Guitar Gear Forum

Hello!

I finally finished my sloclone now it is time for debuging...

I made first start with a friend who knows more about amps then I do. Amp didn't blow any fuse or burn something inside it


But we noticed that the bias is not correct and we couldn't fix that with bias pot.

power amp grid = -65V
Bias measuring over 1Ohm resistor is 20mV

I belive bias is not correct I think it shoud be something arround 50mV?


I also have few hums... but this wil be on the menu later.

Usually more like 35 mv

Awesome thread. I think this is the first time I've seen a build where someone made their own PCB from scratch. That's just amazing to me haha. I'm anxious for the final pics and clips of this beast. One thing nabbed my curiousity - what's the reason for mounting the choke on the inside of the chassis?

should probably check voltages and actually calculate what it should be biased at.

Hi, I almost finished my SLO and fix some issues with hum (just a few cosmetical work has to be done). Now it sounds great, and I love it









More pictures on:
http://www.ampspecs.com/myamps.php

Thank you all for help! Now I'm working on a sound clips/video...

Hello,

After few hours of joy and happiness amp suddenly lost his power. For example, if I played master volume on 9 O' clock now for the same volume I have to open my amp on full, tone also change.

The first time, when I notice this trouble I switch amp on stand and everything work ok, but few days later, trouble doesn't go away. Any ideas what to check? I double check everything again and it looks ok.

Hi,

I have some troubles with my clone, could anybody help me with these values?



Point voltages A B C D E F
365 374 394 509 512 -73

Fuse 1: 235V
Fuse 2: 511V

Bias : Point1 11V
Point2 12V

Thanks.

Omg... the optocouplersLDR1(VTL5C1) and LDR2 are not connected wright, + and - are turned around.

well what's the problem? if your showing only 3volts on your heaters thats totally wrong. maybe im missing something. but the heaters should be 6.3vac +/-10%

am_i_evil wrote:Omg... the optocouplersLDR1(VTL5C1) and LDR2 are not connected wright, + and - are turned around.

That will completely screw up your switching!

Also the voltage at the bias points surely thats mV? And even if so that's incredibly low

shep wrote:well what's the problem? if your showing only 3volts on your heaters thats totally wrong. maybe im missing something. but the heaters should be 6.3vac +/-10%

you have ~3v on either side making a total of 6.3v

am_i_evil wrote:Omg... the optocouplersLDR1(VTL5C1) and LDR2 are not connected wright, + and - are turned around.

That will completely screw up your switching!

Also the voltage at the bias points surely thats mV? And even if so that's incredibly low

Measure the voltage across the +/- of the LDR on either channel only 2 should show anything higher than a mV reading

On the clean channel 1 & 4 should be on getting about 2v and on the OD channel 2 & 3 should be on here's a spreadsheet with some ballpark voltages

https://www.dropbox.com/s/t28ildvzc1bub ... s.xls?dl=0

gotcha. thought that was the case. noticed the bias point voltages as well.

Thanks alot for quick reply!

you have ~3v on either side making a total of 6.3v

Yes, 3v is because my instrument is not precise enough...

That will completely screw up your switching!

Yes I couldn't figure out how switching works



I also change trimer from 25K to 50K.

am_i_evil wrote:Thanks alot for quick reply!

you have ~3v on either side making a total of 6.3v

Yes, 3v is because my instrument is not precise enough...

That will completely screw up your switching!

Yes I couldn't figure out how switching works



I also change trimer from 25K to 50K.

So are you all good now then?

Don't know yet, I will try,test today/tomorrow.

Hello, I fix issue with "channels" now it looks like it works. And now I'm trying to figure out how to fix bias.

On my test points I measure 11mV an 12mV. If I understand correctly, because I have one test point for two tubes this is 22mV and 24mV per tube?

If I check site below, I need to have for my 505V, bias set to 41mV (20 per test point?)

http://www.webervst.com/tubes1/calcbias.htm

On DB102 = 2,61

Later I will check the voltages on my LDR's

i think that might be biasing it hot for the 6l6gc. on the link, if you scroll down there is a chart for biasing hot cold or average. according to the chart, average would be a bit less than 41mA. be closer to 36mA. if i understand it correctly. youd probably wanna be closer to 36mA instead.

just as a correction the measurement is in milliamps not millivolts as the bias calculator states. but i believe in your tester you will be reading the value as millivolts dropped over the 1ohm resistor. millivolts should equal milliamps over a 1ohm resistor because of this equation: r=v/i is equal to 1=v/.036 is equal to 1=.036/.036

r=resistance in ohms v=volts and i= amps

the calculator is calculating for biasing the tubes hot (70%). you'd probably wanna go with average at first, which is 60%

so, mike lx-r was correct about ~35mV

someone may correct me on this, but both test points should read ~36mV if both test point measurements are not close to one another it can mean you have an unmatched pair of tubes.

be careful not to turn your bias trim pot all the way down as it may overload your transformer causing it to over heat and burn out.

there can only be one test point per tube. i believe you are just measuring current over a 1ohm resistor at the cathode. there is only one cathode. my confusion earlier with the heaters is you can actually measure the voltage for the heaters by putting one point of the tester to one leg of the 3v supply coming from the transform and the other point of the tester to the other 3v supply leg and it will read 6.3v on your tester.

http://www.regiscoyne.com/tech/bias/
this is a good link for learning to bias your amp

Thank you both for helping me with this!

I measure voltages across LDRs:

Normal/clean
---------------
LDR1 1.77
LDR2 0
LDR3 0
LDR4 1.77

OD/clean
--------------
LDR1 -0.12
LDR2 1.79
LDR3 1.79
LDR4 -0.11

Normal/crunch
---------------
LDR1 1.78
LDR2 0
LDR3 0
LDR4 1.78

OD/crunch
------------------------
LDR1 -0.09
LDR2 1.79
LDR3 1.79
LDR4 -0.08

Overdrive channel is a lot louder than normal channel, and it has a lot of interferences.

am_i_evil wrote:Thank you both for helping me with this!

I measure voltages across LDRs:

Normal/clean
---------------
LDR1 1.77
LDR2 0
LDR3 0
LDR4 1.77

OD/clean
--------------
LDR1 -0.12
LDR2 1.79
LDR3 1.79
LDR4 -0.11

Normal/crunch
---------------
LDR1 1.78
LDR2 0
LDR3 0
LDR4 1.78

OD/crunch
------------------------
LDR1 -0.09
LDR2 1.79
LDR3 1.79
LDR4 -0.08

Overdrive channel is a lot louder than normal channel, and it has a lot of interferences.

They're looking about right.

The OD channel is considerably louder than the normal channel when normal is set to clean. If you set it to crunch they should be closer but there will still be a difference.

What kind of interferences are you getting? hum? hiss? static?

Just hum. And I also think that there is to much gain on overdrive channel. On 9'o clock there is enough gain for metal... But right now I'm struggling with low bias, any idea where to look?

I play thrash and run my gain just above that. The amp does have a lot of gain on the lead channel.

With regards to the bias double check the entire bias circuit.

Remember though that your test points are reading two valves in series per side

I fixed it, the problem was in R52 resistor. I changed it from 56K to 15K and now is biased correctly. This amp sounds

Next thing to do is cosmetic nature. I used plexi glass to make faceplate, and now I have to draw drawings on it. I'm not sure how to do this but I will have to figure it out how to transfer ink to plexi.

Waterslide decal paper perhaps?

i believe the most common way is silk screen. there are places online that will make custom silk screens. basicly,a professional form of stenciling.