This is a SS amp with a 10" speaker, $129 MSRP, and can be found used for $50 which is a good price for the box, chassis, knobs etc. Some have gutted them and built a tube amp into them:
Fender Products
Tube mod:
http://laird.vectorstar.com/music/amps/6g2princeton
Speaker is the weak link, it sounds fairly good as is with a decent speaker upgrade.
Fender Products
Tube mod:
http://laird.vectorstar.com/music/amps/6g2princeton
Speaker is the weak link, it sounds fairly good as is with a decent speaker upgrade.
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"Has anyone ever played with "Flathead" transformers as OPTs?"
You can find them cheap on surplus sites:
PC MOUNT TRANSFORMER, 16VCT @ 0.35A OR 8V @ 0.70A | AllElectronics.com
I've done some measurements on one here and their problem is high leakage inductance between the split bobbins. So you may find the HF end somewhat compromised even for guitar use.
You can find them cheap on surplus sites:
PC MOUNT TRANSFORMER, 16VCT @ 0.35A OR 8V @ 0.70A | AllElectronics.com
I've done some measurements on one here and their problem is high leakage inductance between the split bobbins. So you may find the HF end somewhat compromised even for guitar use.
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I tried a bunch of low buck low power transformers like this as P-P OPT's a few years ago. They didn't work well at power above a few watts, and I was thinking HiFi amps. I still have them here, and they will be among the first things I try.
Back In high school I was making amps on zero budget. All the transformers came from the trash dump. My guitar amps used OPT's ripped out of HiFi consoles or TV sets but they were rather limited in the power department. I got this brilliant idea to use a power transformer for an OPT. You connect B+ to the HV center tap, each HV wire to a 6L6 plate, wire all heater windings in series, and all speakers in parallel, then connect them together. They rock as a guitar amp OPT and they eat more power than I could make.
I used C-core power supply transformers from Soviet tube TV sets for 100W guitar amps with 6P36S outputs. They were LOUD! 
The same way, I combined windings to get needed impedances.
For the current studio&practice Amp I am going to use some transformer from All-American-Five radios.
Also, I have some 12" and 15" speakers from Magnavox consoles, does anybody know how good they are for guitar amps?
The same way, I combined windings to get needed impedances.
For the current studio&practice Amp I am going to use some transformer from All-American-Five radios.
Also, I have some 12" and 15" speakers from Magnavox consoles, does anybody know how good they are for guitar amps?
The N-68X is a true isolation transformer. There should be ample isolation between the primary and secondary to prevent shorts or leakage current between the windings. It even has a shield between the primary and secondary which should be connected to the ground wire on the line cord and circuit ground. Although it isn't stated in the spec sheet, the transformer I have in front of me carries the UL mark (no CSA though). It is about 5 years old.
It makes no difference which windings you use for primary of secondary as long as you use do not make any connection across the isolation boundry. I have been running the N-68X's backwards for about 5 years with good results. I do this because I need + / - 140 VDC to run my mosfet based PowerDrive circuits. You won't quite get 230 volts since the transformer isn't quite 1:1 to make up for losses.
Eli has suggested running the transformer as intended followed by a voltage doubler. This allows world wide use of the amp if your heater transformer has dual primaries. If it doesn't, run it off the output of the N-68X unless you are running out of VA capability, in whch case your amp is bigger than mine!
I am showing my age by admitting that I saw Jimi live in concert. Most of the "use of body parts other than fingers" to play the guitar is a great stage trick. The real action happening on the guitars neck. Right hand in Jimi's case. Using an amp with excessive preamp gain like a Marshall cranked to 11, you can play one handed. (OK, Jimi can, I can't) The string will vibrate enough just by hitting the fret hard. Having the whole system on the verge of acoustic feedback helps by providing additional stimulus to the strings already set in motion.
When you are done with your amp there should be continuity between the metal parts of the guitar and the ground pin on the power cord.
I had good luck with some, some didn't sound too good, and some didn't live long. I had a pair of 12's from a Maggie that also had die cast aluminum horn tweeters. I used all 4 (2X12 and both horns) speakers and the power amp (2 X 6BQ5 SE) to make a rather nice sounding guitar amp.
