Pop goes the volume - Page 2

thrawn86 · 05-15-2010, 11:21 PM

JCM, thank you for finally intervening here. I appreciate it, as does TimP i'm sure.

tim p · 05-16-2010, 05:49 AM

Hi jcm, everything looks good on the boards nothing burnt. I've checked the connections, have biased the amp with no problems before. I have a multimeter I just dont know what settings to use or what to look for to check the ot. Thanks for your help

jcmjmp · 05-16-2010, 08:39 AM

Quote:

Originally Posted by tim p

Hi jcm, everything looks good on the boards nothing burnt. I've checked the connections, have biased the amp with no problems before. I have a multimeter I just dont know what settings to use or what to look for to check the ot. Thanks for your help

If you want to check the OT, its actually pretty simple. I could do this for free but you'd have to bring it to me, but its quite the drive.

If you go to a small electronics parts store (like Active Electronics - not sure if they have one in Kingston), get yourself a kit signal generator that does sine waves. With that, you should be able to do some testing.

Marstran has a simple, easy to follow procedure on doing this. You can leave the OT in the amp, just unplug the quick connects on the primary side of the OT from the amp's internal boards. On the secondary side, you can just plug in a speaker cable into the amp's speaker outs and put your multimeter on cable's tip/ring connectors (this is easier if you unscrew the metal casing covering the connections and use alligator clips to hold on to the metal pieces.)

Measuring Primary Impedance

tim p · 05-20-2010, 05:24 AM

Hi jcm. There are no electronics stores around here. I would have to order the kit, then build it. then hope it works properly to do any testing. I would rather get another ot. and go from there. where is the bias circuit on these amps. I've replaced the valve board and dont know if it's on there or not. Thanks for your help.

jcmjmp · 05-20-2010, 07:53 AM

Quote:

Originally Posted by tim p

Hi jcm. There are no electronics stores around here. I would have to order the kit, then build it. then hope it works properly to do any testing. I would rather get another ot. and go from there. where is the bias circuit on these amps. I've replaced the valve board and dont know if it's on there or not. Thanks for your help.

The bias board is mounted on the chassis (the three prongs you see on the back of the amp with the back grill off are on the mini bias board).

tim p · 06-06-2010, 02:07 PM

Hi replaced ot .I've got my volume back but I still cant set the bias properly.3 prong connector was loose so I soldered the connections and anything else on the boards that looked cold. Could I have a bad bias pot. I had the amp cranked up to 6 or 7 and it sounded great. no redplating

Buggs.Crosby · 06-06-2010, 02:21 PM

what are your readings now?

tim p · 06-06-2010, 03:44 PM

Hi buggs. I'm still getting the same readings. Other than the bad bias numbers everything seems fine.

Buggs.Crosby · 06-06-2010, 03:54 PM

with 127@idle i dont see how you are not red plating at around 6....then again i'm no tech
one of those guys will chime in with why that it is working that high

tim p · 06-06-2010, 04:10 PM

I cant figure it out either. I played for about 1/2 hour working all 3 channels. I kept a close eye on the tubes. No sign of red plating.

Wilder Amplification · 06-07-2010, 11:46 AM

The fact that one pair biases fine yet the other doesn't I would think points to a problem with the bias pot circuit that controls that pair.

tim p · 06-07-2010, 03:53 PM

Hi Jon, I've been watching wkcchampion thread for a bit . I think I got the pin voltage meas. figured out. I'll take some meas. later when I get a chance and post the numbers. seems odd though the amp sounds great and It's not red plating. I measured the bias circuit resistors when I had the board out. meas. on the board ohms, nothing stood out all were about the same. Dont know if that helps. Thanks for your reply Jon. Have a good one.

tim p · 06-08-2010, 07:54 PM

Ok took some measurements and I'm still alive. The numbers are in order 5/6/7/8

pin 5 33.1 33.2 34.0 34.0

pin 2 3.2 3.2 3.2 3.2

pin 7 3.2 3.2 3.2 3.2

pin 4 512 513 512 512

pin 3 512 512 512 512

How do I measure my grid and bias resistors and which ones are they. Thanks for any help. Oh there is a lot of stuff crammed into a TSL, can I measure them without unsoldering and lifting a leg off the board.

tim p · 06-09-2010, 06:34 AM

Do these numbers seem alright.

Buggs.Crosby · 06-09-2010, 08:00 AM

what is your wall voltage up there....220 correct?....post what it is
also measure pin 5 with the bias at min and max and post those numbers ....it will help the techs out a little more
your plate voltage is about 20v higher than my DSL but that could be the wall voltage

Wilder Amplification · 06-09-2010, 09:08 AM

Your pin 5 voltage should've read as a negative voltage first off (probably did but you may not have thought to type the (-) sign).

