Hi there
I'm new to this forum and a bit of a newb at repair so please be kind!
I have a class A valve amp bought from ebay based on the 6p3p and 6N1 valves. I believe it was based on a kit from SiliconRay and I bought it from UK ebay prebuild.
Is siliconray still here? 🙂
Here is a video and here is the thread that seems to be authoritative for the kit.
The circuit diagram is there in the thread, though apparently there was a second version of the circuit as I recently saw another ebay listing mentioning this.
Long story short, I had a small problem with the amp and was wary of running an amp randomly built on ebay so I gave it to my local hi-fi shop for an expensive once over. They fixed all problems and suggested I only use the 4 ohm taps on the back of the amp for all speakers. It worked fine for some weeks.
Never one to do the sensible thing, I read that the amp is working with KT66 somewhere (not true) so I tried a couple of JJ KT66 in place of the 6p3p. The amp sounded better for a while but soon broke at high volume (as high as 5-8w class A gets anyway) with a little smoke from inside. Since then I have kept it and it's been retired - I've put a lot of money into it so I am loathe to chuck it.
I want to repair this amp and get it working again with the 6p3p valves or perhaps modify it to use KT66 which is apparently quite simple. I have had a look at it and there are no obviously burnt components or smoky bits on the inside. The circuit diagram is available in the linked thread (hopefully)...
... if I figure out how to modify the amp for KT66 maybe these will be the same components to swap out as those that failed already. I'm quite the newb though I can solder and I'm hoping to learn amp repair and valve amp repair in particular.
I can add pictures if that helps. When I gave it to the shop I'm not sure if they massively changed the amp from the original siliconray spec but I hope not. (the shop tech was quite vocal about how unsafe the amp was before he fixed it up!). It looks quite simple inside. I would like to have it as a backup or perhaps swap it into the main system for a change once in a while.
Any suggestions? Maybe which caps to check and replace and how to do so? Maybe not caps? How would this amp be modified for KT66 and would that likely be the fix if this is all that happened so far?
Thanks
Zoea / N
I'm new to this forum and a bit of a newb at repair so please be kind!
I have a class A valve amp bought from ebay based on the 6p3p and 6N1 valves. I believe it was based on a kit from SiliconRay and I bought it from UK ebay prebuild.
Is siliconray still here? 🙂
Here is a video and here is the thread that seems to be authoritative for the kit.
The circuit diagram is there in the thread, though apparently there was a second version of the circuit as I recently saw another ebay listing mentioning this.
Long story short, I had a small problem with the amp and was wary of running an amp randomly built on ebay so I gave it to my local hi-fi shop for an expensive once over. They fixed all problems and suggested I only use the 4 ohm taps on the back of the amp for all speakers. It worked fine for some weeks.
Never one to do the sensible thing, I read that the amp is working with KT66 somewhere (not true) so I tried a couple of JJ KT66 in place of the 6p3p. The amp sounded better for a while but soon broke at high volume (as high as 5-8w class A gets anyway) with a little smoke from inside. Since then I have kept it and it's been retired - I've put a lot of money into it so I am loathe to chuck it.
I want to repair this amp and get it working again with the 6p3p valves or perhaps modify it to use KT66 which is apparently quite simple. I have had a look at it and there are no obviously burnt components or smoky bits on the inside. The circuit diagram is available in the linked thread (hopefully)...
... if I figure out how to modify the amp for KT66 maybe these will be the same components to swap out as those that failed already. I'm quite the newb though I can solder and I'm hoping to learn amp repair and valve amp repair in particular.
I can add pictures if that helps. When I gave it to the shop I'm not sure if they massively changed the amp from the original siliconray spec but I hope not. (the shop tech was quite vocal about how unsafe the amp was before he fixed it up!). It looks quite simple inside. I would like to have it as a backup or perhaps swap it into the main system for a change once in a while.
Any suggestions? Maybe which caps to check and replace and how to do so? Maybe not caps? How would this amp be modified for KT66 and would that likely be the fix if this is all that happened so far?
Thanks
Zoea / N
Simply switching valves from 6P3S to KT66 and nothing else....well the KT are capable of a lot more current, if my recall is right.
So first thing I would do, is check the winding continuity of the output transformer, in case excess quiescent DC bias current has overheated and burned the primary winding.
So first thing I would do, is check the winding continuity of the output transformer, in case excess quiescent DC bias current has overheated and burned the primary winding.
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The KT66 has a higher anode/plate current but a lower distortion figure --so it sounded better but it overheated.
I cant get through to silicon ray in China not even using Tor .
Capacitors don't smoke they leak or blowup.
Probably the power line resistor became open circuit when overheated to the output tubes ----as you say--it worked for a while.
I cant get through to silicon ray in China not even using Tor .
Capacitors don't smoke they leak or blowup.
