|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
193.178.153.240
In Reply to: RE: My 3 years to the goal of the non-compromise SET and still learning.. posted by aknaydenov on September 13, 2015 at 13:53:04
Hello again, it's been awhile...
I did resistor upgrades a week ago and I'm very impressed from the benefits. I replaced the cathode resistor, the grid series resistor and the series resistance to the power supply choke.
Here are my opinions:
1. The cathode resistor upgrade from 4xPhilips 2,4k (600R) to 620R Mills MRA12
a) Immediate subjective impressions (WOW effect) - 3/5
b) Impressions with time (3/5)
c) Contentment of the improvement (4/5)
The most of the improvements are in the soundstage - size, depth, width, heght, pinpoint. In terms of sound signature, the resistor is more on the calm, flat sound side.
2. The series grid resistor upgrade from Vishay VR68 MF to Amtrans CF.
a) Immediate subjective impressions (WOW effect) - 4/5
b) Impressions with time (4/5)
c) Contentment of the improvement (4,5/5)
I can immediately say that this resistor doesn't sound like a common carbon one. It's fast, precise and very detailed just like a MF, but with a subjective feel of eveness, like an even speaker frequency response. I also got improvements in the soundstage in every aspect and more PRAT.
3. The power supply resistor upgrade (in series with the choke) from Philips MF to Holco MF
a) Immediate subjective impressions (WOW effect) - 4/5
b) Impressions with time (2/5)
c) Contentment of the improvement (2/5)
Here I'm not sure if I like the difference this resistor made to me. The whole sound signature became a bit harsher without much improvements in detail and soundstage. Although the harshness is pretty much tolerable to my taste, this upgrade didn't deliver the benefits that the other resistors did.
Best regards,
Alexander.
Follow Ups:
I am happy to report that my amplifier scored a pretty high score on our local DIY audio exposition. Although I was very pessimistic and worried, I was very happy when I heard my amplifier sounding. I am pretty happy with the result and I'll move on to better sound for the next year's expo.
I will share some "know-how" I learned while upgrading my SET for the exposition.
1. HEATER WIRE - very important and influences the whole sound of the amplifier, even on indirectly heated tubes. This is one of the best upgrades I've ever done. The change is like swapping a mediocre to better speaker/power cord.
2. POWER DISTRIBUTOR - it goes together with my whole system. A power distributor made of nice wooden chassis, and good wire with the proper direction was my trump card at the expo and a great upgrade. It should be vibration treated as every other hi-fi equipment. I put soundcare feet on it and the quality of soundstage width, depth and bass increased.
Some photos of our national expo:
https://drive.google.com/folderview?id=0B1Vyfa4EboUhYlVvUVdpVkNWQnc&usp=sharing
Regards,
Alexander.
Some very cool looking and I imagine sounding gear!
I hope you can get your amps up and running soon. Every DIYer needs a simple backup amp just so they can listen to music while working on the main amps! I have some nice DIY PP EL84 monoblocks or a SET 421A amp to throw into my system when my main monoblocks are being worked on (or just for a change).
Thank you!
I'm using my spare time during week-ends to repair them. Fortunately I have another SET playing music for me right now. Not my property, but a friend's. I took it home with me to do some mods to it and currently, I'm "burning it in".
The reason of my accident was the foolish mistake of putting the binding posts near the output transformer. Due to some loosening of one of them, its edges seemed to have dug up in the transformer's insulation and to the primary. I wasn't aware of this.
When the time had come for me to take some measurements last week, my goal was to measure frequency response and power output. I had connected a resistor load and my oscilloscope's probe across the amplifier's output terminals. A function generator was also running with its RCA terminated cable ready to be plugged in the input of the monoblock. The measurements were successful with the first channel. I got 12W RMS at 1kHz and 25Hz-28kHz FR at -3dB, HF limited by the interstage transformer.
Happy from my results, I moved the equipment to the other channel and plugged the load and probe to its output. At the moment I plugged the RCA cable in the input, the amp went BZZZ, the input tube arced heavily in purple and while I rushed for the power switch, I heard a bang and later there was a smell of a burnt component!
The aftermath was "welded" grid to cathode input tube, blown series grid resistor (Amtrans, it hurts), blown function generator and insulation breakdown of the output transformer.
Luckily I managed to repair the function generator last week. The power supply regulators and the final output stage were blown. It took me a few days to find the faults, measure, buy new parts and replace them.