With 512V unloaded with no valves in, that will probably load down to about 480-485 with tubes in and 475-480 on the screens. At that high of a screen voltage, the pin 5 numbers seem way low considering that my 100 watter with 450 on the screens takes about -39 to -40 to bias it to 35mA per valve.

Can you check the pin 5 voltage with the bias pot rotated to both of its extremes and post those min/max pin 5 voltages up?

tim p · 06-09-2010, 03:56 PM

Hi Buggs, The wall voltage here is 118v.
Hi Jon. The pin 5 voltages are- forgot to put that in.
As for the bias measurements I have 2 pots on the TSL , do you want me to turn both to the left meas. than both to the right.
The left pot I can adjust no problem valves 5/6 can go from 7mv to beyond the meters range. the right pot valves 7/8 is the problem. The lowest I can adjust it is 117 mv and thats with the left side way hot around 140 mv.
I cant turn them all the way down then all the way up because they counter act one another

Wilder Amplification · 06-09-2010, 04:40 PM

Quote:

Originally Posted by tim p

Hi Buggs, The wall voltage here is 118v.
Hi Jon. The pin 5 voltages are- forgot to put that in.
As for the bias measurements I have 2 pots on the TSL , do you want me to turn both to the left meas. than both to the right.
The left pot I can adjust no problem valves 5/6 can go from 7mv to beyond the meters range. the right pot valves 7/8 is the problem. The lowest I can adjust it is 117 mv and thats with the left side way hot around 140 mv.
I cant turn them all the way down then all the way up because they counter act one another

Yes...check pin 5 on either V5 or V6 while you rotate its respective pot fully to the left and right and get both voltage readings in both directions. Do the same for V7/8.

One last thing to do is to swap the pairs of valves over and see if the problem switches sides.

tim p · 06-09-2010, 05:41 PM

Hi Jon. I took the measurements, all numbers are -

tube 5 6 7 8

left pot L 33.3 33.3 28.8 28.8
R 33.3 33.3 42.1 42.1

rt pot L 22.7 22.7 37.5 37.5
R 33.3 33.3 37.5 37.5

Moving the tubes around doesn't change anything. The tubes are a new quad of sed =c=.

Wilder Amplification · 06-09-2010, 05:52 PM

Quote:

Originally Posted by tim p

Hi Jon. I took the measurements, all numbers are -

tube 5 6 7 8

left pot L 33.3 33.3 28.8 28.8
R 33.3 33.3 42.1 42.1

rt pot L 22.7 22.7 37.5 37.5
R 33.3 33.3 37.5 37.5

Moving the tubes around doesn't change anything. The tubes are a new quad of sed =c=.

OK so it's the V5 and 6 positions that are the issue.

With power to the amp OFF and no valves installed, can you read out the value of R67 in ohms with a multimeter? Also, check resistors R7 and R66 while you're in there.

tim p · 06-09-2010, 06:29 PM

Hi Jon Me again. Amp off no tubes
R67 open 1 on my meter
R7 5.57
R66 5.59
Was all this BS caused by one bad resistor. I had the same problem with the board I just replaced.

Wilder Amplification · 06-09-2010, 06:33 PM

Quote:

Originally Posted by tim p

Hi Jon Me again. Amp off no tubes
R67 open 1 on my meter
R7 5.57
R66 5.59
Was all this BS caused by one bad resistor. I had the same problem with the board I just replaced.

Check R67 again...sometimes if you don't make good contact with the meter probes it will read open.

tim p · 06-09-2010, 06:56 PM

Hi. I had my meter set at 200k. At 2000k I got
R67 220
R7 006
R66 006

Wilder Amplification · 06-09-2010, 06:58 PM

Quote:

Originally Posted by tim p

Hi. I had my meter set at 200k. At 2000k I got
R67 220
R7 006
R66 006

And also, since you stated that you swapped the board and had the same issue, I'd say you either have a faulty bias pot (they're on their own separate board) or a possible bad solder joint on the bias pot board.

tim p · 06-09-2010, 07:13 PM

Hi Jon I wondered if it might be a bad trim pot, I mentioned it in an earlier post. I re soldered all bias connections, resistors,valve sockets power & pre-amp and anything else I could see that looked like it might be cold. Do you know what the K's are on these trim pots does it matter what size I use if they are close to original. Thanks for your help Jon, your the man.

Wilder Amplification · 06-09-2010, 08:51 PM

Quote:

Originally Posted by tim p

Hi Jon I wondered if it might be a bad trim pot, I mentioned it in an earlier post. I re soldered all bias connections, resistors,valve sockets power & pre-amp and anything else I could see that looked like it might be cold. Do you know what the K's are on these trim pots does it matter what size I use if they are close to original. Thanks for your help Jon, your the man.

