Hello, I know this is not a FAV amp for many but putting that aside, I hope someone can help me fix two problems.
BZZZ in the left channel (faint but there) 120hz type ..like standing under a streetlight at night
High gain hiss, crackle in right channel - again low, neither can be heard 2 feet from the speakers but I DO know they affect the overall sound.
Whats been done
Switched tubes - Currently running NOS GE 6L6GC's (nice sound with them)
Its been biased.
The R89-R96 have been changed to 1kohm 5watt as per another thread here. - No change
Channel path that goes from the right side in front of the transformers and such that feeds the left channel has been jumpered so its not running right past. - No change
Power to the unit is running through an ADC power regulator/filter so power is clean.
Occurs with no input connected.
Pulled the 12AU7 tube and its still there.
Pull the 12AX7's and off course it goes away but thats because there is no feed.
Bottom line, whats next ? What can I check/change/replace to keep myself from going nuts ?
Just so you know, I am a fairly new tube/electronics newbie so speak slow...LOL
Serious, I know someone out there must know these things or knows how to read the schematic and find where I should look...
Thanks in advance !
BZZZ in the left channel (faint but there) 120hz type ..like standing under a streetlight at night
High gain hiss, crackle in right channel - again low, neither can be heard 2 feet from the speakers but I DO know they affect the overall sound.
Whats been done
Switched tubes - Currently running NOS GE 6L6GC's (nice sound with them)
Its been biased.
The R89-R96 have been changed to 1kohm 5watt as per another thread here. - No change
Channel path that goes from the right side in front of the transformers and such that feeds the left channel has been jumpered so its not running right past. - No change
Power to the unit is running through an ADC power regulator/filter so power is clean.
Occurs with no input connected.
Pulled the 12AU7 tube and its still there.
Pull the 12AX7's and off course it goes away but thats because there is no feed.
Bottom line, whats next ? What can I check/change/replace to keep myself from going nuts ?
Just so you know, I am a fairly new tube/electronics newbie so speak slow...LOL
Serious, I know someone out there must know these things or knows how to read the schematic and find where I should look...
Thanks in advance !
Since this is a kit amplifier I have to ask this. Did you build it? If so has it ever run correctly? Did you buy it already running or did you buy it non-working?
Need information here in order to try to help. Might try posting a schematic of it as well as the working voltages. I suggest that you do not start off swapping tubes and modifying a non-working amplifier. Get it working first have proper working voltages and then modify one step at a time.
Need information here in order to try to help. Might try posting a schematic of it as well as the working voltages. I suggest that you do not start off swapping tubes and modifying a non-working amplifier. Get it working first have proper working voltages and then modify one step at a time.
Well, guess what..
I fixed it (95% anyway)
One of the other steps was right from the manual - to increase the resistance value on 2 resistors if you hear bzzz/crackling or oscillation..so change those out last night after I wrote this ..
Buzz on left gone...99% dead silent.
Gain hiss crackle on right gone - replaced by very very low hum..think thats chassis/ground hum of some kind but ALOT more pleasant than gain hiss crackle...lol
SO now I will hunt this down..
Oh, by the way, I bought it this way, I didn't build it...
I fixed it (95% anyway)
One of the other steps was right from the manual - to increase the resistance value on 2 resistors if you hear bzzz/crackling or oscillation..so change those out last night after I wrote this ..
Buzz on left gone...99% dead silent.
Gain hiss crackle on right gone - replaced by very very low hum..think thats chassis/ground hum of some kind but ALOT more pleasant than gain hiss crackle...lol
SO now I will hunt this down..
Oh, by the way, I bought it this way, I didn't build it...
Well...almost fixed.....HELP !!
Okay..got rid of 99% of the buzz, 99% of the hiss...awesome and the amp sounds great BUT...here is the issue. When I measure the 6.3vdc taps, I get 3.5vdc on all 4...huh ? whats up with that...since there is nothing else in the circut at that point, can it be a bad transformer ?
If it is, how the heck do I replace it ? I can;t find any specs for the power transformer except the 6.3v taps..is it bad to run like that ?
Thanks in advance...
Okay..got rid of 99% of the buzz, 99% of the hiss...awesome and the amp sounds great BUT...here is the issue. When I measure the 6.3vdc taps, I get 3.5vdc on all 4...huh ? whats up with that...since there is nothing else in the circut at that point, can it be a bad transformer ?
If it is, how the heck do I replace it ? I can;t find any specs for the power transformer except the 6.3v taps..is it bad to run like that ?
Thanks in advance...
Many Hifi'ers in the past have given me 4040's to fix...some easy, some awkward faults..I have to say it, some have taken on far more they can handle, often not understanding.. after inviting many owners into my shed, I've managed to entice them into a complete redesigned better sounding amp..guaranteed happyiness .
It's often better to 'put an old dog down' than spending monies on a half-working limping amp which becomes a constant source of hassle.
What I don't want to see happen is exactly in the pic. Fortunately, tube amp incidents are rare, but it is festive time. TAKE CARE. Fusing is all important in the design.
richy
It's often better to 'put an old dog down' than spending monies on a half-working limping amp which becomes a constant source of hassle.
What I don't want to see happen is exactly in the pic. Fortunately, tube amp incidents are rare, but it is festive time. TAKE CARE. Fusing is all important in the design.
richy
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Thank you !
