Hello, I have a little problem with my amplifier, It is working very well but time to time it makes a shoot sound - like when powering up an amplifier- while listening to music for some time. I happens one time during a day.
Also the main issue is that when I have received it, it was working very fine while listening during a day, after that when I have turned it off and left it for a night next day it stopped working- the fuse has blow up also soldered connections nearby. I have took off blow tin, put a new fuse and soldered that up. It was working nice for some time and than it happened again - with shooting from the speakers in the meantime- I have repeated the repair and it is working now but the shooting persist.
I have checked all connections on every board in amplifier and resoldered bad looking ones but it haven't solved that, I saw that somebody changed original Siemens EL34 N92 (very used with dark clouds on top) to EL34 TGL 9649 on the second board. So at the moment I have 2 old siemens and 2 TGL (RFT). I will be changing the valves but should I keep these to RFT and buy 2 new RFT or should i rather get 4 valves from Mullard?
Also on board with new RFT valves I have saw odd connection which can be seen on picture, also on preamp board there is a capacitor where I think it shouldn't be, any guess?
Service manual is available here: http://amchome.com/sites/amchome.com/files/Service Manual-CVT3030-CVT3030a_0.pdf
Thank you for going all of this writing If you have any ideas please let me know I will really appriciate it.
Thanks, Jan.
Also the main issue is that when I have received it, it was working very fine while listening during a day, after that when I have turned it off and left it for a night next day it stopped working- the fuse has blow up also soldered connections nearby. I have took off blow tin, put a new fuse and soldered that up. It was working nice for some time and than it happened again - with shooting from the speakers in the meantime- I have repeated the repair and it is working now but the shooting persist.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I have checked all connections on every board in amplifier and resoldered bad looking ones but it haven't solved that, I saw that somebody changed original Siemens EL34 N92 (very used with dark clouds on top) to EL34 TGL 9649 on the second board. So at the moment I have 2 old siemens and 2 TGL (RFT). I will be changing the valves but should I keep these to RFT and buy 2 new RFT or should i rather get 4 valves from Mullard?
Also on board with new RFT valves I have saw odd connection which can be seen on picture, also on preamp board there is a capacitor where I think it shouldn't be, any guess?
Service manual is available here: http://amchome.com/sites/amchome.com/files/Service Manual-CVT3030-CVT3030a_0.pdf
Thank you for going all of this writing If you have any ideas please let me know I will really appriciate it.
Thanks, Jan.
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Update: after dis attaching the little copper wire seen on the 3rd picture- wire which connects top valve to some part on the board ( some service tuning i guess - I don't know what for) the valve connected by the wire doesn't light up. Still occasional shooting from the speakers appear time to time. I will update if the fuse will fail again.
Up2: after dis attaching the copper wire speakers makes a loud brooom sound when powered back on after running for a while, smoke appeared as one of the wires touched the case and started melting 😀 re soldered the copper wire back again and its running again, I guess this copper wire works as a ground.
Up2: after dis attaching the copper wire speakers makes a loud brooom sound when powered back on after running for a while, smoke appeared as one of the wires touched the case and started melting 😀 re soldered the copper wire back again and its running again, I guess this copper wire works as a ground.
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I think you should replace the tubes. Once it has "flashed" ( an internal arcing) it will
do so again.
Get a matched new pair, don't care for expensive "NOS" get a pair of new production
from a dealer with warranty. Just the old ones ( or sell as NOS 🙂
do so again.
Get a matched new pair, don't care for expensive "NOS" get a pair of new production
from a dealer with warranty. Just the old ones ( or sell as NOS 🙂
Thanks for reply, I will replace the valves for sure, I'm thinking about buying a quad of EL34B/TUNG SOL-RU or EL34 MULLARD-GROOVE TUBES. Do you have any recommendations?
Also how about this wire, should I leave it like that or with the new valve set dis attach the wire?
Also how about this wire, should I leave it like that or with the new valve set dis attach the wire?
