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Hi -I am a fairly savvy audio guy, but not familiar with the ins and outs of tube hi-fi gear. I inherited some excellent gear recently, but I cannot get sound out of the power amp. Just to complicate things, it is a quite rare amp so I cannot find info on it.
It is a Silvaweld SWA 20s - it has 2 6U8A's, 2 300B's and 2 5AR4's. The amp powers up and all the tubes glow normally (except for the rectifiers, but I hear that is not unusual). I don't have a tube tester...It puts out no sound at all though - not even hiss. Dead silent. The pre-amp I am using functions fine as do all the other components and wires.
Where so I start with trouble shooting this? I am out of ideas, other than replacing all the tubes, but the fact that the amp puts out no sound at all makes me skeptical that that is the issue.
Thanks in advance for any help at all anyone can offer.
Edits: 09/05/15Follow Ups:
I would start by checking the secondary windings AC voltage.Pull the two 5AR4 rectifier tubes. Power up the amplifier.
First check for 5Vac filament winding voltage between pins 2 & 8 on the 5AR4 tube sockets. (If measuring from the top of the tube socket count counterclockwise from the keyway). You should measure 5Vac. If no voltage,(TURN OFF the amp and unplug from AC power), trace the 5 volt filament winding leads, wires, back to the power transformer. (These leads could be twisted together from the power transformer.) Look for a fuse or resistor that may in series with one of the leads that may be blown. While looking look for a possible poorly soldered cold soldered connection that may have burned free making the connection open.
If nothing is in series between the tube socket pins and the transformer then the 5 volt winding is open, burned out.*But if you measure 5Vac......
Next check for AC voltage on the high voltage secondary winding. Be careful the voltage will be several 100s of volts! Measure the voltage from pin 4 to pin 6. If you measure a high voltage of several hundred volts next measure from pin 4 to the metal chassis of the amp. You should measure 1/2 of the voltage you measured from pin 4 to pin 6. Next measure the voltage from pin 6 to the metal chassis of the amp. The voltage should measure the same as it did from pin 4 to the chassis. (I am assuming the high voltage secondary winding is center tapped.)
Post back what you find.
Edits: 09/09/15
Well, I know little about your amp, but there are some basic things you could check.
I tried looking for a schematic, but no dice. That makes it a lot easier to direct you through checking some things with your volt meter...
Well, either way, I'd check if you have any B+ reaching your tubes, and see if there's maybe a high-tension fuse inside the amp that's gone. The fact your 5AR4's don't glow isn't a huge concern, but they should still at least a little - they have a heater wire like any other tube.
To check the B+, I just take out my main power tubes, connect the red lead into the pin connected to the tube's plate, and then the black lead to the best relevant ground (could be chassis, but largely depends on circuit). When you turn on the amp, and off standby, you should see B+ voltage of a few hundred volts.
If you don't have B+, bring it in to a tech.
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May your tubes be warm, long-lasting, and always lively. Holy be thy heater.
Thank you so much for your guidance so far. I am wondering - if the rectifier tubes are blown, would total silence be the result? I'm trying to start with an easy fix before I get more technical.
Thanks!
Total silence would be the result, in theory. Suppose the rectifiers are blown OR that the B+ fuse is fried, there will be no voltage reaching the valve's plates, no draw, and no sound. So, the valves are effectively offline, regardless of whether heater's are a'glowin.
Another consideration that just occurred to me is the design of the 5AR4 itself. While all rectifiers have anodes (plates), the cathode design can vary. Some are have "filamentary" designs, so it's just a filament to source electrons for the anode. However, some have cathodes heated by the filament, instead. Your 5AR4 has a heater and a cathode, and these two parts are INTERNALLY CONNECTED TOGETHER. So, let's say your amp does NOT have a B+ fuse and there was a run away, a sudden rush could have caused an arc between the plate to the cathode of the rectifiers. The 5v filaments would have suddenly seen hundreds of volts, effectively overloading and killing the tubes.
And not to scare you, it could have damaged the 5V heater winding of the transformer... Tube rectified amps have 6.3v and 5v windings; the 6.3v for pre-amp and power amp tubes, and the 5v solely for rectifiers. If you replace the rectifiers, and they STILL don't turn on... I'd be very concerned as it may indicated the 5v winding has suffered an overload and burnt.
I found an interesting resource that may be of use to you. Check it out :)
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May your tubes be warm, long-lasting, and always lively. Holy be thy heater.
Edits: 09/07/15
if the rectifier tubes ARE blown, dont just plug in new ones, you uneed to figure out what caused them to blow first, or you may blow the new ones also.
Thank you all so much for your advice. This forum is amazing. I'm so glad I found it now that I have all tube hi-fi gear. That said, the simple fix did the trick: new rectifier tubes. The amp sounds beautiful.
Do you own a voltmeter?
Yes.
The easiest place to start is to measure the DC voltage on the our pins of the 300B socket with the amp running (and a tube in the socket of course).
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