Small problem with my kinda TOS

[67polara]

Well I built the TOS but like most of us I changed a few things to suite me.  Mostly I moved the tone circuit on the clean channel to the Master volume area so that it is cut out when changing to overdrive.  I also changed the type of tone circuit to a James type (Bass, Treble) one.  I use KT77 output tubes but other than that it is pretty much the same.  Everything works really well but I am having a little problem noise with it.

There is a kinda of rattle noise in the speaker when I turn the volume up past 12:00 on both channels.  I thought is was my 45 year old speakers so I bought a single Celestion g12M-70 speaker and it does it also just not as bad.  Since it is on both channels I figure it is either in the Clean channel or maybe the PI area.  Any suggestions on where to start looking?  I reflowed all the solder joints and rechecked all my lead dress but can't seem to figure it out.  Maybe a bad cap?  Oh also it seems to be mostly on the 6ths E string mostly around the G.

Tony

[OldHouseScott]

Can you plug into a separate/different speaker cabinet to rule out vibrations in the current cabinet (you didn't specify if this is a combo or head build)? Sometimes you'll get some "slap" from the grill cloth, especially if there's no frame to separate the cloth from the wood baffle.

[rafe]

Have you tried more than one guitar? Pre-amp tube microphonic?

[67polara]

This is a head only unit speaker separate.  I did switch a few of the tubes around but it didn't clear up I think I have a couple more 12a*7's I will try.

Hear is the link to my voltage chart   http://www.el34world.com/charts/valve/ValveData.php?e=view&f=10284  lets see if it works.

Tony

[67polara]

Yea the link works LOL.

Is the pin 8 voltage a bit high on v5 and v6?  Do you think it is the problem?

Tony

[Geezer]

A few questions:

Cathode bias?

Separate cathode resistor for each tube, or single resistor serving both tubes?

What is the value of the cathode resistor(s)

G

[67polara]

cathode biased resistor is per the schematic at 430R.  This is a different anode voltage and a different output tubes so I think I should have changed something along the way LOL

Tony

[Geezer]

Just checking the bias.....you're @ ~~22w & KT77 is a 32w max tube, so you are fine @ ~~68% (personally, I'd lower the bias resistor a bit to get the tubes a bit hotter....closer to 90%, but that's just me....maybe try a 350ohm or so)

Anyway, I doubt that's your problem. I suspect it has something to do with the movement/changes of the tonestack that you made.

Can you post a schematic of what you've got at this point?

G

[67polara]

Well I'm heading out to the Blues jam right now but tomorrow I will try to work one up that isn't hand drawn.  Don't know if I can but I will try.

Tony

[Geezer]

If you can scan in a hand drawn, that will be fine..... Just need something to go by. 

G

[67polara]

Well I have no idea what I did wrong when trying to redo the schematic.  I used expresssch made my changes and saved it and it was no where on my computer to be found.  Is that the program you all use?  The JSchem site is not working right now.

Tony

[tubenit]

Typically, we use SCH unless someone is on a Mac.

Tubenit

[67polara]

OK, I got it fixed must have been a bad install.  I deleted it,reinstalled and redid the Schematic.  I think it will work now.

[67polara]

Yea it worked  

The power supply part of the schematic is not the same as mine.  Mine is a solid state rectifier with a 5 watt 50k wire wound linear pot between C and D to drop the voltages.  I just didn't want to keep messing with the resistor values so I installed the Pot to make it easier on me.  I will probably replace the pot with a resistor once I am happy with my amp.

Tony

[tubenit]

Do you really have 2.2M resistors to ground after the LTPI and prior to power tubes????? Or is that a drawing error?

If so, I think that will be a problem.

With respect, Tubenit

[67polara]

I just looked at it again and I think I see them on the drawing I didn't mess with that part of the schematic.  That is what you drew so is this a mistake?

Mostly the mods I made to the amp are in the Tone circuit.  I moved the tone to the level control area so it would be cut out when in overdrive.  I also changed to tone circuit to a James Braxton style with bass and treble.  This works really well by the way, putting the knobs at 12:00 position gives you a flat tone curve and you can either boost the middle or cut the middle using the bass and treble controls.  The fact that you can get it flat allows the tone control on your guitar to really effect the tone more.  I also removed the effects loop and the master volume trying to fix this problem.  I figured I didn't need them right now, so trimming the circuit down a  little would make it easier to figure out the problem.  I am going to put the effects loop back in but I think I will leave the master out, works just fine the way it is.

Tony

[67polara]

I just noticed that when you take the master volume out your value for those resistors changes.  I will change them to 220k and see if that fixes it.  Thanks for a possibly  really good catch.

Tony

[tubenit]

I just noticed that when you take the master volume out your value for those resistors changes.  I will change them to 220k and see if that fixes it.

Exactly. 250k pot + 2.2M resistor = about 220K              Try that please and report back.

With respect, Tubenit

[Geezer]

Do you really have 2.2M resistors to ground after the LTPI and prior to power tubes?????

Yeah, that would totally mess up the bias on the power tubes....I'll put my money on that fixing it!

[67polara]

Well looks like I really mess up now!  I just had a really bad Blond moment.  After changing the resistors I inserted one of my KT77 wrong!  It slipped in so easy I thought it was indexed correctly but it wasn't.  Then I made my next mistake after turning power on I didn't check to see if all the filaments were lite and took it off stand by.  Very loud noise and squeal and I shut it down.  Put another set of tubes in and NO SOUND at all. 

Checked all my voltages and everything is the same.  Changed to the other speaker still no sound.  Nothing smoked or got hot.  Checked all my resistors and caps all seem good.  Measured the output transformer resistance reads about 4 ohms on 8 ohm tap.  I know the primary on the output is good other wise I wouldn't get a voltage reading at the output tubes right?  Do you think the output transformer is toast?  Or could I have smoked the tube in PI?

What do I do next?

Tony

[67polara]

When I shut the amp off I do hear a click in speaker that is all the sound I get.  No buzz no hiss.

[tubenit]

Have you tried ALL new tubes in it??

When you check voltages, do you get any noise thru the speaker?

Give another visual check of the B+ power rail resistors and caps also. Also look at the screen resistors. Measure the resistor values.

And then repost what you find.

With respect, Tubenit

[67polara]

OK, update.    Problem solved yea!  I guess my relay didn't like the high voltage and fried the contacts.  Replaced the relay and all is good now.  The resistors did the trick thank you Tubenit and Geezer.  Sounds good now at any volume.  I told you about my pot that I control the voltages on D,E,F well I cranked that up about 60 volts and now even better than before.

Thank you to all your input and your knowledge and patients. 

Tony 

[tubenit]

EXCELLENT   !!!!   

Glad you got it resolved and thanks for letting us know.  Congrats!

With respect, Tubenit

[67polara]

No, thank you!  I also changed the two grid resistors on the output to 5.6k as per your vvr circuit.  Here is the updated circuit.  Next is to add reverb to it so standby for another question or two LOL.

Tony