Probably the power line resistor became open circuit when overheated to the output tubes ----as you say--it worked for a while.
Which one is the power line resistor? And is it the case that I would have to change the output transformer (and which one is this...) to use KT66?
If I don't have to change the output transistor what small change (as siliconray put it) would the amp need to use KT66? Once it's fixed that is...
Thanks!
If I don't have to change the output transistor what small change (as siliconray put it) would the amp need to use KT66? Once it's fixed that is...
Thanks!
Attachments
I think I killed the largest transformer on the device, the one pictured with the yellow wrap top left of the picture. Is this the output transformer? Any suggestions for a replacement if so?
its the main power transformer.
It may be a duff solder joint, it may be a burnt winding. Hard to know with the limited info you've given, and I'm not inclined to advise you to dive into a 350VDC circuit.
I would drop it back to your Man (assuming its not a Woman), and they will be able to quickly diagnose the problem.
It may be a duff solder joint, it may be a burnt winding. Hard to know with the limited info you've given, and I'm not inclined to advise you to dive into a 350VDC circuit.
I would drop it back to your Man (assuming its not a Woman), and they will be able to quickly diagnose the problem.
Are you sure its the mains transformer that is faulty Zoea as your "designer " - Silicon Ray seems to have pulled it from an old tube circuit and as he lives in China bought the Chinese tubes locally probably for peanuts wholesale.
One of the reasons I say that is that SR says you "could " use KT66 and that means the mains transformer is good for the heavier current .
Excuse my criticism but it seems SR is either using Google Translator or English is his second language but he is not proficient in it and telling customers about his amplifier while making translation mistakes in a unit that has high voltages that can kill if you have thin-soft-moist skin ( low body resistance ) is asking for trouble .
Secondly I have seen VERY much better layout design from the DIY Audio members here its pretty 1940,s/1950,s looking like you would get from building it from an old audio magazine of the time .
At this rate there are many DIY Audio posters who should go commercial they would make money if they could buy the tubes nearly walking distance from the 100,s of tube factories that China has --and yes can name very many.
Lastly Aardvarkash10 has a good point.
One of the reasons I say that is that SR says you "could " use KT66 and that means the mains transformer is good for the heavier current .
Excuse my criticism but it seems SR is either using Google Translator or English is his second language but he is not proficient in it and telling customers about his amplifier while making translation mistakes in a unit that has high voltages that can kill if you have thin-soft-moist skin ( low body resistance ) is asking for trouble .
Secondly I have seen VERY much better layout design from the DIY Audio members here its pretty 1940,s/1950,s looking like you would get from building it from an old audio magazine of the time .
At this rate there are many DIY Audio posters who should go commercial they would make money if they could buy the tubes nearly walking distance from the 100,s of tube factories that China has --and yes can name very many.
Lastly Aardvarkash10 has a good point.
Over current in a full wave rectifier tube usually blows the tube first not the mains transformer --the rectifier -5Z4P--( obviously no originality in China --re- 5Z4G and that is dangerous as somebody in the West could mistake it for that ) is Chinese and "good " for 125ma .
SE makes it (approx) 90ma for the KT66 tube in total -anode plus screen plus the other tubes brings it near the rectifiers full output , if the transformer is not much more than the total then the safety margin
is very close --again not professional.
SE makes it (approx) 90ma for the KT66 tube in total -anode plus screen plus the other tubes brings it near the rectifiers full output , if the transformer is not much more than the total then the safety margin
is very close --again not professional.
I see a black substance that sprayed from inside the power transformer to the chassis. The transformer looks damaged and I would check it before replacing the mains fuse. The mains connection is not compliant to EU electrical code and it is a safety hazard. If you replace the transformer, this issue should be addressed.
The 6P3 tube filament is 0.9 Amps x 2 each = 1.8 Amps
The KT66 tube filament is 1.3 Amps x 2 each = 2.6 Amps.
That is a current increase of 45%.
Kind of hard on the 6.3V filament winding of the power transformer.
And there may have been lots more B+ current on the KT66 tubes versus the 6P3 tubes.
That could be hard on the power transformer B+ secondary.
The additional load on the power transformer's 6.3V secondary, and the B+ secondary, causes more current in the Primary. That could be hard on the power transformer primary too.
I believe that a lot of Chinese amplifiers have power transformers that do not have excess power capability.
It saves lots of money to design amplifiers that way.
Oh, EL34 tube filament is 1.5A x 2 each = 3.0 Amps. Really hard on the power transformer.
Since the amp ran for quite sometime with the KT66 tubes, it may be that the power transformer did that OK for a time.
Then, as heat did its "quick aging", it gave up the ghost.
Some of my favorite Marketing / Sales pitches, is:
You can use all these tubes (with modifications) . . . what modifications, they did not tell you?
