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#26 2013-06-18 01:26:49

hangman
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From: Seattle Washington
Registered: 2006-09-03
Posts: 1848

Re: Early v4b upgrades and wire?

You measure .475 on the continuity test?  Set it to diode test to be sure.  With the negative terminal connected to the side of the diode with the line and the positive terminal to the other side you should measure about .7 volts maybe a little less,   But if you then switch the test LEDs to the opposite ends the meter should read open.

We now know that the ground is connected... So what is going on?   Do you measure dc voltage on the negative end of c15 with the amp on?

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#27 2013-06-18 11:41:12

greengoblin
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From: FL
Registered: 2009-05-13
Posts: 54

Re: Early v4b upgrades and wire?

Sorry, I switched to the diode test for the diodes themselves after the continuity test..

Will check for DC voltage on the negative side of C15 with the amp on in a little while.

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#28 2013-06-18 17:13:24

greengoblin
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From: FL
Registered: 2009-05-13
Posts: 54

Re: Early v4b upgrades and wire?

Ok according to my DMM the diode was shorted, replaced it..  The negative side of c15 now reads -64mv...

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#29 2013-06-19 08:39:36

hangman
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Registered: 2006-09-03
Posts: 1848

Re: Early v4b upgrades and wire?

Cool,  so are we back up and running?

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#30 2013-06-19 09:01:15

greengoblin
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From: FL
Registered: 2009-05-13
Posts: 54

Re: Early v4b upgrades and wire?

I wish I could say yes.  Unfortunately with the power tubes installed, once I come off standby I am still getting a constant thumbing in my speaker.  The plates get a blue glow at this time as well.... sad

Sorry man....

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#31 2013-06-19 18:07:28

greengoblin
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From: FL
Registered: 2009-05-13
Posts: 54

Re: Early v4b upgrades and wire?

With all preamp tubes pulled except the 12au7, thump still exists. If I pull the ground wire from Pin 8 on V6 that goes to the hole near C15, the blue glow is removed.....

And there is a small hum when the standby is on...  (S/b Light is off)

Last edited by greengoblin (2013-06-19 18:15:44)

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#32 2013-06-22 09:04:29

greengoblin
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From: FL
Registered: 2009-05-13
Posts: 54

Re: Early v4b upgrades and wire?

With all working well, what voltage should be measured at pin 5 on the power tubes?

All letter designation point measure correct voltages, but still getting positive voltage on v7&8 pin 5 and jumping volts on v5&6...

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#33 2013-06-22 17:32:52

hangman
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From: Seattle Washington
Registered: 2006-09-03
Posts: 1848

Re: Early v4b upgrades and wire?

So you don't get the bias voltage on power tubes? But you still get -65 at the negative end of c15?

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#34 2013-06-22 19:47:37

greengoblin
Member
From: FL
Registered: 2009-05-13
Posts: 54

Re: Early v4b upgrades and wire?

Took a break from it to do some stuff on my brothers bassman and to clear my mellon.

But yes, I get -65 on the neg side of c15.  Going to check the voltages across r37, r38, r43 and r44 to see if they correlate tomorrow..

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#35 2013-06-23 09:50:35

greengoblin
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From: FL
Registered: 2009-05-13
Posts: 54

Re: Early v4b upgrades and wire?

Hangman, do you (or anyone that may be reading) have an early v4b handy? I have that black wire coming off v6 pin 8.  Not sure if it goes to the solder hole near r55 or one of the holes at d5 with one leg oh the standby?

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#36 2013-06-26 03:05:44

hangman
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From: Seattle Washington
Registered: 2006-09-03
Posts: 1848

Re: Early v4b upgrades and wire?

8 is the cathode,  it should go to d5.

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#37 2013-06-26 17:15:24

greengoblin
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From: FL
Registered: 2009-05-13
Posts: 54

Re: Early v4b upgrades and wire?

Hey hangman.  So then it should go to the trace that is circled here:

https://docs.google.com/file/d/0BxnnMX7 … view?pli=1

The two holes in front of d5 are filled by a leg from the piolet light and one leg of the standby switch.

Last edited by greengoblin (2013-06-26 17:35:00)

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#38 2013-06-26 18:29:30

greengoblin
Member
From: FL
Registered: 2009-05-13
Posts: 54

Re: Early v4b upgrades and wire?

Ok so I was still getting some odd pin5 values on the power tubes.  Replaced my 100 ohm pot with an 82k resistor as I could not find my 75k. Bias voltage measures -64v.  Sweet, or so I thought.  All voltages were good, bias on tubes v5/v6 were about -61v and v7/v8 were about -64..

Grabbed my tubes and tried again since everything was stable.... Still have the thumping.  Not sure if it is a ground loop or a 60hz thumping.... Argh..

So I hooked the preamp outputs back up to the circuit board and pulled the tubes.  Wanted to see how the preamp sounded as I could pull all preamp tubes except the v4 and the thumping was present.

