• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Convergent Audio Tech SL1 preamp

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#2
CAT sl1

Hello there!
I am also looking for a schematic of the psu of an Convergent SL1, because I don't know if I got the output voltage right. I got the signature with the psu wich you can decouple fro the amplifier. Mr Stevens told me that the output voltage has to be round 370vdc, but there are also three other output connections with 2x 12 vdc and one 10.8 vdc. Is it possible that there is some rectification on the preamplifier board? When I look at some other diy sites, there it says that the psu output has to be around 260vdc, 370vdc looks a bit high to me, but I am not sure, and I dont want to distroy something. Thanks for any answer, Mojo Teake
 
#5
 
#8
transistors in your SL1 preamp power supply

mobyd said:
I have one of these that has shat itself (two of the transistors in the PSU have exploded, erasing all markings [Q1 and Q5]). Anyone out there in interwebland got a schematic for the PSU ?
Cheers
M
Click to expand...

I checked mine in the power supply.

Q1: MPSA44
Q5: MPSA92

I hope this info is useful for you.
 
#9
voltage in the SL1

intense-tavda said:
Hello there!
I am also looking for a schematic of the psu of an Convergent SL1, because I don't know if I got the output voltage right. I got the signature with the psu wich you can decouple fro the amplifier. Mr Stevens told me that the output voltage has to be round 370vdc, but there are also three other output connections with 2x 12 vdc and one 10.8 vdc. Is it possible that there is some rectification on the preamplifier board? When I look at some other diy sites, there it says that the psu output has to be around 260vdc, 370vdc looks a bit high to me, but I am not sure, and I dont want to distroy something. Thanks for any answer, Mojo Teake
Click to expand...

After reading your note, I measured the voltage in my SL1 power supply.

From Bridge Rectifier output: 355VDC
Yellow Wire: 234.5VDC
Also there are Three separate heater 12.6VDC power supplies.

I hope this helps you.
 
#10
No rectifiers in the main preamp section

intense-tavda said:
Hello there!
I am also looking for a schematic of the psu of an Convergent SL1, because I don't know if I got the output voltage right. I got the signature with the psu wich you can decouple fro the amplifier. Mr Stevens told me that the output voltage has to be round 370vdc, but there are also three other output connections with 2x 12 vdc and one 10.8 vdc. Is it possible that there is some rectification on the preamplifier board? When I look at some other diy sites, there it says that the psu output has to be around 260vdc, 370vdc looks a bit high to me, but I am not sure, and I dont want to distroy something. Thanks for any answer, Mojo Teake
Click to expand...

Dear Mojo,
I carefully checked mine but there is no other rectification in the main preamp chassis. All powers coming from the separate power supply, which provides three independent 12.6 volts DC heater supplies and yellow wire which is the main power to support all tubes. Brown wire is just a reference for yellow wire to get the correct voltage, which is about 235VDC.
 
#11
I have two SL1 preamps and checked the power supplies and recently I found out that there are slightly differences between them. One does not have the Q5 (MPSA92😛NP Transistor) and the later one has it. Q5 is very fragile and easily blows out but the older unit seems more reliable. I had to replace Q5 a few times. So be aware of the its failure. Once it fails, the high voltage supply will blow some of the MOS FETs in the main preamp chassis. Very complicated switching circuits used with MOS FETs. Also there are several LM317 regulators in the main preamp board. Be careful if there are some issues in the main power supply, which will cause more damages to the main preamp solid state parts such as FETs, and regulators in case you turns on the power. So hard to trace the circuits though due to its very thick Teflon substrate in the main preamp chassis and also the power supply board has extra thick epoxy glass substrate. One of my electrical engineers had to spend a lot of time to fix the failed parts. It should not be that complicated since it is just a high voltage power supply!
 
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