Anytime Tim! Yes it does matter. That part is a 22K ohm trimpot. If you want I can call my supplier and find out how much it would be for just a replacement bias pot board. Shouldn't be all that much and would be an easier fix.

tim p · 06-09-2010, 08:56 PM

I would be very greatful. Thanks again Jon.

Wilder Amplification · 06-09-2010, 09:03 PM

Quote:

Originally Posted by tim p

I would be very greatful. Thanks again Jon.

On the list for things to do first thing in the AM. I'll let ya know.

tim p · 06-09-2010, 09:11 PM

Appreciate it .I'll check in as soon as I get home from work.

tim p · 06-11-2010, 08:49 PM

Hi Jon. The Marshall tech at JAM ind. e-mailed me and asked me to disconnect conn 12 on main board and try bias. I did so and the amp biased up perfectly. He said to call if it worked but now he's finished work till monday. I followed the leads to the front pot board conn 20 output mute and variable power. Do you know what the quick fix might be or should I wait for monday He is hard to call as he is finished work at the same time as I am, no cell phones allowed on job site. I am greatfull for any help. Thanks

05-16-2010, 05:49 AM	#32 (permalink)
tim p Senior Member Join Date: Mar 2010 Posts: 203	Re: Pop goes the volume Hi jcm, everything looks good on the boards nothing burnt. I've checked the connections, have biased the amp with no problems before. I have a multimeter I just dont know what settings to use or what to look for to check the ot. Thanks for your help

05-20-2010, 05:24 AM	#34 (permalink)
tim p Senior Member Join Date: Mar 2010 Posts: 203	Re: Pop goes the volume Hi jcm. There are no electronics stores around here. I would have to order the kit, then build it. then hope it works properly to do any testing. I would rather get another ot. and go from there. where is the bias circuit on these amps. I've replaced the valve board and dont know if it's on there or not. Thanks for your help.

06-06-2010, 02:07 PM	#36 (permalink)
tim p Senior Member Join Date: Mar 2010 Posts: 203	Re: Pop goes the volume Hi replaced ot .I've got my volume back but I still cant set the bias properly.3 prong connector was loose so I soldered the connections and anything else on the boards that looked cold. Could I have a bad bias pot. I had the amp cranked up to 6 or 7 and it sounded great. no redplating

06-06-2010, 02:21 PM	#37 (permalink)
Buggs.Crosby Banned Join Date: May 2009 Location: S.Jersey Posts: 6,363	Re: Pop goes the volume what are your readings now?

06-06-2010, 03:44 PM	#38 (permalink)
tim p Senior Member Join Date: Mar 2010 Posts: 203	Re: Pop goes the volume Hi buggs. I'm still getting the same readings. Other than the bad bias numbers everything seems fine.

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06-06-2010, 03:54 PM	#39 (permalink)
Buggs.Crosby Banned Join Date: May 2009 Location: S.Jersey Posts: 6,363	Re: Pop goes the volume with 127@idle i dont see how you are not red plating at around 6....then again i'm no tech one of those guys will chime in with why that it is working that high

06-06-2010, 04:10 PM	#40 (permalink)
tim p Senior Member Join Date: Mar 2010 Posts: 203	Re: Pop goes the volume I cant figure it out either. I played for about 1/2 hour working all 3 channels. I kept a close eye on the tubes. No sign of red plating.

06-07-2010, 11:46 AM	#41 (permalink)
Wilder Amplification Senior Member Join Date: Oct 2009 Location: Fresno, CA Posts: 6,165	Re: Pop goes the volume The fact that one pair biases fine yet the other doesn't I would think points to a problem with the bias pot circuit that controls that pair. __________________ Jon Wilder Wilder Amplification - The official home of the 80s cock of the walk "Schwank" http://www.wilderamps.com http://www.facebook.com/wilderamps

06-07-2010, 03:53 PM	#42 (permalink)
tim p Senior Member Join Date: Mar 2010 Posts: 203	Re: Pop goes the volume Hi Jon, I've been watching wkcchampion thread for a bit . I think I got the pin voltage meas. figured out. I'll take some meas. later when I get a chance and post the numbers. seems odd though the amp sounds great and It's not red plating. I measured the bias circuit resistors when I had the board out. meas. on the board ohms, nothing stood out all were about the same. Dont know if that helps. Thanks for your reply Jon. Have a good one.

06-08-2010, 07:54 PM	#43 (permalink)
tim p Senior Member Join Date: Mar 2010 Posts: 203	Re: Pop goes the volume Ok took some measurements and I'm still alive. The numbers are in order 5/6/7/8 pin 5 33.1 33.2 34.0 34.0 pin 2 3.2 3.2 3.2 3.2 pin 7 3.2 3.2 3.2 3.2 pin 4 512 513 512 512 pin 3 512 512 512 512 How do I measure my grid and bias resistors and which ones are they. Thanks for any help. Oh there is a lot of stuff crammed into a TSL, can I measure them without unsoldering and lifting a leg off the board.

