Ampeg V4.com

forum

You are not logged in.

#1 2008-03-20 03:23:39

Ryteone
New member
Registered: 2008-03-07
Posts: 9

Sick V4 Back together - Bias way off

Last night I just finished getting the last of the 30+ parts I've changed or added.  I added the trim pot like I found listed on the forum here using a 50k trim with a 47k to replace the 75K fixed.  Remember I got this amp it wasn't working at all, so had no base point to measure anything from (even had to install a new power cord).  I cleaned out everything re-tensioned & cleaned the sockets (had to replace 1 of the power tube sockets).  I had to rewire the previous heater wire due to insulation melting off of it from a short on the Hum balance pot.
Look here if you need any other info or photos:
http://rytetone.com/ampegv4/

Here is a short list of what I've changed out:
All filter cap's
All the screen, plate & control grid resistors
D1-D6 Diodes
Hum balance pot (luckily this forum showed me where to find one)

Everything cleaned up nicely, received the JJ 6L6's today.  I first (without any of the tubes installed and with a dummy load on the output) powered up the amp through my current limiter, did great let the new caps form a bit.  Shut everything down.  Put in all the tubes, set up my bias meter.  Turned on the (without the current limiter) even had to turn off the lights to see all the heaters glowing, looked good.  After letting it heat up for a few minutes I turned on the power and the Bias was reading 271ma !! shut it back off.  Check another tube, it was like 273ma.  I'm thinking now that this is was caused all the problems before when he switched to the Ruby 6L6's and ran it for 5 minutes till it smoked!  Any tips of where to start looking, for this short bus kid? 

***Note to self*** tape up the RCA plugs that lead to Reverb tank, ouch!

Thanks Scott....

Offline

 

#2 2008-03-20 03:29:53

Ryteone
New member
Registered: 2008-03-07
Posts: 9

Re: Sick V4 Back together - Bias way off

Forgot Sorry, the plate voltage on each of them was running 471v was going to shoot for about about a 38.5 ma setting.

Thanks Scott...

Offline

 

#3 2008-03-20 03:51:59

hangman
Banned
From: Seattle Washington
Registered: 2006-09-04
Posts: 1848

Re: Sick V4 Back together - Bias way off

your plate voltage is really low for a V4.  you should be seeing 540 on all of those.   I've never seen one running less than 525.   

did you measure the bias voltage?

Offline

 

#4 2008-03-20 22:10:48

Ryteone
New member
Registered: 2008-03-07
Posts: 9

Re: Sick V4 Back together - Bias way off

Here is what I have:
without tubes standby off:

       Pin 3        Pin 4
V5     545          545
V6     545          545
V7     545          545
V8     545          545

With tubes installed standby off:

       Pin 3        Pin 4
V5     463          329
V6     465          346
V7     450          333
V8     450          329

I used the old tube when I measured these was afraid to leave them on for any length of time.

Right after dinner I was going to fill out the Voltage Reading chart for all the tubes/pins

Thanks Scott....

Offline

 

#5 2008-03-20 23:45:00

Ryteone
New member
Registered: 2008-03-07
Posts: 9

Re: Sick V4 Back together - Bias way off

Ok Just read all the tube/pins:

I will list both my reading first line then chat listing second line

Pin  1     2  3     4   5 6     7 8     9 10
V1   282   x  2.19  x   x 236.7 x 2.21  x x
V1   230   x  2.10  x   x 195   x 2.0   x x

V2   277.5 x  2.13  x   x 240.4 x 2.10  x x
V2   230   x  2.10  x   x 195   x 2.0   x x

V3   371.8 x  228.8 x   x 243.3 x 1.86  x x
V3   335   x  200   x   x 205   x 1.8   x x

V4   234.8 x  10.35 x   x 238.1 x 10.34 x x
V4   200   x  9.7   x   x 200   x 9.7   x x

No Tubes first
W/tubes  second line
Cart listing third line
Pin  1 2 3     4   5 6 7 8 9 10
V5   x x 545   545 x x x x x x
V5   x x 463   329 x x x x x x
V5   x x 540   530 x x x x x x

V6   x x 545   545 x x x x x x
V6   x x 465   346 x x x x x x
V6   x x 540   530 x x x x x x

V7   x x 545   545 x x x x x x
V7   x x 450   333 x x x x x x
V7   x x 540   530 x x x x x x

V8   x x 545   545 x x x x x x
V8   x x 463   329 x x x x x x
V8   x x 540   530 x x x x x x

Pin  1  2     3     4     5     6    7 8 9     10
V201 x  235.7 24.75 169.9 159.3 1.39 x x 159.3 371.1
V201 x  192   22    140   178   1.2  x x 178   325

Pin  1     2 3      4 5 6     7 8   9 10
V202 113.3 x 4.34   x x 265.7 x 5.7 x x
V202 112   x 4.1    x x 270   x 5.6 x x

V203 150.7 x .80    x x x     x x   x x
V203 115   x .70    x x x     x x   x x

I'm afraid I will lose the formatting I put on this I hope it can be read when I post it and people are able to follow my chart.

