
There is no schematic only an Ampgarage members only Dumble Princeton mod layout so I can't upload that but I was looking around an Slucky has a AB763 Deluxe Lite build info he shared that is the basis to go by.


Treble cap is 330pf with 500kL treble pot, 1MA bass pot ,1uf cap, 250kA mid pot with .01 cap.  Volume is 1mA pot with .0047uf bright cap push/pull switch. PI is .047uf/33k tail/.01/470R bias/1m-1m.  220k/220k and 100k/82k. 1k5 grids and 470R screens.  Right now NFB is 2k7 on 8R tap.


Dumble liked to mod anything Fender Bandmasters, Bassman SF/BF, Tweed Deluxe, and Princeton's.

[Ed_Chambley]

Thanks, I am a member at TAG, just not a big contributor. I will go over there and look around.


And thanks I get the master

[bnwitt]

Barry that wire is like around 12awg sold in rolls in many box stores, doesn't have coating so it solders very well.  To straighten the wire I chuck it up in a drill and hold the other end with pliers spin it and it straightens right out.


Romex in 14 or 12awg works well too.

You sir are a friggin' genius.  I just took a 14AWG bare ground wire from some old romex wire I had and did the drill/pliers twist thing and I now have a very straight ground bus wire.