That may also apply to speakers from old guitar amps too. I found an old Electrolab "shock box" guitar amp in an antique shop for $5. The circuit was derived from an AA5 radio. I replaced the tubes, caps, and a few resistors, and added an N-68X to prevent shocking moments, but did nothing to increase the power. I cranked it up and started playing. The speaker lasted about 5 minutes. The 50 year old paper cone just came apart and the voice coil seperated from the cone.
No but you may lose a few % of the power rating. As the coupling into the core will be a bit less.
The other trick transformer use is to use one of the flatpack variety where there are two bobbins side by side. You can use one of the primaries as a 120 V AC input and the other as an isolated 120 volt output, of course the transformer has to be derated to 1/2 power! But that way you can get a single inexpensive transformer to supply HV and filament voltage.
Is anybody considering building in a switched-in attenuator for low volume crunch? I see that a few low watt commercial units have that feature (eg, VHT Special 6) and people love it since bedroom level playing is so important. Seems like two resistors and a switch would do it unless I'm missing something.
I don't see anything in their schematic other than a Triode/Pentode mode switch that would drop the level much.
http://www.vhtamp.com/pdf/VHT_Special_6_Schematic_5-17-10.pdf
The hi/lo switch adds or removes a resistor in the bottom of the tonestack (fixed) that adds a slight boost for more crunch.
From their description it sounds like they use triode mode to reduce power and add a bit more 2nd harmonic distortion.
http://www.vhtamp.com/pdf/VHT_Special_6_Schematic_5-17-10.pdf
The hi/lo switch adds or removes a resistor in the bottom of the tonestack (fixed) that adds a slight boost for more crunch.
From their description it sounds like they use triode mode to reduce power and add a bit more 2nd harmonic distortion.
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I am building a low volume full-body sounding amp. Especially for practice and studio recordings.
Two resistor approach is well known and widely used, but it is not a solution. More sophisticated devices include some kind of a speaker motor for such purposes.
Okay, sorry, I'm not sure where I got that from now. I knew about the triode/pentode mode, but I thought it also had an attenuator at the speaker. Maybe another mini amp. I only wanted to make a point that there are some simple features that would not have to cost much extra in parts and would add a lot of versatility to what can otherwise be a "one trick pony", as some of the commercial rigs seem to be at the lowest price levels. I would think that it costs a commercial manufacturer more to include such features than it would for a diy'er because they have to value their time and mark up their parts costs about 3x or so. We don't have to.
I don't even know if an attenuator would necessarily help or not, but they sure sell a lot of them as accessories and it would be cheap enough at these power level. I see a lot talk on the forums about these mini amps and a lot of it refers to inability to get a good distortion sound at low levels and it seems like apartment and bedroom dwellers are heavy users of these things. Of course, this would only apply to an amp aimed at the crunch crowd. For cleans, it isn't even an issue.
I'm not very well tuned into sound descriptors. What do you mean by "full body sound"? Lots of clean headroom or distortion or a nice combination? What qualities make a good practice and recording amp?
Is it even possible to build an amp at this cost that has lots of clean room but still saturates nicely when needed? I'm thinking maybe a gain switch or something that is labelled "Fender" on one side and "Marshall" on the other.
I'm sure that the heavy hitters here can address this better, but it's my impression that this is a sweet spot for designers in the cost/benefit equation. Going up to 15 watts or so requires much more expensive tubes, transformers, etc, etc. I'm sure that some the designs coming out of this will be conservatively rated for purposes of this contest but could be easily pushes a few watts up if you need it. I will agree that 5 watts is somewhat limiting for clean headroom, but it's still loud, especially in tube saturation.
Look at the number of commercial offerings in the 5 or 6 watt range right now. This is where it's at for home/practice/recording. Even small gigs.
And don't forget what a good speaker can do.
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Actually, I am. The restive attenuator between the amp and speaker are not uncommon. There are several commercial designs made for running your Mega-Gigawatt amp at full tilt into a resistive attenuator to get down to practice amp volume levels. Yeah, it makes a lot of sense to power a 100 watt Marshall (which takes about 300 watts), then turn 99 of those watts into heat, but it is common. I plan on adding a switchable attenuator to reduce the (yet unknown) power of my amp to less than a watt. I mentioned this back in post #146 but I used the name "power soak" which is one brand of attenuator. I have seen "power brakes" and "hot plates" too.
I had to spend the afternoon at a baby shower of all places, and my wife wasn't even there, but now the iron is hot and I am soldering stuff together. The 5 tube amp will be built. I don't know if it will work, but there is only one way to find out.