The first thing about using an EL34 in an amp that was designed for all those other tubes that are listed by the amp manufacturer . . .
Connect a wire from Pin 1 to Pin 8. None of those other tubes need that, so it is probably not in there.
The KT66 tube filament is 1.3 Amps x 2 each = 2.6 Amps.
That is a current increase of 45%.
Kind of hard on the 6.3V filament winding of the power transformer.
And there may have been lots more B+ current on the KT66 tubes versus the 6P3 tubes.
That could be hard on the power transformer B+ secondary.
The additional load on the power transformer's 6.3V secondary, and the B+ secondary, causes more current in the Primary. That could be hard on the power transformer primary too.
I believe that a lot of Chinese amplifiers have power transformers that do not have excess power capability.
It saves lots of money to design amplifiers that way.
Oh, EL34 tube filament is 1.5A x 2 each = 3.0 Amps. Really hard on the power transformer.
Since the amp ran for quite sometime with the KT66 tubes, it may be that the power transformer did that OK for a time.
Then, as heat did its "quick aging", it gave up the ghost.
Some of my favorite Marketing / Sales pitches, is:
You can use all these tubes (with modifications) . . . what modifications, they did not tell you?
The first thing about using an EL34 in an amp that was designed for all those other tubes that are listed by the amp manufacturer . . .
Connect a wire from Pin 1 to Pin 8. None of those other tubes need that, so it is probably not in there.
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Zoea,
I am sorry for your troubles.
I hope that others will learn not to do tube rolling without checking for advice from a knowledgable person.
You need to have a good technician to evaluate which parts are good, and which parts may have been weakened, and which parts are destroyed.
Then you can decide whether or not, to restore the amplifier to its original 6P3 condition.
Or whether to use the chassis, to try another kind of tubes, power transformer, output transformer, which ever one, two, or several of those that will be needed to do that.
Get something up and running, and then Happy listening!
I am sorry for your troubles.
I hope that others will learn not to do tube rolling without checking for advice from a knowledgable person.
You need to have a good technician to evaluate which parts are good, and which parts may have been weakened, and which parts are destroyed.
Then you can decide whether or not, to restore the amplifier to its original 6P3 condition.
Or whether to use the chassis, to try another kind of tubes, power transformer, output transformer, which ever one, two, or several of those that will be needed to do that.
Get something up and running, and then Happy listening!
Thank you for all the help everyone. I agree it was silly to just swap the tubes over but I bought them and was keen to try them (and it worked great for some days).
Is there any chance of getting a replacement transformer? Otherwise I will sell it on for parts I guess.
(I might ask in the main thread here and on AudioKarma if I don't find the transformer. Just reading those threads now).
Best wishes
edit: quote from AudioKarma:
I didn't change any feedback resistors. Also I am in the UK so our voltage is 240 not 220 this is probably specced at. Could this be the reason the main transformer gave up?
Is there any chance of getting a replacement transformer? Otherwise I will sell it on for parts I guess.
(I might ask in the main thread here and on AudioKarma if I don't find the transformer. Just reading those threads now).
Best wishes
edit: quote from AudioKarma:
I didn't change any feedback resistors. Also I am in the UK so our voltage is 240 not 220 this is probably specced at. Could this be the reason the main transformer gave up?
That was mine on ebay recently. It had a UK spec TX and it ran pretty warm but not dangerously so. I like things running cool, just a personal preference, but a lot of valve gear the power TX are pretty hot (i.e. hot to the touch). I am sure if you look around you could get another TX, the kit or similar is still for sale.
A plug in power meter is a good tool. I plug my valve amp(s) in to one to keep an eye on what's going on, I think it took about 70 watts, but don't quote me on that. A PSU cap went OC on one of my Quad iis recently, instantly noticed something wrong on the power meter.
A plug in power meter is a good tool. I plug my valve amp(s) in to one to keep an eye on what's going on, I think it took about 70 watts, but don't quote me on that. A PSU cap went OC on one of my Quad iis recently, instantly noticed something wrong on the power meter.
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It used to be the case in the UK at least that mains transformers manufactured IN the UK by REPUTABLE manufacturers were --well--over designed .
Sadly with the demise of engineering in the UK most and I emphasis --most -transformers the UK imports are Chinese .
I bought 3 versions of the same ( same case ) soldering station--
One =£25.
One at £35.
and lastly one at £60.
I the first two not only was the transformers UNDERSPECIFIED but the internals were dangerous as far as UK safety standards were concerned .
The third lasted several years and --yes-- the primary winding's shorted.
I reported that on the UK website I used to be on and what did I get ?
Criticism from "interested parties " namely IMPORTERS.
I have said before when I build an audio power amp the mains transformer is over specified , this engenders confidence in the finished product that if a fault occurs then it is LESS likely to be the transformer .
