n_maher
Resistorous Conflagorous
- Joined
- Nov 20, 2004
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Disclaimer: I am not a professional. The information provided below is intended as a community service. Any work or repairs performed should be done by a professional. Any use of the information provided is at the owner's risk. The pictures and contents of this post are not to be re-used or re-printed with my consent.
The following details my experiences after having been asked to look at a Singlepower Extreme for a fellow member here at Head-Fi. What I found is, in my opinion, a very serious problem. The amp in question appears to be one of the early Extremes and a pretty basic, stock unit. The first thing that I did was to open up the chassis and look for obvious signs of damage, there weren't any. And despite using a PPX3 pcb (evidently at some point Mikhail offered to mod existing PPX3s into Extremes) everything on the board checked out just fine. The owner had complained that the transformer smelled burnt the last time he tried to use the amp so I figured that was probably where the problem was located and set about trying to figure out how to get at the transformer without taking the entire amp apart. Mikhail made these very difficult to work on, that's for sure.
Here are some basic internal shots.
Overall
Filament Rectifier (note the lack of thermal compound)
Tubes sockets air-wired to PCB
Wires pulled so tight they are nearly cut through the casing, no grommets on any of the holes in the chassis or pcb
So the kicker here is that in order to get at both the fasteners that hold the transformer cover and the fasteners that hold transformer itself you have to remove the pcb. What makes the situation worse is that as you can see the tube sockets are air wired and what you can't see is that the sockets are mounted in such a fashion that in order to remove them you have to remove the pcb. So, in order to remove the pcb you have to desolder each and every connection to the 3 tube sockets. I decided that before going through all that effort that I would attempt to find a way to at least remove the transformer cover. I was able to figure out that at those two locations the pcb was basically clear enough for me to drill access holes.
What I found when I removed the transformer cover was not pretty and was entirely unexpected.
What you're looking at is a completely cooked transformer. What struck me as very strange is that it is only a filament transformer and I know that this amp doesn't only run off of 6.3V. I'll do my best to describe this and ultimately I'll draw a small schematic but for now words will have to suffice. The transformer in question is a dual primary, dual secondary transformer. The two primaries are 2x117VAC (for use in both ~115 and ~230VAC countries) and each secondary is 6.3V @ 4A. So in normal use in the US one would wire up the two primaries in parallel and each secondary would be 6.3V @ 4A. What Mikhail did was to wire one primary to the IEC inlet and one to the PCB. In essence this is using the second primary as a secondary (very bad) and the real problem is that by doing so he cut the secondary current capacity in half (2A vs. 4A). So now when he ran both secondaries in parallel he got a total of 6.3V @ 4A instead of the rated 8A.
The following is taken directly from Hammond's (the manufacturer of this transformer) FAQ on their website:
Clearly Hammond never intended for their transformers to be used like Mikhail did and they are very clear on the consequences.
Now in a best case scenario this might not be a terminal problem if the amp required less than 4A on the low voltage windings but this isn't the case. Each 6AS7 on the output pulls 2.5A and the 6SN7 input can pull up to almost 1A (depending on which 6SN7ish tube the owner uses) but generally will use .6A. So in a pretty average operating case the low voltage section needs to provide at least 5.6A and has only 4A to give. What that means is the minute you turn on the amp the low voltage section is running 40% over spec, not good. No, back to the "HV" section of the trafo. There's some debate about just how bad it is to use a primary as a secondary and I'm not qualified to say for sure but you can bet that the UL and Hammond had no intention of this being done. And we've observed that what Hammond predicted has in fact happened.
Now what is it going to take to fix it? The transformer must be replaced with a proper spec'd unit. I've seen examples that might work that range in price from ~$80 to well over $100. And that is just for the part. I'd also estimate that owner's will be looking at at least a couple hours of labor, potentially much more. More importantly what is the danger here? Well that is, in my opinion, the worst part of this. I am not able to say exactly what would happen if the transformer was able to fail completely and essentially melt itself together but in a best case it will simply pop the fuse on the IEC input of the amp and the amp will die a quiet death. In a worse (not worst, who knows what worst is) case it will run for a while and produce a ton of heat any potentially short live AC to the chassis and then maybe pop the fuse before it throws a breaker. The Extreme that I looked at did have the chassis connected to safety ground but I cannot say if that is the case for every amp Mikhail built using a transformer setup this way. But most casual owners that I know would probably try to replace the fuse if it blew and would then subject the transformer to another round of abuse and who knows what would happen there. I did run this scenario past a couple of friends that I have in the electronics business and they were amazed by just how dangerous this is for the consumer/owner. Owners should understand that some of the possible failure modes for the transformer could be lethal and I'm not in any way trying to over-state situation.
So my advice to any SP Extreme owner is to find out what transformer your amp uses or stop using the amp altogether. Please understand that I am not a professional, cannot look at your amp for you or offer to repair it. You will want to seek professional help since there may be other issues with your particular amp that I have not seen and therefore did not mention in this post. Sorry to be the bearer of bad news but after seeing what I did I could not simply remain silent.