Does this amp has the power tubes solder directly to the board?
That will make tube upgrade/test difficult.
I agree with petertub, change the tube and put back the trace/circuit the way they are.
Find the schematic and debug from there.
This is a fine amp.
That will make tube upgrade/test difficult.
I agree with petertub, change the tube and put back the trace/circuit the way they are.
Find the schematic and debug from there.
This is a fine amp.
If there is sufficient clearance for a set of sockets I would install those prior to installing the new tubes. Belton makes good ones..
Thanks for reply kevinkr! That's a good idea, the tubes are all soldered to the board it will be good to switch to other solution.
@Brice I'm not yet well experienced with schematics, would you be able to take a look and say if this little wire is necessary? I haven't saw any other odd connections on the boards, the capacitor seen on the back of the board is rather fitted as standard.
I have also saw such odd connection in another thread: https://www.audioasylum.com/cgi/vt.mpl?f=amp&m=148527 Any thoughts why someone would connect it that way?
So when setting the bias and center current, it would be best to fit new Belton sockets first, set the currents and after that fit the valves or do that with valves applied into the sockets?
Cheers Jan
@Brice I'm not yet well experienced with schematics, would you be able to take a look and say if this little wire is necessary? I haven't saw any other odd connections on the boards, the capacitor seen on the back of the board is rather fitted as standard.
I have also saw such odd connection in another thread: https://www.audioasylum.com/cgi/vt.mpl?f=amp&m=148527 Any thoughts why someone would connect it that way?
So when setting the bias and center current, it would be best to fit new Belton sockets first, set the currents and after that fit the valves or do that with valves applied into the sockets?
Cheers Jan
I have recently reworked a cvt 3030a, the el34 boards are quite similar. Crap pcb quality though. Unsolder the trace and it's a coin toss if it stays on the board yes or no.. that's what my assumption the copper wire going to the variable resistor is for.
AMC's servicing would have been tossing the whole board away and jam in 2 new boards in the amp.. I would if I could... Anyways, go for el34 from jj. Solid good sounding tubes; there's a ton of things to do before the tubes' sound really goes all the way (like replacing the crap coupling capacitors) I'd save up that money and go for stability.
Be sure to keep an EYE out when you do the rebias procedure. Mine kept on blowing fuses when following their steps, so I went like this: powered the ampand checked if any grid heated up until it glows red (obviously bad) and switched the amp off, adjusted the resistance and switched it back on. I know it's not the textbook procedure, but the textbook procedure didn't work so...
AMC's servicing would have been tossing the whole board away and jam in 2 new boards in the amp.. I would if I could... Anyways, go for el34 from jj. Solid good sounding tubes; there's a ton of things to do before the tubes' sound really goes all the way (like replacing the crap coupling capacitors) I'd save up that money and go for stability.
Be sure to keep an EYE out when you do the rebias procedure. Mine kept on blowing fuses when following their steps, so I went like this: powered the ampand checked if any grid heated up until it glows red (obviously bad) and switched the amp off, adjusted the resistance and switched it back on. I know it's not the textbook procedure, but the textbook procedure didn't work so...
Since you are adjusting for the tube characteristics you must do the actual adjustments with the tubes installed, that said making sure you have proper bias on pin # 5 before you install the new tubes is not a bad idea.
Note that you need to make sure there is sufficient clearance with sockets and tubes for everything to fit before you make the modification of adding the sockets.
Note that you need to make sure there is sufficient clearance with sockets and tubes for everything to fit before you make the modification of adding the sockets.
Regardless of any other solution remove the solder flux and carbonized sectors of the PCB with a cutter, paint thinner and cotton, flux and carbon both conduct electricity at some extent, I have so many unbelievable stories...
Also pay attention to two electrolytics on the left side in your last picture, from here they seem overheated, be sure that the bigger one has its top perfectly flat, in the picture seems a little bit swollen, another symptom of overheating.
