Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Oddvar on March 15, 2018, 06:32:30 am

Title: Soldano Slo clone build bias problem and no sound
Post by: Oddvar on March 15, 2018, 06:32:30 am

Hi.  I was wondering if anyone here has built a Soldano Slo fro c3amps pcb board.  I have just finished one and there are some issues.  Firstly the bias pot isn't responding, the bias is at 79 whatever I do.  Then there is no sound when turned on, the tubes light up and everything looks fine.  Only sound I have heard is a scratching sound when I accidentally touched the 470 resistor wire on one of the 5881 tubes.  I have gone through most of the connections and they look ok. 
Can anyone give some hints as to where to look first?

Title: Re: Soldano Slo clone build bias problem and no sound
Post by: MFowler on March 15, 2018, 08:11:12 am

I have a C3Amps chassis and board set, soon to start on it.  I've built over 150 amps from scratch so as long as the schematic and layout are good I shouldn't have problems.


I would start with your PT bias tap and measure voltage, then follow wire from bias on cap board to main board bias circuit. Make sure all bias caps and resistors leads are soldered well.  Check circuit from there to the two 220K/220k resistors.  Check wiring from bias circuit to the 50kL bias pot.  Also, check the bias test leads to make sure the black test point is grounded and it has the 1R resistors to the black test point to ground.


Lots of testing is needed.  The layout is busy so checking between layout to schematic to your amplifier is needed.


Mark

Title: Re: Soldano Slo clone build bias problem and no sound
Post by: bnwitt on March 15, 2018, 08:45:24 am

Oddvar,
How about some photos of your build?

Title: Re: Soldano Slo clone build bias problem and no sound
Post by: Oddvar on March 15, 2018, 09:08:39 am

Thanks for answering, I will follow the advice.  I have tried to start the amp with tubes, there is hum in the speaker as in "on", but no sound from the preamp.

Title: Re: Soldano Slo clone build bias problem and no sound
Post by: Oddvar on March 15, 2018, 09:57:51 am

Here are some pics.

Title: Re: Soldano Slo clone build bias problem and no sound
Post by: dunner84 on March 15, 2018, 10:07:25 am

It's hard to tell from the photo,. It I can't see where your bias ground jack is wired too. All I can make out is the resistors are connected to it, but where does it go from there?

Title: Re: Soldano Slo clone build bias problem and no sound
Post by: Oddvar on March 15, 2018, 10:13:04 am

The white and purple leads coming from the pot, the white is the neutral I believe?

Title: Re: Soldano Slo clone build bias problem and no sound
Post by: sluckey on March 15, 2018, 10:17:10 am

Quote from: dunner84 on March 15, 2018, 10:07:25 am

I can't see where your bias ground jack is wired too.

Black wire is connected to the ground buss at second from left tube socket pin 1.

Title: Re: Soldano Slo clone build bias problem and no sound
Post by: Oddvar on March 15, 2018, 04:49:20 pm

Finally I found the problem, one of the 0oh, connection were faulty.  Now there is ok bias, the amp is working, only problem the output is very low, almost like 1 w. 

Title: Re: Soldano Slo clone build bias problem and no sound
Post by: MFowler on March 16, 2018, 05:40:37 am

Like others I'm studying your photo but so far not seeing anything.


Chop stick time to try find poor solder joint.
Tube checking
Scope time.


Mark

Title: Re: Soldano Slo clone build bias problem and no sound
Post by: Oddvar on March 16, 2018, 11:24:50 am

Hi guys, just to finish off: The fault was one loose 0 ohm jumper and a loose Cap soldier joint.  It's up and running now and sounds amazing.  Thanks for all your help.