In contrast I owned a Taylor 45 valve tester at one time it was over 50 years till the transformer failed and yes I inadvertently overloaded it with too big power pentodes when testing --got hot ?--yes failed--no.
I could name the UK prestige transformer manufacturers in the UK but it nearly brings me to tears to see high quality engineering disappear just so a fast buck can be made .
The point about 220volt AC transformers being imported into the UK is a genuine one when my own mains voltage stands at --this moment --245 volts rms .
Any transformer guy can do the figures and work out the increase in heat when under full load.
Sadly with the demise of engineering in the UK most and I emphasis --most -transformers the UK imports are Chinese .
I bought 3 versions of the same ( same case ) soldering station--
One =£25.
One at £35.
and lastly one at £60.
I the first two not only was the transformers UNDERSPECIFIED but the internals were dangerous as far as UK safety standards were concerned .
The third lasted several years and --yes-- the primary winding's shorted.
I reported that on the UK website I used to be on and what did I get ?
Criticism from "interested parties " namely IMPORTERS.
I have said before when I build an audio power amp the mains transformer is over specified , this engenders confidence in the finished product that if a fault occurs then it is LESS likely to be the transformer .
In contrast I owned a Taylor 45 valve tester at one time it was over 50 years till the transformer failed and yes I inadvertently overloaded it with too big power pentodes when testing --got hot ?--yes failed--no.
I could name the UK prestige transformer manufacturers in the UK but it nearly brings me to tears to see high quality engineering disappear just so a fast buck can be made .
The point about 220volt AC transformers being imported into the UK is a genuine one when my own mains voltage stands at --this moment --245 volts rms .
Any transformer guy can do the figures and work out the increase in heat when under full load.
Agreed there, frustrating to find a 220V primary, on the OLD standard, rather than a 230V primary, Especially when mains voltage in my area is also frequently at 245V
Those of you who have Power Mains problems, need to build a Buck Transformer.
Usually a metal box, an overrated filament transformer, 1 IEC socket, one power cord with the plug cut off and hard wired in the metal box, and with the other end of the power cord ready to plug into your amp's IEC power socket.
Why the overrated filament transformer?
The filament transformer is probably 220V primary, not your mains that are 245V.
So, use a secondary that is rated for 2X to 4X the current you need to draw to power the amplifier.
The primary will be slightly hot, but not nearly as much as if you used all the current rating of the secondary.
Use a UL rated, CSA rated, or other reputable regulatory agency rated transformer, and a company that actually abides by those regulations, not just cheats.
You can even fuse the transformer primary, for extra safety.
Usually a metal box, an overrated filament transformer, 1 IEC socket, one power cord with the plug cut off and hard wired in the metal box, and with the other end of the power cord ready to plug into your amp's IEC power socket.
Why the overrated filament transformer?
The filament transformer is probably 220V primary, not your mains that are 245V.
So, use a secondary that is rated for 2X to 4X the current you need to draw to power the amplifier.
The primary will be slightly hot, but not nearly as much as if you used all the current rating of the secondary.
Use a UL rated, CSA rated, or other reputable regulatory agency rated transformer, and a company that actually abides by those regulations, not just cheats.
You can even fuse the transformer primary, for extra safety.
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Just be sure to measure the voltage out of the Buck box.
Depending on the phase, you either get what you want (Buck voltage),
Or you get Boost voltage (even higher voltage)
Depending on the phase, you either get what you want (Buck voltage),
Or you get Boost voltage (even higher voltage)
1. Tapped Auto Transformer if you have one, and if it can handle the total power requirement.
I have an Auto Transformer, it is big and heavy, and I did not have a metal box big enough to put it in.
2. A Buck Transformer only has to handle much less power, is smaller, lighter, and less expen$ive.
Plus, many of you have a filament transformer in your box of extra parts that will do just fine.
A 4 Amp filament secondary winding handles 480 Watts for 120V power mains, and handles 880 Watts for 220V power mains.
3. Isolation Transformers with taps work too, but are big, heavy, and expen$ive.
But if you use that, and if you also use the power mains ground . . .
then you are wasting an isolation transformer to change the voltage, but not using the isolation feature.
Decide which one you will use.
I have an Auto Transformer, it is big and heavy, and I did not have a metal box big enough to put it in.
2. A Buck Transformer only has to handle much less power, is smaller, lighter, and less expen$ive.
Plus, many of you have a filament transformer in your box of extra parts that will do just fine.
A 4 Amp filament secondary winding handles 480 Watts for 120V power mains, and handles 880 Watts for 220V power mains.
3. Isolation Transformers with taps work too, but are big, heavy, and expen$ive.
But if you use that, and if you also use the power mains ground . . .
then you are wasting an isolation transformer to change the voltage, but not using the isolation feature.
Decide which one you will use.
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