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Maybe I can ask you fellas about capacitors.
In my collection I recently added four 8uF PIO's which are rated to 1,000V that I think would be good for a PSU for an 845 if I stick to a B+ slightly under 1,000V.
However, one of them has a small dent. I had the capacitor x-ray'd to look at the inside. I am advised that this capacitor may not be best used at maximum voltage due to the dent. I attach a photo. I contacted the seller in the US, who ignores me completely - possibly he's away.
In the X-ray image the dent is on the right hand side, close to where the foil-paper edges are; there's an arrow to show how the dent is near the edge of the foil-paper.
In my collection I recently added four 8uF PIO's which are rated to 1,000V that I think would be good for a PSU for an 845 if I stick to a B+ slightly under 1,000V.
However, one of them has a small dent. I had the capacitor x-ray'd to look at the inside. I am advised that this capacitor may not be best used at maximum voltage due to the dent. I attach a photo. I contacted the seller in the US, who ignores me completely - possibly he's away.
In the X-ray image the dent is on the right hand side, close to where the foil-paper edges are; there's an arrow to show how the dent is near the edge of the foil-paper.
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Will there be enough primary inductance? Might be worth doing the maths to check before committing.
I couldn’t agree more, And I would definitely use those transformers again when I get a chance. I spent quite a lot of time taking measurements of these transformers and you will see on my website the measurements and results. Most importantly the resulting amplifier sounded amazing.
There are few transmitting valves I would like to try, however I simply don’t have time now and I have two young children around
Ale
Hello,
I had the same problem with some other caps from ebay but they were aluminium and the dents were smaller. I opened the open with the biggest dent and noticed the role of paper/foil was surrounded by some oil before '' touching '' the alumium so no problem
I know the caps you are using and you will need a decent hit to have dent like this. I wouldnt take the risk. With the x ray you could easily find the innner and outer foil i guess. Do you work at the airport?
I just got some caps from ebay which have no real polarity but only got an A and a B connector. Long time ago someone told me that sometimes there will be a red dot just in case you wanna branch two in series.
Greetings,
Eduard
Well in about one month I go back for holidays and can have a 10-11K OPT done.
This time however, for few euros more, I would try with a more complicated geometry to get well above 50KHz.The idea of the two stage amp in class A1 using the 6HV5a is attracting. One could even start with simple resistive load and RC coupling if the 845 uses self bias and effective plate voltage is around 1200-1250V.
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Well I still have 3 of the 4 that I can use, the other 3 have only minor damage and look good to use. All I can say is that the seller is either on holiday and forgot to leave an away notice or my advice will be DO NOT BUY from 'bestsound'.
A friend of mine has access to an x-ray machine.
How does the math work ?
The datasheet (attached) says nominal 55H for the primary. At 20Hz that's an impedance of 7k. The ra of the 845 is 1.7k. Am I getting warm ?
Let me also add that I want to use the Hammond because they have treated me very well. I started out with an old version, the 1629SE which had a design fault producing a dip in the frequency response in the treble. Hammond are giving me a replacement, for what is a decade old transformer with no questions asked and I get to pick it up from their factory. It was a very pleasant conversation with the factory, they were very responsive and helpful. I'm not used to this kind of service and it deserves my praise. And what higher praise than to put the new 1629SE to use in an amplifier.
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I too have had excellent dealing with Hammond.
I bought a 278CX and asked them if it was normal for it to run at 95c under load? They did some tests, and "reversed an engineering change" they had made, and sent me a new one which runs 10c cooler. I still use the hotter one and years later it's still working fine.
I bought a 278CX and asked them if it was normal for it to run at 95c under load? They did some tests, and "reversed an engineering change" they had made, and sent me a new one which runs 10c cooler. I still use the hotter one and years later it's still working fine.
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Those teflon sockets look gorgeous but I don't think I'd pay the premium. Other than cosmetics, I don't think they have an advantage for this particular socket.
814 SE Amplifier: Custom Output Transformers – Bartola(R) Valves
I’m up for a pair of 10-11K OPTs. Let me know please.Well in about one month I go back for holidays and can have a 10-11K OPT done.
This time however, for few euros more, I would try with a more complicated geometry to get well above 50KHz.
The idea of the two stage amp in class A1 using the 6HV5a is attracting. One could even start with simple resistive load and RC coupling if the 845 uses self bias and effective plate voltage is around 1200-1250V.
Thanks
Ale
Only thing, that guy Vincenzo has moved to another job. He was borrwing the winding machine but it's no problem. I now where it is and cam be done again.
They can help reduce resonance from the chassis. I actually use 1/4" Delrin sheets for my top plates. Once you hear the smoothness you'll never go back to metal.
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The transformers and things are quite heavy so I don't think an off-the-shelf chassis is going to work for me either. I do have a large plate of Aluminium in my garage, it is already anodized and I could cut it in half to make a top plate for an amp. The metal is 6mm thick. I see good reasons to make sure the amplifier is sitting on some 'comfy feet' in case of vibrations. Would you be concerned that vibration from power transformer is coupled through the chassis to the pins of the tubes ? Is the 845 sensitive to this, I thought it was not microphonic, maybe it's more important for phono amp ?
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Yes, it matters. I once went through an enormous amount of trouble to build an SE 845 amp on a nice, shiny steel chassis. The difference was clearly audible. If you've ever read Thomas Meyer's excellent blog, Vinyl Savor, you'll notice that he takes great pains to isolate his DHT tubes from the top plate. I also have friend who builds some of the best DIY amps I've ever heard, and he is adament about Delrin for at least the tube portion of the board. He builds a sub-plate that he mounts on a metal chassis.
A 12" x12" white Delrin sheet is $25 from McMaster & Carr. Two should make nice monoblocks. Just my two cents!
Fair point, grovegardner! I've never used DHTs... I'm mainly speaking from a physical perspective.
None of my tubes are microphonic enough to hear it. Tap the tube and don't hear it from the speaker (small signal tubes at the front of the chain excepted, but never from a power tube). Hell, to test for bad solder joints etc, I usually lift the amp 6 inches off the desk and drop it while it's on and playing to see if it passes my expectations... There is no ringing or other typical symptoms of microphony. The only sound I hear is the sound of it hitting the desk
None of my tubes are microphonic enough to hear it. Tap the tube and don't hear it from the speaker (small signal tubes at the front of the chain excepted, but never from a power tube). Hell, to test for bad solder joints etc, I usually lift the amp 6 inches off the desk and drop it while it's on and playing to see if it passes my expectations... There is no ringing or other typical symptoms of microphony. The only sound I hear is the sound of it hitting the desk
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this is only about bass response, it wound't affect loading at all. takes 2 seconds to calculate the cut off frequency, depending on the amount of bias, the inductance drops... just use a conservative bias, boost voltage to like 1200V
Note that it is a compromise to use this transformer, the hammon set are OK, (its probably better than cheap china set transformers, but you will get a great improvement of all aspects with something like James, Audionote etc.
Chassis resonances can be quite subtle. It's not just about obvious microphony. Of course, many good-sounding amps are built on metal chassis. But we're not talking about mass production or shortcuts here. It's your amp. ;-)
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