The following details my experiences after having been asked to look at a Singlepower Extreme for a fellow member here at Head-Fi. What I found is, in my opinion, a very serious problem. The amp in question appears to be one of the early Extremes and a pretty basic, stock unit. The first thing that I did was to open up the chassis and look for obvious signs of damage, there weren't any. And despite using a PPX3 pcb (evidently at some point Mikhail offered to mod existing PPX3s into Extremes) everything on the board checked out just fine. The owner had complained that the transformer smelled burnt the last time he tried to use the amp so I figured that was probably where the problem was located and set about trying to figure out how to get at the transformer without taking the entire amp apart. Mikhail made these very difficult to work on, that's for sure.
Here are some basic internal shots.
Overall
Filament Rectifier (note the lack of thermal compound)
Tubes sockets air-wired to PCB
Wires pulled so tight they are nearly cut through the casing, no grommets on any of the holes in the chassis or pcb
So the kicker here is that in order to get at both the fasteners that hold the transformer cover and the fasteners that hold transformer itself you have to remove the pcb. What makes the situation worse is that as you can see the tube sockets are air wired and what you can't see is that the sockets are mounted in such a fashion that in order to remove them you have to remove the pcb. So, in order to remove the pcb you have to desolder each and every connection to the 3 tube sockets. I decided that before going through all that effort that I would attempt to find a way to at least remove the transformer cover. I was able to figure out that at those two locations the pcb was basically clear enough for me to drill access holes.
What I found when I removed the transformer cover was not pretty and was entirely unexpected.
What you're looking at is a completely cooked transformer. What struck me as very strange is that it is only a filament transformer and I know that this amp doesn't only run off of 6.3V. I'll do my best to describe this and ultimately I'll draw a small schematic but for now words will have to suffice. The transformer in question is a dual primary, dual secondary transformer. The two primaries are 2x117VAC (for use in both ~115 and ~230VAC countries) and each secondary is 6.3V @ 4A. So in normal use in the US one would wire up the two primaries in parallel and each secondary would be 6.3V @ 4A. What Mikhail did was to wire one primary to the IEC inlet and one to the PCB. In essence this is using the second primary as a secondary (very bad) and the real problem is that by doing so he cut the secondary current capacity in half (2A vs. 4A). So now when he ran both secondaries in parallel he got a total of 6.3V @ 4A instead of the rated 8A.
The following is taken directly from Hammond's (the manufacturer of this transformer) FAQ on their website:
Clearly Hammond never intended for their transformers to be used like Mikhail did and they are very clear on the consequences.
Now in a best case scenario this might not be a terminal problem if the amp required less than 4A on the low voltage windings but this isn't the case. Each 6AS7 on the output pulls 2.5A and the 6SN7 input can pull up to almost 1A (depending on which 6SN7ish tube the owner uses) but generally will use .6A. So in a pretty average operating case the low voltage section needs to provide at least 5.6A and has only 4A to give. What that means is the minute you turn on the amp the low voltage section is running 40% over spec, not good. No, back to the "HV" section of the trafo. There's some debate about just how bad it is to use a primary as a secondary and I'm not qualified to say for sure but you can bet that the UL and Hammond had no intention of this being done. And we've observed that what Hammond predicted has in fact happened.
Now what is it going to take to fix it? The transformer must be replaced with a proper spec'd unit. I've seen examples that might work that range in price from ~$80 to well over $100. And that is just for the part. I'd also estimate that owner's will be looking at at least a couple hours of labor, potentially much more. More importantly what is the danger here? Well that is, in my opinion, the worst part of this. I am not able to say exactly what would happen if the transformer was able to fail completely and essentially melt itself together but in a best case it will simply pop the fuse on the IEC input of the amp and the amp will die a quiet death. In a worse (not worst, who knows what worst is) case it will run for a while and produce a ton of heat any potentially short live AC to the chassis and then maybe pop the fuse before it throws a breaker. The Extreme that I looked at did have the chassis connected to safety ground but I cannot say if that is the case for every amp Mikhail built using a transformer setup this way. But most casual owners that I know would probably try to replace the fuse if it blew and would then subject the transformer to another round of abuse and who knows what would happen there. I did run this scenario past a couple of friends that I have in the electronics business and they were amazed by just how dangerous this is for the consumer/owner. Owners should understand that some of the possible failure modes for the transformer could be lethal and I'm not in any way trying to over-state situation.
So my advice to any SP Extreme owner is to find out what transformer your amp uses or stop using the amp altogether. Please understand that I am not a professional, cannot look at your amp for you or offer to repair it. You will want to seek professional help since there may be other issues with your particular amp that I have not seen and therefore did not mention in this post. Sorry to be the bearer of bad news but after seeing what I did I could not simply remain silent.
