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Old 27th June 2011, 01:57 AM   #351
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Sorting NE-2s please don't forget about the aim: sound, that must be musical, and changed from soft to aggressive easily, by the guitarist himself.
Speaking of epoxy, when I invented what was known in Western countries as Phaser (I called it multi-rejector comb filter), my friend made it of small cubes, with springs between them. Open the box, and they jump around.
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Old 27th June 2011, 02:29 AM   #352
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Interesting. How about little pill capsules of sand attached to a spring delay line? Sort of like sand filled shakers. Would give some interesting sound effects. Hmmm, getting ideas here. How about making the OT with loose laminations? Sort of like gravel washed jeans. Or a gapped SE OT with powdered iron sprinkled into the gap. The old telephone mics had some kind of carbon granules for variable resistors. Could be cool if the amp gave off sounds when it got shaken. Or maybe put a mini speaker on the pre-amp tube to inject microphonics. With little tuning fork like resonators epoxied to the tube. I saw a piano perfomance once where the piano had various size screws inserted between the strings for effects. I suggested afterwards that they try putting some marbles onto the piano strings.
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Old 27th June 2011, 03:01 AM   #353
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This is getting us back to the old "secret components sealed in a tar filled box" scenario.
Ever take apart a 60's vintage Standel guitar amp? There were several plastic boxes each filled with a different colored epoxy. Each box had colored wires coming out of the epoxy going to terminal strips. About the only thing not encapsulated were the output transistors and the power supply.

Ever see a Standel amp today? Even heard of Standel? You couldn't fix them and they blew up a lot. Bye Bye Standel!

Fast forward 25 years and Standel is back.....and the schematics to all the little colored boxes are posted on their web site. OH, and their "new amp" is a copy of one of the first Standel tube amps.
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Old 27th June 2011, 03:16 AM   #354
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Never heard of Standel. But I'm no expert on guitar amps either. Did Heathkit ever make a guitar amp? We could just copy their construction manual. Problem solved.....
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Old 27th June 2011, 03:27 AM   #355
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Did Heathkit ever make a guitar amp?
Yes they did. I fixed one of them too back in about 1972. It would not be allowed here. It was infested with sand based life forms and didn't glow. Unless you count the millisecond flash given off by the emitter resistors when the output transistors short out.

It is interesting to note that the power amplifier section of the big Heathkit guitar amp, and the power amp section of the Kustom 50 watt models were exactly the same. The Kustom 100 watt model just ran two 50 watt amps in parallel. Why were the circuits the same? Because they were both copied from the RCA transistor manual.

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Never heard of Standel.
They were expensive amps used by some big name bands. So "unique" that there was a Band named the Standels, and they werent playing Fenders. Their one hit, Dirty Water.

http://www.youtube.com/watch?v=p8h2gVcDQ9E
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Old 27th June 2011, 03:36 AM   #356
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I just scanned thru the RCA tube manual to see if it had a guitar amp, no luck. Maybe one of their application reports had one. Then maybe they didn't think much of guitar amp designs to bother either. I have this subconcious feeling that guitar amp sound evolved from cheapest amplifier design.
I keep trying to find the best OT and HV xfmr when I should be settling on the cheapest junk. It just has to be loud.

My last "brilliant" idea for the night before sleepy brain fog sets in:
Seems that RF amplifiers were built using the negative resistance slope of tunnel diodes. Now gas regulator tubes are supposed to have negative resistance too. So maybe there IS some way to get gain out of an NE-2 after all. Would be novel anyway. Probably hugely wasteful of power or something. Have to look up tunnel diode amplifiers to see how they worked. I'm envisioning a single NE-2 for the 1st stage, and then parallel banks of increasing numbers for the subsequent stages, until useful power is reached. Probably thousands of NE-2s for the output stage. Anybody who builds this WILL have to hoard NE-2s. Well, maybe a mercury street light could be used for the output stage.
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Old 27th June 2011, 04:21 AM   #357
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hehe... Thinking about this negative resistance amplifier scheme further, the old tetrode tubes have a large negative resistance region due to secondary emission. Now there's a tube type that no one will hoard or even miss if they do all sell out.