The only tubes that have been changed have been the power tube (they didn't want to change the others)

Thanks Scott...

Offline

 

#6 2008-03-21 02:37:24

hangman
Banned
From: Seattle Washington
Registered: 2006-09-04
Posts: 1848

Re: Sick V4 Back together - Bias way off

Thats really goofy... 
do you have a second quad of tubes to check?
you might double check your work too... make sure you didn't make a mistake anywhere.   then get back to us

-steve

Offline

 

#7 2008-03-25 02:39:03

Ryteone
New member
Registered: 2008-03-07
Posts: 9

Re: Sick V4 Back together - Bias way off

Let me start by saying sorry for using the part numbers from my board, notice between drawings none of them match but also tried to give the value and location in the description)  I tried yesterday to draw up the circuit with smartdraw with my values and part numbers, but it was more frustrating to use than trouble shooting this as been.

I did correct one mistake I had, I had switched R-55 (the 470 5w resistor that ties in the filter caps to the screen resistors) with the R-53 (the 3K 5w resistor, between the + filter cap and the standby indicator).  I corrected those and it brought all my other tube/pin reading back within range see below.

I switched tubes and when I take it off of stand by its pulling the voltage on Pins 3 and 4 on all 4 power tubes down from (549v without tubes) to 429v on pin 4 and 450v on pin 3 with tubes installed.  I've doubled check every resistor I've put in (made sure none are open or any cold joints or witched others). 

My circuit seems to vary from the 1971 V4 power drawing I'm using the two 10uf 100v electo caps that have the 10k resistor between them on the negative side that feed the output bias, my circuit only has a single 100uf 100v cap with no resistor.  I also notice that the drawing is show a -52v where the output bias joins the two 100k resistors that feed the control grid.  I'm reading 0v there.  I know I need a negative bias voltage.

Double check Diodes they are correct in polarity, gone over the filter caps time and time again to make sure I've got the configuration just perfect with polarity, non grounded where I need to float the cap, etc. 

I even pulled and checked ever resistor that control the phase inverter 12AU7 tube.  That is where someone has hacked the board to put in a master volume control removing the etching from pin 2 to C-10 (the .o1uf cap feeding into the 12AU7 from the 12DW7)  The etching is further removed from that connection on C-10 down to R-29 (the 1M resistor that comes off of the .01, down to the other 1M resistor).  The Pot is wired as follows: Center to pin 2 V4, left to the C-10 Cap (where it was etching was broken), right down to - side of R-29 (to bypass  the 1M resistor, so the pot is replacing it).  I wasn't sure how standard of a way this is to wire in a MV on an V4.

Here is my updated voltage/pin readings:
Pin  1     2  3     4   5 6     7 8     9 10
V1   250.9 x  1.95  x   x 211.2 x 2.0   x x
V1   230   x  2.10  x   x 195   x 2.0   x x

V2   248.7 x  1.94  x   x 214.8 x 1.91  x x
V2   230   x  2.10  x   x 195   x 2.0   x x

V3   333   x  202.5 x   x 218.7 x 1.67  x x
V3   335   x  200   x   x 205   x 1.8   x x

V4   210.6 x  9.28  x   x 213   x 9.29  x x
V4   200   x  9.7   x   x 200   x 9.7   x x

No Tubes first
W/tubes  second line
Cart listing third line
Pin  1 2 3     4   5 6 7 8 9 10
V5   x x 549   549 x x x x x x
V5   x x 450   429 x x x x x x
V5   x x 540   530 x x x x x x

V6   x x 545   545 x x x x x x
V6   x x 450   429 x x x x x x
V6   x x 540   530 x x x x x x

V7   x x 545   545 x x x x x x
V7   x x 450   429 x x x x x x
V7   x x 540   530 x x x x x x