06-09-2010, 06:34 AM	#44 (permalink)
tim p Senior Member Join Date: Mar 2010 Posts: 203	Re: Pop goes the volume Do these numbers seem alright.

06-09-2010, 08:00 AM	#45 (permalink)
Buggs.Crosby Banned Join Date: May 2009 Location: S.Jersey Posts: 6,363	Re: Pop goes the volume what is your wall voltage up there....220 correct?....post what it is also measure pin 5 with the bias at min and max and post those numbers ....it will help the techs out a little more your plate voltage is about 20v higher than my DSL but that could be the wall voltage

06-09-2010, 09:08 AM	#46 (permalink)
Wilder Amplification Senior Member Join Date: Oct 2009 Location: Fresno, CA Posts: 6,165	Re: Pop goes the volume Your pin 5 voltage should've read as a negative voltage first off (probably did but you may not have thought to type the (-) sign). With 512V unloaded with no valves in, that will probably load down to about 480-485 with tubes in and 475-480 on the screens. At that high of a screen voltage, the pin 5 numbers seem way low considering that my 100 watter with 450 on the screens takes about -39 to -40 to bias it to 35mA per valve. Can you check the pin 5 voltage with the bias pot rotated to both of its extremes and post those min/max pin 5 voltages up? __________________ Jon Wilder Wilder Amplification - The official home of the 80s cock of the walk "Schwank" http://www.wilderamps.com http://www.facebook.com/wilderamps

06-09-2010, 03:56 PM	#47 (permalink)
tim p Senior Member Join Date: Mar 2010 Posts: 203	Re: Pop goes the volume Hi Buggs, The wall voltage here is 118v. Hi Jon. The pin 5 voltages are- forgot to put that in. As for the bias measurements I have 2 pots on the TSL , do you want me to turn both to the left meas. than both to the right. The left pot I can adjust no problem valves 5/6 can go from 7mv to beyond the meters range. the right pot valves 7/8 is the problem. The lowest I can adjust it is 117 mv and thats with the left side way hot around 140 mv. I cant turn them all the way down then all the way up because they counter act one another

06-09-2010, 05:41 PM	#49 (permalink)
tim p Senior Member Join Date: Mar 2010 Posts: 203	Re: Pop goes the volume Hi Jon. I took the measurements, all numbers are - tube 5 6 7 8 left pot L 33.3 33.3 28.8 28.8 R 33.3 33.3 42.1 42.1 rt pot L 22.7 22.7 37.5 37.5 R 33.3 33.3 37.5 37.5 Moving the tubes around doesn't change anything. The tubes are a new quad of sed =c=.

06-09-2010, 06:29 PM	#51 (permalink)
tim p Senior Member Join Date: Mar 2010 Posts: 203	Re: Pop goes the volume Hi Jon Me again. Amp off no tubes R67 open 1 on my meter R7 5.57 R66 5.59 Was all this BS caused by one bad resistor. I had the same problem with the board I just replaced.

06-09-2010, 06:56 PM	#53 (permalink)
tim p Senior Member Join Date: Mar 2010 Posts: 203	Re: Pop goes the volume Hi. I had my meter set at 200k. At 2000k I got R67 220 R7 006 R66 006

06-09-2010, 07:13 PM	#55 (permalink)
tim p Senior Member Join Date: Mar 2010 Posts: 203	Re: Pop goes the volume Hi Jon I wondered if it might be a bad trim pot, I mentioned it in an earlier post. I re soldered all bias connections, resistors,valve sockets power & pre-amp and anything else I could see that looked like it might be cold. Do you know what the K's are on these trim pots does it matter what size I use if they are close to original. Thanks for your help Jon, your the man.

06-09-2010, 08:56 PM	#57 (permalink)
tim p Senior Member Join Date: Mar 2010 Posts: 203	Re: Pop goes the volume I would be very greatful. Thanks again Jon.

06-09-2010, 09:11 PM	#59 (permalink)
tim p Senior Member Join Date: Mar 2010 Posts: 203	Re: Pop goes the volume Appreciate it .I'll check in as soon as I get home from work.

06-11-2010, 08:49 PM	#60 (permalink)
tim p Senior Member Join Date: Mar 2010 Posts: 203	Re: Pop goes the volume Hi Jon. The Marshall tech at JAM ind. e-mailed me and asked me to disconnect conn 12 on main board and try bias. I did so and the amp biased up perfectly. He said to call if it worked but now he's finished work till monday. I followed the leads to the front pot board conn 20 output mute and variable power. Do you know what the quick fix might be or should I wait for monday He is hard to call as he is finished work at the same time as I am, no cell phones allowed on job site. I am greatfull for any help. Thanks

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