I would put this dog down but to be honest, I have too much invested in tubes.... (over a grand). And she is the amp from hell.
I had this puppy sounding awesome. Made a minor tweak. Went to put the covers on, hum. Took them off, no hum, Repeat twice and hum was gone. So was 30% of the sound in the lft channel. I spent 9.5 hours last night till 1:30 am reworking, etc. and FINALLY got it right again, covers on an all.
I DONT want to to touch it anymore ...serious. I am sick of the journey. The sad part ? It sounds so good ! Very hard to let go...If I didi I would have to find an amp that would appreciate my 6L6GC's...
Thanks again...
I would put this dog down but to be honest, I have too much invested in tubes.... (over a grand). And she is the amp from hell.
I had this puppy sounding awesome. Made a minor tweak. Went to put the covers on, hum. Took them off, no hum, Repeat twice and hum was gone. So was 30% of the sound in the lft channel. I spent 9.5 hours last night till 1:30 am reworking, etc. and FINALLY got it right again, covers on an all.
I DONT want to to touch it anymore ...serious. I am sick of the journey. The sad part ? It sounds so good ! Very hard to let go...If I didi I would have to find an amp that would appreciate my 6L6GC's...
Thanks again...
Hello...its been a long time - VELLEMAN HELP
Well, after my posts a while back I got the Velleman running perfect (almost but you'll see)
No hums or buzz through the speakers, sweet sounding...ahhh..except..the damn power transformer buzzes/hums..dead quiet at warm up and as soon as it comes out of protection..BZZZZZZ
I have tried power conditioners, etc. It is not a ground issue on the unit nor a line issue - No vibration in the place so its not vibrating in the chassis...
IF I need to change the transformer (lord help me) I don't know what to get...I know how to wire it...reverse engineer..I just don't know what the specs are on the power tran...anyone ?
Also if you have suggestions on the HUM....Thanks
Well, after my posts a while back I got the Velleman running perfect (almost but you'll see)
No hums or buzz through the speakers, sweet sounding...ahhh..except..the damn power transformer buzzes/hums..dead quiet at warm up and as soon as it comes out of protection..BZZZZZZ
I have tried power conditioners, etc. It is not a ground issue on the unit nor a line issue - No vibration in the place so its not vibrating in the chassis...
IF I need to change the transformer (lord help me) I don't know what to get...I know how to wire it...reverse engineer..I just don't know what the specs are on the power tran...anyone ?
Also if you have suggestions on the HUM....Thanks
Is it like this?
I am sure the Velleman K4000 has some MOV suppressors across the OP Tx from anode to anode connection..(two in series) I also had reverse biased diodes HV soft Fast rec diodes across my OP tubes ran for years something like byv96E..you can series them.. (All these things are at your own risk)..... should be fusing in the PSU. If your on DC fuses you can put a 0.1 UF high voltage polypropylene across them.
You could check it with a meter..see if it matches..and a pad of cork from a cork tile under the power Tx works wonders..
One of the main problems with the K4000 was OP tube flash over and it took out the stupid row of half watt cathode resistors <<replace with equal value 5W WW..the cheap maplin ones are OK..Change the set pots for the bias to multi turn pots..much better..
Its a good Idea to have soft start and a mov across the primary of the mains TX..its a toroid so its got plenty of inrush surge..
You can change the bias voltage which is unreliable (its to low)..its easy keep two diodes in the bridge and put two 100uF in place of two af them you will get a voltage doubler that will give about 90V.. then you can bias up for other tubes..
Regards
M. Gregg
I am sure the Velleman K4000 has some MOV suppressors across the OP Tx from anode to anode connection..(two in series) I also had reverse biased diodes HV soft Fast rec diodes across my OP tubes ran for years something like byv96E..you can series them.. (All these things are at your own risk)..... should be fusing in the PSU. If your on DC fuses you can put a 0.1 UF high voltage polypropylene across them.
You could check it with a meter..see if it matches..and a pad of cork from a cork tile under the power Tx works wonders..
One of the main problems with the K4000 was OP tube flash over and it took out the stupid row of half watt cathode resistors <<replace with equal value 5W WW..the cheap maplin ones are OK..Change the set pots for the bias to multi turn pots..much better..
Its a good Idea to have soft start and a mov across the primary of the mains TX..its a toroid so its got plenty of inrush surge..
You can change the bias voltage which is unreliable (its to low)..its easy keep two diodes in the bridge and put two 100uF in place of two af them you will get a voltage doubler that will give about 90V.. then you can bias up for other tubes..
Regards
M. Gregg
Attachments
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I did put some MOV on another vellman..
Just thinking about it...
Can't remember the value now its to far in the past
...it was eating power tubes...
I remember keeping the transients below the max rating of the power tube..If I remember any more I will post it..probably something like (its a guess two at 420V in series..)
I suppose vellman would be able to advise.. (Maybe).. LOL
Regards
M. Gregg
Just thinking about it...
Can't remember the value now its to far in the past
...it was eating power tubes...I remember keeping the transients below the max rating of the power tube..If I remember any more I will post it..probably something like (its a guess two at 420V in series..)
I suppose vellman would be able to advise.. (Maybe).. LOL
Regards
M. Gregg
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