The output transformer is also okay right now. In order to fix it, I carefully cut the outer insulation to reach the burnt spot of the primary. Visually there was a winding turn with charred insulation at the top that resulted from the arcing.
I know the person who wounded my OPT, so I was familiar with the materials he used to manufacture it. I put a tiny droplet of solvent, waiting for it to soften the glue and using a very thin plastic card, I inserted it between the charred turn and the healthy ones, separating them with a micron distance. Afterwards I sprayed some PCB insulating lacquer on the windings and finally sealed it back using the same glue. This procedure was made to make sure I won't get a primary winding shorted turn, which would result in a lesser useful transformer inductance, downgrading its performance.
The resistor and the tube are, of course, beyond repair. Thankfully, I had some spare EL802 tubes left that I managed to match using our uTracer at work. I'll be replacing the resistors with Vishay metal films, which IMHO are inferior the Amtrans, but still very good for the money.
My explanation for the accident is that the current found itself a nice path, from the scope probe to the OPT primary, then from the main power supply filter capacitor holding 390V to amplifier ground, then to cathode of the input tube where it easily broke through, arcing to the grid, then from the grid resistor to the RCA input and from the low output impedance of the function generator finally going to the shared neutral between it and the scope. I guess the current was somewhere between 0,8A at its peak, considering the resistances of the primary, the arc inside the tube and the grid resistor. It was plenty enough to weld the tube and blow the resistor.
Now, the light inside the tunnel - I take each defeat as a new start. Now I've begun repairing my monoblocks and upgrading them a bit. I made oiled solid birch plywood binding posts ready to be installed, but unfortunately I'll have to wait until Monday in order to buy myself long brass screws for them.
I'm finally putting plate cap on the output tubes and I'm covering the enameled OPT wires with thick cotton sleeve.
About the Telefunken EY83s, for now I prefer letting them be, standing plugged in their ugly looking adapters until I get the opportunity to find some EY500 of the same brand.
I sincerely hope the sharing of my mistake will be useful as a safety tip and warning to other fellow audio enthusiasts.
Best regards,
Alexander.
Wow, that was a significant failure! Glad you have fixed it. A warning indeed!
Beautiful binding posts!
Thank you.I thought of using my DIY time more usefully with the sharing of some detailed photos, something I didn't do before.
Behold, my indian rosewood bias battery holder.
The screw is nickel plated brass and the wires are Neotech UP-OCC.
The holder is placed in series between the input and the grid to provide -1.6V bias. The battery is VR303 Varta AgO, chosen for its transparent sound.
Best regards,
Alexander.
Edits: 08/22/16
:)
The first monoblock is already running. I made the addition of making a simple fixed bias. The output tube is dissipating 45W on the plate. Don't be scared, it's a sturdy tube. I've ran a pair for a year without any signs of noticeable deterioration. I have a few friends who have ran it even at 55W. I cannot guarantee the same for a western EL519 though.
It is apparent that the plate glows on one side only. This is due to structural inside asymmetry. A perfect tube will share an even redness on both anode sides. Unfortunately, when I tried matching tubes by this criteria, only 2 from 20 did it.
Thanksfully, only two tubes red plate out of 20 tubes. Some tube may red plate (even a little) due to the a little more sensitive grid voltage or some kind of shorts or leakage between elements.
Are you using those tubes with the redness on the plate? I think it's called a red plating!
And no, you don't want to match tubes with the color of the redness on the plate!
.
.
.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
You did not understand my point. All 20 tubes red plated, but only 2 of them did it symmetrically.
Currently, I'm using it with the little red plating. This is a tube that doesn't mind it, deducing it by my own and the experience of others.
Yes, I did not understand before but now I do! You are one lucky guy to find all 20 tubes that will red plate at "normal operating condition" or you are pushing the tubes too hard so all of them are red plating.
What's so desirable about the sonic quality of the red plated tubes other than being somewhat useful in the Class C/D/E transmitters?
.
.
.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
I'm pushing the tube a bit harder because the temptation for more power, the pushing of a tube in a more linear region and the lack of possibility to lower B+.
Regards,
Alexander.
Updates??
Well, at least they are a lot cheaper than most triode output tubes!
The truth is, each time I go to a radio flea market, I get some at the cost of cents. I've gathered nearly 30 pcs.
Regards,
Alexander.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: