Picked up this little beast on ebay. Yes I have ordered an iso tranny and other stuff.
What is the function of that adjustable cap?
What is the function of that adjustable cap?
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An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
The variable capacitor seems to increase any mains born interference from the cathode of the main rectifier to the screen grid of the 1st stage amplifier.
In other words, not a lot!
I should think it makes a better spark gap.
In other words, not a lot!
I should think it makes a better spark gap.
I have a 99% identical Airline 8511 amp, even down to layout, and the cap does nothing for me except change the 60 Hz tone from a buzz to a hum to a rumble, its very odd and I am surprised that on the cheapest amps made by these companies, they included an expensive variable cap solely for this, when they couldn't even afford a tone knob... lol
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replace electrolytics all of them especially the B+ caps...
probably late 40's early 50's electrolyte all dried up.
regards, El
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probably late 40's early 50's electrolyte all dried up.
regards, El
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The electrolytics of the day were pretty useless for filtering out high frequency noise. Try plugging in an electric drill that uses a motor with brushes into the same outlet as the amp. Pull the trigger on the drill and tune the cap for minimum scream! Brushed motors were a lot more common back then. Amps with power transformers were more immune to this noise.
I had an old amp back in the 60's that picked up my mother's vacuum cleaner in the other end of the house. It was a 4 tube design without a power transformer. Fortunately it didn't survive my hot rodding experiments.
This type of cap was common in the IF cans of old radios. They weren't all that expensive when bought by the 10,000 piece lot.
So the only purpose of this little cap is to reduce noise on the AC line, kind of like a death cap would on a fender, only even more pointless? And yes, of course the electrolytics are replaced...
Can anyone tell me the idea behind omitting the mains transformer? Just to get the user closer to Darwin's award?
Best regards!
Best regards!
The death cap serves to AC couple one side of the line to chassis ground. The user flipped the line plug over or flipped the ground switch for lowest coupled noise. This amp is far worse.....the death cap has been replaced with a piece of wire.....examine the schematic, the guitar is connected DIRECTLY to one side of the line input. Usually these amps had a polarized plug so that the guitar is connected to neutral. This relies on proper house wiring, no extension cord use, and never replacing the line cord to avoid KILLING people!
It's all about the money. Transformers are expensive. In the 40's the radio manufacturers created a transformerless AM radio that was cheap. Known as the All American 5, it used similar circuitry and as long as the case and knobs were intact nobody got fried.
It didn't take long for the second tier guitar amp companies to make an amp out of the audio section of an AA5 without thinking about frying people. This is the worse example I have seen. Usually the amp circuitry floats from the chassis and input jack, with the "death cap" providing isolation. This design only shocks the user enough to remind him to reverse the line plug.....until the old wax paper cap shorts out.......
It's all about the money. Transformers are expensive. In the 40's the radio manufacturers created a transformerless AM radio that was cheap. Known as the All American 5, it used similar circuitry and as long as the case and knobs were intact nobody got fried.
It didn't take long for the second tier guitar amp companies to make an amp out of the audio section of an AA5 without thinking about frying people. This is the worse example I have seen. Usually the amp circuitry floats from the chassis and input jack, with the "death cap" providing isolation. This design only shocks the user enough to remind him to reverse the line plug.....until the old wax paper cap shorts out.......
Yes, I do know the philosophy of these AC/DC power supplies. Until the advent of totally transistorized designs, almost all TV receivers, and lots of radios, in Germany featured them. But no one had the idea to connect guitars or other things to them, except he opted to play Russian roulette with a 50/50 chance to get electrocuted.
Best regards!
Best regards!
Same in the UK, radios and TV's were commonly live-chassis, but NEVER guitar amps, that's an incredibly dangerous thing to do.
This is a very early 50's example if I'm believing it's appearance. This one also excedes the 12au6's cathode-heater rating if the plug is inserted the wrong way. Mine has a 3 prong cord wired as a polarized 2 prong until I order an Iso transformer that is appropriately sized, as I only have an ~8 amp one lying around from an old oscilloscope, but it also has filament taps, so I am saving it for a bigger project. I have never been shocked to the point of pain, but it is an annoyance... as every-time my laptop is plugged in and I touch one of the side inputs which are grounded, I am slightly shocked. Honestly, these amps were a horrible design idea, but I was wondering, couldn't they just put an audio isolation transformer on the input to isolate the guitarist? Also, shipping costs was a big reason, as a transformer and large speakers are the biggest weights in an amp normally, especially with this one's cardboard tweed cab...
I think it would be much easier to get a reliable and proven power isolation transformer, rather than an audio one. So I'd prefer the first one I mentioned.
Best regards!
Best regards!
I know of at least one Danelectro amp that used an isolated power transformer for the preamp section followed by a driver transformer for isolation then a pair of TV horizontal deflection transistors running directly off of rectified line power. The speaker cabinet ran 4 speakers in series to avoid overcurrent in the output transistors. Quite a LOUD amp for its price.
This was OK until someone decided to wire up some extra speakers. The speakers were connected directly to line power which is a good way to fry someone, but the amp only lived long enough to play one very loud power chord before scattering emitter resistors all over the place!
Triad N-68X...$11.20 at Mouser. Get one NOW before something really bad happens. I have used them on several of these shock box amps. The last one I had was an "Electrolab" 4 tube wonder that I replaced just about every part inside before powering up. It then took me only about 5 minutes to turn the speaker cone back to pulp!
I’ve been letting the Silvertone sit and will get too it very soon. I will install the iso tranny and a 3 prong power cord with its ground wire to the chassis.
Should I bypass the 68k/.05u connection between the chassis and the B- ? The schematic shows the 10vdc I’m seeing on the chassis (from B-.) Presumably this is from dc flowing from B- to the cathode of the 12au6 and the math says it would be 0.15ma. The plate current appears to be about 0.1ma from the math on its resistor. Screen current appears very small thru its 2.2meg feeder.
The grid is at -0.7vdc to the chassis/cathode. The amp appears to function properly based on the audio and scope.
I’m guessing this 10vdc between the chassis and B- is not relevant to the preamp since the B- is not the ground reference for it’s grid or cathode? I’ve seen others just ground all these “B-“ and chassis connections during an iso tranny/3 prong installation.
Any reason to, or not to, bypass the 68k/.05u ? Maybe the 68k/.05u setup avoids some ground loops?
Should I bypass the 68k/.05u connection between the chassis and the B- ? The schematic shows the 10vdc I’m seeing on the chassis (from B-.) Presumably this is from dc flowing from B- to the cathode of the 12au6 and the math says it would be 0.15ma. The plate current appears to be about 0.1ma from the math on its resistor. Screen current appears very small thru its 2.2meg feeder.
The grid is at -0.7vdc to the chassis/cathode. The amp appears to function properly based on the audio and scope.
I’m guessing this 10vdc between the chassis and B- is not relevant to the preamp since the B- is not the ground reference for it’s grid or cathode? I’ve seen others just ground all these “B-“ and chassis connections during an iso tranny/3 prong installation.
Any reason to, or not to, bypass the 68k/.05u ? Maybe the 68k/.05u setup avoids some ground loops?
Short them out, they are there simply to 'reduce' the lethal shock capability of the live chassis design.
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