New Build TB OVERDRIVE

[SILVERGUN]

[TIMBO]

Hi guy's, I've noticed that there is a lot of different combinations of resistors/caps around power tubes and i'm sure there is a good reason for this.
Anyway i thought that i might get you guys to give up your thoughts about the different components and how they affect the TONE, SOUND and DISTORTION of the OUTPUT.
Also i am using a Hammond 1750k OT (because i had it) 8K into 4ohms which may not be the best for this build but i am hoping that it may add a bit of magic 
The components in question :-
Coupling caps off the PI
Grid resistors on power tubes
Screen resistors on power tubes
Cathode cap/resistor

Just some thoughts before i heat up the soldering iron.Thanks

[kagliostro]

Hi TIMBO

nice work 

I've seen something in your photos that say to me you're cheating   

please explain the use you do of the copper on the back side of the board

are you using it only as a shield or also as a ground bus ?


K

[TIMBO]

Hi k, No, nothing special, i'm just using PCB board and taped out the copper but not for any real reason. 

[TIMBO]

Hi guy's, Fired her up with no real problems.

BUT, there is always a BUT.
The first thing is that with no guitar plugged in and all knobs at "0" - quiet as a mouse  
When turning up the volume on the ppimv - still quiet
when turning up the FX level - loud 50HZ type hum
when turning up the volume - even louder hum

Did the usual thing chop stix - hum
remove relay 1 to disconnect the fuzz circuit - hum
disconnected the relay power supply - hum
checked tubes/swapped - hum
checked the circuit several times - hum
tried both fixed/cathode bias - hum
removed tubes from V1 and hum gone when PI removed

so not being able to track the source of the hum,i plugged the guitar in to see what would happen........
a nice guitar sound comes out the speaker....
I found this to be odd when the volume turn up the hum would rise as the sound of the guitar....
but with volume @"0" i could strum and still get sound, i rechecked the pot grounding and all is good and i rechecked the wireing around the TS but nothing stood out????? this blew me away
So i disconnected the wire from pin7 V2 and i STILL are getting signal through    

I rechecked that there IS NO connection between the volume pot and pin7 of V2 also the signal does not pass if V2 is removed as you would expect
This one has got me stumped as i did this same TS in the MIMI BTO with no problems  

[tubenit]

So i disconnected the wire from pin7 V2 and i STILL are getting signal through    

In other words, ........... there is NO wire at all connected to V2-7?

OR do you mean there is no wire between the volume and V2-7?

It looks like that a signal could go thru the input jack thru the fuzz circuit to V2-7 if the fuzz circuit is still hooked up to V2-7.

I don't see how it would be possible to get a signal thru if there are absolutely NO wires at all on V2-7?

With respect, Tubenit

[TIMBO]

This is really got me stuffed  All i can do is throw some things out there cause i can't see where the problem is:-

This is what is happening... when all wires are in place and checked several times off original schem,my schem and the same circuit i used in another build that worked well, with guitar plugged in, signal pass with some control of the volume/tone but when the volume is at "0" the signal still passes, one would think that the signal would be directed to ground.

Things i have done:-
I disconnected the 220k/680p from pin7 of V2 and the signal still passed, signal quiet
Removed relay1 and V1 to completely disconnect any connection between input and pin7 of V2
reconnected wire to pin7 V2 disconnected pin1 V2 from .02 cap and signal passed,signal loud
Disconnected wires from from pin1 and pin7 V2 no signal passed
disconnected SW1b and SW2b just in case

This might be REALLY out there, the only connection i can see is the plate resistors that feed pin1 and pin6

Thats all i've got at the moment,Thanks

[DummyLoad]

you are missing 2 caps in the PPIMV ckt. - in fixed bias mode - you'll upset power tube bias without them. please see attached schematic.

it is likely that you mis-wired something - likely a plate load resistor & some audio is leaking through PS chain. disconnect FX, OD, and Fuzz. trace clean pre-amp path then reinsert FX, OD, Fuzz one at a time.
you're amp is extremely complex circuit and the PS is not optimal IMO. triplers and qauadruplers may work in single tube class A and P-P in class pure class A where current demand is more or less constant; i do believe that you may need to re-think that part of your design once you work out the pre-amp kinks. keep an eye on the bias voltage under heavy loading when output stage is running in fixed bias mode.

respectfully,

--DL

edit: deleted bogus schema...

[TIMBO]

Hey DL, First up this is a topic http://www.el34world.com/Forum/index.php?topic=15026.0ms seems to have different opinions but when i check the voltage reading across the 1ohm resistors it remains the same at all settings.

Is it realy possible for some audio to travell through the PS   if you are able to expand on the subject i'm all ears. Thanks

OOPs, forgot to add, have disconnected reverb,OD and have found that the FX loop seems to be causing the majority of the hum

[sluckey]

you are missing 2 caps in the PPIMV ckt. - in fixed bias mode - you'll upset power tube bias without them. please see attached schematic.

The 2 caps you added will destroy the tube bias for fixed bias as well as cathode bias. Timbo's bias circuit works fine just as he has it drawn.

[DummyLoad]

you are missing 2 caps in the PPIMV ckt. - in fixed bias mode - you'll upset power tube bias without them. please see attached schematic.

The 2 caps you added will destroy the tube bias for fixed bias as well as cathode bias. Timbo's bias circuit works fine just as he has it drawn.

you're right. sorry timbo.

--DL

[TIMBO]

Hi guy's, Looks like i'll have to lay this one to rest for the moment  The debugging has got the better of me as i have spent the last three day poking and prodding this thing to DEATH  and with little knowledge and equiptment to find trhe problem 

I think the project is a great one and maybe using more standard components PSU,OT etc... and less bells and whistles maybe this one would have flown.Thanks to all for your help........... on to the next one