Once I hooked the preamp to my Micro SVT and my pbass.  At first it was dead quiet and had great tone.  But after about 40 seconds or so I could hear a faint ticking..  The ticking seemed to have the same beat as the thumping...  But was very quiet through the preamp...

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#39 2013-06-26 21:43:08

greengoblin
Member
From: FL
Registered: 2009-05-13
Posts: 54

Re: Early v4b upgrades and wire?

So I listened to the preamp again through my Micro and Sennheisers.  I moved some preamp wires are as they were laying on the board and thought maybe there was feedback or arcing.  No dice....

I played my bass a little and noticed that the ticking speeds up when a note is played.

Pulled out a chopstick and started poking around and one solid orange wire coming off the preamp control board changes the tick when it moves.  If I pull it away from the main boards and close to the front panel the tick gets quieter. So this may be a partial culprit...  Will pull the front off again and replace that wire to see if it clears up the issue...

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#40 2013-06-27 20:19:28

greengoblin
Member
From: FL
Registered: 2009-05-13
Posts: 54

Re: Early v4b upgrades and wire?

Well no luck tonight on my gremlin ticking in the amp...  Replaced the orange wire coming off the preamp/control board to the main board.  Replaced a few other wires in the same route if I saw any melts...

Still the ticking persists....

Again, if I pull all preamp tubes except for v4, the ticking persists.  I tried a few different tubes in v4 and some slowed the ticking some, but it is still there. V4 removed, (not tubes) no ticking.  LOL

I tapped the board more on both sides with my chopstick.  No noises except if I hit R25 just right I would get a bit of crackle through the headphones.  Will try swapping it tomorrow.

Also shut out all the lights and I see no arcing...  Any other possible suggestions?

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#41 2013-06-28 00:19:42

hangman
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From: Seattle Washington
Registered: 2006-09-03
Posts: 1848

Re: Early v4b upgrades and wire?

Have you checked your rewire job again?   It seems like you are just blindly replacing stuff, which might be a good plan of action if you could narrow it down to one part of the circuit... But at this point it seems like you have no idea where this ticking is coming from.

rehash what we have.

The ticking is barely audible through the ext amp out correct?
If you plug a guitar in, you get no output?
All dc voltages on the pins on the preamp tubes look good, but v4 has a high reading on pin 6?

It might be a good idea to take this to someone that has a better grasp of electronics/knows what they are doing.  You are gonna end up gutting this thing and still have no idea why it is misbehaving.

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#42 2013-06-29 09:19:35

greengoblin
Member
From: FL
Registered: 2009-05-13
Posts: 54

Re: Early v4b upgrades and wire?

The ticking is very faint through the preamp out.. The tone through the preamp sounds awesome with the exception of the ticking.  Which seems to also be the thumping when the power tubes are installed.

Originally I mixed the location of two wires on c18 &c20.  That was corrected...

All voltages are showing correct.

I've never encountered a ticking like this before. And after going through chopsticks and pulling tubes to see where it is coming from, it is in V4 or after...

I replaced the preamp wiring because of some melt spots and one wire seemed to make noise during a move with a chopstick..

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#43 2013-07-06 14:34:53

greengoblin
Member
From: FL
Registered: 2009-05-13
Posts: 54

Re: Early v4b upgrades and wire?

Well she is up and running!!!

Made a signal tracer as per the instructions from BillM's audio site.  Narrowed the thumping to the area of v4...

Changed a few caps c11-13 and found a resistor of the wrong value in R33.  Grabbed an 820 ohm rather than an 820k.... Cleaned and retentioned the v4 socket..

She is purring like a kitten now!  Thank you for your help Steve, I owe you and hopefully didn't try your patience too much! smile

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#44 2013-07-07 00:09:20

hangman
Banned
From: Seattle Washington
Registered: 2006-09-03
Posts: 1848

Re: Early v4b upgrades and wire?

I'm glad you got it figured out.  Wrong components can be a rough one.  I once had a nightmare if a time repairing an SVT 4pro.  Had to rebuild the power section and the bias circuit of one of the amplifiers.   I pulled two 100 ohm resistors for the bias circuit, and installed them.  But the amp still was drawing too much current,    Turns out that some 10ohm resistors had been returned to the wrong drawer.  So the 100 ohm resistors I had installed had actually been 10 ohms.   I was pulling my hair out before I realized what I had done.
Anyway... Have fun with the amp!

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#45 2013-07-26 15:03:51

greengoblin
Member
From: FL
Registered: 2009-05-13
Posts: 54

Re: Early v4b upgrades and wire?

How are you guys biasing your amps that you have converted to adjustable bias? I was going to use the 1 ohm resistor method off pin 8 of v6, but not getting a reading. The resistor is between the ground wire to the large corner multi-cap and pin 8 of v6.....

Last edited by greengoblin (2013-07-26 15:06:03)

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