Seeing more carefully your third picture, the failure maybe is due to bad solder joints between both sides of the PCB, the copper wire seems to be a reinforcement for one of them, if you put sockets, be sure of the proper contact on the other side (solder side) of PCB, sometimes metalized holes (if any) fail, and do not forget cleanning al solders with paint thinner, or a good nail polish remover, my wife use one with lemon perfume...😀
Cheers everybody for all the tips 🙂 that's very helpful. That is right that the pcb board is a very low quality, all connections are coming apart, and this is probably the reason why there is a wire.
I will go for EL34 from JJ than, cheers.
@Hvlemmi I have the money for that purpose and I can go play with it, tune it to the best, could you explain more which parts are good to be replaced and which brand would you recommend?
Any other parts worth looking after? I have just bought nice PMC GB1i speakers and I will hold with playing them until I fix the amp to avoid destroying the tweeters in any way so I can go all the way for stability first.
Could you tell me what grid you mean? Also by getting red you mean heating up right?
@popilin By two electrolytics you mean the blue ones? They seem ok but I will check for sure capacity of each capacitor in amp.
I will follow all steps and let you know later how everything worked.
I will go for EL34 from JJ than, cheers.
@Hvlemmi I have the money for that purpose and I can go play with it, tune it to the best, could you explain more which parts are good to be replaced and which brand would you recommend?
Any other parts worth looking after? I have just bought nice PMC GB1i speakers and I will hold with playing them until I fix the amp to avoid destroying the tweeters in any way so I can go all the way for stability first.
Could you tell me what grid you mean? Also by getting red you mean heating up right?
@popilin By two electrolytics you mean the blue ones? They seem ok but I will check for sure capacity of each capacitor in amp.
I will follow all steps and let you know later how everything worked.
When an electrolytic was overheated, the first symptom is the plastic cover shrinks, as I can see in the two blue ones on the left, other symptom of overheating is the tap on the top inflates, not clear in the picture, measuring capacitance is not enough, you must measure ESR, or just replace them, they are cheap.
I meant plate, sorry for the confusion. My experience tell if you are as red as around 40 seconds, the fuse will pop. 😉 https://www.youtube.com/watch?v=9SfJJ8A8XNM
I would recommend to replace c505/c506 with a Russian Paper in oil capacitor called k40y; high quality and the sound is for its price really good. If you notice a difference, you can go on from there. You can try for R522/R521 a tantalum resistor like audio note or shinkoh, but you can also take something like a Takman resistor.. see what you notice there!
Also, for the Electrolytics that poplin mentioned.. I would replace them with Elna Silmic II. They're quite old, it would be an improvement anyways, and for the 10/30 cents you'd save on them I wouldn't go otherwise. I've let quite a few caps compete with each other and they're definitely worth the few extra cents. Note that you can always go higher with the voltage value of a capacitor, never lower.
Thanks that's valuable info, I'm going to change all capacitors on preamp board and on both valve boards, leaving only big Hitachi capacitor which looks good.
Also I have found that one diode on right of the lower valve is burned underneath and is other size than one nearby top valve so I will replace it as well.
@kevinkr On this board 8 pin belton sockets doesn't fit- the ring for 2 screw is to big and will collide with paths, do you know maybe if these sockets: https://watfordvalves.com/product_detail.asp?id=4756 will be any good?
@Hvlemmi On c505 I have 1uF 250V and I can't find any k40y with these parameters only 1uF 200V. I'm thinking about getting other capacitors from Vishay as they are well reviewed or maybe better would be to get rest Elna Silmic II what you think?
Maybe I will receive new boards from AMC 🙂 will see if they have any spares, until it happens I will replace all wasted paths with additional copper wire.
Also I have found that one diode on right of the lower valve is burned underneath and is other size than one nearby top valve so I will replace it as well.
@kevinkr On this board 8 pin belton sockets doesn't fit- the ring for 2 screw is to big and will collide with paths, do you know maybe if these sockets: https://watfordvalves.com/product_detail.asp?id=4756 will be any good?