In any case, I think this outlines a new strategic approach for me on this project. An ultra cheap guitar amplifier is likely to be built in very large quantities, and so will soon remove all supplies of its parts/tubes, so the objective should be to use the junkiest parts that should be disposed of, yet function just sufficiently well to meet the cost requirements.
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Old 27th June 2011, 04:56 AM   #358
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If my numbers are correct, I just hit 11W plate dissipation on a tube spec'd at 4W plate dissipation, and there was no sign of red plate (4.76V on the 130R cathode resistor and 320V on the plate).

I got a whopping 2.5W out in push pull. However, that is over twice what I got in SE, and is more than enough for me. I'll dial it back and see what it does tomorrow.
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Old 27th June 2011, 02:12 PM   #359
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I just scanned thru the RCA tube manual to see if it had a guitar amp, no luck. Maybe one of their application reports had one.
There wasn't one in the transistor manual either. Most of the Fender designs evolved from curcuits published for HiFi or radio use. Many of the Marshall designs evolved from Fender designs. Look at the similarities in the early schematics.

The early solid state guitar amp designs ofthe copied the output circuitry directly from HiFi designs. The most extreme solid state amp I ran across was an old Danelectro. It used the totem pole with trifilar driver transformer design that was very popular in early solid state HiFi's using PNP germanium output transistors. Danelectro ran the output stage directly off of rectified wall outlet using high voltage silicon devices from Delco and used a speaker cabinet with all the speakers wired in series. Wire up a conventional 8 ohm cabinet and the fire gods will dance all over the amp.

I did a "Transistorlab" version of this using 24 X 2N3773's that made over 1200 watts (military surplus heat sink with transistors already on it). Serious rock and roll in 1970. That amp was still running last time I saw it in the late 80's. I just replaced the power supply caps.

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Seems that RF amplifiers were built using the negative resistance slope of tunnel diodes....Have to look up tunnel diode amplifiers to see how they worked.
They required a piece of RF magic known as a circulator. Ferrite, magnets, and resonance all combine to create a device that has 3 ports aranged in a circle. It works like the RF version of a traffic circle, the RF only flows one direction. Now add a negative resistance device to one port and you will have gain across the othar two ports. The circulator keeps the output energy from flowing back to the input, or you will have a tunnel diode oscillator.

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I just hit 11W plate dissipation on a tube spec'd at 4W plate dissipation, and there was no sign of red plate
Welcome to my world. As many know I have found tubes that can be operated well beyond the ratings. I have also found tubes that can't. Most of the little 7 pin radio tubes don't take too kindly to overload. I have found that there is a very fine line on the 6AQ5 that divides between "cranked" and "sucking air". The glass is so close to the plate, and the plate hot spots in a localized area, so the glass will melt and a crater will form. Wait about 2 minutes and there will be no more vacuum.
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Old 27th June 2011, 02:24 PM   #360
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I did build a 6SL7/6SN7 SE guitar amp. Good sound but not enough power.
Someone with a 100dB/1m speaker would have been happy and satisfied. I wasn't. Mine is 96dB. Little by little I've realized I'm no teenager and I can play as loud as I want to. Sooooo who wants a puny 1 watter?

Ok, I've covered now the 'not really loud area' and I'm not interested. Of course I could spend the money on a very sensitive speaker. Celestion Vintage 30 is pretty good. 1W amp with that speaker will be enough for some fun. LOUD.

After all these years the Champ is still the low wattage amp to copy anyway. No designer has beaten it, I see clones with el84's but almost same circuit. So if Wavebourn can make those Russian tubes sing, he's got many chances of winning. IMO.
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