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In Reply to: RE: How reliable have your SET or SE tube amps been? posted by RGA on April 13, 2016 at 23:37:05
I have an ANK kit 1 300b set amp that I just built in November.
After about two hundred hours of use and incredible satisfaction, the rectifier tube started to spark upon start up.
Then it started blowing fuses. I was guided to try a replacment rectifier tube (5v3).
I bought a pair and each worked for a little while, but then they started to do the same thing.
Now I have been guided to try a 5u4g type rectifier tube.
I built this amp to go with a set of high sensitivity speakers I built for myself last summer.
It replaced a ss amp I used to use (audio upgrades modified- 1985 Adcom 555).
It's a bummer because I love this new SET amp so much.
It smokes my old Adcom, making it sound etched and grainy in comparison.
I have since switched back in my Adcom555, but it pales in comparison to the degree that I have prefered to not listen to music at all.
I will do anything I can to get this problem rectified (pun intended)!
Follow Ups:
Hi johnny, Is the power supply for your amp capacitor input or choke input? If it is cap input what is the value of the first cap after the rectifier? A large cap will also fry your rectifier. cheers, Dak
Hey DAC.
I know that the smallest transformer of the bunch (mains, choke, outputs) on top of the amp deck/chassis is called the "choke transformer".
Does that answer your question?
Since this is a kit, they provided a schematic. Look at the schematic at the power supply and at the tube rectifier. The B+ will come off pin 8 usually, on the rectifier and after that there will be either a capacitor then the choke then another cap. This is called a Pi filter. If it is a choke input filter the schematic would show no capacitor connected between the rectifier and the choke. The choke would be connected to pin 8 and then there would be a cap after the choke.
So if you have the Pi filter what is the value of the first cap? If it is a choke filter the size of the cap following is not as critical.
So I checked both my wiring schematic and build manual.
They aren't all that descriptive, as the amp uses 3 pcb's (filament, driver, power supply). It is not all point to point wired.
So I opened it up and pulled up (gently) the power supply board.
It looks like the scenario you describe-
B+ comes off of pin 8 of the rectifier base, then directly to the choke, no cap in between, that I can see while tracing the circuit.
This connection is on the pcb, but I see the pads are connected.
.
If I can attach pics to my post, then im sure I can.
Ill get it posted a bit later.
But its like I said, more of a diagram or cartoon than an actual schematic.
There is also the build Manual.
The pcb looks to be double sided. Seems pretty easy to trace, but as you know, Im no electronics wiz.
The largest cap I see on the PS board is a 220uf. It seems its AFTER the B+ and choke.
I could be wrong, so ill post pics.
Regards!
.
DAK-
Sorry but its not working for me.
The post looks normal when I hit "preview post" with the pics attached, but when I hit "post message, it doesn't show up.
Perhaps I'm not a member long enough (6 days) :)
I ordered 20 new fuses, and a new rectifier tube.
I figured I should have plenty extra of these anyway lol.
If this doesn't do it, then ill have to send it out for sure.
I know ANK uses a builder for their kits when customers choose not to DIY, but I cannot recall who it was.
I think he calls himself "Digital Pete".
I had a couple of hurdles to cross during the build of this amp back in November,so between that and now this, perhaps I've wore out my welcome with Brian :(
I'll report back on how it goes.
Thanks for trying to help me out.
Regards!
Hello all.
I said I would report back with my attempted repairing of my ANK kit 1 300b set amp.
A few days ago, when I received my new fuses and my new 273b/5u4g rectifier tube in the mail, I installed a new fuse, installed the new rec. tube, and gave it a shot.
Once again, upon switching on the amp, the new rectifier tube would spark, and the fuse would blow. I replaced the fuse and re-tried two or three more times, with the same result.
With still not hearing back from Brian, I decided to try and reach out to "Digital Pete",
ANK's kit builder.
Well, I got lucky there,
as Pete took the time to walk me through some different voltage tests.
He came to the conclusion that I should try a 5u4gb, which apparently passes twice (approx.) the current of the other rectifier tubes I tried (including the 5u4g).
I was rained out from work today,
so I was able to confirm some final voltage measurements with Pete (which he described as "textbook"). I then tried one of my new 5u4gb tubes, which I received yesterday.
So far so good.
No spark in this new rectifier tube on start-up, and no blown fuses as of yet.
I have turned it on and off several times, and I also let it play for several hours today (getting nice and hot).
I sure hope this takes care of it.
Regards!
in this "post a message" box, go down to upload images, to the right is the "browse" box. As long as your file is in your computer you can access it for download by hitting the browse button. when your files are viewable, Click the relevant one, and it should darken to indicate that it was chosen then at the bottom of the page should be an "open" button. press that, which will send your file to this website allowing it to be posted. good luck, dak
Edits: 04/23/16
Late but as you seem interested and never got the reply I did find this manual on the net which I believe has schematics.
I'll check it out and report.
Regards!
The Kit 1 is a well-proven design with years of use by many satisfied builders. I'm suspecting something is not quite right, and that Brian could help you problem solve this.
I have been consulting with Brian.
I haven't heard back from him in a week or so.
Im guessing he is away on business or vacation, or just overwhelmed busy.
I too felt that it was a well established kit, hence why I chose it.
To Brians suggestion, I replaced the original rectifier tube that came with the kit, to a 5v3 tube.
I bought s pair.
Both began to spark upon powering on, and blow fuses, so he suggested the 5u4g next, but said the 5v3 should have worked.
I guess I'll have to give them a go.
Regards!
Tube rectifiers have a minimum plate supply resistance (Rs) for a given voltage. The 5U4G at say 450~500V (as is typical for cathode biased 300B amps) needs to see about 70 to 80 Ohms ahead of it. That is the combined resistance of the transformer's primary and secondary given by the formula: Rs = Rsec + (N^2)xRpri + Ra. It's this this last term, the additional resistance, that must be added in order to bring the Rs to the desired value.
Depending on size, a typical transformer in an amp such as yours will have a source resistance of about 30 to 40 Ohms. You would probably need to add a ~30 Ohm resistor just before each plate of the rectifier (total of 2 resistors) to bring the source resistance (Ra in the equation above) to the required level as specified in the tube data sheets. I would use at least a 10W resistor.
I forgot to mention that with these added series resistors, you should be mindful of their voltage ratings. If for example the transformer secondary is at 400V, then a 500V resistor rating would not be ideal. Resistors need to be at or bellow 70% of their max voltage rating for a long and happy life. Either up the rating, or use two resistors in series.
I also forgot to mention in the previous post that the series resistors will also have the effect of lowering the B+. If your line voltage is on the high end of the scale as is the case in many places, there should be no issue. If you were to use the 5V3 which drops less voltage than the 5U4, you would probably end up at the original B+ level with the use of the series resistors. Hope this helps. Let us know if you resolve the issue with whatever means you might try.
Thanks sonicboom.
I wish I was electronically savy enough to try an make the changes you recommend, or to even fully understand them!
I am not.
I was only able to build the amp because of its kit design and build manual, and the fact that I have some soldering experience with RC cars.
Ill have to trust that this amps initial, intended design is a proven one, and hope that I have been unlucky with THREE different rectifier tubes (the stock kit supplied 274b, and the pair of 5v3's), which I find hard to believe.
Ill report back with my outcome on this, and if indeed it is or is not the rectifier tube/tubes. Then perhaps someone here can recomend an honest repairman for my amp.
Regards!
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