V8   x x 545   545 x x x x x x
V8   x x 450   429 x x x x x x
V8   x x 540   530 x x x x x x

Pin  1  2     3     4     5     6    7 8 9     10
V201 x  208.5 22.06 150.8 141   1.26 x x 141   332.1
V201 x  192   22    140   178   1.2  x x 178   325

Pin  1     2 3      4 5 6     7 8    9 10
V202 101.6 x 3.86   x x 272   x 5.85 x x
V202 112   x 4.1    x x 270   x 5.6  x x

V203 136.7 x .71    x x x     x x    x x
V203 115   x .70    x x x     x x    x x

Once again this was a DOA amp when I opened it up.  One thing I noticed while playing with everything this weekend that I failed to notice when I first started is that one of the "new" Ruby 6L6's that they had installed still had nice clean bright red letters on the tube where as the other three had gotten so hot they were brown.  That same tube I noticed the heaters didn't work on it (switched sockets thinking I might of had a problem with the socket or wiring, but same results), when I tested the amp with the old tubes.

Sorry for going on for so long, just trying to cover any possible things that might help give a clue.

Thanks Scott...

Offline

 

#8 2008-03-25 14:08:27

Ryteone
New member
Registered: 2008-03-07
Posts: 9

Re: Sick V4 Back together - Bias way off

Ok I'll do it.  I'm such a fool!!  I've been overlooking the .047uf 600v cap feeding the bias circuit.  I've been so caught up in the resistors and filter caps I over looked it!  The 0v at the start of the control grid should of been my clue.

Sorry again!

Thanks Scott...

Offline

 

#9 2008-03-25 16:35:42

hangman
Banned
From: Seattle Washington
Registered: 2006-09-04
Posts: 1848

Re: Sick V4 Back together - Bias way off

yeah.. you'll need that cap to get bias voltage.   
replace that and let us know how it runs.   the plate voltages you measured are still WAY low.   they should measure 500V at least,  and I would expect 525-535
but lets see how it likes having the power tubes biased.

if the tubes all look really cooked you could have a problem with those tubes.  so consider that a possibility

I should mention that my VT-22 is roughly a 72 and the reference numbers are all accurate with the schematic.  this is not to say that I don't believe you or that it isn't in the realm of possibility,  but it does surprise me a little. 

as for the master volume,  its not the way I would do it,  but it will work.

keep checking your work, and let us know what happens with the new .047 cap

Offline

 

#10 2008-04-01 03:48:38

Ryteone
New member
Registered: 2008-03-07
Posts: 9

Re: Sick V4 Back together - Bias way off

Ok I know I shouldn't even show this or mention it but I can't tell you how many times I looked this over and over and never noticed my stupid mistake.  If you look in the photo and look at the post used to mount the terminal strip oh and did I mention that is the same terminal I used to mount the 47K resistor in series with the trim pot.  Yeah that might be a problem.  I can't believe I didn't catch that before.  I replaced the capacitor I thought was causing my problems and went through the entire circuit item by item and happened to catch this tonight.  That brought my Bias voltage down to -56v.  I just had to share my award for the DA of the week if not month.  This damn amp is loud I mean clean loud damn.  After playing through it all night I don't want to give it back!

Thank you everyone.  I know everyone says double check you work.  I think you need to take a break from your work for a day then come back to see with fresh eyes!!  I know you kept saying double check you work hangman but I didn't see it!

Thanks Scott....

http://www.rytetone.com/ampegv4/images/Stupid.jpg

Offline

 

#11 2008-04-03 04:49:55

hangman
Banned
From: Seattle Washington
Registered: 2006-09-04
Posts: 1848

Re: Sick V4 Back together - Bias way off

Congratulations on getting your amp back up and running! it can be a difficult thing checking your own work.  because if you overlook something once,  it is easy to continue overlooking it. 

I once worked on an amp for hours unable to figure out why the voltages were all way too low,  only to find out that it was pluged into a powerstrip that the other tech had plugged into a variac set to 90volts!   that possibility just didn't enter into my mind that the power coming out of the outlet I had plugged into was less than 120V
I'm sure you got a lot out of this problem though.  I'm sure you've practically memorized the v-4 schematic.   everytime I have get stumped or get caught up on something in an amplifier,  I always leave the situation with a much better understanding of that amplifier.  next V-4 you work on will be a stroll through the park.

anyway,   glad your amp is ticking again.

-steve

Offline

 

Board footer

Powered by PunBB
© Copyright 2002–2005 Rickard Andersson