@Hvlemmi On c505 I have 1uF 250V and I can't find any k40y with these parameters only 1uF 200V. I'm thinking about getting other capacitors from Vishay as they are well reviewed or maybe better would be to get rest Elna Silmic II what you think?
Maybe I will receive new boards from AMC 🙂 will see if they have any spares, until it happens I will replace all wasted paths with additional copper wire.
I'd say stick with altering the tube boards first for the following reasons:
- You are able to evaluate if, then what the changes are you made.
- You're sticking with dealing with the most important 'problem' first. If anything goes wrong, you know you can find it at the board you just worked on.. (unless there is already a problem in your pre-section)
For the coupling capacitor, don't go lower in voltage:
I see yours has this schematic:
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the one you posted was this, so I have followed that one:
https://elektrotanya.com/files/CVT3030_r.JPG
I see that they're hard to find, they are very popular. You can also try an Amtrans capacitor. I really am fond of their amazing build quality, and I think size-wise you're still able to fit them onto the board (not a bad criteria either 😉 )
One of the places where you can get them is Acoustic Dimension, they also stock the 10k shinkoh. (R21/R22 has a different value as well, measure before buying).
As for the tube sockets. Beware that the tubes will only go in halfway because of the pcb being in the way. Unless you drill the pcb so the tubes can go into the sockets completely. As you see in your own amp, the tubes just fit. You need to either drill the pcb or take the cooling elements out... one way or the other, it's a bit of a messy job.
Not sure I am following the tube socket/pcb comment in the previous post. I use octal pcb mount sockets on pcbs all the time and the pins fit all the way into the socket. The problem I actually see is that the combination of socket height and tube height may be too long (too tall) depending on how the modules install in the amp. I have not seen a CVT-3030 in well over a decade and don't remember the details.
Perhaps the OP would be kind enough to post some pictures of the amps showing these details.
Perhaps the OP would be kind enough to post some pictures of the amps showing these details.
If you check the PCB of the amc and how it fits in you'll see what i mean.. the only wau of getting a socket on this board is by putting it underneath it. The pcb is mounted to the tubes are horizontally fitting into the amp, and with the tubes directly soldered on the pcb there's like 1 mm space between the tube and it's cooling block.
I'm not against pcb mount tube sockets, in the configuration of this amp it's just not easily done...
I'm not against pcb mount tube sockets, in the configuration of this amp it's just not easily done...
Here you see an example of how it's done, there where the top of the tubes are previously was another part of the cooling block..
https://youtu.be/c41rf69yYMk
https://youtu.be/c41rf69yYMk
I think the other channel is all good, only this one is failing, I spotted that accidentally when I haven't plugged the board connecting cable- also valves on this board are powering up later than on second board.
I will change other capacitors as all of them have over 3000 hours life span, so for sure they all need to be changed also there might be sound quality improvement.
@Hvlemmi thanks for the right drawing I received that one from AMC and it was misleading, I wrote down what to buy by looking at the boards.
I have found few JJ valves like:
MK2-JJTesla CRYO
JJ Tesla / EL34/6CA7-JJ TESLA
MK2-JJ Tesla MESA
Which JJ are best? I will go for quad.
Here you can see the distance- around 20mm when board is fitted. When the board isn't fitted in the slot there is much more space- around 100mm- the board is pretty stable there:
I will change other capacitors as all of them have over 3000 hours life span, so for sure they all need to be changed also there might be sound quality improvement.
@Hvlemmi thanks for the right drawing I received that one from AMC and it was misleading, I wrote down what to buy by looking at the boards.
I have found few JJ valves like:
MK2-JJTesla CRYO
JJ Tesla / EL34/6CA7-JJ TESLA
MK2-JJ Tesla MESA
Which JJ are best? I will go for quad.
Here you can see the distance- around 20mm when board is fitted. When the board isn't fitted in the slot there is much more space- around 100mm- the board is pretty stable there:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
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